JPWO2008078595A1 - Surface emitting laser - Google Patents

Abstract

The surface emitting laser according to the present invention includes a first multilayer Bragg reflector 11 including a first layer 113 and a first high refractive index layer having a higher refractive index than that of the first layer 113, and a second layer 131. And a second multilayer Bragg reflector 13 including a second high refractive index layer having a higher refractive index than that of the second layer 131, and an optical resonance including the active layer portion sandwiched between these multilayer Bragg reflectors And a vessel portion 12. The first multilayer 113 is in contact with the optical resonator unit 12 with respect to the first multilayer Bragg reflector 11 and the second multilayer Bragg reflector 13 is in contact with the optical resonator 12. The layer is the second layer 131. The effective refractive index neff of the resonator unit 12 is larger than that of the first and second layers 113 and 131, and the optical path length neffL of the optical resonator unit 12 is equal to the oscillation wavelength λ of the surface emitting laser and 0.5λ < neffL ≦ 0.7λ. Further, an active layer 121 is provided at a position that is ΔL (= neffL−0.5λ) away from the boundary between the optical resonator unit 12 and the first multilayer Bragg reflector 11 or the second multilayer Bragg reflector 13. It has been.

Description

  The present invention relates to a surface emitting laser used for a light source for data communication.

  A surface emitting laser (VCSEL) is widely used as a light source for data communication such as Ethernet (registered trademark) and fiber channel because of its low cost and low power consumption. With respect to the modulation speed of these VCSELs, high-speed modulation operation such as 10 Gbps (gigabit per second) has been required in accordance with the recent increase in data communication capacity. VCSELs are also expected as a light source for optical interconnection, and elements such as parallel / ultra-high speed (20 Gbps / channel) are required.

  In order to modulate the VCSEL at high speed, it is necessary to increase the relaxation oscillation frequency (fr) and reduce the CR time constant. A CR time constant exceeding 20 Gbps can be manufactured by lowering the electrical resistance of the VCSEL and reducing the electric capacity around the light emitting part by ion implantation or insulator embedding. On the other hand, with respect to fr, it is generally possible to increase fr by increasing the injection current to increase the photon density. However, if the current injected into the active layer is increased, the temperature around the light emitting portion of the VCSEL becomes very high compared to the environmental temperature, and this is one of the major factors determining the upper limit of the VCSEL fr.

  In VCSEL, in order to increase fr, the volume in which light exists is reduced so that a large photon density can be obtained even with the same current. As one of the methods, there is narrowing of the oxidation diameter by an oxidation current confinement structure having a large light confinement effect. In this structure, an AlGaAs layer having a high Al composition is oxidized from the side surface of the mesa by water vapor to change a part of the AlGaAs layer into an AlOx insulator.

  In this structure, not only a fine current confinement structure but also a strong light confinement effect due to the difference in refractive index between the semiconductor and the insulator can be obtained. Considering the area and stacking direction, the volume of the portion where the light exists is reduced, and a large photon density can be obtained with a small current. For this reason, the current modulation efficiency of the fr of the VCSEL becomes very high, and a high fr can be obtained before the influence of heat generation due to current injection becomes significant.

  The above technique is to reduce the volume of light in the VCSEL in-plane direction. Similarly, by reducing the volume of light in the stacking direction, even if the gain of the active layer is the same, fr The current modulation efficiency can be increased.

  The structure of the VCSEL in the stacking direction is composed of upper and lower DBR (Distributed Bragg Reflector) parts and optical resonator parts sandwiched between them, and the light intensity forms a standing wave in the vertical direction. If the light intensity is designed to be strongest in the active layer portion, a VCSEL characteristic with a low threshold and high efficiency can be obtained. The light intensity of the DBR portion becomes weaker as the distance from the optical resonator portion increases, and the “antinode”, which is the portion of the standing wave having a high light intensity, attenuates exponentially. The method of attenuation depends on the refractive index difference of the multilayer film forming the DBR. The larger the refractive index difference, the faster the attenuation and the stronger the confinement of light in the stacking direction. In the optical resonator section, the light intensity has a constant standing wave distribution with almost no attenuation.

  Thus, the light distribution in the stacking direction is determined by the light penetration length in the DBR portion and the layer thickness of the optical resonator portion. In order to increase the current modulation efficiency of fr, it is effective to reduce the light penetration length in the DBR portion and the layer thickness of the optical resonator portion as much as possible.

  The layer thickness of the optical resonator portion cannot be an arbitrary value because it is necessary to form a standing wave with the upper and lower DBR portions. In general, the effective optical path length of the optical resonator is an integral multiple of λ / 2 where λ is the oscillation wavelength of the VCSEL. Therefore, the structure in which the layer thickness of the optical resonator portion is minimized is when the effective optical path length of the optical resonator portion is λ / 2. Such a small optical resonator is a microresonator (microcavity). ) Known as structure. Since the microcavity structure has an effect of suppressing spontaneous emission light other than the oscillation wavelength, the oscillation threshold is lowered, and the heat generation of the VCSEL at the same current value can be further reduced.

  Techniques relating to the structure of this λ / 2 resonator are disclosed in Japanese Patent Laid-Open Nos. 05-212346, 07-193325, and 10-256665. The technique is also disclosed in literature (DG Deppe et al., Photonic Technology Letters, 1995, Vol. 7, No. 9, pages 965-967).

  In any of the structures disclosed in these documents, both sides of the λ / 2 resonator are sandwiched between layers having a higher refractive index than the effective refractive index of the resonator portion. Accordingly, it is disclosed that a surface emitting laser having a microcavity structure can be formed by placing an active layer on the antinode of the standing wave substantially in the middle of the resonator portion. Hereinafter, the surface emitting laser having this structure is referred to as a λ / 2 microcavity surface emitting laser.

  Here, a λ / 2 microresonator surface emitting laser, which is an example of a half-wavelength resonator among the microresonators, will be briefly described.

  FIG. 1 is a diagram showing a band structure and an electric field strength curve of the structure of a λ / 2 microcavity surface emitting laser. In FIG. 1, the horizontal axis indicates the position in the stacking direction (optical axis direction), and the vertical axis schematically indicates the band gap energy of each layer. The electric field strength means the square of the absolute value of the electric field vector.

  Therefore, in the electric field intensity curve, the “node” of the peak position of the peak and valley of the standing wave before squaring the electric field vector has the maximum value, and the “node” of the standing wave has the minimum value. The maximum value mentioned here includes the maximum value. In the following, the region where the maximum value of the electric field intensity curve is called “antinode”, and the region where the minimum value is obtained is called “node”.

  As shown in FIG. 1, an optical resonator unit 212 is sandwiched between a first multilayer Bragg reflector 211 and a second multilayer Bragg reflector 213. In the optical resonator portion 212, an active layer portion 2121 is formed between layers (corresponding to a low refractive index layer) 2123 having a large band gap. In the first multilayer Bragg reflector 211, a plurality of pairs of the first low refractive index layer 2111 and the first high refractive index layer 2112 are stacked.

  In the second multilayer Bragg reflector 213, a plurality of pairs of the second low refractive index layer 2132 and the second high refractive index layer 2131 are stacked. The first high refractive index layer 2112 and the second high refractive index layer 2131 are in contact with the optical resonator unit 212. Looking at the electric field strength curve 2122 showing the electric field strength of the optical resonator 212, the antinode of the electric field strength curve 2122 is located in the active layer portion 2121.

  However, the λ / 2 microcavity surface emitting laser described in the above document has a problem in terms of current injection. In the λ / 2 microcavity surface emitting laser shown in FIG. 1, the effective refractive index of the optical resonator unit 212 is the first high refractive index layer 2112 and the second high refractive index layer on both sides of the optical resonator unit 212. The refractive index is lower than that of the refractive index layer 2131. In general, there is a correlation between the refractive index and the semiconductor band gap, and the refractive index tends to decrease as the band gap increases. Therefore, the semiconductor forming the optical resonator portion needs to be composed of a layer (corresponding to a low refractive index layer) 2123 having a large band gap.

  On the other hand, the optical resonator section 212 needs to include an active layer section 2121 inside. The band gap of the active layer portion 2121 needs to be smaller than the band gap of the material constituting the DBR. That is, the band gap of the active layer portion 2121 is small, but the band gap of the low refractive index layer 2123 of the optical resonator portion 212 surrounding the active layer portion 2121 is large.

  In the DBR part, it is possible to apply a doping or graded layer for reducing electric resistance to a place with such a large band gap difference, but when applied to an optical resonator part, light absorption increases, Device characteristics deteriorate because a large electric field is applied to the active layer portion. For this reason, this layer with a large band gap cannot be doped. Therefore, even if an attempt is made to inject current into such a structure, the low refractive index layer 2123 corresponding to a layer having a large band gap serves as a current blocking layer, and it is difficult to inject current into the active layer portion. Become.

  An object of the present invention is to provide a surface-emitting laser capable of low threshold, high efficiency, and high-speed modulation in a microcavity structure in which the optical path length of the optical resonator section is close to λ / 2.

The surface-emitting laser of the present invention includes a first multilayer Bragg reflector including a first layer and a first high-refractive index layer having a higher refractive index than the first layer, a second layer, and a second layer. A second multilayer Bragg reflector including a second high-refractive index layer having a refractive index larger than that of the first layer, and an active layer portion that is sandwiched between the first and second multilayer Bragg reflectors and generates an optical gain. The first multilayer Bragg reflector is a first layer, and the second multilayer Bragg reflector is a surface emitting laser having an optical resonator portion. The layer in contact with the optical resonator section is the second layer, the effective refractive index n _eff of the resonator section is larger than those of the first and second layers, and the optical path length n of the optical resonator section. _eff L is in a relationship of 0.5λ <n _eff L ≦ 0.7λ with the oscillation wavelength λ of the surface emitting laser, and the optical path length n _eff L is 0. When the value obtained by subtracting 5λ is ΔL, an active layer is provided at a position apart by ΔL from the boundary between the optical resonator unit and the first multilayer Bragg reflector or the second multilayer Bragg reflector. It is.

  According to the present invention, in the microresonator structure in which the optical path length of the optical resonator portion is close to λ / 2, it becomes possible to increase the light intensity of the active layer portion, and to obtain low threshold and high-efficiency element characteristics. . In addition, current injection into the active layer is facilitated, the injection current is increased, the relaxation oscillation frequency is increased, and high-speed modulation is improved.

FIG. 1 is a diagram showing a band structure and an electric field strength curve of a related half wavelength resonator. FIG. 2 is a diagram showing a band structure and an electric field strength curve of the surface emitting laser according to the present embodiment. FIG. 3 is a diagram showing a band structure and an electric field strength curve according to the basic structure of the surface emitting laser of the present embodiment. 4A is a diagram showing a band structure and an electric field strength curve of the surface emitting laser according to Example 1. FIG. FIG. 4B is a diagram illustrating a calculation result of an electric field intensity curve of the surface emitting laser according to Example 1. FIG. 5A is a diagram showing a band structure and an electric field strength curve of a surface emitting laser that is a comparative example of the surface emitting laser of Example 1. FIG. 5B is a diagram illustrating a calculation result of an electric field intensity curve of a surface emitting laser which is a comparative example of the surface emitting laser of Example 1. FIG. 6A is a diagram showing a band structure of a surface emitting laser according to Example 2. FIG. 6B is a diagram illustrating a cross-sectional structure of the surface emitting laser according to the second embodiment. FIG. 7 is a schematic diagram showing a band structure of the surface emitting laser of Example 3. FIG. 8 is a schematic diagram showing the band structure of the surface emitting laser of Example 4. FIG. 9 is a schematic diagram showing the band structure of the surface emitting laser of Example 5. FIG. 10 is a schematic diagram showing the band structure of the surface emitting laser of Example 6. In FIG.

Explanation of symbols

11, 211, 221, 31, 41 First multilayer black reflector 111, 1122, 311, 411 First high refractive index layer 112, 113, 2111, 312, 313, 412, 413 First low refractive index Layer 12, 212, 222, 32, 42 Optical resonator part 121, 1211, 321, 421 Active layer part 122, 2222, 2222, 322, 422 Electric field strength curve 123, 323, 423 High refractive index layer 13, 213, 33 43 Second multilayer black reflector 131, 1322, 331, 431 Second low refractive index layer 132, 2131, 332, 432 Second high refractive index layer 2123 Layer having a large band gap (low refractive index layer )
50 n-type GaAs substrate 51, 61, 71, 81, 91 1st multilayer black reflector 511 Si-doped GaAs layer 512 Si-doped Al _0.9 Ga _0.1 As layer 513 n-type Al _0.9 Ga _0. DESCRIPTION OF SYMBOLS ₁ As layer 514 Si dope AlGaAs graded layer 52, 62, 72, 82, 92 Optical resonator part 521, 621, 721, 821, 921 Triple quantum active layer 522 p-type Al _0.3 Ga _0.7 As electron Block layers 523, 623, 723 Tunnel junction 524 Si-doped GaAs layers 53, 63, 73, 83, 93 Second multilayer black reflectors 531, 631, 731, 831 SiO ₂ layers 532, 632, 732, 832 Amorphous Si layer 54, 55 electrode 611 n-type GaAs layer 612 n-type AlGaAs layer 613 n-type A GaAs layer 614 Si doped _Al 0.98 _{Ga 0.02} As layer (current confinement layer)
622 p-type AlGaAs electron blocking layer 624, 715, 724, 822 n-type GaAs contact layer 711 GaAs layer 712 AlOx oxide low refractive index layer 713 n-type Al _0.9 Ga _0.1 As layer 714, 913 n-type AlGaAs graded Layer 722 p-type AlGaAs electron block layer 811 p-type GaAs high refractive index layer 812 p-type AlGaAs low refractive index layer 813 p-type AlGaAs low refractive index layer 814 C-doped Al _0.98 Ga _0.02 As layer (oxidized constriction layer)
815 p-type AlGaAs graded layer 911 n-type GaAs high refractive index layer 912 n-type AlGaAs low refractive index layer 931 p-type AlGaAs low refractive index layer 932 p-type GaAs high refractive index layer 933 p-type AlGaAs oxide constriction layer (current confinement layer) )

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  The configuration of the surface emitting laser according to this embodiment will be described. FIG. 2 is a diagram showing a band structure and an electric field strength curve of the surface emitting laser according to the present embodiment. In FIG. 2, the horizontal axis indicates the position in the stacking direction (optical axis direction), and the vertical axis schematically shows the band gap energy of each layer.

  The curve indicated by reference numeral 122 in the figure shows the electric field strength distribution formed in the VCSEL. The electric field strength distribution is a distribution of values obtained by squaring a standing wave electric field vector. The surface emitting laser of the present embodiment includes a first multilayer Bragg reflector 11, a second multilayer Bragg reflector 13, and an optical resonator unit 12 sandwiched between these reflectors. The first multilayer Bragg reflector 11 and the second multilayer Bragg reflector 13 are a kind of DBR.

  Assuming that λ is the oscillation wavelength of the surface emitting laser, the first multilayer Bragg reflector 11 has alternating multilayers of λ / 4 layer thicknesses of the first low refractive index layer 112 and the first high refractive index layer 111, respectively. It consists of a membrane. The second multilayer Bragg reflector 13 is composed of alternating multilayer films each having a λ / 4 layer thickness of the second low refractive index layer 131 and the second high refractive index layer 132. The optical resonator unit 12 includes an active layer 121 that generates an optical gain.

In the surface emitting laser of this embodiment, both sides of the optical resonator unit 12 are sandwiched between the first low refractive index layer 113 and the second low refractive index layer 131, and the optical resonator unit 12 is effective. The refractive index n _eff is larger than that of the first low refractive index layer 113 and the second low refractive index layer 131. Furthermore, if the layer thickness of the optical resonator is L, the optical path length n _eff L of the optical resonator unit 12 is 0.5λ <n _eff L ≦ 0.7λ. The optical path length n _eff L is slightly larger than the half wavelength, and the active layer portion 121 is formed in the vicinity of the antinode of the electric field strength curve 122.

When the value obtained by subtracting 0.5λ from the optical path length n _eff L is ΔL, ΔL from the boundary between the first multilayer Bragg reflector 11 or the second multilayer Bragg reflector 13 and the optical resonator unit 12. If the active layer 121 is provided at a distant position, the position of the active layer 121 becomes an antinode portion of the electric field strength curve 122. In FIG. 2, the first multilayer Bragg reflector 11 is shown as having n-type conductivity, and therefore the active layer 121 is provided on the side close to the first multilayer Bragg reflector 11.

  Next, the operation principle of the surface emitting laser having the above-described configuration will be described.

  As one means for increasing the relaxation oscillation frequency of the VCSEL, there is a method of reducing the effective light volume by increasing the light intensity spread in the optical axis direction and increasing the photon density. The spread of light in the optical axis direction is measured by adding the penetration depth of light into the upper and lower DBRs and the optical path length of the optical resonator.

  In the present embodiment, in order to reduce the spread of the light intensity in the optical axis direction, the optical path length of the optical resonator is set to about the half-wave cavity that is the minimum value. The related half-wavelength cavity (microresonator) structure has a problem in that current injection is hindered as described in the problem section. In order to solve this problem, in the surface emitting laser of the present embodiment, the effective refractive index of the optical resonator unit is increased, and both sides of the optical resonator unit are sandwiched between low refractive index layers.

  FIG. 3 is a diagram showing a band structure and an electric field strength curve of the basic structure of the surface emitting laser according to the present embodiment.

  As shown in FIG. 3, in the surface emitting laser that is the basic structure of the present embodiment, the optical resonator unit 222 is sandwiched between the first multilayer Bragg reflector 221 and the second multilayer Bragg reflector 13. This is a configuration. The active layer portion 2121 of the optical resonator portion 222 is sandwiched between layers (corresponding to a high refractive index layer) 123 having a band gap similar to that of the active layer portion 2121.

  In such a structure, since the band gap is relatively small and the layer 123 having the same band gap as that of the active layer can be formed around the active layer portion 2121, current injection into the active layer portion 2121 is easy. It becomes.

  However, in the basic structure shown in FIG. 3, since the vicinity of the center of the optical resonator unit 222 corresponds to the node of the electric field strength curve 2222, even if the active layer unit 2121 is disposed here, the gain of the active layer is effective in the resonator. Since it is not amplified, good VCSEL characteristics cannot be obtained. In the VCSEL structure as shown in FIG. 3, the antinode of the electric field intensity curve 2222 is at the boundary between the optical resonator unit 222 and each of the DBRs 221 and 13, so that the active layer position is from the antinode position of the electric field intensity curve 2222. It ’s far away.

Therefore, in the present embodiment, the basic structure shown in FIG. 3 is developed, and the optical path of the optical resonator unit 12 is arranged so that the active layer 121 can be arranged at the antinode of the electric field strength curve 122 as shown in FIG. The length n _eff L is 0.5λ <n _eff L ≦ 0.7λ, which is slightly longer than the half wavelength. On the other hand, if the optical path length of the optical resonator unit 12 is longer than 0.7λ, the resonance peak wavelength of the VCSEL becomes longer, and the difference from the wavelength at which the DBR reflectivity becomes maximum becomes larger. The characteristics of the decrease.

  The optical path length of the first low-refractive index layer 113 on the DBR 11 side in contact with the optical resonator unit 12 is set so that the optical path length of the optical resonator unit 12 is slightly longer than λ / 2. The optical path length becomes smaller as the optical path length increases, and becomes smaller than λ / 4.

The antinode of the electric field strength curve 122 is located inward from the boundary of the first multilayer Bragg reflector 11 by ΔL (= n _eff L−0.5λ) corresponding to the length of the optical path length n _eff L. The active layer 121 is disposed at this position. FIG. 2 shows a case where the conductivity of the first multilayer Bragg reflector 11 is n-type. Therefore, the active layer 121 is disposed at a position ΔL from the boundary of the first multilayer Bragg reflector 11, but if the conductivity of the second multilayer Bragg reflector 13 is n-type, the second layer The active layer 121 is disposed at a position ΔL from the boundary of the multilayer Bragg reflector 13. The reason why the active layer is provided on the side closer to the n-type DBR is that electrons are more likely to cross the potential barrier than holes, and the active layer is provided on the side closer to the electron supply source.

  By adopting such a structure, a surface emitting laser having a microresonator structure in which current injection is easy can be realized.

In the surface emitting laser according to the present embodiment, the optical resonator portion has an effective refractive index n _eff larger than the refractive indexes of the first layer and the second layer sandwiching the optical resonator portion. Get smaller. When the optical path length of such an optical resonator unit is 0.5λ, an antinode of electric field strength is located at the boundary between each of the first layer and the second layer and the optical resonator unit. In the present embodiment, the optical path length n _eff L of the optical resonator unit is made longer than 0.5λ by ΔL (0 <ΔL ≦ 0.2λ), so that the position of the antinode of the electric field strength is the same as that of the multilayer Bragg reflector. The active layer portion is disposed at a position away from the boundary by ΔL. As a result, the gain of the active layer can be effectively amplified by the resonator, and low threshold and high efficiency element characteristics can be obtained. In addition, since the active layer portion is sandwiched between layers having a small band gap, current can be easily injected even in a microresonator structure. Therefore, the relaxation oscillation frequency is increased and the high-speed modulation property is improved.

  In addition, since the optical resonator unit 12 can be composed of a layer having a relatively small band gap, a sufficient tunnel current can be supplied at a low voltage to the node portion of the electric field strength at the center of the optical resonator unit 12. It is possible to introduce a good tunnel junction structure. This is because the tunnel current has a property that it becomes exponentially larger as the band gap is smaller. The tunnel junction can convert current carriers from holes to electrons, and both electrodes for current injection can be n-type electrodes. As a result, even when the DBR 13 is formed of a non-conductive material such as a dielectric multilayer film, a VCSEL having good current-voltage characteristics can be realized.

Furthermore, since the tunnel junction in which both electrodes for current injection are low resistance n-type electrodes can be disposed near the active layer portion, the resistance of the element is reduced, and the microresonator is realized. It is possible to draw out the low threshold characteristics, high-speed modulation characteristics, and the like, which are characteristics inherent in the structure. For this reason, the surface emitting laser according to the present embodiment can be used as a light source for optical interconnection that particularly requires low power consumption and high-speed modulation characteristics.
Hereinafter, a specific VCSEL structure will be described using examples. In each embodiment, L is the layer thickness of the optical resonator, and λ is the oscillation wavelength of the surface emitting laser.

  FIG. 4A is a diagram showing a band structure and an electric field strength curve of the surface emitting laser according to this example. The configuration of the surface emitting laser according to this embodiment will be described with reference to FIG. 4A.

  The surface emitting laser of this example is sandwiched between a first multilayer Bragg reflector 31 made of a semiconductor material, a second multilayer Bragg reflector 33 made of a dielectric material, and these DBRs. And an optical resonator unit 32. The first multilayer Bragg reflector 31 corresponds to a semiconductor DBR. The second multilayer Bragg reflector 33 corresponds to the dielectric DBR.

  The first multilayer Bragg reflector 31 is composed of alternating multilayer films each having a λ / 4 layer thickness of the first low refractive index layer 312 and the first high refractive index layer 311. The second multilayer Bragg reflector 33 is composed of alternating multilayer films each having a λ / 4 layer thickness of the second low refractive index layer 331 and the second high refractive index layer 332. The optical resonator unit 32 includes an active layer unit 321 that generates an optical gain.

Further, both sides of the optical resonator section 32 are sandwiched between the first low refractive index layer 313 and the second low refractive index layer 331. The active layer portion 321 is sandwiched between layers (corresponding to a high refractive index layer) 323 having the same band gap as that of the active layer portion 321. Therefore, the effective refractive index n _eff of the resonator portion is larger than that of the first low refractive index layer 313 and the second low refractive index layer 331.

Further, the optical path length n _eff L of the optical resonator section 32 is 0.5λ <n _eff L ≦ 0.7λ, which is larger than a half wavelength, and the active layer section 321 has an electric field strength curve 322 of It is formed at a position corresponding to the belly.

  FIG. 4B shows the result of calculating the absolute value of the electric field strength of the VCSEL shown in FIG. 4A. In FIG. 4B, the horizontal axis indicates the position in the optical axis direction, and the vertical axis indicates the electric field strength.

In the calculation, the optical path length of the optical resonator unit 32 is set to 0.6λ, an AlAs layer is used as the first low refractive index layer 312 of the semiconductor DBR 31, and a GaAs layer is used as the first high refractive index layer 311. In addition, a SiO ₂ layer was used for the second low refractive index layer 331 of the dielectric DBR 33 and an amorphous Si layer was used for the second high refractive index layer 332. Assuming one pair of SiO ₂ layer / amorphous Si layer, the number of pairs of dielectric DBR33 was 3, the number of pairs of semiconductor DBR was 20, and the design wavelength of DBR was 1070 nm.

  The resonance peak wavelength of this VCSEL structure is calculated to be 1075 nm, the design wavelength of DBR 1070 nm is changed only by 5 nm, and the reflectance from DBR is in a sufficiently high wavelength range. Further, the active layer portion 321 substantially coincides with the position of the antinode of the electric field strength, and is sufficiently large in strength. When this VCSEL is irradiated with excitation light while changing the light intensity, good VCSEL oscillation can be obtained with low excitation light intensity.

  Here, a case will be described in which the optical path length of the optical resonator unit is 0.5λ, the layer thicknesses of the upper and lower DBRs of the optical resonator unit are adjusted, and the active layer is adjusted to the position of the antinode of the electric field strength. The surface emitting laser in this case is a comparative example for comparing with the surface emitting laser of the present embodiment.

  FIG. 5A is a diagram showing a band structure and an electric field strength curve of a surface emitting laser according to a comparative example.

  As shown in FIG. 5A, the surface emitting laser of the comparative example includes a first multilayer Bragg reflector 41 made of a semiconductor material, a second multilayer Bragg reflector 43 made of a dielectric material, And an optical resonator 42 sandwiched between these DBRs. The first multilayer Bragg reflector 41 corresponds to the semiconductor DBR, and the second multilayer Bragg reflector 43 corresponds to the dielectric DBR.

  The first multilayer Bragg reflector 41 is composed of alternating multilayer films each having a λ / 4 layer thickness of the first low refractive index layer 412 and the first high refractive index layer 411. The second multilayer Bragg reflector 43 is composed of alternating multilayer films each having a λ / 4 layer thickness of the second low refractive index layer 431 and the second high refractive index layer 432. The optical resonator unit 42 includes an active layer unit 421 that generates an optical gain.

  In the comparative example shown in FIG. 5A, the optical path length of the optical resonator is 0.5λ. The active layer part 421 is sandwiched between layers (corresponding to a high refractive index layer) 423 having a band gap comparable to that of the active layer part 421. In addition, regarding the optical path length of the upper and lower DBRs, the second low refractive index layer 431 on the dielectric DBR 43 side is made longer than that in this embodiment, and the first low refractive index layer 413 on the semiconductor DBR 41 side is made longer than in this embodiment. As shown in the electric field strength curve 422, the positions of the antinodes and nodes of the electric field strength are shifted.

  FIG. 5B is a diagram showing the calculation result of the absolute value of the electric field strength in the VCSEL having the structure of FIG. 5A. In this structure, the resonance peak wavelength is calculated to be 1052 nm, which is 18 nm shorter than the DBR design wavelength of 1070 nm, which is greatly deviated from the peak reflectance wavelength of DBR. Further, it can be seen that the active layer portion 421 is shifted from the position of the antinode of the electric field strength and is also lowered in strength.

  As can be seen from the results of the comparative example, in the structure in which the active layer portion is spatially shifted by adjusting the layer thickness of the upper and lower DBRs in order to adjust the active layer portion to the position of the antinode of the electric field strength, It was clarified that the standing wave between the resonators was disturbed. Such a phenomenon becomes prominent particularly when the dielectric / semiconductor interface having a large refractive index difference is not properly positioned at the antinode of the standing wave.

  When one DBR is made of a dielectric material as in this embodiment, the optical path length of the optical resonator is longer than 0.5λ, and the active layer is arranged at the antinode of the standing wave. This is very important.

  In this embodiment, a configuration example of a current injection type VCSEL structure will be described. FIG. 6A is a schematic diagram showing a band structure of the surface emitting laser of this example, and FIG. 6B is a schematic diagram showing a cross section of the element structure. Although the vertical axis and the horizontal axis are not shown in FIG. 6A, the vertical axis and the horizontal axis are the same as those in FIG.

  As shown in FIG. 6A, the surface emitting laser of the present embodiment includes a first multilayer Bragg reflector 51, a second multilayer Bragg reflector 53, and an optical resonator 52 sandwiched between these DBRs. And have. The first multilayer Bragg reflector 51 corresponds to an n-type DBR layer, and the second multilayer Bragg reflector 53 corresponds to a dielectric DBR.

The n-type DBR layer 51 is a combination of a high refractive index layer Si-doped GaAs layer 511 and a low refractive index layer Si-doped Al _0.9 Ga _0.1 As layer 512 as a basic unit. Contains multiple pairs. All of these layers have a Si-doped concentration of 2 × 10 ¹⁸ cm ⁻³ .

A Si-doped AlGaAs graded layer 514 is provided between the low refractive index layer and the high refractive index layer to reduce electric resistance. The dielectric DBR 53 includes a plurality of pairs of SiO ₂ layer 531 / amorphous Si layer 532. The optical resonator 52 includes a triple quantum well active layer 521, a carbon (C) doped p-type Al _0.3 Ga _0.7 As electron blocking layer 522, a tunnel junction 523, and a Si-doped GaAs layer. 524 are stacked. Hereinafter, the triple quantum well active layer is simply referred to as an active layer. Since the optical path length n _eff L of the optical resonator 52 and the arrangement of the active layer 521 are the same as those in the first embodiment, detailed description thereof is omitted.

  Next, a method for manufacturing the surface emitting laser according to the present embodiment will be described.

An n-type DBR layer 51 having 35.5 pairs with a pair of a Si-doped GaAs layer 511 as a high refractive index layer and a Si-doped Al _0.9 Ga _0.1 As layer 512 as a low refractive index layer as a basic unit. It is formed on the n-type GaAs substrate 50 by metal organic chemical vapor deposition (MOCVD). The n-type GaAs substrate 50 is a substrate having a Si doping concentration of 2 × 10 ¹⁸ cm ⁻³ . Instead of the MOCVD method, a molecular beam epitaxy (MBE) method may be used.

A Si-doped AlGaAs graded layer 514 is formed between the low refractive index layer and the high refractive index layer in order to reduce electric resistance. Each layer is formed so that each layer constituting the n-type DBR layer 51 is a multilayer reflective film having a so-called λ / 4 multilayer thickness. The n-type Al _0.9 Ga _0.1 As layer 513 of the last low-refractive index layer of the n-type DBR layer 51 is thinned by an optical path length of 0.1λ.

In the manufacturing process of the optical resonator portion 52, a triple quantum well active layer comprising an undoped In _0.3 Ga _0.7 As well layer having a thickness of 5 nm and an undoped GaAs barrier layer having a thickness of 10 nm on the n-type DBR layer 51 ( (Hereinafter referred to as the active layer) 521 is grown. Subsequently, a carbon (C) -doped p-type Al _0.3 Ga _0.7 As electron blocking layer 522 having a thickness of 30 nm and a tunnel junction layer made of high-concentration C-doped GaAsSb and high-concentration Si-doped InGaAs are stacked as an electron blocking layer. To do.

  Here, the growth wafer is once removed from the growth furnace, a circular mesa mask resist is formed on the tunnel junction layer, and etching is performed on the mask resist to pattern the tunnel junction 523. By this step, when the element is energized, the portion without the tunnel junction 523 is reverse-biased by the pn junction and the current is blocked, so that the current finally flows only to the remaining portion of the tunnel junction 523, and the current confinement structure Is realized.

  Thereafter, the resistance of a part of the active layer region is increased by oxygen ion implantation, the mask resist is removed, the wafer is again placed in the growth furnace, and the Si-doped GaAs layer 524 is grown to form the optical resonator 52. . The last 30 nm thick Si-doped GaAs layer 524 is a contact layer.

  Here, the spacer layer thickness is designed so that the tunnel junction 523 is formed at the node of the electric field strength of the optical resonator 52. Thereby, the light absorption by high concentration doping can be suppressed to the minimum. The active layer 521 is formed so that the position where the active layer 521 is formed is an antinode of the electric field strength, and the optical path length of the optical resonator 52 is 0.6λ in this embodiment.

Thereafter, the wafer is taken out of the growth furnace, and a dielectric DBR 53 in which three pairs of SiO ₂ layer 531 / amorphous Si layer 532 are laminated is formed.

  The laminated structure formed as described above is processed into a surface emitting laser element in a device process step. First, a part of the dielectric DBR 53 is removed by etching, and the Si-doped GaAs layer 524 is exposed. An n-type electrode 55 made of AuGe alloy is formed there as an electrode. An n-type electrode 54 made of AuGe alloy is also formed on the back surface of the n-type GaAs substrate 50.

  When a voltage is applied to the VCSEL element, a current flows, and laser oscillation occurs when the current value exceeds a threshold current. A voltage is applied between the electrode 54 and the electrode 55 so that the electrode 55 has a higher voltage than the electrode 54. As a result, the pn reverse bias is applied and the depletion layer spreads at places other than the tunnel junction 523, and the current is blocked. In the tunnel junction 523, a current flows by applying a reverse bias, and holes are injected from the p-type GaAsSb layer or the p-type AlGaAs layer toward the active layer 521.

  This VCSEL device with a current confinement diameter of 5 μm has good static characteristics with an oscillation threshold current of 0.5 mA and a differential resistance of 80Ω. According to this embodiment, since a semiconductor layer having a small band gap can be disposed around the active layer portion, the problem of current injection inhibition is solved. Further, since the tunnel junction can be disposed near the active layer portion, the resistance of the element can be reduced.

  Furthermore, from small signal modulation experiments, the relaxation oscillation frequency fr of this element was about 26 GHz, significantly exceeding the 20 GHz of the related λ resonator oxidized constriction VCSEL.

  The reason is considered as follows. The effective resonator length in the stacking direction of the oxide confinement type VCSEL of the λ resonator is about 1.24 μm, whereas the element of this example is 0.705 μm smaller than the related λ resonator. . As a result, it is considered that the current modulation efficiency of fr is about 1.33 times that of the related λ resonator, and the upper limit of the relaxation oscillation frequency fr is extended.

  In particular, in this VCSEL structure, since the dielectric DBR 53 is used for the upper DBR, the light penetration length of that portion is as small as 0.054 μm. For this reason, when the optical path length of the optical resonator section is about half that of the related λ resonator, the influence on the entire effective resonator length is increased.

  In this embodiment, the n-side electrode is taken from the back surface of the substrate, but it is also possible to perform etching from a part of the surface to the n-type DBR layer 51 to take the n-side electrode from the exposed surface of the substrate.

  In the second embodiment, current confinement is performed at the tunnel junction 523, whereas in this embodiment, an oxidation current confinement structure is provided in a part of the n-type semiconductor DBR portion.

  FIG. 7 is a schematic diagram showing the band structure of the surface emitting laser of this example. Although the vertical axis and the horizontal axis are not shown in FIG. 7, the vertical axis and the horizontal axis are the same as those in FIG.

  As shown in FIG. 7, the surface emitting laser according to the present embodiment includes a first multilayer Bragg reflector 61, a second multilayer Bragg reflector 63, and an optical resonator unit 62 sandwiched between these DBRs. And have. The first multilayer Bragg reflector 61 corresponds to the lower n-type DBR layer, and the second multilayer Bragg reflector 63 corresponds to the upper n-type DBR layer.

The lower n-type DBR layer 61 includes a plurality of pairs of this combination, with a pair of a high-refractive-index n-type GaAs layer 611 and a low-refractive-index n-type AlGaAs layer 612 as a basic unit. . A Si-doped AlGaAs graded layer 615 is provided between the low refractive index layer and the high refractive index layer to reduce electric resistance. Further, a part of the n-type AlGaAs layer 613 serving as a low refractive index layer near the optical resonator 62 is a Si-doped Al _0.98 Ga _0.02 As layer 614 that is a current confinement layer.

The upper n-type DBR layer 63 includes a plurality of pairs of SiO ₂ layer 631 / amorphous Si layer 632. The optical resonator unit 62 includes a triple quantum well active layer (hereinafter simply referred to as an active layer) 621, a p-type AlGaAs electron blocking layer 622, a tunnel junction 623, and an n-type GaAs contact layer 624. Has been.

  The upper n-type DBR layer 63 and the optical resonator unit 62 have the same configurations as those of the second embodiment, and thus detailed description thereof is omitted.

As described above, in this embodiment, a part of the lower n-type DBR layer 61 is a Si-doped Al _0.98 Ga _0.02 As layer (hereinafter simply referred to as a current confinement layer) as a current confinement layer. 614 is formed. Further, in this structure, since n-type current confinement is caused by electrons, a GaAs layer with high mobility is not stacked as much as possible between the current confinement layer 614 and the active layer 621.

  It is known that the mobility of electrons is as small as that of holes when the Al composition of AlGaAs is 0.35 or more. By using AlGaAs having such a composition, a sufficient current confinement effect can be obtained. Further, the material is not limited to AlGaAs but may be a material with low mobility, and may be a diluted N-type semiconductor or the like. Examples of diluted N-based semiconductors include GaAsN, InGaPN, AlGaAsN, and GaAsPN.

  Further, since current confinement is performed in the AlGaAs oxide layer portion, the tunnel junction 623 does not need to be patterned. Since the process steps for device fabrication are the same as those of the related oxide confined surface emitting laser device, detailed description thereof is omitted here, and the formation process of the oxidized constriction structure is briefly described.

The oxidized constriction structure is formed into a columnar structure having a diameter of about 30 μm by performing selective etching until the uppermost n-type GaAs layer 611 of the high-refractive index layer of the lower n-type DBR layer 61 is exposed. . By this step, the side surface of the Al _0.98 Ga _0.02 As current confinement layer is exposed. And it heats for about 10 minutes at the temperature of about 400 degree | times within the furnace in water vapor | steam atmosphere. The Al composition of the current confinement layer is as large as 0.98, which is different from the Al composition 0.9 of the low refractive index AlGaAs layer 612 in the lower n-type DBR layer 61, so that the oxidation rate is fast and is selected by the current confinement layer 614. Oxidation progresses. As a result, a donut-shaped current block structure is formed, and a current passage layer having a diameter of about 6 μm is formed at the center.

  This embodiment is different from the second embodiment in that the in-plane light confinement is performed by the oxide layer, but the effective resonator length in the stacking direction is the same. Therefore, the high-speed modulation characteristic is the same as that of the second embodiment. is there.

  In this example, a part of the lower n-type DBR layer of Example 2 is replaced with a DBR composed of a semiconductor / insulator multilayer film.

  FIG. 8 is a schematic diagram showing the band structure of the surface emitting laser of this example. Although the vertical axis and the horizontal axis are not shown in FIG. 8, the vertical axis and the horizontal axis are the same as those in FIG.

  As shown in FIG. 8, the surface emitting laser according to the present embodiment includes a first multilayer Bragg reflector 71, a second multilayer Bragg reflector 73, and an optical resonator unit 72 sandwiched between these DBRs. And have. The first multilayer Bragg reflector 71 corresponds to the lower n-type DBR layer, and the second multilayer Bragg reflector 73 corresponds to the upper n-type DBR layer.

The lower n-type DBR layer 71 includes a plurality of pairs of combinations, with a pair of a GaAs layer 711 as a high refractive index layer and an AlOx oxidized low refractive index layer 712 as a basic unit. In the present embodiment, the AlOx oxidized low refractive index layer 712 is obtained by oxidizing an Al _0.98 Ga _0.02 As layer. Further, an n-type GaAs contact layer 715, an n-type AlGaAs graded layer 714, and n of the low-refractive index layer are disposed on the optical resonator 72 side of the uppermost AlOx oxide low-refractive index layer 712 in the upper n-type DBR layer 71. A type Al _0.9 Ga _0.1 As layer 713 is sequentially formed.

The upper n-type DBR layer 73 includes a plurality of SiO ₂ layer 731 / amorphous Si layer 732 pairs. The optical resonator unit 72 includes a triplet well active layer (hereinafter simply referred to as an active layer) 721, a p-type AlGaAs electron blocking layer 722, a tunnel junction 723, and an n-type GaAs contact layer 724. Has been.

  The upper n-type DBR layer 73 and the optical resonator unit 72 are the same as the configurations corresponding to each of the second embodiment, and thus detailed description thereof is omitted. Similarly to the second embodiment, an electrode connected to a part of the n-type GaAs contact layer 724 is provided.

As described above, in this embodiment, in the lower n-type DBR layer 71, the low refractive index layers other than the n-type Al _0.9 Ga _0.1 As layer 713 closest to the optical resonator portion 72 can be easily oxidized. It is formed by al _0.98 Ga _0.02 As layer. An AlOx oxidized low refractive index layer 712 obtained by oxidizing this layer is provided. The Al _0.98 Ga _0.02 As layer is formed so that the optical path length after oxidation is λ / 4.

The number of pairs of the GaAs layer 711 and the Al _0.98 Ga _0.02 As layer (corresponding to the AlOx oxidized low refractive index layer 712) was five. In addition, since no current flows in this portion, the layer corresponding to the Si-doped AlGaAs graded layer 514 provided in Example 2 is necessary only on both sides of the n-type Al _0.9 Ga _0.1 As layer 713. It is.

The oxidation process of the Al _0.98 Ga _0.02 As layer is the same as that described in the third embodiment. In this embodiment, since no electrode can be taken from the GaAs substrate, the surface electrode is taken from a part of the GaAs contact layer 715 of the high refractive index layer closest to the optical resonator portion 72.

  The relaxation oscillation frequency fr of this VCSEL device having a current confinement diameter of 5 μm is about 30 GHz, which is higher than the VCSEL structures of the second and third embodiments. This is because the effective resonator length in the stacking direction of the VCSEL of Example 2 is as very small as 0.43 μm, and the current modulation efficiency of fr is about 1.7 of that of the related λ resonator oxidized constriction type VCSEL. This is considered to be because the upper limit of the relaxation oscillation frequency fr has been increased.

  However, in calculation, fr should extend to about 34 GHz, but the upper limit does not extend to that extent. This is because there is an AlOx oxidation low refractive index layer 712 which is an insulator layer obtained by oxidizing a semiconductor on the GaAs substrate side, and the thermal resistance of this layer is high, and the temperature of the active layer rises quickly when the drive current is increased. This is probably because the elongation of the relaxation oscillation frequency fr with respect to the current was saturated early.

  In this embodiment, p-type GaAs is used for the substrate, and the lower DBR layer is composed of a p-type doped layer.

  FIG. 9 is a schematic diagram showing the band structure of the surface emitting laser of this example. Although the vertical axis and the horizontal axis are not shown in FIG. 9, the vertical axis and the horizontal axis are the same as those in FIG.

  As shown in FIG. 9, the surface emitting laser according to the present embodiment includes a first multilayer Bragg reflector 81, a second multilayer Bragg reflector 83, and an optical resonator unit 82 sandwiched between these DBRs. And have. The first multilayer Bragg reflector 81 corresponds to the lower DBR layer, and the second multilayer Bragg reflector 83 corresponds to the upper DBR layer.

  The lower DBR layer 81 includes a plurality of pairs of combinations, with a pair of a p-type GaAs high refractive index layer 811 and a p-type AlGaAs low refractive index layer 812 as a basic unit. A p-type AlGaAs graded layer 815 is provided between the low refractive index layer and the high refractive index layer to reduce electric resistance.

A part of the p-type AlGaAs low refractive index layer 813 near the optical resonator portion 82 is a C-doped Al _0.98 Ga _0.02 As layer (oxidized constriction layer) 814 that is a current confinement layer. The upper DBR layer 83 includes a plurality of pairs of SiO ₂ layer 831 / amorphous Si layer 832. In the optical resonator section 62, a triple quantum well active layer 821 and an n-type GaAs contact layer 822 are stacked.

Since the optical path length n _eff L of the optical resonator section 62 and the arrangement of the triple quantum well active layer 821 are the same as those in the first embodiment, detailed description thereof is omitted. Similarly to the second embodiment, an electrode connected to a part of the n-type GaAs contact layer 822 is provided.

As described above, in this embodiment, the C-doped Al _0.98 Ga _0.02 As layer 814 for oxidation confinement is provided on a part of the p-type AlGaAs low refractive index layer 813 close to the optical resonator portion 82. ing. A part of the optical resonator 82 is provided with an n-type contact layer 822 of Si-doped GaAs. The upper DBR layer 83 is composed of three pairs of dielectric DBRs of an SiO ₂ layer 831 / amorphous Si layer 832.

  In this embodiment, the combination of the two DBRs is a p-type semiconductor layer (corresponding to the lower DBR layer 81) and a dielectric layer (corresponding to the upper DBR layer 83), and the semiconductor layer is p-type. Is different from the other embodiments described above. Due to the difference in refractive index between the optical resonator unit 82 and the upper DBR layer 83, the antinodes of the electric field strength are located at these boundaries, and the optical path length of the optical resonator unit 82 may be increased by ΔL as in the first embodiment. The position of the belly of these boundaries does not change. Therefore, when the optical path length is increased by ΔL, the active layer 821 is disposed on the antinode closer to the boundary between the lower DBR layer 81 and the optical resonator unit 82.

  Since this VCSEL structure element fabrication process is the same as that of the related oxide constriction type VCSEL, its detailed description is omitted.

  In this example, the p-type electrode used when operating the surface emitting laser was a titanium (Ti) / gold (Au) p-type electrode from the back side of the substrate. The effective resonator length in the stacking direction of the VCSEL of this example was the same as in Examples 2 and 3, and the relaxation oscillation frequency fr was also equivalent to 26 GHz.

  A p-type electrode may be provided on a part of the p-type semiconductor layer of the first multilayer Bragg reflector 81. Since the p-type substrate and the p-type semiconductor layer have high resistance, it is easy to inject holes into the active layer by applying an electrode with a voltage closer to the active layer.

  In the present embodiment, both the first multilayer Bragg reflector and the second multilayer Bragg reflector described in Embodiment 5 are made of semiconductor DBR.

  FIG. 10 is a schematic diagram showing the band structure of the surface emitting laser of this example. Although the vertical axis and the horizontal axis are not shown in FIG. 10, the vertical axis and the horizontal axis are the same as those in FIG.

  As shown in FIG. 10, the surface emitting laser according to the present embodiment includes a lower DBR layer 91, an upper DBR layer 93, and an optical resonator unit 92 sandwiched between these DBRs. The lower DBR layer 91 corresponds to a first multilayer Bragg reflector, and the upper DBR layer 93 corresponds to a second multilayer Bragg reflector. Each of lower DBR layer 91 and upper DBR layer 93 is composed of a semiconductor DBR.

  The lower DBR layer 91 includes a plurality of pairs of this combination with a pair of the n-type GaAs high refractive index layer 911 and the n-type AlGaAs low refractive index layer 912 as a basic unit. An n-type AlGaAs graded layer 913 is provided between the low refractive index layer and the high refractive index layer in order to reduce electric resistance. The optical resonator unit 92 has a triple quantum well active layer 921.

The upper DBR layer 93 includes a plurality of pairs of a p-type AlGaAs low refractive index layer 931 and a p-type GaAs high refractive index layer 932. A part of the p-type AlGaAs low refractive index layer 933 near the optical resonator portion 92 is a p-type AlGaAs oxide constriction layer (current confinement layer) 933 which is a current confinement layer. The p-type AlGaAs oxidation confinement layer 933 is, for example, a C-doped Al _0.98 Ga _0.02 As layer.

  As described above, in this embodiment, the n-type semiconductor DBR portion (corresponding to the lower DBR layer 91) is formed on the n-type GaAs substrate, and the optical resonator portion 92 and the p-type semiconductor DBR portion (upper portion) are formed thereon. DBR layer 93) is sequentially formed. The current confinement layer 933 is provided at the low refractive index layer closest to the optical resonator 92 in the p-type semiconductor DBR portion. The n-side electrode can be taken from the front side or the back side.

  In this embodiment, semiconductor DBRs are used for the lower DBR layer 91 and the upper DBR layer 93 provided above and below the optical resonator unit 92. For this reason, the light penetration length of this part is as large as about 0.47 μm on one side, and even if the optical path length of the optical resonator unit 92 is about halved, the total effective resonator length is not so small.

  In this embodiment, the effective resonator length is about 1.15 μm. This is 0.93 times the effective resonator length (about 1.242 μm) of the VCSEL of the related λ resonator, the current modulation efficiency of fr is about 1.04 times, and the relaxation oscillation frequency fr is about 21 GHz. Be expected.

  In any of the first to sixth embodiments described above, an example where the oscillation wavelength of the surface emitting laser is 1070 nm is given, but the same effect is expected in different wavelength bands using other material systems.

  In addition, although selective oxidation of AlGaAs is used for a part of the current confinement structure, a current confinement structure in which ions such as protons are implanted instead may be used. Further, although the number of wells in the quantum well structure is set to 3, the number of wells is not limited to this as long as a gain necessary for oscillation can be obtained.

The optical path length n _eff L of the optical resonator has been described as 0.6λ, but the optical path length n _eff L may be in the range of 0.5λ <n _eff L ≦ 0.7λ. Further, although the VCSEL is formed on the n-type GaAs substrate, the stacking order may be reversed using a p-type substrate. Further, although the p-type oxidation current confinement structure is shown as the current confinement structure in the sixth embodiment, an n-type oxidation current confinement structure as shown in the third embodiment may be used.

  Although the present invention has been described with reference to the exemplary embodiments and examples, the present invention is not limited to the above exemplary embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  This application incorporates all the contents of Japanese Patent Application No. 2006-352535 filed on Dec. 27, 2006, and claims priority based on this Japanese application.

Claims (7)

A first multilayer Bragg reflector including a first layer and a first high refractive index layer having a higher refractive index than that of the first layer; and a second layer and a refractive index higher than that of the second layer. An optical resonator unit including a second multilayer Bragg reflector including a large second high-refractive index layer, and an active layer unit sandwiched between the first and second multilayer Bragg reflectors and generating an optical gain A surface emitting laser having:
The layer in contact with the optical resonator unit in the first multilayer Bragg reflector is the first layer, and the layer in contact with the optical resonator unit in the second multilayer Bragg reflector is The second layer;
The effective refractive index n _eff of the resonator part is larger than that of the first and second layers, and the optical path length n _eff L of the optical resonator part is determined by the oscillation wavelengths λ and 0.5λ of the surface emitting laser. <N _eff L ≦ 0.7λ,
When the value obtained by subtracting 0.5λ from the optical path length n _eff L is ΔL, from the boundary between the optical resonator section and the first multilayer Bragg reflector or the second multilayer Bragg reflector A surface emitting laser in which the active layer portion is provided at a position apart by ΔL. The first layer and the first high refractive index layer are semiconductor layers;
The second layer and the second high refractive index layer are dielectric layers;
The boundary between the second multilayer Bragg reflector and the optical resonator is located at the antinode portion of the electric field strength,
The surface emitting laser according to claim 1, wherein the active layer portion is provided at a position separated by ΔL from the boundary of the first multilayer Bragg reflector. The first layer and the first high refractive index layer have n-type conductivity;
A tunnel junction having a current confinement effect is provided in the node portion of the electric field strength in the optical resonator, and the n-type conductivity is closer to the second multilayer Bragg reflector than the tunnel junction. A contact layer is formed,
The surface emitting laser according to claim 2, wherein an electrode is provided on a part of the contact layer. The first layer and the first high refractive index layer have n-type conductivity;
A current confinement structure is provided in a portion of the first layer;
A tunnel junction is provided at the node portion of the electric field strength in the optical resonator, and a contact layer having n-type conductivity is provided closer to the second multilayer Bragg reflector than the tunnel junction. Formed,
The surface emitting laser according to claim 2, wherein an electrode is provided on a part of the contact layer.   5. The surface emitting laser according to claim 3, wherein a part of the first multilayer Bragg reflector includes a semiconductor and a layer obtained by oxidizing a semiconductor having a constituent element different from that of the semiconductor. The first layer and the first high refractive index layer have p-type conductivity;
A current confinement structure is provided in a portion of the first layer;
In the optical resonator portion, a contact layer having n-type conductivity is formed closer to the second multilayer Bragg reflector than the active layer portion,
A first electrode having p-type conductivity is provided on a part of the first multilayer Bragg reflector;
The surface emitting laser according to claim 2, wherein a second electrode is provided on the contact layer. The first layer and the first high refractive index layer are semiconductor layers having a first conductivity type;
The second layer and the second high refractive index layer are semiconductor layers having a second conductivity type;
The surface emitting laser according to claim 1, wherein at least one of the first multilayer Bragg reflector and the second multilayer Bragg reflector has a current confinement structure.

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