JP4409484B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a surface emitting semiconductor laser device.

  In recent years, demand for semiconductor light emitting devices such as semiconductor laser devices has increased as light sources for optical recording and optical communication. Among these, the surface emitting semiconductor laser device has features such as a low threshold current, a circular beam spot, easy direct coupling with an optical fiber, and inspection in a wafer state. It is expected as a light emitting device with low power and low cost.

A surface emitting laser device has a structure in which an active layer having a multiple quantum well structure is sandwiched between an n-type mirror made of an n-type semiconductor laminated film and a p-type mirror made of a p-type semiconductor laminated film. Is known (for example, see Patent Document 1). The emitted light generated in the active layer is transmitted inside a resonator constituted by an n-type mirror and a p-type mirror, and is emitted to the outside from an opening provided on the p-type mirror side.
JP 2003-188471 A

  However, the conventional surface emitting semiconductor laser device has a problem that the polarization mode is not stable. The light emitted from the semiconductor laser device has three modes: a longitudinal mode, a transverse mode, and a polarization mode. Among these, stabilization of the polarization mode is very important when the surface emitting laser device is applied to optical communication. However, in the conventional surface-emitting type semiconductor laser device, since the device structure is symmetric, a gain difference between orthogonally polarized waves cannot be obtained. For this reason, since the polarization mode is not stable, switching in the polarization direction easily occurs due to subtle changes in external conditions such as temperature and drive current. As a result, excessive noise and mode contention are likely to occur during optical communication, resulting in an increase in errors and a limitation on the transmission band.

  In the conventional surface emitting semiconductor laser device, since the p-type mirror is formed of a semiconductor laminated film having a heterojunction, the valence band spike generated at the heterojunction interface restricts the electric conduction of holes. There is a problem that a very large applied voltage is required to operate the surface emitting laser. In particular, the p-type mirror needs to be processed into a post structure, and the cross-sectional area becomes small, so that the series resistance of the element becomes very large. When the series resistance of the element increases, the modulation band of the laser is limited, which becomes an obstacle when used for high-speed optical communication. Further, the high resistance leads to a problem that heat is generated in the p-type mirror. Since the cross-sectional area of the p-type mirror is small, the generated heat is not released sufficiently. As a result, the light emission efficiency of the laser is lowered and high-speed modulation operation becomes difficult.

  An object of the present invention is to solve the above-mentioned conventional problems and to realize a semiconductor light emitting device used for high-speed optical communication in which the polarization mode of emitted light is stable and the modulation band of the laser is wide.

  In order to achieve the above-described conventional object, the present invention has a configuration in which a semiconductor light emitting device includes a metal film provided with an opening and a resin film for flattening a mesa.

  Specifically, the semiconductor light emitting device of the present invention includes a resonator having a mesa portion including an active layer formed on a substrate and insulated by a recess formed in the periphery, a resin layer filling the recess, and a resonance And a metal film provided on a light extraction surface for extracting emitted light from the active layer in the vessel and having an opening having a diameter smaller than the emission wavelength of the emitted light.

  According to the semiconductor light emitting device of the present invention, since the metal film having the opening having a diameter smaller than the emission wavelength of the emitted light is provided, the emitted light having a high TM polarization component ratio can be obtained. In addition, since the resistance value of the light emitting device can be reduced, the operating voltage can be reduced. Furthermore, since the resin layer that fills the concave portion is provided, the parasitic capacitance of the light emitting device can be reduced, so that a high-speed modulation operation is possible. As a result, a semiconductor device used for high-speed optical communication in which the polarization mode is stabilized can be realized.

  In the semiconductor light emitting device of the present invention, it is preferable that a plurality of openings are formed and periodically arranged.

  In the semiconductor light emitting device of the present invention, the diameter of the opening is preferably less than or equal to one half of the emission wavelength.

  In the semiconductor light emitting device of the present invention, the light extracted from the light extraction surface is laser light, and the value of the ratio of the TM polarization component intensity to the TE polarization component intensity of the laser light is 2 or more. preferable. With such a configuration, a semiconductor light emitting device with a stable polarization direction can be reliably realized even when changes in external conditions such as temperature and driving current occur.

  In the semiconductor light emitting device of the present invention, it is preferable that the openings are arranged in a lattice shape in the metal film.

In the semiconductor light emitting device of the present invention, when the opening period of the opening is P, the dielectric constant of the metal film is ε ₁ , the dielectric constant of the member in contact with the metal film is ε ₂ , and i and j are non-negative integers, P Preferably satisfies the relationship P = λ × (i ² + j ² ) ^0.5 / (ε ₁ ε ₂ / (ε ₁ + ε ₂ )) ^0.5 . With such a configuration, energy conversion between light and surface plasmon can be performed efficiently, so that the light output of the semiconductor light emitting device can be increased.

  In the semiconductor light emitting device of the present invention, the metal film preferably has openings arranged in a triangular lattice shape or a hexagonal lattice shape. With such a configuration, the density of the openings can be increased, so that the light transmittance of the metal film can be improved.

  In the semiconductor light emitting device of the present invention, the shape of the opening surface of the opening is preferably an anisotropic shape. By adopting such a configuration, the refractive index distribution becomes asymmetric at the light exit surface. Therefore, since the gain of the resonator changes depending on the polarization direction, the polarization control becomes easy.

  In the semiconductor light emitting device of the present invention, the metal film preferably has a thickness of 100 nm or more and 500 nm or less. By adopting such a configuration, it is possible to improve the attenuation factor of the TE polarization component while keeping the transmittance of the TM polarization component high.

  In the semiconductor light emitting device of the present invention, the metal film is preferably made of silver, gold or aluminum. The metal film is preferably formed of two layers made of different materials. In this case, of the two layers of the metal film, the upper layer is preferably thinner than the lower layer, and the lower layer is preferably made of silver, gold, or aluminum. Of the two layers of the metal film, the lower layer is preferably made of silver, and the upper layer is preferably made of gold. With such a configuration, conversion of light into surface plasmon is facilitated.

  The semiconductor light emitting device of the present invention preferably further includes an intermediate layer formed on the surface of the metal film on the active layer side. By adopting such a configuration, it is possible to prevent the semiconductor layer from being damaged in the metal film forming process or the like.

  In the semiconductor light emitting device of the present invention, the intermediate layer preferably has a film thickness that corrects a phase change when the emitted light is reflected by the metal film. By adopting such a configuration, the phase shift of the reflected light from the metal film is suppressed, and a reflecting mirror having a high reflectance can be realized. In this case, the thickness of the intermediate layer is such that d is 0.6 × λ / when the thickness of the intermediate layer is d, the refractive index of the intermediate layer is n, the wavelength of the emitted light is λ, and i is a non-negative integer. It is preferable that the relationship of n × (1/4 + 1 / 2i) ≦ d ≦ λ / n × (1/4 + 1 / 2i) is satisfied.

  In the semiconductor light emitting device of the present invention, the intermediate layer is preferably a dielectric film. In this case, the dielectric is preferably a single layer film made of any one of silicon oxide, silicon nitride, aluminum oxide, titanium oxide and tantalum oxide, or a laminated film made of two or more.

  In the semiconductor light emitting device of the present invention, the intermediate layer is preferably a transparent conductive film. With such a configuration, the contact resistance can be reduced without reducing the light emission efficiency. In this case, the transparent conductive film is preferably tin-doped indium oxide (ITO), zinc oxide, or tin oxide.

  In the semiconductor light emitting device of the present invention, the intermediate layer is preferably a semiconductor laminated film.

  The semiconductor light emitting device of the present invention further includes two reflecting mirrors provided on the light extraction surface side and the side opposite to the light extraction surface of the active layer, and the metal film functions as a reflection mirror provided on the light extraction surface side. It is preferable to do.

  In the semiconductor light emitting device of the present invention, the reflecting mirror provided on the light extraction surface side preferably includes a first semiconductor multilayer film formed on the active layer side surface of the metal film.

  In the semiconductor light emitting device of the present invention, it is preferable that the stacking period of the first semiconductor multilayer film is adjusted according to the reflectance of the metal film. In this case, the stacking cycle of the first semiconductor multilayer film is preferably 9 cycles or more and 22 cycles or less. With such a configuration, it is possible to increase the reflectance of the reflecting mirror and to keep the resistance value of the device low.

  In the semiconductor light emitting device of the present invention, the reflectance of the reflecting mirror is preferably 99.4% or more and 99.9% or less. With such a configuration, the light output can be improved.

  In the semiconductor light emitting device of the present invention, the reflecting mirror provided on the surface opposite to the light extraction surface is preferably a reflecting mirror made of a second semiconductor multilayer film.

The semiconductor light emitting device of the present invention preferably further comprises an upper layer formed on the surface of the metal film opposite to the surface on the active layer side.
With such a configuration, surface plasmon resonance can be generated also at the interface between the metal film and the upper layer, and re-conversion from surface plasmon to light can be performed efficiently. In addition, the metal film can be protected.

  In the semiconductor light emitting device of the present invention, the first protective layer formed between the resin layer and the side and bottom surfaces of the recess, the second protective layer covering the upper surface of the resin layer, and the second protective layer And an electrode for injecting current into the active layer. By adopting such a configuration, it is possible to reliably reduce the parasitic capacitance due to the electrodes.

  In the semiconductor light emitting device of the present invention, it is preferable that the resin layer is completely surrounded by the first protective layer and the second protective layer.

In the semiconductor light emitting device of the present invention, the first protective layer and the second protective layer are preferably any of SiO ₂ , SiN, SiON, Nb ₂ O ₅ , ZrO _2, and Ta ₂ O ₅ .

  In the semiconductor light emitting device of the present invention, it is preferable that at least a part of the resin layer is located higher than the upper surface of the mesa portion. By adopting such a configuration, the thickness of the resin layer can be increased, and the parasitic capacitance can be further reduced.

  In the semiconductor light emitting device of the present invention, it is preferable that the upper surface of the resin layer and the upper surface of the mesa portion are connected flat. With such a configuration, it is possible to improve the processing accuracy when forming the fine opening in the metal film. In addition, disconnection of the electrode can be prevented.

  In the semiconductor light emitting device of the present invention, the relative dielectric constant of the resin layer is preferably 3 or less. In this case, the resin layer is preferably a benzocyclobutene resin.

  The semiconductor light emitting device of the present invention is provided between the active layer and the metal film in the mesa portion, and is a high resistance region which is a selectively oxidized region or a region where protons are selectively implanted. And a current confinement layer including a current confinement region surrounded by the high resistance region. In this case, the diameter of the current confinement region is preferably 10 μm or less. With such a configuration, the relaxation oscillation frequency can be increased and the modulation band can be improved.

In the semiconductor light emitting device of the present invention, it is preferable that the diameter of the mesa portion is adjusted so that the capacity of the mesa portion is equal to or more than half of the capacity of the entire device.
By adopting such a configuration, the influence of the parasitic capacitance other than the mesa portion is relatively reduced, so that the product value of the capacitance value and the resistance value of the entire device can be reduced, so that high-speed modulation can be performed. It becomes possible.

  In the semiconductor light emitting device of the present invention, the side surface of the mesa portion is preferably inclined. By adopting such a configuration, since the stress applied to the resin layer in contact with the first protective layer formed on the side surface of the mesa portion is uniform, it is possible that a void is generated between the resin layer and the mesa portion. Can be prevented.

  According to the semiconductor light emitting device of the present invention, it is possible to realize a semiconductor light emitting device used for high-speed optical communication in which the polarization mode of the emitted light is stable and the modulation band of the laser is wide.

(First embodiment)
A semiconductor light emitting device according to a first embodiment of the present invention will be described with reference to the drawings. 1A and 1B show a semiconductor light emitting device according to the first embodiment. FIG. 1A shows a planar configuration, and FIG. 1B shows a cross-sectional configuration taken along line Ib-Ib in FIG. Yes.

  As shown in FIG. 1, on a substrate 10 made of n-type GaAs, a first reflecting mirror 11 made of an n-type semiconductor multilayer film, a lower spacer layer 12, a quantum well layer 13, an upper spacer layer 14, and a current confinement layer. 16, a second reflecting mirror 17 made of a p-type semiconductor multilayer film and a p-type contact layer 18 are sequentially stacked.

The first reflecting mirror 11 is a multilayer film in which n-type Al _0.12 Ga _0.88 As layers and n-type Al _0.90 Ga _0.10 As layers are alternately stacked, and silicon is used for n-type impurities. . The thickness of each layer is λ / 4n (λ: laser oscillation wavelength, n: refractive index of the medium), and 34.5 cycles are laminated.

The quantum well layer 13 is formed by alternately stacking three periods of a well layer made of non-doped GaAs and a barrier layer made of Al _0.30 Ga _0.70 As. The lower spacer layer 12 and the upper spacer layer 14 are Al _0.30 Ga _0.70 As layers, respectively, and the total thickness of the quantum well active layer 15 constituted by the quantum well layer 13, the lower spacer layer 12, and the upper spacer layer 14 is λ. / N (λ: laser oscillation wavelength, n: refractive index of the medium).

The current confinement layer 16 is made of a p-type Al _0.98 Ga _0.02 As layer, and is formed so that a high resistance region 16b formed by oxidation surrounds the current confinement region 16a through which current flows. The second reflecting mirror 17 is a multilayer film in which nine periods of Al _0.12 Ga _0.88 As layers and Al _0.90 Ga _0.10 As layers, which are doped with carbon as a p-type impurity, are alternately stacked. The p-type contact layer 18 is made of a p-type GaAs layer, and is doped with carbon, which is a p-type impurity, at a concentration of 1 × 10 ¹⁹ cm ⁻³ or more in order to reduce the contact resistance with the upper contact electrode 27. .

  A part of the element formation region composed of the first reflecting mirror 11, the active layer 15, the current confinement layer 16, the second reflecting mirror 17, and the p-type contact layer 18 is selectively selected until the first reflecting mirror 11 is exposed. A mesa portion 30 made of an active layer 15, a current confinement layer 16, a second reflecting mirror 17, and a p-type contact layer 18 is formed separated from other regions by a recess formed by etching.

In the mesa portion 30, an intermediate layer 21 made of silicon oxide (SiO ₂ ) having a thickness of 113 nm is formed on the p-type contact layer 18, and gold (Au) or silver (Ag) is formed on the intermediate layer 21. A metal film 23 having a thickness of 200 nm is formed. In the metal film 23, a plurality of openings 23a each having a diameter smaller than the oscillation wavelength of the laser light are periodically formed. The metal film 23 is covered with an upper layer 22 made of silicon nitride (SiN) having a thickness of 200 nm, which prevents the metal film 23 from being deteriorated and also at the interface between the upper surface of the metal film 23 and the upper layer 22. The surface plasmon excitation condition is satisfied. Therefore, reconversion of energy from surface plasmons to light is efficiently performed.

  In the semiconductor light emitting device of this embodiment, the metal film 23 functions as an upper reflecting mirror together with the second reflecting mirror 17, and a mesa having an active layer 15 sandwiched between the first reflecting mirror 11 and the metal film 23. A resonator region 31 having a portion 30 is formed.

A first protective film 24 is formed so as to cover the side wall and bottom surface of the recess surrounding the mesa portion 30. The first protective film 24 is composed of a SiO ₂ film, a SiN film, a SiON film, a Nb ₂ O ₅ film, a ZrO film. It is an inorganic insulating film of _two films or a Ta ₂ O ₅ film. A resin film 25 made of benzocyclobutene (BCB) resin is formed so as to fill the concave portion covered with the first protective film 24. A second protective film 26 is formed so as to cover the upper surface of the resin film 25 and the upper surface of the element formation region except for the central portion of the mesa unit 30. The resin film 25 includes the first protective film 24 and the first protective film 24. Two protective films 26 are surrounded.

  An upper contact electrode 27 is formed on the upper surface of the second protective film 26 so as to partially contact the p-type contact layer 18, and a lower contact electrode 28 is formed on the lower surface of the substrate 10. When a bias voltage is applied between the upper contact electrode 27 and the lower contact electrode 28, the current injected from the portion of the upper contact electrode 27 in contact with the p-type contact layer 18 enters the current confinement portion 16 a in the current confinement layer 16. After constriction, the quantum well layer 13 is injected, and carrier recombination occurs in the quantum well layer 13. As a result, the light emission generated in the quantum well layer 13 is a resonator region formed between the lower reflecting mirror made of the first reflecting mirror 11 and the upper reflecting mirror made of the second reflecting mirror 17 and the metal film 23. The laser beam oscillates in the laser beam 31 and becomes laser light. In the semiconductor light emitting device of this embodiment, the oscillation wavelength is about 850 nm.

  In the semiconductor light emitting device of this embodiment, since the metal film 23 is periodically provided with the openings 23a, the light that reaches the metal film 23 from inside the resonator region 31 is easily converted into surface plasmons. It is in. The excited surface plasmon is again converted into light and emitted outside the resonator region 31. As a result, light transmission that is orders of magnitude greater than the transmittance determined by the area of the opening 23a is generated, so that laser light can be emitted from the metal film 23 to the outside.

FIG. 2 shows a result of studying light emission from a metal film provided with an opening. In FIG. 2, the horizontal axis indicates the wavelength of light incident on the metal film, and the vertical axis indicates the intensity of light transmitted through the metal film. The metal film used in FIG. 2 was Ag, and was formed on a SiO ₂ film having a thickness of 113 nm formed on a quartz substrate. In the metal film, circular openings were formed in a square lattice pattern by electron beam (EB) lithography and etching. Further, in order to protect the metal film, it was covered with a SiN film having a thickness of 200 nm. The metal film has a thickness of 200 nm and the opening has a diameter of 200 nm. Moreover, the opening period which is the distance between the centers of adjacent openings was 550 nm.

As shown in FIG. 2, the phenomenon of transmitting through the metal film was observed even with light having a wavelength longer than the diameter of the opening. When the openings are arranged in a square lattice shape, it is known that the opening period P of the openings that excite the surface plasmons can be obtained by the following formula 1.
P = λ × (i ² + j ² ) ^0.5 / (ε ₁ ε ₂ / (ε ₁ + ε ₂ )) ^0.5 Equation 1
Here, i and j are integers of 0 or more, ε ₁ is the dielectric constant of the metal in which the opening is formed, and ε ₂ is the dielectric constant of the medium in contact with the metal.

In FIG. 2, the intensity of transmitted light is strongest at a wavelength of 1150 nm. Since the dielectric constant of Ag at a wavelength of 1150 nm is −49 and the dielectric constant of SiN is 4, assuming that i ² + j ² is 1, the aperture period P at which surface plasmon resonance occurs at a wavelength of 1150 nm is 550 nm from Equation 1. Become. This coincides with the opening period of the opening formed in the metal film used for measurement. Therefore, it is clear that the peak of transmitted light intensity at a wavelength of 1150 nm originates from surface plasmon resonance at the interface between Ag and SiN.

In FIG. 2, a peak is also observed at a wavelength of 886 nm. This is because Ag has a dielectric constant of −33.5 at a wavelength of 886 nm and SiO _{2 has} a dielectric constant of 2.25. It is clear that it originated from surface plasmon resonance at the interface with ₂ . Furthermore, we examined in detail the change in peak wavelength when the incident angle of the light incident on the metal film was changed, but we obtained results supporting that surface plasmon resonance is involved in the transmission of such light. It was.

  FIG. 3 shows the result of measuring the relationship between the opening period of the opening and the output of the semiconductor light emitting device for the semiconductor light emitting device of this embodiment. In FIG. 3, the horizontal axis indicates an aperture ratio which is the ratio between the aperture diameter of the aperture and the emission wavelength, and the vertical axis indicates the output of light extracted from the apparatus. The semiconductor light emitting device used for the measurement has an emission wavelength of about 850 nm, a film made of silver having a thickness of 200 nm is used as the metal film 23, and an upper portion made of SiN having a thickness of 200 nm covering the metal film 23. Layer 22 is provided. The injection current was 5 mA.

As shown in FIG. 3, when the aperture period of the aperture is 450 nm and 550 nm, the light output is about twice as large as when the aperture period is 650 nm and 750 nm. The opening periods of the openings that satisfy the surface plasmon resonance at the interface between Ag and SiN and the interface between Ag and SiO ₂ at a wavelength of 850 nm are 450 nm and 550 nm, respectively, from Equation 1. Therefore, it is clear that the light output is improved by the surface plasmon resonance.

From the continuous condition of the electric flux density at the interface between the resonator region 31 and the metal film 23, the polarization component of light capable of exciting the surface plasmon is only TM polarization (Transverse Magnetic Wave), and TE polarization. (Transverse Electric Wave) cannot excite surface plasmons. For this reason, the TE polarization component is greatly attenuated in the metal film as is generally known. In the case of a metal film made of Au, Ag, or the like having a thickness of 200 nm as in this embodiment, the light transmittance of the metal film 23 is as small as 10 ⁻⁷ cm ⁻³ or less. Almost no polarized light component is emitted. As for light transmission through the opening, it is known that if the diameter of the opening is smaller than the wavelength, the light transmittance is proportional to (d / λ) ⁴ when the diameter of the opening is d. When the aperture diameter is small with respect to the wavelength as in this embodiment, the light transmittance is also small. Therefore, TE polarized light is hardly emitted to the outside, and only TM polarized light that can excite surface plasmons is emitted from the metal film 23 to the outside.

  As described above, the metal film 23 provided with the openings 23 periodically makes it possible to selectively extract the TM polarization of the laser light out of the resonator region 31 and emit it from the surface emitting laser device. It becomes possible to control the polarization mode of the laser beam.

  FIG. 4 shows the result of simulating the light transmittance of a metal film having an opening formed on a glass substrate. An FDTD (Finite Difference Time Domain) method was used for the simulation. Note that the metal film was Au having a thickness of 200 nm, and the opening period was 550 nm. For each of the cases where the excitation light is TE polarized light and TM polarized light, the transmittance was calculated by changing the aperture diameter, and the dependency of the light transmittance on the aperture ratio was obtained.

  As shown in FIG. 4, when the aperture ratio is reduced with respect to the TE polarized light, the light transmittance is rapidly reduced. When the aperture ratio is less than 0.4, the TE polarized light is cut off. On the other hand, for TM polarized light, although the light transmittance decreases as the aperture ratio decreases, light transmission is possible even when the aperture ratio is about 0.2. This result shows that light transmission through the surface plasmon occurs in the TM polarized light.

FIG. 5 shows a result obtained by simulating the aperture diameter dependence of the polarization ratio (TM / TE), which is the ratio of the intensity of the TM polarized light and the intensity of the TE polarized light. As shown in FIG. 5, it is clear that a large polarization ratio can be obtained by reducing the aperture diameter. This is because the light transmission through the opening decreases as the opening diameter becomes smaller, and the effect of light transmission through the surface plasmon becomes remarkable. From the above results, the opening diameter of the opening should be less than the emission wavelength. Thus, the polarization mode can be controlled so that the intensity of the TM polarization component is higher than the intensity of the TM polarization component. In addition, by setting the aperture diameter to ½ or less of the emission wavelength, a semiconductor light emitting device having a deflection ratio of 2 or more generally suitable for optical communication can be obtained.

  In general, since a surface emitting laser has a short resonator length, a reflecting mirror having a high reflectance of 99% or more is required on the light emitting surface side in order to obtain laser oscillation. FIG. 6 shows the result of obtaining the light output of the semiconductor light emitting device in this embodiment by simulation. The injection current is calculated as 5 mA. As shown in FIG. 6, it is clear that a high light output can be obtained by increasing the reflectance of the reflecting mirror on the light exit surface side. For example, in order to obtain a light output of 1 mW or more when a current of 5 mA is injected, it is necessary to set the reflectance of the reflection intensity on the light emitting surface side to 99.4% or more. On the other hand, according to FIG. 6, the light output becomes maximum at a reflectance of 99.9%, and the light output decreases conversely at a reflectance higher than this.

  In order to obtain such a reflectance, it is effective to combine a reflecting mirror made of a metal film and a reflecting mirror made of a semiconductor multilayer film. In order to obtain such a high reflectivity by using only a reflector made of a semiconductor multilayer film, the period must be 20 cycles or more and 25 cycles or less. Thus, when the reflective mirror which consists of a multi-cycle semiconductor multilayer film is provided, the element resistance of a semiconductor light-emitting device will rise. However, in the semiconductor light emitting device of this embodiment, since the metal film 23 and the second reflecting mirror 17 made of a semiconductor multilayer film are combined, the stacking period of the second reflecting mirror 17 is about nine. Good. Therefore, an increase in element resistance of the semiconductor light emitting device can be suppressed, and the element can be operated at high speed. Further, since the heat resistance of the metal is extremely small, the heat generated in the metal film 23 can be efficiently released to the outside, so that the heat dissipation of the element can be improved.

  Since the reflectance of the metal film 23 varies depending on the material of the metal film 23 and structural parameters such as the diameter of the opening 23a, the period of the second reflecting mirror 17 may be set appropriately. Specifically, the stacking cycle of the second reflecting mirror 17 may be 9 cycles or more and 22 cycles or less.

  In the present embodiment, the thickness of the intermediate layer 21 is 113 nm. The intermediate layer 21 is formed by the metal film 23, the intermediate layer 21, and the upper electrode 17 by setting the film thickness of the intermediate layer 21 to about 0.8 times the 1 / 4th of the emission wavelength λ (n is the refractive index of the intermediate layer). The Bragg condition of the reflecting mirror can be satisfied. Therefore, it is possible to compensate for the phase change caused by the light absorption of the metal film 23, and the reflectance of the reflecting mirror formed by the metal film 23, the intermediate layer 21, and the upper electrode 17 can be maximized.

FIG. 7 shows the result of calculating the dependence of the reflectance and phase change on the SiO ₂ film thickness when light with a Bragg wavelength is incident on a reflector composed of Au, SiO ₂ , and a nine-layer semiconductor multilayer film. . As shown in FIG. 7, when the film thickness is 113 nm, that is, 0.8 × λ / (4n), the reflectance becomes maximum. In addition, in the region where the film thickness of SiO ₂ is 85 nm (0.6 × λ / (4n)) or more and 142 nm (λ / (4n)) or less, the phase change of reflected light is suppressed, and the high reflectance is obtained. can get.

  Further, the intermediate layer 21 may be formed of a transparent conductive material such as ITO (tin doped indium oxide), zinc oxide, or tin oxide. By doing so, an electrode can be formed also on the mesa portion 30, so that a semiconductor light emitting device with low contact resistance can be realized. Further, the intermediate layer 21 may be a dielectric multilayer film or a semiconductor multilayer film to have the function of a reflective film.

  In the semiconductor light emitting device of this embodiment, since the thickness of the second reflecting mirror 17 is reduced, the height of the mesa unit 30 is reduced. In general, when the distance between the upper contact electrode 27 and the first reflecting mirror 11 is reduced, the parasitic capacitance of the element is increased. However, in the semiconductor light emitting device of the present embodiment, since the concave portion forming the mesa portion 30 is buried with the resin film 25 made of BCB resin having a low dielectric constant, the upper contact electrode 27 is connected to the first reflecting mirror 11. The parasitic capacitance formed between them can be reduced.

  Moreover, since the step structure around the mesa portion 30 can be eliminated by embedding the recess with the resin film 25, a flat resist can be formed when the opening 23a is formed in the metal film 23. It becomes. As a result, the metal film 23 having excellent accuracy and reproducibility of the opening diameter and opening period of the opening 23a can be formed. Further, it is possible to prevent the upper contact electrode 27 from being disconnected at the step portion.

  FIG. 8 shows the result of estimating the modulation band of the laser device limited by the parasitic capacitance and the series resistance. The 3 dB modulation band is about 10 GHz in the conventional laser device, whereas in the semiconductor light emitting device of the present invention, the series resistance is reduced by not providing the upper multilayer reflector and the parasitic capacitance by embedding the low dielectric constant material. As a result of this reduction, the modulation band is improved by a factor of four or more. According to FIG. 8, a high modulation band exceeding 40 GHz is obtained when the width of the mesa portion is 22 μm or more. The reason why the modulation band is improved when the diameter of the mesa portion is increased is that the influence of the parasitic capacitance other than the mesa portion is relatively reduced, and the product of the capacitance and resistance of the entire element is reduced.

  By the way, it is necessary to consider the relaxation oscillation frequency as a factor for limiting the modulation band of the laser. Since the relaxation oscillation frequency is inversely proportional to the half power of the laser resonator volume, it is preferable to reduce the width (oxidized aperture diameter) of the current confinement portion 16a in the current confinement layer 16. FIG. 9 shows the result of estimating the dependence of the oxidized aperture diameter on the modulation band limited by the relaxation oscillation frequency. The light output is set to 2 mW. The modulation band is improved by reducing the oxidized aperture diameter. As shown in FIG. 9, by setting the oxidized aperture diameter to 10 μm or less, a high modulation band of 15 GHz or more can be obtained.

  In addition, although the example which uses gold | metal | money or silver as the metal film 23 was shown, you may use aluminum etc. The metal film 23 may be a laminated film. For example, the metal film 23 may be formed by sequentially laminating a first metal film made of Ag having a thickness of 50 nm and a second metal film made of Al having a thickness of 150 nm. By using Ag for the first metal film, surface plasmons can be generated efficiently, and oxidation of Ag can be prevented by providing a second metal film made of Al on the top. Also, a combination of Au and Ag may be used. In this case, it is preferable to make the upper layer thinner than the lower layer.

  Further, the example in which the film thickness of the metal film 23 is 200 nm is shown. However, if the film thickness is 100 nm or more, it is possible to sufficiently attenuate the TE polarization component and prevent the attenuation of the TM polarization component. Therefore, the film thickness is preferably 500 nm or less.

  The planar shape of the opening surface of the opening 23 a provided in the metal film 23 is not limited to a circular shape, and may be an elliptical shape or a rectangular shape having anisotropy. By making the planar shape of the opening surface of the opening 23a an anisotropic shape, the refractive index distribution in the metal film 23 can be made asymmetric. Therefore, since the resonator gain can be changed depending on the polarization direction, the polarization control becomes easy.

  Further, the arrangement of the openings 23a may be a triangular lattice shape or a hexagonal lattice shape in addition to the square lattice shape. The triangular lattice shape or the hexagonal lattice shape can increase the density of the openings, so that the light transmittance can be increased.

  In the present embodiment, the intermediate layer 21 is provided between the metal film 23 and the p-type contact layer 18, but the intermediate layer 21 is not provided and the metal film 23 is formed directly on the p-type contact layer 18. Also good. In this case, since the medium in contact with the metal film is GaAs, it is necessary to change the opening period of the opening 23.

  For example, when the emission wavelength is 850 nm, the dielectric constant of GaAs is 13.3, so the aperture period P may be 180 nm.

  Moreover, although the example which forms the upper layer 22 which covers the metal film 23 was shown, the upper layer 22 does not necessarily need to be provided. Further, the upper layer 22 and the intermediate layer 21 may be formed of the same material. Further, the upper layer 22 does not need to cover the side surface of the metal film 23 in order to cause surface plasmon resonance at the interface between the metal film 23 and the upper layer 22.

  In the present embodiment, the resin film 25 is formed of BCB resin, but SiLK (registered trademark), fluorinated polyarylene ether-based resin, or the like may be used. Moreover, when forming the mesa part 30, it is preferable that the slope of the mesa part 30 has an inclination. By providing the side surface of the mesa unit 30 with an inclination, the stress applied to the resin film 25 in contact with the first protective film 24 formed on the side surface of the mesa unit 30 can be made uniform. Thereby, since it is possible to prevent a gap from being generated between the mesa portion 30 and the resin film 25, the reliability of the semiconductor light emitting device can be improved.

(Second Embodiment)
A semiconductor light emitting device according to the second embodiment of the present invention will be described below with reference to the drawings. FIG. 10 shows a cross-sectional configuration of the semiconductor light emitting device according to the second embodiment. In FIG. 10, the same components as those in FIG.

  In the semiconductor light emitting device of this embodiment, the second reflecting mirror 17 is not provided, and the upper reflecting mirror is formed only by the metal film 23. Since the semiconductor light emitting device of this embodiment does not have the second reflecting mirror 17, the resistance of the element can be greatly reduced.

  On the other hand, in the semiconductor light emitting device of the present embodiment, the height of the mesa portion 30 becomes very low, and there is a possibility that the parasitic capacitance increases. In this case, it is possible to reduce the parasitic capacitance by forming the resin film 25 thick as necessary and projecting it from the upper surface of the mesa portion 30.

(Third embodiment)
A semiconductor light emitting device according to the third embodiment of the present invention will be described below with reference to the drawings. FIG. 11 shows a cross-sectional configuration of a semiconductor light emitting device according to the third embodiment. In FIG. 11, the same components as those of FIG.

  As shown in FIG. 11, in the semiconductor light emitting device of this embodiment, a dielectric multilayer film 41 is formed under the metal film 23. Since the reflecting mirror is formed by the metal film 23 and the dielectric multilayer film 41, the reflectance of the reflecting mirror can be improved as compared with the case of the metal film 23 alone. Further, since the metal film 23 is not formed on the semiconductor layer, an effect of preventing the metal film 23 from being alloyed can be obtained.

(Fourth embodiment)
The semiconductor light emitting device according to the fourth embodiment of the present invention will be described below with reference to the drawings. FIG. 12 shows a cross-sectional configuration of the semiconductor light emitting device according to the fourth embodiment. In FIG. 12, the same components as those in FIG.

  As shown in FIG. 12, in the semiconductor light emitting device of this embodiment, a contact hole exposing the substrate 10 is formed, and the lower contact electrode 28 is drawn out to the upper surface of the element. For this reason, since wiring can be formed on the same surface of the substrate, the mounting efficiency of the semiconductor light emitting device can be increased.

  The unevenness generated in the semiconductor light emitting device is increased by forming the contact hole, but the upper contact electrode 27 and the lower contact electrode 28 can be planarized by adjusting the film thickness of the resin film 25. .

  In each of the embodiments, the metal film is described as an example in which the metal film is provided in the surface emitting semiconductor laser. However, the metal film is similarly applied to other laser devices such as a Fabry-Perot semiconductor laser, a solid-state laser, or a gas laser. In these cases, the same effects as those shown in each embodiment can be obtained.

(Fifth embodiment)
The method for manufacturing the semiconductor light emitting device according to the fifth embodiment will be described below with reference to the drawings. FIG. 13 shows a method of manufacturing the semiconductor light emitting device according to the fifth embodiment in the order of steps.

As shown in FIG. 13A, the first reflecting mirror 11, the lower spacer layer 12, the quantum well layer 13 and the upper portion are formed on the n-type GaAs substrate 10 by using, for example, metal organic chemical vapor deposition (MOCVD). A quantum well active layer 15 composed of a spacer layer 14, a current confinement layer 16, a second reflecting mirror 17, and a p-type contact layer 18 are successively grown. Subsequently, after a silicon oxide film (SiO ₂ film) is formed on the entire substrate surface using a CVD method or a sputtering method, an SiO ₂ film having a predetermined pattern shape is formed using a photolithography method and a dry etching method.

Next, as shown in FIG. 13B, the p-type contact layer 18, the second reflector 17, the current confinement layer 16, the quantum well active layer 15, and the dry etching method using the SiO ₂ film as an etching mask. The mesa part 30 is formed by etching up to a part of the first reflecting mirror 11. Since this step is intended to expose the current confinement layer 16 on the side surface of the mesa portion 30, it is not always necessary to perform etching until reaching the first reflecting mirror 11.

  After the mesa portion 30 is formed, the mesa portion 30 is oxidized from the outer peripheral portion by being exposed to a steam atmosphere at 400 ° C. for about 15 minutes. The oxidation rate at this time varies depending on the Al content of each layer, and the oxidation rate increases as the Al content increases. Here, by making the Al content of the current confinement layer 16 larger than that of the other layers, the current confinement layer 16 is oxidized faster than the other layers. Accordingly, since the current confinement layer 16 is oxidized except for the central portion of the mesa portion 30, the current confinement portion 16 a has the current confinement portion 16 a at the center portion of the mesa portion 30, and the oxidized high resistance portion 16 b at the peripheral portion of the mesa portion 30. The current confinement layer 16 having can be easily formed.

Next, as shown in FIG. 13C, a first protective film 24 made of SiO ₂ is formed on the upper surface of the mesa unit 30 and the surface of the first reflecting mirror 11. Subsequently, after a resin film 25 made of BCB resin is applied on the first protective film 24, heat treatment is performed in a nitrogen atmosphere to cure the resin film 25. Next, a second protective film 26 made of SiO ₂ is formed so as to cover the upper surface of the resin film 25 and the upper surface of the mesa portion 30. Thereafter, in order to form a contact window necessary for bringing the upper contact electrode 27 and the p-type contact layer 18 into contact with each other, a part of the second protective film 26 formed on the upper surface of the mesa portion 30 is wet-etched. Remove.

  Next, as shown in FIG. 14A, a mask having a predetermined shape is formed at the center of the mesa structure using a photoresist, Ti, Pt and Au are sequentially formed, and then the photoresist is formed by a lift-off method. The upper contact electrode 27 having a predetermined shape is formed.

Next, as shown in FIG. 14B, an intermediate layer 21 made of SiO ₂ having a thickness of 113 nm is formed on the p-type contact layer 18, and then gold having an opening 23a on the intermediate layer 21 is formed. A metal film 23 to be formed is formed using electron beam evaporation and lithography.

  Since the opening diameter and opening period of the opening 23a must be formed accurately, the flatness of the resist used for lithography is required. Conventionally, in order to ensure the flatness of the resist, it has been necessary to form a metal film having an opening before forming the mesa. However, in the manufacturing method of the present embodiment, the recess around the mesa portion 30 is buried with the resin film 25, and the surface of the region where the mesa portion is formed is flattened. Therefore, it is possible to ensure the flatness of the resist, and the metal film 23 having an accurate opening diameter and opening period can be formed. Thereby, it is possible to prevent the metal film 23 from being damaged in the step of forming the mesa portion 30.

  Next, as shown in FIG. 14C, an upper layer 22 made of SiN covering the metal film 23 is formed. Subsequently, after the thickness of the substrate 10 is adjusted to an arbitrary thickness using polishing and etching, a film made of an alloy of Au, Ge, Ni, or the like is formed on the lower surface of the substrate 10 as the lower contact electrode 28. Subsequently, heat treatment is performed in a nitrogen atmosphere at about 400 ° C. for 10 minutes to bring the lower contact electrode 28 and the substrate 10 into contact with each other, and the upper contact electrode 27 and the p-side contact layer 18 are in ohmic contact.

  In the present embodiment, the method for manufacturing the semiconductor light emitting device shown in the first embodiment has been described. However, the semiconductor light emitting device shown in other embodiments can be manufactured in the same manner. Further, although the high resistance region 16b of the current confinement layer 16 is formed by thermal oxidation, it may be formed by proton implantation.

  In the present embodiment, the example in which the upper surface of the resin film 25 is formed so as to coincide with the upper surface of the p-type contact layer 18 has been described. However, if the resin film 25 and the mesa portion 30 are formed without a step. The processing accuracy of the metal film 23 can be improved, and the central portion of the resin film 25 may be protruded.

In this case, the resin film 25 may be formed as follows. After the mesa portion 30 is formed, a first protective film 24 made of SiO ₂ is formed on the upper surface of the mesa portion 30, the side surface of the mesa portion 30, and the surface of the first reflecting mirror 11. Subsequently, after a part of the resin film 25 made of BCB resin is applied on the first protective film 24, heat treatment is performed in a nitrogen atmosphere to cure the resin. BCB resin is applied again on the cured resin.

  Next, the resin film 25 other than the upper surface of the mesa unit 30 is exposed and developed to remove the uncured resin film 25 from the upper surface of the mesa unit 30. Thus, the surface of the resin film 25 on the upper surface of the mesa unit 30 is processed so as to be lower than the surface of the resin film 25 on the peripheral portion of the mesa unit 30.

The resin film 25 is removed by dry etching so that the first protective film 24 is exposed on the upper surface of the mesa unit 30. As a gas for etching, a mixed gas of CF ₄ and O ₂ can be used. Further, the first protective film 24 formed on the surface of the mesa unit 30 is used as a protective film during dry etching. Thereafter, the resin film 25 is cured in a nitrogen atmosphere.

  By doing so, the resin film 25 protruding from the upper surface of the mesa portion 30 can be formed without causing a step between the resin film 25 and the mesa portion 30.

  The semiconductor light-emitting device of the present invention has the effect of realizing a semiconductor light-emitting device used for high-speed optical communication in which the polarization mode of outgoing light is stable and the modulation band of the laser is wide, and includes a surface-emitting laser device. It is useful as a semiconductor light emitting device.

(A) And (b) shows the semiconductor light-emitting device concerning the 1st Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the Ib-Ib line | wire of (a). . It is a graph which shows the light transmittance of the metal film used for the semiconductor light-emitting device concerning the 1st Embodiment of this invention. 4 is a graph showing the relationship between the opening period of the opening and the output in the semiconductor light emitting device according to the first embodiment of the present invention. 5 is a graph showing a relationship between an aperture ratio of an opening and light transmittance in the semiconductor light emitting device according to the first embodiment of the present invention. 4 is a graph showing a relationship between an opening diameter of an opening and a polarization ratio of output light in the semiconductor light emitting device according to the first embodiment of the present invention. It is a graph which shows the relationship between the reflectance of an upper reflective mirror and light output in the semiconductor light-emitting device concerning the 1st Embodiment of this invention. 6 is a graph showing a relationship between a mesa width and a modulation / modulation band in the semiconductor light emitting device according to the first embodiment of the present invention, as compared with a conventional device. 4 is a graph showing a relationship between an aperture diameter and a modulation / modulation band in the semiconductor light emitting device according to the first embodiment of the present invention. 4 is a graph showing a relationship between a film thickness of an intermediate layer, a reflectance, and a phase change in the semiconductor light emitting device according to the first embodiment of the present invention. It is sectional drawing which shows the semiconductor light-emitting device concerning the 2nd Embodiment of this invention. It is sectional drawing which shows the semiconductor light-emitting device concerning the 3rd Embodiment of this invention. It is sectional drawing which shows the semiconductor light-emitting device concerning the 4th Embodiment of this invention. It is sectional drawing which shows the manufacturing method of the semiconductor light-emitting device concerning the 5th Embodiment of this invention in process order. It is sectional drawing which shows the manufacturing method of the semiconductor light-emitting device concerning the 5th Embodiment of this invention in process order.

Explanation of symbols

10 substrate 11 first reflecting mirror 12 lower spacer layer 13 quantum well layer 14 upper spacer layer 15 active layer 16 current confining layer 16a current confining region 16b high resistance region 17 second reflecting mirror 18 p-type contact layer 21 intermediate layer 22 Upper layer 23 Metal film 23a Opening 24 First protective film 25 Resin film 26 Second protective film 27 Upper contact electrode 28 Lower contact electrode 30 Mesa part 31 Resonator region 41 Dielectric multilayer film 51 Contact hole

Claims (35)

A resonator having a mesa portion formed on a substrate, insulated by a recess formed by digging the periphery, and including an active layer;
A resin layer filling the recess;
A metal film provided on a light extraction surface for extracting emitted light from the active layer in the resonator, and having a plurality of openings having a diameter smaller than the emission wavelength of the emitted light;
The plurality of openings are arranged in a triangular lattice or a hexagonal lattice and penetrate the metal film .   2. The semiconductor light emitting device according to claim 1, wherein a diameter of the opening is equal to or less than a half of the emission wavelength. The light extracted from the light extraction surface is a laser beam,
3. The semiconductor light emitting device according to claim 2, wherein the value of the ratio of the intensity of the TM polarization component to the intensity of the TE polarization component of the laser light is 2 or more. When the opening period of the opening is P, the dielectric constant of the metal film is ε1, the dielectric constant of the member in contact with the metal film is ε2, i and j are non-negative integers, P is
P = λ × (i ² + j ² ) ^0.5 / (ε1ε2 / (ε1 + ε2)) ^0.5
The semiconductor light emitting device according to claim 1 , wherein: The shape of the opening surface of the opening, the semiconductor light emitting device according to claim 1, any one of 4, which is a shape having anisotropy. The metal film, the semiconductor light emitting device according to claim 1, any one of 5, wherein the film thickness is 100nm or more and 500nm or less. The metal film is silver, the semiconductor light-emitting device according to 6 claim 1, characterized in that it consists of gold or aluminum. The metal film, the semiconductor light emitting device according to any one of claims 1 6, characterized in that it is formed by two layers made of different materials. Of the two layers of the metal film, the upper layer is thinner than the lower layer,
9. The semiconductor light emitting device according to claim 8 , wherein the lower layer is made of silver, gold, or aluminum. 9. The semiconductor light emitting device according to claim 8 , wherein, of the two layers of the metal film, a lower layer is made of silver and an upper layer is made of gold.   The semiconductor light emitting device according to claim 1, further comprising an intermediate layer formed on a surface of the metal film on the active layer side. The semiconductor light emitting device according to claim 11 , wherein the intermediate layer has a film thickness that corrects a phase change when the emitted light is reflected by the metal film. The thickness of the intermediate layer is such that d is 0.6 × λ when the thickness of the intermediate layer is d, the refractive index of the intermediate layer is n, the wavelength of the emitted light is λ, and i is a non-negative integer. / N × (1/4 + 1 / 2i) ≦ d ≦ λ / n × (1/4 + 1 / 2i)
The semiconductor light emitting device according to claim 12 , wherein the relationship is satisfied. The semiconductor light emitting device according to claim 11 , wherein the intermediate layer is a dielectric film. 15. The dielectric according to claim 14 , wherein the dielectric is a single layer film made of any one of silicon oxide, silicon nitride, aluminum oxide, titanium oxide, and tantalum oxide, or a laminated film made of two or more. Semiconductor light emitting device. The semiconductor light emitting device according to claim 11 , wherein the intermediate layer is a transparent conductive film. The semiconductor light-emitting device according to claim 16 , wherein the transparent conductive film is tin-doped indium oxide, zinc oxide, or tin oxide. The semiconductor light emitting device according to claim 11 , wherein the intermediate layer is a laminated film of a semiconductor. Further comprising two reflecting mirrors provided on the light extraction surface side and the side opposite to the light extraction surface of the active layer,
The metal film, the semiconductor light emitting device according to any one of claims 1 to 17, characterized in that the function as a reflecting mirror provided on the light extraction face side. The semiconductor light emitting device according to claim 19 , wherein the reflecting mirror provided on the light extraction surface side includes a first semiconductor multilayer film formed on a surface of the metal film on the active layer side. 21. The semiconductor light emitting device according to claim 20 , wherein a stacking period of the first semiconductor multilayer film is not less than 9 periods and not more than 22 periods. The semiconductor light emitting device according to claim 19 , wherein the reflectance of the reflecting mirror is 99.4% or more and 99.9% or less. Reflectors provided on the surface opposite to the light extraction surface, the semiconductor light emitting device according to any one of claims 19 to 22, characterized in that a reflecting mirror made of the second semiconductor multilayer film . The semiconductor light emitting device according to claim 11 , further comprising an upper layer formed on a surface opposite to the surface on the active layer side of the metal film. A first protective layer formed between the resin layer and the side and bottom surfaces of the recess;
A second protective layer covering the upper surface of the resin layer;
Wherein formed on the second protective layer, the semiconductor light-emitting device according to any one of claims 1 24, characterized by further comprising an electrode for injecting current into said active layer. 26. The semiconductor light emitting device according to claim 25 , wherein the resin layer is completely surrounded by the first protective layer and the second protective layer. It said first protective layer and the second protective _layer, SiO _{2, SiN, SiON,} a semiconductor light emitting device according to claim 25, characterized in that is any one of Nb ₂ O 5, ZrO2 and Ta2O5 . 26. The semiconductor light emitting device according to claim 25 , wherein at least a part of the resin layer is located higher than an upper surface of the mesa portion. 26. The semiconductor light emitting device according to claim 25 , wherein an upper surface of the resin layer and an upper surface of the mesa portion are connected flatly. 26. The semiconductor light emitting device according to claim 25 , wherein a relative dielectric constant of the resin layer is 3 or less. The semiconductor light emitting device according to claim 30 , wherein the resin layer is a benzocyclobutene resin. Provided between the active layer and the metal film in the mesa portion;
A high resistance region that is a selectively oxidized region or a region into which protons are selectively implanted;
The semiconductor light emitting device according to claim 1, further comprising a current confinement layer including a current confinement region surrounded by the high resistance region. The semiconductor light emitting device according to claim 32 , wherein the current confinement region has a diameter of 10 µm or less.   2. The semiconductor light emitting device according to claim 1, wherein a diameter of the mesa unit is adjusted so that a capacity of the mesa unit is equal to or more than half of a capacity of the entire device. 26. The semiconductor light emitting device according to claim 25 , wherein a side surface of the mesa portion is inclined.

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