JP5854417B2 - Two-dimensional photonic crystal laser - Google Patents

Description

  The present invention relates to a two-dimensional photonic crystal laser having a structure suitable for fabrication by an epitaxial method.

  In recent years, a new type of laser using a two-dimensional photonic crystal has been developed. A two-dimensional photonic crystal is a base material made of a dielectric material with a periodic structure of refractive index. Generally, a region having a refractive index different from that of the base material (different refractive index region) is periodically formed in the base material. It is produced by providing. Due to this periodic structure, Bragg diffraction occurs in the crystal, and an energy band gap appears in the energy of light. There are two-dimensional photonic crystal lasers that use point defects as resonators using the band gap effect, and two-dimensional photonic crystal lasers that use standing waves at the band edge where the group velocity of light is zero. Laser oscillation is obtained by amplifying light of a predetermined wavelength.

  In a two-dimensional photonic crystal laser, a different refractive index region of a layer having a two-dimensional photonic crystal structure (hereinafter referred to as a “two-dimensional photonic crystal layer”) is often a hole. This is because the refractive index difference between the base material and the holes can be increased, and the performance of the two-dimensional photonic crystal layer as a resonator can be improved.

  In Patent Document 1, fusion is performed by heating a layer prepared separately on a layer having a two-dimensional photonic crystal structure in which holes (different refractive index regions) are periodically arranged in a base material. A method of (thermal fusion) is described.

  However, in the two-dimensional photonic crystal laser produced by this method, a two-dimensional photonic crystal layer that has been thermally fused and a layer (hereinafter referred to as an “upper layer”) laminated on the two-dimensional photonic crystal layer. Therefore, the electrical resistance is increased at these interfaces. For this reason, the operating voltage becomes high, and the continuous oscillation of the laser becomes difficult to occur. Moreover, when performing heat sealing | fusion, the shape of a void | hole collapse | crumbles and the performance as a resonator of a two-dimensional photonic crystal layer may fall.

  On the other hand, Patent Document 2 describes a method of forming an upper layer by epitaxially growing AlGaN directly on a two-dimensional photonic crystal layer in which GaN is a base material and holes are periodically formed. ing.

  The method described in Patent Document 2 is broadly divided into (i) a method of forming an upper layer while leaving holes, (ii) a method of forming an upper layer while filling holes, and (iii) columnar heterorefringence. There are three methods of forming an upper layer while forming a base material by first forming a rate region and filling the periphery thereof by epitaxial growth.

  In the methods (ii) and (iii), the different refractive index region is filled with a material other than air (specifically, the same material as the upper layer). In such a structure, the light confinement effect is lowered as compared with the case where the different refractive index region is a hole, but on the other hand, it is easy to oscillate a laser in a single mode and a large area.

JP 2000-332351 A International Publication WO2006 / 062084

  In the method described in Patent Document 2, there is no problem that the electric resistance becomes high at the interface between the two-dimensional photonic crystal layer and the upper layer. However, the method (i) has a problem that when the upper layer is epitaxially grown, part of the vacancies are filled with the material of the upper layer, and the shape of the vacancies changes. Further, the methods (ii) and (iii) have a problem that it is difficult to completely fill the voids or between the columnar different refractive index regions with the material of the upper layer, and a cavity is easily formed. In these cases, the periodic structure of the refractive index becomes incomplete, causing a problem that the performance of the two-dimensional photonic crystal layer as a resonator deteriorates.

  The problem to be solved by the present invention is that a two-dimensional photonic crystal in which the performance as a resonator of the two-dimensional photonic crystal layer is not deteriorated when an upper layer of the two-dimensional photonic crystal layer is formed by an epitaxial method. It is to provide a crystal laser.

A two-dimensional photonic crystal laser according to the present invention, which has been made to solve the above problems,
Al _α Ga _1-α As (0 <α <1) or (Al _β Ga _1-β ) _γ In _1-γ P (0 ≦ β <1, 0 <γ <1) A two-dimensional photonic crystal layer periodically provided with different refractive index regions made of holes ,
An epitaxially grown layer made of an Al-containing p-type or n-type semiconductor formed on the two-dimensional photonic crystal layer by an epitaxial method;
A clad layer made of a p-type or n-type semiconductor containing Al, laminated on the epitaxial growth layer;
The Al content in the epitaxial growth layer is higher than the Al content in the cladding layer.

  In this application, the terms “upper” and “lower” are used for convenience in order to indicate the relative positional relationship of each layer, but these are the direction of each layer at the time of fabrication and the two-dimensional photonic after fabrication. The direction of the crystal laser is not limited.

In order to produce a layer above the two-dimensional photonic crystal layer by an epitaxial method, it is necessary to raise the temperature of the two-dimensional photonic crystal layer to around 600 ° C. However, when the upper layer is formed by an epitaxial method in a state where holes are provided in the two-dimensional photonic crystal layer, for example, when the different refractive index region is holes, migration occurs at such a high temperature. The shape of the holes may collapse. On the other hand, Al _α Ga _1-α As materials and (Al _β Ga _1-β ) _γ In _1-γ P materials are strong even at high temperatures, so the shape of the vacancies collapses when the upper layer is epitaxially grown. The performance of the two-dimensional photonic crystal layer as a resonator can be maintained high.

The material of the epitaxial growth layer is preferably Al _x Ga _1-x As (0 <x <1). Al _x Ga _1-x As has different gas diffusion lengths depending on the Al content, and its growth characteristics change. Therefore, by setting the value of x to an optimum value according to the structure of the photonic crystal layer that is the lower layer, the performance of the two-dimensional photonic crystal layer as a resonator can be maintained high as described above. .

  The epitaxial growth layer can be used as it is as a p-type or n-type cladding layer in a light-emitting diode (LED), but can also be used as a regrowth interface layer for epitaxial growth of this cladding layer separately. As described above, since x is changed according to the structure of the photonic crystal layer, if the epitaxial growth layer is used as it is as the cladding layer, the composition of the cladding layer also changes according to the structure of the photonic crystal layer. On the other hand, if a regrowth interface layer is introduced, a clad layer can be produced regardless of the structure of the photonic crystal layer, so that a two-dimensional photonic crystal laser can be manufactured with a more flexible structure.

The two-dimensional photonic crystal laser according to the present invention has a structure suitable for producing the upper layer of the two-dimensional photonic crystal layer by an epitaxial method. In the structure of the present invention, the holes provided in the two-dimensional photonic crystal layer are not deformed or collapsed during the epitaxial growth. In addition, the material of the epitaxial growth layer, which is the upper layer, is Al _x Ga _1-x As, and the value of x is an optimum value based on the growth characteristics, thereby improving the performance of the two-dimensional photonic crystal layer as a resonator. Can be kept high. Furthermore, by using the epitaxial growth layer as a regrowth interface layer for producing a p-type or n-type cladding layer by epitaxial growth, it is possible to increase the structural freedom of the two-dimensional photonic crystal laser.

1 is a perspective view showing a first embodiment of a two-dimensional photonic crystal laser according to the present invention. FIG. The top view which shows an example of the structure of a two-dimensional photonic crystal layer. 1 is a longitudinal sectional view showing a method for manufacturing a two-dimensional photonic crystal laser of Example 1. FIG. FIG. 6 is a longitudinal sectional view showing a second embodiment of the two-dimensional photonic crystal laser according to the present invention. FIG. 6 is a longitudinal sectional view showing a method for manufacturing the two-dimensional photonic crystal laser of Example 2. FIG. 6 is a longitudinal sectional view showing a third embodiment of the two-dimensional photonic crystal laser according to the present invention. The figure for demonstrating the depth h and maximum width d of a void | hole. FIG. 10 is a longitudinal sectional view showing a method for manufacturing the two-dimensional photonic crystal laser of Example 3. FIG. 6 is a longitudinal sectional view showing a fourth embodiment of the two-dimensional photonic crystal laser according to the present invention. FIG. 10 is a longitudinal sectional view showing a method for manufacturing the two-dimensional photonic crystal laser of Example 4. FIG. 10 is a longitudinal sectional view showing a fifth embodiment of the two-dimensional photonic crystal laser according to the present invention. FIG. 10 is a longitudinal sectional view showing a method for manufacturing the two-dimensional photonic crystal laser of Example 5.

1 to 12, an embodiment of the present invention and a two-dimensional photonic crystal laser that does not belong to the present invention but is related to the present invention will be described.

The two-dimensional photonic crystal laser 10 of Example 1 does not belong to the present invention, but is related to the present invention . As shown in FIG. 1, a first cladding layer 12 and an active layer are formed on a substrate 11. 13, a carrier block layer 14, a two-dimensional photonic crystal layer 15, a second cladding layer (epitaxial growth layer) 16, and a contact layer 17 are sequentially stacked. A lower electrode 18 is provided below the substrate 11, and an upper electrode 19 is provided above the contact layer 17.

In the two-dimensional photonic crystal layer 15, holes 151 having a planar shape such as a circle or a triangle are periodically formed in a plate-like base material layer 152 as shown in FIG. In this embodiment, Al _0.1 Ga _0.9 As is used for the material of the base material layer 152. This is because this material is strong even at high temperatures, and the shape of the holes 151 does not collapse even when the temperature is increased when the second cladding layer 16 is produced by an epitaxial method as will be described later. It is.

The material of the base material layer 152 is not limited to that of the present embodiment, and Al _α Ga _1-α As (0 <α <1) or (Al _β Ga _1-β ) _γ In _1-γ P (0 ≦ β <1, 0 <γ <1) can be used. The former can be suitably used when oscillating laser light having a wavelength in the near infrared region, and the latter can be suitably used when oscillating laser light having a wavelength in the red region.

As the material of the second cladding layer 16, a material that can be formed on the two-dimensional photonic crystal layer 15 by an epitaxial method is used. In this embodiment, the material of the second cladding layer 16 is p-type Al _0.65 Ga _0.35 As, that is, a material in which a small amount of +2 valent impurities are added to a (Al _0.65 Ga _0.35 ) site that is +3 valent. . The material of the second cladding layer 16 is not limited to that of the present embodiment, and p-type Al _x Ga _1-x As (0.4 ≦ x <1) can be suitably used. In Al _x Ga _1-x As, the greater the value of x, the shorter the gas diffusion length, and the more difficult it is to penetrate into the holes 151. Therefore, formation of unnecessary p-type Al _0.65 Ga _0.35 As crystals in the holes 151 can be suppressed.

In the present embodiment, the following layers are used for the layers other than the two-dimensional photonic crystal layer 15 and the second cladding layer 16. The substrate 11 is made of n-type GaAs, and the first cladding layer 12 is made of n-type Al _0.65 Ga _0.35 As. These are obtained by adding a small amount of +4 valent impurities to the Ga site of GaAs or the (Al _0.65 Ga _0.35 ) site of Al _0.65 Ga _0.35 As. The active layer 13 is made of InGaAs / GaAs multiple quantum wells. The carrier block layer 14 is made of Al _0.4 Ga _0.6 As. The contact layer 17 is made of p-type GaAs. Note that materials other than those described above can also be used for these layers.

  In contrast to the present embodiment, a p-type material may be used for the substrate 11 and the first cladding layer 12, and an n-type material may be used for the second cladding layer 16 and the contact layer 17.

  Next, an example of a method for manufacturing the two-dimensional photonic crystal laser 10 of the present embodiment will be described with reference to FIG. First, the first clad layer 12, the active layer 13, and the carrier block layer 14 are formed on the substrate 11 by epitaxial growth in this order by a vapor phase method. Next, the base material layer 152 is formed on the carrier block layer 14 by epitaxial growth by a vapor phase method (b). Subsequently, a resist 21 is applied to the upper surface of the base material layer 152, and a pattern corresponding to the arrangement of the holes 151 is formed on the resist 21 by an electron beam lithography method. The two-dimensional photonic crystal layer 15 is produced by forming the holes 151 (c).

Thereafter, the resist 21 is removed, and the second cladding layer 16 is epitaxially grown on the two-dimensional photonic crystal layer 15 by a vapor phase method (d). Further, the two-dimensional photonic crystal layer 15 is heated to about 600 ° C. while the second cladding layer 16 is epitaxially grown. When heated to such a temperature, if the material of the base material layer 152 is GaAs that does not contain Al, migration may occur and the shape of the holes 151 may be destroyed. By using Al _0.1 Ga _0.9 As for the material of the layer 152, the shape of the holes 151 can be maintained.

  After the second cladding layer 16 is produced in this way, the contact layer 17 is epitaxially grown on the second cladding layer 16 by a vapor phase method. Then, the lower electrode 18 is formed on the lower side of the substrate 11 and the upper electrode 19 is formed on the contact layer 17 by vapor deposition, whereby the two-dimensional photonic crystal laser 10 of this embodiment is obtained (e). .

A second embodiment of a two-dimensional photonic crystal laser that does not belong to the present invention but is related to the present invention will be described with reference to FIG. The two-dimensional photonic crystal laser 10A of this embodiment uses a two-dimensional photonic crystal layer 15A described below instead of the two-dimensional photonic crystal layer 15 of the first embodiment. Other configurations are the same as those of the two-dimensional photonic crystal laser 10 of the first embodiment.

In the two-dimensional photonic crystal layer 15A, the second base material layer 1522A made of Al _0.1 Ga _0.9 As (α = 0.1) is formed on the upper surface of the first base material layer 1521A made of Al _0.65 Ga _0.35 As (α = 0.65). A base material layer 152A having a two-layer structure is formed thinner than the first base material layer 1521A. In the base material layer 152A, the holes 151A are formed in the same shape and cycle as in the first embodiment. Since the second base material layer 1522A has a lower Al content than the first base material layer 1521A, the second base material layer 1522A has a feature that it is difficult to oxidize in the manufacturing process described later.

  A method for manufacturing the two-dimensional photonic crystal laser 10A of the present embodiment will be described with reference to FIG. First. The first clad layer 12, the active layer 13, and the carrier block layer 14 are sequentially formed on the substrate 11 by epitaxial growth by a vapor phase method in the same manner as in Example 1 (a). Next, a first base material layer 1521A is epitaxially grown on the carrier block layer 14 by a vapor phase method (b). Subsequently, the second base material layer 1522A is formed on the first base material layer 1521A by epitaxial growth by a vapor phase method (c). Each process so far is performed by changing the source gas in the same chamber.

  Next, as in Example 1, holes 151A are formed in the base material layer 152A by using an electron beam lithography method and an etching method (d). Since this method uses a method other than the epitaxial method, it is performed in a chamber different from the previous steps. Subsequently, the chamber is changed to the original one, and the second cladding layer 16 is epitaxially grown on the surface of the second base material layer 1522A by a vapor phase method (e). Thereafter, the contact layer 17, the lower electrode 18, and the upper electrode 19 are fabricated by the same method as in Example 1, thereby obtaining the two-dimensional photonic crystal laser 10A of the present example.

  Thus, it is necessary to change the chamber before and after the step of forming the hole 151A, and the surface of the base material layer may be oxidized at that time. In this embodiment, the surface of the base material layer is prevented from being oxidized by using, for the second base material layer 1522A, a material that is less likely to be oxidized than the material of the first base material layer 1521A.

A third embodiment of the two-dimensional photonic crystal laser according to the present invention will be described with reference to FIG. The two-dimensional photonic crystal laser 10B of the present embodiment is made of Al _x Ga _1-x As (0.4 ≦ x <1) between the two-dimensional photonic crystal layer 15 and the second cladding layer 16 in the first embodiment. A regrowth interface layer 31 is provided.

  The holes 151 have a maximum planar shape width d of 200 nm or less and a ratio h / d (aspect ratio) between the depth h and the maximum width d of 1.3 or more and 5 or less. Here, the maximum width d refers to the length of the longest line segment that fits in the planar shape of the hole 151 (FIG. 7). For example, the diameter of the hole 151 is a circle when the plane shape is a circle, the side is a triangle when it is a regular triangle, and the length of the longest side among the three sides is a maximum width when it is a triangle other than a regular triangle. It corresponds to.

  In this embodiment, the Al content x in the regrowth interface layer 31 is set to a relatively high value and the aspect ratio h / d is set to 1.3 or more, so that the source gas of the regrowth interface layer 31 becomes the vacancy 151. It is made difficult to enter inside. This suppresses the formation of crystals made of the material of the regrowth interface layer 31 in the holes 151. Note that if h is too large or d is too small, the two-dimensional periodic structure of the holes 151 may not be sufficiently formed, so the upper limit of the aspect ratio h / d is set to 5.

  A method of manufacturing the two-dimensional photonic crystal laser 10B of this example will be described with reference to FIG. First. A first cladding layer 12, an active layer 13, a carrier block layer 14, and a two-dimensional photonic crystal layer 15 are formed on the substrate 11 by the same method as in Example 1 (a). Next, the regrowth interface layer 31 is formed by epitaxial growth on the two-dimensional photonic crystal layer 15 by a vapor phase method, and the upper portion of the hole 151 is blocked (b). At that time, as described above, the material of the regrowth interface layer 31 is prevented from entering the pores 151. In addition, since the above-described materials are used for the base material layer 152, migration can be prevented from occurring in this step. Subsequently, the second cladding layer 16 is epitaxially grown on the regrowth interface layer 31 by a vapor phase method (c). Thereafter, the contact layer 17, the lower electrode 18, and the upper electrode 19 are fabricated by the same method as in Example 1, whereby the two-dimensional photonic crystal laser 10B of this example is obtained.

A fourth embodiment of a two-dimensional photonic crystal laser that does not belong to the present invention but is related to the present invention will be described with reference to FIG. In the two-dimensional photonic crystal laser 10C of the present embodiment, a regrowth interface layer 31A made of Al _x Ga _1-x As (0 <x ≦ 0.8) is provided instead of the regrowth interface layer 31 in the third embodiment. At the same time, a different refractive index member 32 made of the same material as the regrowth interface layer 31A is periodically provided in place of the holes 151 in the two-dimensional photonic crystal layer 15C. The different refractive index member 32 has a maximum planar shape width d of 200 nm or less and an aspect ratio h / d of 0.1 to 1.2. The definition of the maximum width d and the aspect ratio h / d is the same as in the case of the holes 151.

  In this example, the Al content x in the regrowth interface layer 31A is set to a relatively low value, and the aspect ratio h / d is set to 1.2 or less. The source gas of the regrowth interface layer 31 </ b> A is likely to enter the hole 151. If h is too small or d is too large, the two-dimensional periodic structure of the holes 151 may not be sufficiently formed, so the lower limit of the aspect ratio h / d is set to 0.1.

  A method for manufacturing the two-dimensional photonic crystal laser 10C of the present embodiment will be described with reference to FIG. First, the first cladding layer 12, the active layer 13, the carrier block layer 14, and the two-dimensional photonic crystal layer 15 are formed on the substrate 11 by the same method as in Example 1 (a). However, the two-dimensional photonic crystal layer 15 produced here has the holes 151 as in the first embodiment, and the different refractive index member 32 is not yet formed. Next, the regrowth interface layer 31A is formed on the two-dimensional photonic crystal layer 15, and the different refractive index member 32 is simultaneously epitaxially grown in the holes 151 by the vapor phase method (b). At that time, since the source gas easily enters the hole 151 as described above, the different refractive index member 32 can be formed without generating a cavity. In addition, since the above-described materials are used for the base material layer 152, migration can be prevented from occurring in this step. Subsequently, the second cladding layer 16 is epitaxially grown on the regrowth interface layer 31A by a vapor phase method (c). Thereafter, the contact layer 17, the lower electrode 18, and the upper electrode 19 are fabricated by the same method as in Example 1, whereby the two-dimensional photonic crystal laser 10C of this example is obtained.

A fifth embodiment of a two-dimensional photonic crystal laser that does not belong to the present invention but is related to the present invention will be described with reference to FIG. In the two-dimensional photonic crystal laser 10D of the present embodiment, the two-dimensional photonic crystal layer 15D includes a columnar different refractive index member 32A periodically arranged on the upper surface of the carrier block layer 14, and a different refractive index member 32A. The structure which consists of the base material 152B embedded around is taken. In the present embodiment, the material of the different refractive index member 32A is not limited to Al _x Ga _1-x As (0 <x ≦ 0.8), and other semiconductor materials and dielectric materials can also be used. Further, a regrowth interface layer 31B made of the same material as the base material 152B is formed on the upper surface of the two-dimensional photonic crystal layer 15D. Other configurations are the same as those of the first embodiment.

  A method for manufacturing the two-dimensional photonic crystal laser 10D of the present embodiment will be described with reference to FIG. First, the first cladding layer 12, the active layer 13, and the carrier block layer 14 are formed on the substrate 11 by the same method as in Example 1. Next, a different refractive index region precursor layer 33 made of the material of the different refractive index member 32A is formed on the carrier block layer 14 by epitaxial growth by a vapor phase method (a). Subsequently, by using an electron beam lithography method and an etching method, the different refractive index region precursor layer 33 is removed from the upper surface to the middle while leaving the periodically arranged columnar regions. Thus, the columnar different refractive index member 32A is formed on the spacer layer 33A formed by leaving a part of the lower side of the different refractive index region precursor layer 33 (b). Next, the base material 152B is formed on the spacer layer 33A by epitaxial growth using a vapor phase method. Then, even after the base material 152B is formed up to the upper surface of the different refractive index member 32A, the crystal production is continued by the epitaxial method. Thereby, the regrowth interface layer 31B is formed on the different refractive index member 32A and the base material 152B (c). Then, the second cladding layer 12 is epitaxially grown on the upper surface of the regrowth interface layer 31B by a vapor phase method (d). Thereafter, the contact layer 17, the lower electrode 18, and the upper electrode 19 are fabricated by the same method as in Example 1, thereby obtaining the two-dimensional photonic crystal laser 10D of the present example.

  The present invention is not limited to the above embodiments. For example, the base material layer can be composed of a plurality of layers made of different materials, and one of these layers may be a layer made of GaAs not containing Al. Even in this case, the influence of migration can be suppressed as compared with the case where the entire base material layer is made of GaAs.

DESCRIPTION OF SYMBOLS 10, 10A, 10B, 10C, 10D ... Two-dimensional photonic crystal laser 11 ... Substrate 12 ... First clad layer 13 ... Active layer 14 ... Carrier block layers 15, 15A, 15C, 10D ... Two-dimensional photonic crystal layer 151, 151A ... Holes 152, 152A ... Base material layer 1521A ... First base material layer 1522A ... Second base material layer 152B ... Base material 16 ... Second cladding layer (epitaxial growth layer)
17 ... Contact layer 18 ... Lower electrode 19 ... Upper electrode 21 ... Resist 31, 31A, 31B ... Regrown interface layer 32, 32A ... Different refractive index member 33 ... Different refractive index region precursor layer 33A ... Spacer layer

Claims (5)

Al _α Ga _1-α As (0 <α <1) or (Al _β Ga _1-β ) _γ In _1-γ P (0 ≦ β <1, 0 <γ <1) A two-dimensional photonic crystal layer periodically provided with different refractive index regions made of holes,
An epitaxially grown layer made of a p-type or n-type semiconductor containing Al, laminated on the two-dimensional photonic crystal layer;
Wherein are stacked on the epitaxial growth layer, a cladding layer made of p-type or n-type semiconductor containing Al,
The two-dimensional photonic crystal laser characterized in that the Al content in the epitaxial growth layer is higher than the Al content in the cladding layer. The base material layer includes a plurality of layers having different values of α, a single layer having a specific value of α, a plurality of layers having different values of α, and a plurality of layers made of GaAs, or 2. The two-dimensional photonic crystal laser according to claim 1, wherein the two-dimensional photonic crystal laser has a structure in which a plurality of layers different in one or both of the values of β and γ are stacked.   3. The two-dimensional photonic crystal laser according to claim 2, wherein among the plurality of layers constituting the base material layer, an Al content in a layer closest to the epitaxial layer is 0.1 or less.   4. The two-dimensional photonic crystal laser according to claim 2, wherein the base material layer has a layer made of GaAs. 5. The two-dimensional photonic crystal laser according to claim 1, wherein a material of the epitaxial growth layer is Al _x Ga _1-x As (0 <x <1).

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