JP2012151140A - Photonic crystal surface-emitting laser and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photonic crystal surface-emitting laser or the like which ensures high light diffraction efficiency and carrier injection efficiency while suppressing light absorption.SOLUTION: In the photonic crystal surface-emitting laser, a plurality of semiconductor layers, each including an active layer 104, and a two-dimensional photonic crystal layer 105 provided near the active layer and having a resonance mode in the in-plane direction, are laminated on a substrate 101. In the two-dimensional photonic crystal layer 105, a low diffractive index medium 105b and a high diffractive index medium 105a, having a high diffractive index when compared with the low diffractive index medium, are arranged periodically in the in-plane direction of the substrate, and a sidewall member 105c having conductivity is interposed between the low diffractive index medium and the high diffractive index medium.

Description

  The present invention relates to a photonic crystal surface emitting laser and a manufacturing method thereof.

In recent years, research on two-dimensional photonic crystal surface emitting lasers using a photonic crystal as a two-dimensional diffraction grating has been actively conducted (for example, see Patent Document 1).
This two-dimensional photonic crystal surface emitting laser has a structure in which a refractive index is periodically changed between a semiconductor and a medium such as air or a dielectric in the vicinity of the active layer.
Light generated in the active layer by carrier injection is oscillated by feedback and amplification at a wavelength defined by the two-dimensional photonic crystal.
Furthermore, light is extracted in the vertical direction by first-order diffraction with a two-dimensional photonic crystal.
The intensity of the light diffraction effect of the photonic crystal surface emitting laser is proportional to the light confined by the cladding layer and Γ _PhC which is the overlap of the two-dimensional photonic crystal layer.
In order to improve Γ _PhC , it is desirable to arrange a two-dimensional photonic crystal layer in the vicinity of the active layer having a high light intensity.

JP 2008-130731 A

By the way, the photonic crystal surface emitting laser of Patent Document 1 has a two-dimensional photonic crystal layer disposed on an electron block layer in the vicinity of an active layer having a strong light distribution intensity.
However, under such a structure, there are the following problems.
When the two-dimensional photonic crystal layer is composed of an undoped semiconductor, holes are injected from the p-type cladding layer into the active layer via the undoped layer.
Since holes have a lower mobility than electrons, the efficiency of hole injection into the active layer decreases with the thickness of the two-dimensional photonic crystal layer.
Further, if the two-dimensional photonic crystal layer is made thicker in order to improve light extraction, the distance between the p-type cladding layer and the active layer becomes longer, and a decrease in hole injection efficiency becomes more problematic.

On the other hand, when the two-dimensional photonic crystal layer is doped in order to prevent such a decrease in hole injection efficiency, light absorption by the dopant in the two-dimensional photonic crystal layer becomes a problem.
In particular, the influence is large in nitride semiconductors. In a nitride semiconductor, Mg is doped to about 10 ¹⁹ cm ⁻³ in order to obtain a p-type having a low electric resistance.
Comparing the absorption coefficient of light in the wavelength band of 400 nm, the absorption coefficient of undoped GaN is several cm ⁻¹ , but p-GaN doped with 19th power of Mg has a very large absorption coefficient of about 100 cm ⁻¹ .

As described above, in the photonic crystal surface emitting laser in which the two-dimensional photonic crystal layer is disposed in the vicinity of the active layer, the hole injection efficiency and the light absorption by the dopant are in a trade-off relationship.
Therefore, there is a problem that light absorption cannot be suppressed while maintaining the carrier injection efficiency.
In the above description, the nitride semiconductor has been described as an example, but the same problem occurs in other material systems.

  In view of the above problems, the present invention has an object to provide a photonic crystal surface emitting laser having high light diffraction efficiency and carrier injection efficiency and capable of suppressing light absorption, and a method for manufacturing the same. To do.

The photonic crystal surface emitting laser of the present invention has a plurality of semiconductor layers including an active layer and a two-dimensional photonic crystal layer provided in the vicinity of the active layer and having a resonance mode in an in-plane direction on a substrate. A stacked photonic crystal surface emitting laser,
The two-dimensional photonic crystal layer is
A low refractive index medium and a high refractive index medium having a higher refractive index than the low refractive index medium are periodically arranged in the in-plane direction of the substrate,
A side wall member having conductivity is disposed between the low refractive index medium and the high refractive index medium.
The method for manufacturing a photonic crystal surface emitting laser according to the present invention is a method for manufacturing a photonic crystal surface emitting laser having a two-dimensional photonic crystal layer having a resonance mode in an in-plane direction,
Forming an active layer on the substrate;
Forming a layer serving as a base material of a two-dimensional photonic crystal layer on the active layer;
A layer serving as a base material of the two-dimensional photonic crystal layer is used, and a high refractive index medium and a hole that is a low refractive index medium having a lower refractive index than the high refractive index medium are arranged in an in-plane direction of the substrate. Forming periodically arranged layers;
A layer in which the high refractive index medium and holes are periodically arranged in an in-plane direction of the substrate,
A side wall member having a resistivity lower than that of the high refractive index medium is provided on the side wall of the hole while heat treatment is performed at a temperature at which the high refractive index medium causes mass transport while supplying a dopant. And a step of forming.

  According to the present invention, it is possible to realize a photonic crystal surface emitting laser and a method for manufacturing the same, which have high light diffraction efficiency and carrier injection efficiency and can suppress light absorption.

It is sectional drawing explaining the photonic crystal surface emitting laser in embodiment of this invention. It is sectional drawing explaining the manufacturing process of the two-dimensional photonic crystal layer in embodiment of this invention. The experimental result for demonstrating the heat processing of the two-dimensional photonic crystal layer in embodiment of this invention is shown. (A) is a cross-sectional electron microscope image of the sample which formed the void | hole in the GaN surface. (B) is a cross-sectional electron microscope image of a sample heat-treated at a heat treatment temperature of 850 ° C. and a holding time of 30 minutes. (C) is a cross-sectional electron microscope image of a sample heat-treated at a heat treatment temperature of 1025 ° C. and a holding time of 0 minutes. It is sectional drawing explaining the photonic crystal surface emitting laser in Example 1 of this invention. It is sectional drawing explaining the photonic crystal surface emitting laser in Example 2 of this invention. It is sectional drawing explaining the photonic crystal surface emitting laser in Example 3 of this invention.

An embodiment of a photonic crystal surface emitting laser according to the present invention will be described.
The photonic crystal surface emitting laser of this embodiment includes a plurality of semiconductor layers including an active layer and a two-dimensional photonic crystal layer provided in the vicinity of the active layer and having a resonance mode in an in-plane direction on a substrate. Are laminated.
These configurations will be described with reference to the drawings. In FIG. 1, 101 is a substrate, 102 is an n-type cladding layer, 103 is an n-side guide layer, 104 is an active layer, 105 is a two-dimensional photonic crystal layer, and 106 is an electron. Block layer.
107 is a p-type cladding layer, 108 is a p-type contact layer, 109 is an n-electrode, and 110 is a p-electrode. In the two-dimensional photonic crystal layer 105, 105a is a high refractive index medium, 105b is a low refractive index medium, and 105c is a side wall member.

More specifically, the photonic crystal surface emitting laser 100 of this embodiment is provided with the following layers in order on a substrate 101.
That is, an n-type cladding layer 102, an n-side guide layer 103, an active layer 104, a two-dimensional photonic crystal layer 105, an electron block layer 106, a p-type cladding layer 107, and a p-type contact layer 108 are formed on a substrate 101. They are provided in this order.
Further, as an electrode for energization, an n-electrode 109 is provided on the back surface of the substrate 101, and a p-electrode 110 is provided on the surface of the p-type contact layer 108.
The photonic crystal surface emitting laser 100 emits light by injecting carriers into the active layer 104 by applying a voltage between the electrodes and energizing them.
Light generated in the active layer 104 is confined in the n-type cladding layer 102 and the p-type cladding layer 107. Part of the trapped light resonates and amplifies in the two-dimensional photonic crystal layer 105.
Then, the amplified light is diffracted vertically by the two-dimensional photonic crystal layer 105 to be extracted as laser light.

Next, the configuration of the two-dimensional photonic crystal layer 105 of the present embodiment will be described.
The two-dimensional photonic crystal layer 105 of this embodiment is provided in the vicinity of the active layer in order to increase Γ _PhC .
Specifically, it is provided between the p-type cladding layer 107 and the active layer 104. Further, the two-dimensional photonic crystal layer 105 may extend over a part or the whole of the p-type cladding layer 107.
The two-dimensional photonic crystal layer 105 includes a high refractive index medium 105a, a low refractive index medium 105b, and a side wall member 105c.
The high refractive index medium 105a and the low refractive index medium 105b are periodically arranged in the in-plane direction of the substrate.
The side wall member 105c is provided between the high refractive index medium 105a and the low refractive index medium 105b in the in-plane direction of the substrate.

The high refractive index medium 105a is composed of an AlGaInN group III nitride semiconductor. The low refractive index medium 105b is composed of air, SiO ₂ , SiN, Al ₂ O ₃ , AlN, TiO, TiN, or the like.
The side wall member 105c is formed by mass transporting the high refractive index medium 105a while supplying a dopant.
The side wall member 105 c has conductivity and becomes a passage for holes supplied from the p-type cladding layer 107.
The holes supplied from the p-type cladding layer 107 by energization are injected into the active layer 104 via the side wall member 105c.
Therefore, the hole injection efficiency can be made constant regardless of the thickness of the two-dimensional photonic crystal layer 105.

Next, the doping of the high refractive index medium and the side wall member will be described.
The sidewall member 105c only needs to be doped with impurities to such an extent that holes can be sufficiently injected.
Specifically, if the carrier concentration is 1 × 10 ¹⁷ cm ³ or more, it functions as a carrier injection path.
In order to further lower the resistivity and facilitate carrier injection, it is 5 × 10 ¹⁷ cm ³ or more.
More preferably, it is 1 × 10 ¹⁸ cm ³ or more. Mg, Zn, Be etc. are contained as a p-type impurity.
The activation rate of Mg doped as an acceptor in a nitride semiconductor is about several percent.
If the Mg activation rate is about 5%, the Mg doping concentration is preferably 2 × 10 ¹⁸ cm ³ or more.
More preferably, it is 1 × 10 ¹⁹ cm ³ or more. More preferably, it is 2 × 10 ¹⁹ cm ³ or more.
The high refractive index medium 105a is preferably undoped from the viewpoint of light absorption, but may be doped as long as light absorption is not a problem.
For example, the entire high refractive index medium 105a may be doped to about 10 ¹⁷ to 10 ¹⁸ cm ³ , or the high refractive index medium 105a may be doped at a high concentration on the p-type cladding layer 107 side.

The sidewall member 105c is doped as described above. Therefore, the side wall member 105c has a larger absorption coefficient than the high refractive index medium 105a.
Therefore, the light absorption coefficient of the two-dimensional photonic crystal layer 105 also changes in proportion to the volume ratio of the high refractive index medium 105a and the side wall member 105c.
In order to minimize light absorption, the volume of the side wall member 105c is preferably equal to or less than the volume of the high refractive index medium 105a.
When the volume of the side wall member 105c is Vc and the volume of the high refractive index medium 105a is Va, Vc / Va ≦ 1 is preferable. More preferably, Vc / Va ≦ 0.5. More preferably, Vc / Va ≦ 0.25.

Next, a method for manufacturing the photonic crystal surface emitting laser 100 and the two-dimensional photonic crystal layer 105 of the present invention will be described with reference to FIG.
First, as shown in FIG. 2A, on a substrate 101, a device structure having a structure up to the active layer 104 using a MOCVD apparatus or an MBE apparatus, and a semiconductor layer 205 serving as a base material of a two-dimensional photonic crystal layer are formed. Are laminated.
Next, the substrate is taken out from the film forming apparatus, and using a dry etching apparatus such as electron beam lithography, photolithography, RIE, or ICP, the semiconductor layer is made of a semiconductor layer 205 as shown in FIG. A rate medium 105a and a hole 205c are formed.
Next, heat treatment is performed at a temperature at which the semiconductor layer 205 causes mass transport while supplying a dopant serving as a p-type impurity, thereby forming a sidewall member 105c on the sidewall of the high refractive index medium 105a as shown in FIG. To do.
By applying thermal energy, the atoms of the high refractive index medium 105a are disconnected and the surface freely diffuses.
By controlling the heat treatment conditions and the shape of the holes 205c, atoms can be mass transported to the side wall of the high refractive index medium 105a without filling the holes 205c.
And since a dopant is taken in and it adheres again, the side wall member 105c lower resistance than the high refractive index medium 105a can be formed in the side wall of the high refractive index medium 105a. The width of the hole 205 is reduced by the thickness of the side wall member 105c in the in-plane direction of the substrate, and becomes a low refractive index medium 105b composed of air (FIG. 2D).
In addition, after mass transport, a dielectric such as SiO ₂ or SiN may be formed in the low refractive index medium 105b.

The two-dimensional photonic crystal layer 105 is formed by the above process. Thereafter, the remaining layers are regrown using an MOCVD apparatus or MBE apparatus.
A dedicated apparatus may be used for the heat treatment step, but the heat treatment process can also be performed using an MOCVD apparatus or an MBE apparatus.
At that time, the heat treatment step for forming the side wall member 105c and the regrowth step for the layer thereon can be performed by the same apparatus.
Since it is only necessary to control the substrate temperature and raw material of the apparatus, it is not necessary to increase the number of process steps.

Next, the heat treatment for forming the side wall member 105c while leaving the holes 205c by mass transport and the shape of the holes will be described.
The aspect ratio, which is the depth / width ratio of the holes 205c, is desirably 1 or more.
This is because when the hole 205c is shallow, the hole 205c is filled by mass transport.
Since the group V atoms constituting the semiconductor layer 205 are easily desorbed into the gas phase during the heat treatment, the gas atmosphere during the heat treatment is performed in a gas atmosphere containing group V atoms.
For example, a nitride semiconductor has a gas atmosphere containing NH ₃ or dimethylhydrazine.

The heat treatment is performed at a temperature of about 10% to 20% lower than the growth temperature of the semiconductor layer 205. The reason will be described below.
The amount of atoms diffusing on the surface and the diffusion distance of the atoms depend on the heat treatment temperature.
For example, when heat treatment is performed at the growth temperature, the migration of atoms on the surface is active and the diffusion distance is sufficiently long.
Therefore, it is possible to change the shape of a concavo-convex structure having a size of several μm by mass transport.
The period of the photonic crystal 105 is 100 nm to several hundred nm, and the side wall member 105c only needs to be formed with a thickness of several tens of nm to several tens of nm in the in-plane direction of the substrate.
Therefore, even if the heat treatment temperature is lower by about 10 to 20% than the growth temperature, the diffusion distance of atoms is sufficient with respect to the size of the hole 205c. Therefore, the side wall member 105c is formed using the mass transport. Can do.

Next, experimental results obtained by forming holes 205c in the semiconductor layer 205 and performing heat treatment will be described.
FIG. 3 shows the results of an experiment in which photonic crystal holes 205c are formed in GaN and heat-treated under various conditions.
FIG. 3A is a cross-sectional electron microscope image before heat treatment of a sample in which photonic crystal vacancies are formed in GaN.
The shape of the holes is circular, the depth is 240 nm, and the diameter is 90 nm at the top of the hole and 35 nm at the bottom.
The sample of this structure was heat-treated and the shape was changed by mass transport.

FIG. 3B is a cross-sectional electron microscope image of a sample that was subjected to a heat treatment temperature of 850 ° C. and a holding time of 30 minutes.
The heat treatment temperature is 150 ° C. lower than about 1000 ° C., which is the growth temperature of GaN. The diameter from the top of the hole to the middle is about 50 nm, which is thinner than before the heat treatment.
It can be said that the GaN itself was mass transported into the holes, and the side wall member 105c was formed on the GaN side wall.

FIG. 3C is a cross-sectional electron microscope image of a sample heat-treated at a heat treatment temperature of 1025 ° C. and a holding time of 0 minutes.
With the mass transport, the shape of the holes changed, and the diameter became about 55 nm and the depth became about 170 nm. It can be said that the side wall member 105c was formed because the diameter of the pores was reduced.
Furthermore, the upper part of the hole was blocked with GaN. Since the heat treatment is performed near the growth temperature of GaN, the amount of atoms transported by mass is large. For this reason, the shape inside the hole changes greatly.
In addition, because of the long diffusion distance of Ga atoms, Ga tends to adhere to the upper part of the holes.

From the above results, in the nitride semiconductor, the heat treatment temperature for forming the sidewall member 105c of the present invention is preferably 850 ° C. or higher.
As shown in FIG. 3B, when heat treatment is performed at a temperature lower by about 10% to 20% than the growth temperature, the amount of mass transported atoms decreases, and the shape change proceeds slowly.
Therefore, by controlling the heat treatment time, the thickness of the side wall member 105c in the in-plane direction can be controlled.
During the heat treatment, the heat treatment may be performed by supplying a group III material in addition to the dopant. However, since the holes 205c are filled when the supply amount is too large, it is desirable that the supply amount be smaller than the group III supply amount when the semiconductor layer 205 is stacked.

Next, the emission wavelength of the active layer and the thickness of the two-dimensional photonic crystal layer will be described.
The photonic crystal surface emitting laser of the present invention is not particularly limited as long as it is a wavelength region that can be constituted by a semiconductor, but a nitride semiconductor is particularly effective in a photonic crystal surface emitting laser in a long wavelength region such as green.
The amount of diffraction in the vertical direction of light in the photonic crystal is determined by Γ _PhC and the thickness of the two-dimensional photonic crystal layer.
When the thickness of the two-dimensional photonic crystal layer is described, the light extraction increases in proportion to the thickness d of the two-dimensional photonic crystal layer up to λ / 2n. Here, λ is the emission wavelength, and n is the refractive index of the two-dimensional photonic crystal layer.
After λ / 2n, interference occurs due to the thickness of the two-dimensional photonic crystal layer, but it becomes a substantially constant value.
That is, in order to improve the light output with the photonic crystal surface emitting laser, it is desirable to increase the thickness of the two-dimensional photonic crystal layer to about λ / 2n.
When the thickness of the two-dimensional photonic crystal layer is set to λ / 2n in order to increase the extraction of light, λ / 2n increases as the emission wavelength λ increases.
Therefore, when the light output is increased, the two-dimensional photonic crystal layer becomes thicker in the photonic crystal surface emitting laser having a longer wavelength than that of the photonic crystal surface emitting laser emitting in purple or blue.
That is, the problem of trade-off between carrier injection efficiency and light absorption by the dopant becomes more serious.
In the above description of the embodiment, the description has focused on the nitride semiconductor, but the present invention can also be applied to other materials.

Examples of the present invention will be described below.
[Example 1]
As Example 1, a specific configuration example of the photonic crystal surface emitting laser according to the embodiment of the present invention will be described with reference to FIG.
In this example, a violet photonic crystal surface emitting laser having an emission wavelength of 400 nm was prepared.
At the time of the production, GaN was used as a base material of the two-dimensional photonic crystal layer, and heat treatment was performed at 850 ° C., which is about 150 ° C. lower than the growth temperature of GaN, to form the side wall member 405c.
In this embodiment, an n-GaN substrate is used as the substrate 401 as shown in FIG.
Next, the following layers are formed in order with an MOCVD apparatus. First, n-GaN is grown to 2 μm as a buffer layer 411 for improving crystallinity.
Subsequently, n-Al _0.07 Ga _0.93 N is grown to 800 nm as the n-type cladding layer 402, and GaN is grown to 100 nm as the n-side guide layer 403.
A three-period In _0.10 Ga _0.90 N / GaN multiple quantum well is grown thereon as the active layer 404.
The thickness of In _0.10 Ga _0.90 N that is a well layer is 2.5 nm, the thickness of GaN that is a barrier layer is 7.5 nm, and the emission wavelength is 400 nm.
Then, GaN (405) serving as a base material of the two-dimensional photonic crystal layer 105 is grown on the active layer 404 by 120 nm.

Next, the two-dimensional photonic crystal layer 105 is formed as follows.
First, the substrate is taken out from the MOCVD apparatus, and SiO ₂ is formed on the surface by plasma CVD.
Next, a resist is applied, and a photonic crystal pattern is drawn by electron beam lithography.
As the pattern, a circular pattern is arranged in a square lattice shape, and is drawn with a diameter of 80 nm and a lattice interval of 160 nm.
After development, SiO ₂ is etched by ICP using CF ₄ gas with the resist as a mask.
Since the pattern of the photonic crystal is formed on the SiO _2, now the SiO ₂ as a hard mask to 100nm etched GaN (405) in ICP using Cl ₂ gas.
After the etching, the SiO ₂ mask is removed, so that convex portions 405a and vacancies made of GaN are formed as a high refractive index medium in GaN (405).

Next, p-type conductive p-GaN is formed as a side wall member 405c on the side wall of the convex portion 405a.
First, the substrate is set again in the MOCVD apparatus. While supplying Cp ₂ Mg as a p-type impurity, the substrate is heated to 850 ° C. in a mixed gas atmosphere of N ₂ and NH ₃ and held for 30 minutes after the temperature rise.
The supply amount of Cp ₂ Mg is adjusted to such a supply amount that p-GaN (405c) can be doped with 2 × 10 ¹⁸ cm ⁻³ of Mg.
By the heat treatment, GaN in the convex portion 405a is decomposed, and Ga atoms are transported to the side wall of the convex portion 405a.
Then, nitrogen and Mg in the gas phase are taken in, and p-type conductive p-GaN having lower resistance than the convex portion 405a is formed as the side wall member 405c.
The pores become narrow and have a diameter of 60 nm. At the bottom of the vacancies, atoms are mass transported and become 20 nm shallow.

Then, p-GaN (412) is grown to 50 nm by heating to 1000 ° C. and supplying trimethylgallium as a group III raw material.
The upper part of the hole of the two-dimensional photonic crystal layer 105 is blocked, and a two-dimensional photonic crystal layer 105 composed of GaN (convex portion 405a), p-GaN (405c), and air having a depth of 80 nm is formed.
As the remaining layers, p-Al _0.20 Ga _0.80 N is 20 nm as an electron blocking layer 406 for preventing electron overflow, p-Al _0.05 Ga _0.95 N is 500 nm as a p-type cladding layer 407, and a contact layer 408 for electrode formation. p-GaN is grown in order of 100 nm.
The substrate is taken out of the MOCVD apparatus, and the n-type GaN substrate 401 is formed with an n-electrode 409 and a p-electrode 410 made of Ni / Au on the surface of p-GaN (408), thereby completing a photonic crystal surface emitting laser. To do.

[Example 2]
As Example 2, a configuration example different from Example 1 of the photonic crystal surface emitting laser according to the embodiment of the present invention will be described with reference to FIG.
In this example, a blue photonic crystal surface emitting laser having an emission wavelength of 450 nm was prepared.
At the time of the preparation, a two-dimensional structure of GaN / p-GaN was used as the base material of the two-dimensional photonic crystal layer, and heat treatment was performed at 850 ° C., which is about 150 ° C. lower than the GaN growth temperature, to form the side wall member 105c.
In this embodiment, as shown in FIG. 5, the following layers are grown in the same manner as in the first embodiment.
An n-GaN substrate is used as the substrate 501, 2 μm of n-GaN is used as the buffer layer 511, 500 nm of n-Al _0.05 Ga _0.95 N is grown as the n-type cladding layer 502, and GaN is grown as 120 nm as the n-side guide layer 503.
On top of this, an In _0.20 Ga _0.80 N / GaN multiple quantum well having three periods is grown as the active layer 504.
The thickness of In _0.20 Ga _0.80 N that is a well layer is 2.5 nm, the thickness of GaN that is a barrier layer is 7.5 nm, and the emission wavelength is 450 nm.
On the active layer 504, a two-dimensional structure 505 of GaN (5051) having a thickness of 110 nm and p-GaN (5052) doped with 3 × 10 ¹⁹ cm ⁻³ of Mg with a thickness of 30 nm as the two-dimensional photonic crystal layer 105. Grow.

The substrate is taken out from the MOCVD apparatus, and a two-dimensional photonic crystal layer pattern is formed in the same procedure as in the first embodiment.
A circular pattern is arranged in a square lattice pattern, and is drawn with a diameter of 100 nm and a lattice spacing of 180 nm.
By etching 110 nm of the GaN / p-GaN two-layer structure 505 by ICP using SiO ₂ as a mask, the convex portion 505a and the voids using the GaN / p-GaN two-layer structure 505 as a high refractive index medium as a base material Is formed.

Next, mass transport is generated by heat treatment to form p-type conductive p-GaN as a side wall member 505c on the side wall of the convex portion 505a.
While supplying Cp ₂ Mg as a p-type impurity, it is heated to 850 ° C. in a mixed gas atmosphere of N ₂ and NH ₃ and held for 30 minutes.
The supply amount of Cp ₂ Mg is adjusted so that p-GaN (505c) can be doped with 2 × 10 ¹⁹ cm ⁻³ of Mg.
The GaN of the convex portion 505a is decomposed, and Ga atoms are transported to the side wall of the convex portion 505a. Then, nitrogen and Mg in the gas phase are taken in, and p-GaN having a doping concentration of 2 × 10 ¹⁹ cm ^{−3 having} a lower resistance than the convex portion 505a is formed as the side wall member 505c.
The pores become narrow and have a diameter of 70 nm. At the bottom of the vacancies, atoms are mass transported and become 20 nm shallow.

Next, a resist is formed on the convex portion 505a, and SiO ₂ is deposited to 80 nm by electron beam lithography using plasma CVD.
When lifted off, a two-dimensional photonic crystal layer 105 is formed in which holes are filled with SiO ₂ (505b).
Thereby, a high refractive index medium having a refractive index lower than that of the high refractive index medium and higher than that of air can be formed in the holes.
Thereafter, the substrate is heated to 1000 ° C. with an MOCVD apparatus, and trimethyl gallium, which is a group III raw material, is supplied to grow p-GaN (512) by 50 nm to cover the two-dimensional photonic crystal layer.
Thereby, the upper side of the high refractive index medium can be formed of a member having a lower resistance than the side wall member.
As the remaining layers, p-Al _0.20 Ga _0.80 N (506) is 20 nm as an electron blocking layer to prevent electron overflow, p-Al _0.05 Ga _0.95 N (507) is 500 nm as a p-type cladding layer, and an electrode is formed. As a contact layer, p-GaN (508) is grown to 100 nm in this order.
The substrate is taken out of the MOCVD apparatus, and the n-type GaN substrate 501 is formed with an n-electrode 509 and a p-electrode 510 made of Ni / Au on the surface of p-GaN (508), thereby completing a photonic crystal surface emitting laser. To do.

[Example 3]
As Example 3, a configuration example different from the above examples of the photonic crystal surface emitting laser according to the embodiment of the present invention will be described with reference to FIG.
In this example, a green photonic crystal surface emitting laser having an emission wavelength of 530 nm was prepared.
In this example, In _0.05 Ga _0.95 N is used as the base material of the two-dimensional photonic crystal layer, heat treatment is performed at 1025 ° C., which is near the growth temperature of GaN, and the vacancies are formed by mass transport simultaneously with the formation of the side wall member. A two-dimensional photonic crystal layer is formed by closing.
The thickness of the two-dimensional photonic crystal layer is designed to be 110 nm which is about λ / 2n. In the present embodiment, as shown in FIG. 6, the following layers are grown in the same manner as in the first embodiment.
An n-GaN substrate is used as the substrate 601, 2 μm of n-GaN is grown as the buffer layer 611, 500 nm of n-Al _0.04 Ga _0.96 N is grown as the n-type cladding layer 602, and GaN is grown as 120 nm as the n-side guide layer 603.
On top of this, a multi-quantum well of In _0.35 Ga _0.65 N / GaN having three periods is grown as the active layer 604.
The thickness of InGaN as the well layer is 2.5 nm, the thickness of GaN as the barrier layer is 7.5 nm, and the emission wavelength is 530 nm.
In _0.05 Ga _0.95 N (605) serving as a base material of the two-dimensional photonic crystal layer 105 is grown on the active layer 604 by 160 nm.

The substrate is taken out from the MOCVD apparatus, and a two-dimensional photonic crystal layer pattern is formed in the same procedure as in the first embodiment.
A circular pattern is arranged in a square lattice pattern, and is drawn with a diameter of 110 nm and a lattice spacing of 220 nm.
By etching 140 nm of In _0.05 Ga _0.95 N (605) with ICP using SiO ₂ as a mask, a convex portion 605a and a hole having In _0.05 Ga _0.95 N (605) as a base material are formed as a high refractive index medium. .

Next, a mass of p-type conductivity as a sidewall member on the side walls of the transport caused the _{In 0.05 Ga 0.95 N p-In} 0.05 Ga 0.95 N (605c) in the heat treatment. While supplying trimetridium (TMIn) as an In source and Cp ₂ Mg as a p-type impurity, it is heated to 1025 ° C. in a mixed gas atmosphere of N ₂ and NH ₃ and held for 5 minutes.
The supply amount of Cp ₂ Mg is adjusted to such a supply amount that p-In _0.05 Ga _0.95 N (605c) can be doped with 2 × 10 ¹⁹ cm ⁻³ of Mg.
When In _0.05 Ga _0.95 N (605) is heat-treated at a high temperature of 1000 ° C. or more, In is desorbed, heat treatment is performed while TMIn is also supplied. Since heat treatment is performed in the vicinity of the growth temperature of GaN, atoms flow into the vacancies and atoms concentrate on the top of the projections 605a.
As a result, p-type conductive p-In _0.05 Ga _0.95 N having a lower resistance than the convex portion 605a is formed as a side wall member 605c on the side wall of the convex portion 605a.
In addition, p-In _0.05 Ga _0.95 N having a thickness of 30 nm is formed on the top of the hole, and the hole is closed. The diameter of the hole is reduced by 40 nm to 70 nm.
In addition, atoms are mass transported at the bottom of the vacancies to become 20 nm shallow, to a depth of 110 nm, and the two-dimensional photonic crystal layer 105 can be formed by mass transport in the heat treatment near the growth temperature.

As the remaining layers, p-Al _0.20 Ga _0.80 N (606) is 20 nm as an electron blocking layer to prevent the overflow of electrons, p-Al _0.04 Ga _0.96 N (607) is 500 nm as a p-type cladding layer, and an electrode is formed. As a contact layer, p-GaN (608) is grown to 100 nm in this order.
The substrate is taken out of the MOCVD apparatus, and an n-electrode 609 and a p-electrode 610 made of Ni / Au are formed on the surface of the p-GaN (608) on the back surface of the n-type GaN substrate 601, thereby producing a photonic crystal surface light emission that emits green light. The laser is complete.

100: photonic crystal surface emitting laser 101: substrate 102: n-type cladding layer 103: n-side guide layer 104: active layer 105: two-dimensional photonic crystal layer 105a: high refractive index medium 105b: low refractive index medium 105c: sidewall Member 106: Electron blocking layer 107: p-type cladding layer 108: p-type contact layer 109: n-electrode 110: p-electrode

Claims (13)

A photonic crystal surface-emitting laser in which a plurality of semiconductor layers including an active layer and a two-dimensional photonic crystal layer provided in the vicinity of the active layer and having a resonance mode in an in-plane direction are stacked on a substrate. And
The two-dimensional photonic crystal layer is
A low refractive index medium and a high refractive index medium having a higher refractive index than the low refractive index medium are periodically arranged in the in-plane direction of the substrate,
A photonic crystal surface emitting laser, wherein a side wall member having electrical conductivity is disposed between the low refractive index medium and the high refractive index medium.   2. The photonic crystal surface emitting laser according to claim 1, wherein the side wall member has a resistance lower than that of the high refractive index medium, and is configured to be equal to or less than a volume of the high refractive index medium.   3. The photonic crystal surface emitting laser according to claim 1, wherein an upper side of the high refractive index medium is formed of a member having a resistance lower than that of the side wall member.   4. The photonic crystal surface emitting laser according to claim 1, wherein the conductivity of the side wall member is p-type. 5. 5. The photonic crystal surface-emitting laser according to claim 1, wherein the side wall member is doped with a doping concentration of 2 × 10 ¹⁸ cm ⁻³ or more.   6. The photonic crystal surface emitting laser according to claim 1, wherein the active layer is formed of an active layer that emits light having a green emission wavelength. A method of manufacturing a photonic crystal surface emitting laser having a two-dimensional photonic crystal layer having a resonance mode in an in-plane direction,
Forming an active layer on the substrate;
Forming a layer serving as a base material of a two-dimensional photonic crystal layer on the active layer;
A layer serving as a base material of the two-dimensional photonic crystal layer is used, and a high refractive index medium and a hole that is a low refractive index medium having a lower refractive index than the high refractive index medium are arranged in an in-plane direction of the substrate. Forming periodically arranged layers;
A layer in which the high refractive index medium and holes are periodically arranged in an in-plane direction of the substrate,
A side wall member having a resistivity lower than that of the high refractive index medium is provided on the side wall of the hole while heat treatment is performed at a temperature at which the high refractive index medium causes mass transport while supplying a dopant. Forming, and
A method for producing a photonic crystal surface emitting laser, comprising:   8. The photonic according to claim 7, further comprising a step of forming a high refractive index medium having a lower refractive index than the high refractive index medium and higher in refractive index than air after the heat treatment. A method of manufacturing a crystal surface emitting laser.   9. The method of manufacturing a photonic crystal surface emitting laser according to claim 7, wherein an upper side of the high refractive index medium is formed of a member having a resistance lower than that of the sidewall member.   10. The method of manufacturing a photonic crystal surface emitting laser according to claim 7, wherein an aspect ratio, which is a depth / width ratio of the holes, is 1 or more. 11.   11. The photonic crystal surface emitting laser according to claim 7, wherein the photonic crystal layer is made of a nitride semiconductor, and a heat treatment temperature of the heat treatment is 850 ° C. or more. Method.   The method for manufacturing a photonic crystal surface emitting laser according to claim 11, wherein the dopant is Mg.   13. The method of manufacturing a photonic crystal surface emitting laser according to claim 12, wherein the active layer is formed by an active layer that emits light having an emission wavelength of green.

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