JP2012109410A - Two-dimensional photonic crystal surface emitting laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-dimensional photonic crystal surface emitting laser that can control intensity of diffraction light by a two-dimensional photonic crystal by a simple configuration comprising a light intensity distribution control layer.SOLUTION: A two-dimensional photonic crystal surface emitting laser comprises a lower clad layer 102 formed on a substrate 101, an active layer 103 that is formed on the lower clad layer and emits light by injecting carriers and a two-dimensional photonic crystal layer 104 that is formed on the active layer and resonates light generated in the active layer in the surface. The two-dimensional photonic crystal surface emitting laser comprises a light intensity distribution control layer 105 that is formed on the two-dimensional photonic crystal layer and controls light intensity distribution in the two-dimensional photonic crystal layer, and configures a slab waveguide made of laminate structure comprising the lower clad layer, the active layer, the photonic crystal layer, the light intensity distribution control layer and an upper clad layer formed on the light intensity distribution control layer. A refractive index in the light intensity distribution control layer is higher than an effective refractive index in the slab waveguide, and the film thickness distribution is uneven in the surface of the light intensity distribution control layer.

Description

  The present invention relates to a two-dimensional photonic crystal surface emitting laser.

In recent years, research on a two-dimensional photonic crystal surface emitting laser using a two-dimensional 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 structure in which a refractive index is periodically changed two-dimensionally with a semiconductor and a medium such as air or a dielectric is disposed in the vicinity of the active layer.
The 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 direction perpendicular to the surface by first-order diffraction with a two-dimensional photonic crystal.

Japanese Patent No. 3989333

In the two-dimensional photonic crystal surface emitting laser, it is a problem to control the intensity of the diffracted light as necessary in the following cases.
In other words, if necessary, the shape of the laser beam is controlled, or the diffraction of the diffracted light is controlled by the electrode or dielectric formed on the surface and the diffracted light is emitted from a specific location. It is required to have a light intensity distribution.
For example, in the two-dimensional photonic crystal surface emitting laser of Patent Document 1, carriers are injected with an electrode formed on the surface, and light generated in the active layer is extracted from the end of the electrode.
In such a case, since the diffracted light immediately below the electrode is absorbed by the electrode, the intensity of the diffracted light just below the electrode is weakened, and the intensity of the diffracted light is controlled to be stronger at the opening than directly below the electrode. Is required.

  In view of the above problems, the present invention provides a two-dimensional photonic crystal surface emitting laser capable of controlling the intensity of diffracted light by a two-dimensional photonic crystal with a simple configuration using a light intensity distribution control layer. Objective.

The two-dimensional photonic crystal surface emitting laser of the present invention comprises a lower clad layer provided on a substrate,
An active layer that emits light by injecting carriers provided on the lower cladding layer;
A two-dimensional photonic crystal surface emitting laser having a two-dimensional photonic crystal layer that resonates light generated in the active layer provided on the active layer in a plane;
A light intensity distribution control layer provided on the two-dimensional photonic crystal layer and controlling a light intensity distribution in the two-dimensional photonic crystal layer;
A slab waveguide having a laminated structure of the lower cladding layer, the active layer, the photonic crystal layer, the light intensity distribution control layer, and an upper cladding layer provided on the light intensity distribution control layer; Configured,
A refractive index of the light intensity distribution control layer is larger than an effective refractive index of the slab waveguide, and an in-plane film thickness distribution is different.

  According to the present invention, it is possible to realize a two-dimensional photonic crystal surface emitting laser that can control the intensity of diffracted light by a two-dimensional photonic crystal with a simple configuration using a light intensity distribution control layer.

It is the schematic for demonstrating the interference of the diffracted light by the thickness of the two-dimensional photonic crystal of this invention. It is a figure which shows the relationship between the film thickness of the two-dimensional photonic crystal of this invention, and diffracted light intensity. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser for demonstrating the structural example of control of the light distribution by the light intensity distribution control layer in Embodiment 1 of this invention. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser in Embodiment 2 of this invention. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser in Embodiment 3 of this invention. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser in Embodiment 4 of this invention. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser in Example 1 of this invention. It is a figure which shows light distribution and refractive index distribution of the cross-sectional direction of the two-dimensional photonic crystal surface emitting laser in Example 1 of this invention. It is a figure which shows the relationship between the film thickness of the light intensity distribution control layer of the two-dimensional photonic crystal surface emitting laser in Example 1 of this invention, and diffracted light intensity. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser in Example 2 of this invention. It is a figure which shows light distribution and refractive index distribution of the cross-sectional direction of the two-dimensional photonic crystal surface emitting laser in Example 2 of this invention. It is a figure which shows the relationship between the film thickness of the light intensity distribution control layer of the two-dimensional photonic crystal surface emitting laser in Example 2 of this invention, and diffracted light intensity. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser in Example 3 of this invention. It is sectional drawing of the two-dimensional photonic crystal surface emitting laser in Example 4 of this invention. It is a figure which shows the light distribution and refractive index distribution of a cross-sectional direction of the structure where the low refractive index medium of the two-dimensional photonic crystal surface emitting laser in Example 1 of this invention is comprised with air. It is the figure which compared the relationship between the film thickness of the light intensity distribution control layer of the structure used in Example 1 and Comparative Example 1 of this invention, and diffracted light intensity.

The present invention makes it possible to control the intensity of the diffracted light with a simple configuration that only controls the film thickness of the light intensity distribution control layer. Next, interference of diffracted light by the two-dimensional photonic crystal used in the present invention will be described.
In the two-dimensional photonic crystal, a high refractive index medium and a low refractive index medium are two-dimensionally arranged in a plane, and light generated in the active layer is resonated in the two-dimensional plane.
Further, the light is first-order diffracted by the two-dimensional photonic crystal to emit the light in the vertical direction.
The intensity of light diffracted in the vertical direction is affected by the film thickness of the two-dimensional photonic crystal. FIG. 1 is a schematic diagram showing the state of diffracted light, and shows how a standing wave is formed by light generated in an active layer in a two-dimensional photonic crystal having a lattice constant a and is diffracted in the vertical direction.
Since light is diffracted at any position with respect to the thickness direction of the two-dimensional photonic crystal, an optical path difference is generated like diffracted lights L1 and L2 in FIG.
Then, when such diffracted light is superimposed, the diffracted light interferes and strengthens or weakens each other.
Whether the interference increases or decreases is determined by the film thickness d of the two-dimensional photonic crystal.

FIG. 2 is a diagram showing the relationship between the electric field intensity of the diffracted light diffracted by the two-dimensional photonic crystal and emitted to the outside and the film thickness of the two-dimensional photonic crystal.
The solid line is calculated when the light distributed in the two-dimensional photonic crystal is constant, and the dotted line is calculated when the light is attenuated by an exponential function (Exp) like the light distributed on the actual laser structure.
As the film thickness d of the two-dimensional photonic crystal increases from 0 to 0.5a, the intensity of the diffracted light increases and increases. When the film thickness is further increased, the diffracted light weakens.
When the film thickness d of the two-dimensional photonic crystal is a, it becomes the weakest. Thereafter, strengthening and weakening are repeated at intervals of 0.5a.
When the film thickness d of the photonic layer is d = (0.5 + p) a with respect to the lattice constant a of the two-dimensional photonic crystal, it is most strongly strengthened (however, (p = 0, 1, 2,...) Is). On the other hand, they are most weakened when d = qa (however, (q = 1, 2, 3...)).

There is a method of changing the film thickness of the two-dimensional photonic crystal in the plane as a method of applying the intensity of the diffracted light within the plane of the two-dimensional photonic crystal surface emitting laser.
By changing the film thickness of the two-dimensional photonic crystal in the plane, the diffracted light intensity can be changed, for example, between AB in FIG.
Furthermore, if the light distribution in the two-dimensional photonic crystal is uniform, the intensity can be changed greatly as between CD.
However, in order to change the film thickness of the two-dimensional photonic crystal within the plane, it is necessary to make a fine structure with a scale of several tens of nm with high precision within the plane. Therefore, it is difficult to produce a method that changes the depth of the two-dimensional photonic crystal in the plane.

For this reason, the present invention has found a configuration in which the intensity of diffracted light can be controlled with a simple structure that only controls the film thickness of the light intensity distribution control layer.
That is, in the present invention, a lower clad layer provided on a substrate, an active layer that emits light by injecting carriers provided on the lower clad layer, and a two-dimensional photonic crystal layer provided on the active layer A two-dimensional photonic crystal surface emitting laser having the following structure is configured as follows.
That is, a light intensity distribution control layer is provided on the two-dimensional photonic crystal layer and controls the light intensity distribution in the two-dimensional photonic crystal layer.
Then, a light intensity distribution control layer for controlling the intensity of light distributed in the two-dimensional photonic crystal is provided, and the thickness of the light intensity distribution control layer is changed in the plane, thereby changing the interference intensity of the diffracted light and performing diffraction. It is configured to give a light intensity distribution. Specifically, referring to FIG. 2, the intensity is changed between A and C and B and D.
Further, the present invention is easy to manufacture because it only controls the film thickness of the light intensity distribution control layer.

[Embodiment 1]
As Embodiment 1, a configuration example of light distribution control by a light intensity distribution control layer in a two-dimensional photonic crystal surface emitting laser will be described with reference to FIG.
As shown in FIG. 3, the two-dimensional photonic crystal surface emitting laser of the present embodiment includes an n-type substrate 101, a lower cladding layer 102, an active layer 103, and a two-dimensional photonic crystal layer 104. A light intensity distribution control layer 105 is formed on the two-dimensional photonic crystal layer, and a slab waveguide having a laminated structure in which an upper clad layer 106 is laminated on the light intensity distribution control layer is provided.
The light guided to the slab waveguide of the two-dimensional photonic crystal surface emitting laser is expressed by the following equation.

Where E is the electric field component of the guided light, β is the propagation constant, n is the refractive index, and λ is the wavelength of the guided light.
n _eff is an effective refractive index, which is an effective refractive index for light propagating in the slab waveguide, and is an eigenvalue of the waveguide mode.
The light distribution is obtained by substituting the refractive index of each layer into the differential equation and obtaining n _eff satisfying the boundary condition.
The refractive index of the two-dimensional photonic crystal layer 104 uses a volume average value of a high refractive index medium and a low refractive index medium.

The light generated in the active layer 103 has a maximum value near the active layer 103 and has a distribution that attenuates toward the lower clad layer 106 and the lower clad layer 102 having a low refractive index.
When the refractive index of the light intensity distribution control layer 105 is made larger than n _eff , the active layer 103 depends on the film thickness of the light intensity distribution control layer 105, the refractive index of the light intensity distribution control layer 105, and the refractive index difference between n _eff. The peak of the nearby light distribution spreads so as to be drawn into the light intensity distribution control layer 105.
When light spreads to the light intensity distribution control layer 105, light spreads to the two-dimensional photonic crystal layer 104 sandwiched between the active layer 103 and the light intensity distribution control layer 105, and the uniformity of the light distribution is improved.

Next, the interference of diffracted light due to the film thicknesses of the light intensity distribution control layer 105 and the two-dimensional photonic crystal layer 104 will be described.
The light distribution in the two-dimensional photonic crystal layer 104 can be controlled by the film thickness of the light intensity distribution control layer 105.
Furthermore, by changing the light distribution in the two-dimensional photonic crystal layer 104, the intensity of interference of light diffracted in the vertical direction by the two-dimensional photonic crystal layer 104 can be changed.
That is, the diffracted light intensity can be changed in the plane by changing the film thickness of the light intensity distribution control layer 105 in the plane.

The relationship between the film thickness d of the two-dimensional photonic crystal layer 104 and the film thickness of the light intensity distribution control layer 105 is as follows.
When the film thickness d of the two-dimensional photonic crystal layer 104 is in the vicinity of (0.5 + p) a, the diffracted light intensifies and interferes (however, p = 0, 1, 2,...).
Therefore, the film thickness of the light intensity distribution control layer 105 is such that the region where the intensity of the diffracted light is desired to be increased is thickened and the region where the diffracted light is desired to be weakened is reduced.
When the film thickness d of the two-dimensional photonic crystal 104 is in the vicinity of qa, the diffracted light weakens and interferes (however, (q = 1, 2, 3...)).
Therefore, the film thickness of the light intensity distribution control layer 105 is such that a region where the intensity of diffracted light is desired to be weakened is thickened and a region where the intensity of diffracted light is desired is thinned.
As can be seen from FIG. 2, when the film thickness d of the two-dimensional photonic crystal layer 104 is in the vicinity of (0.75 + 0.5r) a, the diffraction is performed even if the film thickness of the light intensity distribution control layer 105 is changed. The intensity of light hardly changes (however, (r = 0, 1, 2,...)).

In this embodiment, the two-dimensional photonic crystal 104 has a structure in which diffracted light weakens and interferes.
When the diffracted light interferes so as to weaken each other, the film thickness d of the two-dimensional photonic crystal layer 104 is set to a film thickness that satisfies the conditional expression (q−0.125) a <d <(q + 0.125) a. (However, (q = 1, 2, 3...))
More preferably, the film thickness should satisfy the conditional expression (q−0.100) a <d <(q + 0.100) a. More preferably, the film thickness should satisfy the conditional expression (q−0.075) a <d <(q + 0.075) a.
Further, it is desirable to change the film thickness distribution of the light intensity distribution control layer 105 smoothly rather than changing it stepwise.
When the film thickness of the light intensity distribution control layer 105 changes, the effective refractive index n _eff changes in the plane.
That is, light reflection occurs at the interface where the film thickness of the light intensity distribution control layer 105 changes. The light reflected at the interface does not couple well with the two-dimensional photonic crystal layer 104 and is lost.
There is a mass transport as a method of smoothing the stepped shape. After processing the light intensity distribution control layer 105, the step can be smoothed by causing mass transport by heat treatment.

Next, the structure and material of the two-dimensional photonic crystal surface emitting laser of this embodiment will be described.
As described above, the two-dimensional photonic crystal surface emitting laser of this embodiment includes the substrate 101, the lower cladding layer 102, the active layer 103, the two-dimensional photonic crystal layer 104, the light intensity distribution control layer 105, and the upper cladding layer 106. The structure of the slab waveguide laminated | stacked in this order is provided.
Alternatively, the two-dimensional photonic crystal layer 104 may be disposed below the active layer 103 with the stacking order reversed. The lower electrode 107 is provided on the back surface of the substrate 101, and the upper electrode 108 is provided on the front surface.
Here, an example of providing a guide layer will be described.
A guide layer can be provided between the active layer 103 and the lower cladding layer 102 so that light is appropriately distributed in the active layer 103 and the two-dimensional photonic crystal layer 104.
When the refractive index of the guide layer is higher than that of the light intensity distribution control layer 105, the light distribution is shifted to the guide layer, and the effect of spreading light to the two-dimensional photonic crystal layer 104 of the light intensity distribution control layer 105 is weakened. End up. Therefore, it is desirable to make the refractive index of the light intensity distribution control layer 105 higher than the refractive index of the guide layer.

The two-dimensional photonic crystal layer 104 includes a high refractive index medium 104a and a low refractive index medium 104b in the layer plane.
Examples of the high refractive index medium 104a and the low refractive index medium 104b include the following.
The high refractive index medium 104a is a group III-V semiconductor containing Al, Ga, In, N, As, P, and Sb. The low refractive index medium 104b is _{air, SiO 2, SiN, Al 2} O 3, AlN, TiO, TiN , etc..
The intensity of interference of light diffracted by the two-dimensional photonic crystal layer 104 becomes stronger as the light distribution is uniform in the thickness direction of the two-dimensional photonic crystal layer 104.
In order to make the interference of diffracted light stronger, the average refractive index n _PhC of the two-dimensional photonic crystal obtained by averaging the refractive indexes of the high refractive index medium 104a and the low refractive index medium 104b of the two-dimensional photonic crystal layer 104 by volume. Is preferably larger than the refractive index of the cladding layer.
When the average refractive index n _PhC is made larger than the refractive index of the cladding layer, the refractive index difference between the average refractive index n _PhC and the active layer 103 or the light intensity distribution control layer 105 becomes small, so the two-dimensional photonic crystal layer 104 Light tends to spread inside, and the uniformity of light distribution is improved.
On the other hand, if the average refractive index n _PhC is larger than the refractive index of the light intensity distribution control layer 105, the light distribution peak moves to the two-dimensional photonic crystal layer 104, and the film thickness of the light intensity distribution control layer 105 is changed. However, the light distribution in the two-dimensional photonic crystal layer 104 is less likely to change.
Therefore, changing the film thickness of the light intensity distribution control layer 105 weakens the effect of modulating the interference intensity of the diffracted light. From the above, it is desirable that the average refractive index n _PhC is smaller than the refractive index of the light intensity distribution control layer 105.

[Embodiment 2]
As a second embodiment, a configuration example of light distribution control by a light intensity distribution control layer in a two-dimensional photonic crystal surface emitting laser will be described with reference to FIG.
The two-dimensional photonic crystal surface emitting laser in the present embodiment is the same as that of the first embodiment except for the two-dimensional photonic crystal layer 104 and the light intensity distribution control layer 105. The light intensity distribution control layer 105 will be described.

In the present embodiment, the thickness of the light intensity distribution control layer is configured as follows in order to construct a structure in which the diffracted light from the two-dimensional photonic crystal layer 104 intensifies and interferes.
The film thickness d of the two-dimensional photonic crystal layer 104 is set so that ((p + 0.5) −0.125) a <d <((p + 0.5) +0.125) a so that the diffracted light intensifies and interferes. The film thickness is set to satisfy the conditional expression (however, (p = 0, 1, 2,...)).
More preferably, the film thickness should satisfy the conditional expression of ((p + 0.5) −0.100) <d <((p + 0.5) +0.100) a. More preferably, the film thickness should satisfy the conditional expression ((p + 0.5) −0.075) a <d <((p + 0.5) +0.075) a.
The film thickness of the light intensity distribution control layer 105 is increased in order to increase interference in a region where diffracted light is to be emitted strongly. In the region where it is desired to emit light weakly, the region is thinned to reduce interference.

[Embodiment 3]
As a third embodiment, a configuration example of light distribution control by a light intensity distribution control layer in a two-dimensional photonic crystal surface emitting laser will be described with reference to FIG.
The two-dimensional photonic crystal surface emitting laser in the present embodiment has the same layer configuration as that of the first embodiment.
A p-electrode 108 and an opening 109 for extracting light are provided on the surface. In FIG. 5, an opening is provided in the p-electrode for extracting light from the front surface, but an opening 109 may be provided in the n-electrode 107 on the back surface.
The opening 109 may form a structure that transmits light, such as a translucent electrode or a transparent electrode.

In this embodiment, since the diffracted light of the two-dimensional photonic crystal layer 104 is weakened and interferes, the thickness of the two-dimensional photonic crystal layer 104 and the light intensity distribution control layer is configured as follows.
The film thickness d of the two-dimensional photonic crystal layer 104 is set to a film thickness satisfying the conditional expression (q−0.125) a <d <(q + 0.125) a, as in the first embodiment (however, ( q = 1, 2, 3...
More preferably, the film thickness should satisfy the conditional expression (q−0.100) a <d <(q + 0.100) a. More preferably, the film thickness should satisfy the conditional expression (q−0.075) a <d <(q + 0.075) a.
The film thickness of the light intensity distribution control layer 105 is set to be smaller than that immediately below the p-electrode 108 (ie, the region corresponding to the opening).
The light distribution in the two-dimensional photonic crystal layer 104 immediately below the p-electrode 108 is spread over the entire two-dimensional photonic crystal layer 104 by the light intensity distribution control layer 105, and the uniformity of the light distribution of the two-dimensional photonic crystal 104 is improved. By doing so, interference becomes strong and diffracted light becomes weak.
On the other hand, since the light intensity distribution control layer 105 of the two-dimensional photonic crystal 104 in the region corresponding to the opening 109 is thin, the light distribution uniformity of the two-dimensional photonic crystal 104 is low and interference does not occur strongly.
Accordingly, the diffracted light is stronger directly below the opening 109 (region corresponding to the opening) than directly below the electrode (region other than the region corresponding to the opening).

[Embodiment 4]
As a fourth embodiment, a configuration example of light distribution control by a light intensity distribution control layer in a two-dimensional photonic crystal surface emitting laser will be described with reference to FIG.
The two-dimensional photonic crystal surface emitting laser in the present embodiment has the same layer structure as that of the second embodiment.
Further, as in the third embodiment, a p-electrode 108 and an opening 109 for extracting light are provided on the surface.
In FIG. 6, an opening 109 is provided on the front surface for extracting light from the front surface, but an opening may be provided on the n-electrode 107 on the back surface.
The opening 109 may form a structure that transmits light, such as a translucent electrode or a transparent electrode.

In this embodiment, since the diffracted light of the two-dimensional photonic crystal layer 104 intensifies and interferes, the thickness of the two-dimensional photonic crystal layer 104 and the light intensity distribution control layer is configured as follows.
The film thickness d of the two-dimensional photonic crystal layer 104 satisfies the conditional expression ((p + 0.5) −0.125) a <d <((p + 0.5) +0.125) a as in the second embodiment. The film thickness is set (however, in the conditional expression here (p = 0, 1, 2,...)).
More preferably, the film thickness should satisfy the conditional expression ((p + 0.5) −0.100) a <d <((p + 0.5) +0.100) a. More preferably, the film thickness should satisfy the conditional expression ((p + 0.5) −0.075) a <d <((p + 0.5) +0.075) a.
The film thickness of the light intensity distribution control layer 105 is made thinner just below the p-electrode 108 than just below the opening 109 (region corresponding to the opening).
The light distribution of the two-dimensional photonic crystal layer 104 immediately below the opening 109 is spread over the entire two-dimensional photonic crystal layer 104 by the light intensity distribution control layer 105, so that the uniformity of the light distribution is improved and the diffracted light is strong. Become.
On the other hand, since the light intensity distribution control layer 105 is thin in the two-dimensional photonic crystal layer 104 directly under the electrode, the uniformity of the light distribution of the two-dimensional photonic crystal layer 104 is not so high and interference does not occur strongly.
Therefore, the diffracted light is stronger directly below the opening 109 (region corresponding to the opening) than immediately below the p-electrode 108 (region other than the region corresponding to the opening).

Examples of the present invention will be described below.
[Example 1]
As Example 1, a specific configuration example of the two-dimensional photonic crystal surface emitting laser according to Embodiment 1 will be described with reference to FIG.
In this embodiment, the two-dimensional photonic crystal has a lattice constant a and a film thickness d of d = a, and the diffracted light is most weakened.
The two-dimensional photonic crystal surface emitting laser in the present embodiment is configured as follows.
An n-type GaN substrate 701 is used as the substrate 101.
Next, the following layers are grown in order using a metal organic chemical vapor deposition (MOCVD) apparatus.
First, an n-GaN layer 710 is grown by 5 μm as a buffer layer for improving crystallinity.
Subsequently, n-Al _0.07 Ga _0.93 N702 is grown to 800 nm as the lower cladding layer 102, and a GaN layer 711 is grown to 100 nm as the guide layer.
On top of this, a multiple quantum well 703 is grown as an active layer 103. A pair of In _0.10 Ga _0.90 N with a thickness of 3 nm is grown as a well layer, and a pair of GaN with a thickness of 7 nm is grown as a barrier layer for three periods. The emission wavelength of the multiple quantum well 703 is 400 nm. Further, p-Al _0.15 Ga _0.85 N712 is grown to 20 nm as a carrier block layer for suppressing carrier overflow, and In _0.04 Ga _0.96 N704a is grown as a base material (high refractive index medium 104 a) of the two-dimensional photonic crystal layer 104.
The film thickness of In _0.04 Ga _0.96 N 704a is made slightly thicker than the lattice constant of the two-dimensional photonic crystal in consideration of damage to the active layer due to dry etching used in the subsequent two-dimensional photonic crystal production process.
In this embodiment, In _0.04 Ga _0.96 N704a is grown to 162 nm in order to set the lattice constant of the two-dimensional photonic crystal to 152 nm.
Next, the two-dimensional photonic crystal layer 104 is formed.
First, the substrate is taken out from the MOCVD apparatus, and a resist is applied on the substrate.
Next, a circular square lattice pattern is drawn and developed using electron beam lithography. The lattice constant a (period) is 152 nm, and the diameter of the circle is 55 nm.
Next, holes of a two-dimensional photonic crystal having a layer depth of 152 nm are formed so that 10 nm of In _0.04 Ga _0.96 N704a remains by dry etching, and the holes are filled with Al ₂ O ₃ by sputtering.
Thereafter, the resist is removed by lift-off to form a two-dimensional photonic crystal layer 104 composed of In _0.04 Ga _0.96 N 704a as the high refractive index medium 104a and Al ₂ O ₃ 704b as the low refractive index medium 104b.
After lift-off, the substrate on which the two-dimensional photonic crystal layer 104 is formed is set in an MOCVD apparatus, and In _0.04 Ga _0.96 N705 is grown as a light intensity distribution control layer 105 by 45 nm.

The substrate is taken out of the MOCVD apparatus again, and a film thickness distribution is provided for In _0.04 Ga _0.96 N705 by photolithography and dry etching to give an in-plane diffracted light intensity distribution.
In this embodiment, in order to obtain a circular beam spot, the film thickness distribution is provided in a circular shape. Specifically, photolithography and dry etching are divided into three times to form a film thickness distribution.
First, a circular pattern having a diameter of 10 μm and a depth of 15 nm is formed. Next, a circular pattern having a diameter of 5 μm is formed at a depth of 15 nm in alignment with the center of the circular pattern having a diameter of 10 μm. Finally, a pattern having a diameter of 3 μm is formed at a depth of 10 nm, whereby a distribution in which the film thickness decreases stepwise toward the center of the pattern is formed in In _0.04 Ga _0.96 N705.
In order to grow the remaining layers, a substrate having a thickness distribution of In _0.04 Ga _0.96 N705 is set in an MOCVD apparatus. Then, p-Al _0.07 Ga _0.93 N706 is grown to 500 nm as the upper clad layer 106, and p-GaN 713 is grown to 50 nm as a contact layer for electrode formation.
Finally, a lower electrode 707 made of Ti / Al is formed as the n electrode 107 on the back surface of the n-type GaN substrate 701, and a translucent electrode 708 made of Ni / Ai is formed as the upper electrode 108 on the contact layer.
Through the above steps, a two-dimensional photonic crystal surface emitting laser that oscillates by current injection and has a circular spot is completed.

FIGS. 8A and 8B are calculation results of the light distribution in the vertical direction in the two-dimensional photonic crystal surface emitting laser of this example.
The light intensity distribution control layer 105 has a 45 nm thickness (outside pattern) and a 5 nm thickness (pattern center), respectively.
It can be seen that the light intensity distribution control layer 105 having a 45 nm film thickness spreads more uniformly in the two-dimensional photonic crystal layer than the 5 nm structure.
FIG. 9 is a graph showing the relationship between the electric field intensity ratio of diffracted light and the light intensity distribution control layer 105 for the structure of the two-dimensional photonic crystal surface emitting laser of Example 1.
The electric field intensity of the diffracted light when the film thickness of the light intensity distribution control layer 105 is 0 nm is used as a reference. As the film thickness of the light intensity distribution control layer 105 increases, the diffracted light intensity decreases. This is because the spread of light to the two-dimensional photonic crystal layer 104 is increased as shown in FIG. 8A, the uniformity of the light distribution is improved, and the interference of diffracted light is increased.
When the film thickness of the light intensity distribution control layer 105 becomes thicker than around 45 nm, the diffracted light intensity increases.
This is because the maximum value of the light distribution near the active layer is shifted to the vicinity of the light intensity distribution control layer 105, the uniformity of the light distribution of the two-dimensional photonic crystal layer 104 is lowered, and the interference is weakened. Because.
Further, since the overlap between the active layer and light is reduced and it becomes difficult to obtain a gain, it is not desirable to increase the film thickness of the light intensity distribution control layer 105 beyond this.

[Example 2]
As Example 2, a specific configuration example of the two-dimensional photonic crystal surface emitting laser according to Embodiment 2 will be described with reference to FIG.
In this embodiment, the two-dimensional photonic crystal has a lattice constant a and a film thickness d of d = 0.5a, and is configured as a form in which diffracted light is most intensified.
The two-dimensional photonic crystal surface emitting laser in the present example is different in that the film thickness distribution of the two-dimensional photonic crystal layer 104, the light intensity distribution control layer 105, and the light intensity distribution control layer 105 are different. Same as Example 1. The differences will be described below.
The film thickness of In _0.04 Ga _0.96 N704 that is the two-dimensional photonic crystal layer 104 is set to 86 nm.
This is the sum of 76 nm, which is 0.5 times the lattice constant of 152 nm of the two-dimensional photonic crystal, and 10 nm for suppressing etching damage.
The light intensity distribution control layer 105 is formed up to 50 nm thick In _0.04 Ga _0.96 N705. Next, a film thickness distribution for providing an in-plane intensity distribution of diffracted light is provided on In _0.04 Ga _0.96 N705 by photolithography and dry etching.
In this embodiment, In _0.04 Ga _0.96 N705 is provided with a circular film thickness distribution that increases in thickness toward the center.
Specifically, a circular mask having a diameter of 3 μm is formed by photolithography, and Ga _0.04 In _0.96 N705 is etched by 15 nm by dry etching.
Next, a circular mask having a diameter of 5 μm is formed by aligning the center of the pattern of 3 μm before, and is etched by 15 nm by dry etching.
Finally, a mask having a diameter of 10 μm is similarly formed and etched by 15 nm, thereby forming a distribution in In _0.04 Ga _0.96 N705 in which the film thickness increases stepwise toward the center of the pattern.
Thereafter, the remaining layers and electrodes are formed to complete a two-dimensional photonic crystal surface emitting laser.

FIGS. 11A and 11B show calculation results of the light distribution in the vertical direction in the two-dimensional photonic crystal surface emitting laser of this example.
The light intensity distribution control layer 105 has a structure with a thickness of 50 nm (pattern center) and a structure with a thickness of 5 nm (outside of the pattern).
It can be seen that the light intensity distribution control layer 105 having a thickness of 50 nm has light spread more uniformly in the two-dimensional photonic crystal layer than the structure of 5 nm.
FIG. 12 is a graph in which the relationship between the electric field intensity ratio of diffracted light and the light intensity distribution control layer 105 is calculated.
The electric field intensity of the diffracted light when the film thickness of the light intensity distribution control layer 105 is 0 nm is used as a reference.
As the film thickness of the light intensity distribution control layer 105 increases, the intensity of diffracted light increases as a result of strong interference.
When the light intensity distribution control layer 105 is made too thick, the diffracted light intensity decreases because the maximum value of the light distribution is in the light intensity distribution control layer 105, as in the first embodiment, and the two-dimensional photonic crystal layer 104. This is because the uniformity of the light distribution is reduced.

[Example 3]
As Example 3, a specific configuration example of the two-dimensional photonic crystal surface emitting laser according to Embodiment 3 will be described with reference to FIG.
The configuration of the two-dimensional photonic crystal surface emitting laser of this example is the same as that of Example 1 except that the film thickness distribution of the light intensity distribution control layer 105 and the opening 109 for extracting light are provided on the surface. is there. The differences will be described below.
First, the structure up to In _0.04 Ga _0.96 N705 which is the light intensity distribution control layer 105 is formed in the same manner as in the first embodiment.
Next, a part of the In _0.04 Ga _0.96 N705 layer is thinned by dry etching. The shape is circular, the diameter is 5 μm, and the depth is 40 nm. Thereafter, the remaining layers are formed by regrowth.
An n electrode 707 made of Ti / Al is formed on the back surface, and a p electrode 708 made of Ni / Au is formed on the front surface.
The p-electrode 708 is provided with a circular opening having a diameter of 5 μm as the opening 109 for extracting light. The opening 109 is formed so as to overlap with a region where a circular pattern of In _0.04 Ga _0.96 N705 is formed.
Through the above steps, a two-dimensional photonic crystal surface emitting laser in which light is strongly emitted from the opening 109 is completed.

[Example 4]
As Example 4, a specific configuration example of the two-dimensional photonic crystal surface emitting laser according to Embodiment 4 will be described with reference to FIG.
The configuration of the two-dimensional photonic crystal surface emitting laser of this example is the same as that of Example 2 except that the film thickness distribution of the light intensity distribution control layer and the opening 109 are provided on the surface. The differences will be described below.
First, a structure up to In _0.04 Ga _0.96 N705 which is a light intensity distribution control layer is formed in the same manner as in the second embodiment.
Next, a pattern is formed in In _0.04 Ga _0.96 N705 by dry etching. The shape is a circle having a diameter of 5 μm, and the circular portion is protected by a mask so as not to be etched, and the other region is thinned to a thickness of 5 nm. Thereafter, the remaining layers are formed by regrowth.
An n electrode 707 made of Ti / Al is formed on the back surface, and a p electrode 708 made of Ni / Au is formed on the front surface. The p-electrode 708 has a circular opening having a diameter of 5 μm as the opening 109 for extracting light, and is formed so as to overlap with a circular pattern of In _0.04 Ga _0.96 N705.
Through the above steps, a two-dimensional photonic crystal surface emitting laser in which light is strongly emitted from the opening 109 is completed.

(Comparative example)
Next, a comparative example will be described.
In this comparative example, the average refractive index n _PhC of the two-dimensional photonic crystal surface layer of the two-dimensional photonic crystal surface emitting laser in Example 1 is
The light intensity distribution and diffracted light intensity in the two-dimensional photonic crystal layer 104 having a structure higher than the refractive index n _{clad of the} cladding layer and a structure lower than the refractive index n _{clad of the} cladding layer will be compared.
Example 1 is used for a structure having a relationship of n _PhC > n _clad . The structure having a relationship of n _PhC <n _clad uses a structure in which the low refractive index medium 104b of Example 1 is replaced with air.
Further, regarding the film thickness of the light intensity distribution control layer 105, In _0.04 Ga _0.96 N705 having a strong interference effect in Example 1 is compared with a thickness of 45 nm.

FIG. 15 shows a calculation result of a structure in which the low refractive index medium 104b is replaced with air.
In FIG. 8A of Example 1, the electric field in the two-dimensional photonic crystal layer is uniform, whereas in FIG. 15 of the comparative example, the light distribution becomes a valley in the two-dimensional photonic crystal layer 104. It can be seen that the uniformity is reduced.
From this, the structure of n _PhC <n _clad has a weaker interference of diffracted light than the structure of n _PhC > n _clad .
FIG. 16 is a graph comparing the relationship between the electric field imaginary ratio of diffracted light and the film thickness of the light intensity distribution control layer.
The solid line has a structure of n _PhC > n _clad , and the dotted line has a structure of n _PhC <n _clad .
The structure of n _PhC <n _clad has a smaller modulation of the intensity ratio of diffracted light than the structure of n _PhC > n _clad , but it can be confirmed that the effect of the present invention is achieved.
From the above comparison results, even if n _PhC is lower than n _clad , the effect of the present invention is obtained. However, it can be said that it is desirable to make n _PhC higher than n _clad in order to exert more effect.

DESCRIPTION OF SYMBOLS 101: Substrate 102: Lower clad layer 103: Active layer 104: Two-dimensional photonic crystal layer 104a: High refractive index medium 104b: Low refractive index medium 105: Light intensity distribution control layer 106: Upper clad layer 107: Lower electrode 108: Upper electrode 109: opening

Claims (5)

A lower cladding layer provided on the substrate;
An active layer that emits light by injecting carriers provided on the lower cladding layer;
A two-dimensional photonic crystal surface emitting laser having a two-dimensional photonic crystal layer that resonates light generated in the active layer provided on the active layer in a plane;
A light intensity distribution control layer provided on the two-dimensional photonic crystal layer and controlling a light intensity distribution in the two-dimensional photonic crystal layer;
A slab waveguide having a laminated structure of the lower cladding layer, the active layer, the photonic crystal layer, the light intensity distribution control layer, and an upper cladding layer provided on the light intensity distribution control layer; Configured,
The two-dimensional photonic crystal surface emitting laser characterized in that the refractive index of the light intensity distribution control layer is larger than the effective refractive index of the slab waveguide and the in-plane film thickness distribution is different. Provided with an opening for light extraction on the back surface or surface of the surface emitting laser,
The photonic crystal has a lattice constant of a and a film thickness of d.
The photonic crystal layer has a thickness that satisfies the following conditional expression:
The film thickness of the region corresponding to the opening of the light intensity distribution control layer is configured to be thinner than the region other than the region corresponding to the opening of the light intensity distribution control layer. The two-dimensional photonic crystal surface emitting laser according to claim 1.
(Q−0.125) a <d <(q + 0.125) a
However, (q = 1, 2, 3 ...) Provided with an opening for light extraction on the back surface or surface of the surface emitting laser,
When the lattice constant of the photonic crystal is a and the film thickness is d,
The photonic crystal has a film thickness that satisfies the following conditional expression:
The film thickness of the region corresponding to the opening of the light intensity distribution control layer is configured to be thicker than the region other than the region corresponding to the opening of the light intensity distribution control layer. The two-dimensional photonic crystal surface emitting laser according to claim 1.
((P + 0.5) -0.125) <d <((p + 0.5) +0.125) a
However, (p = 0, 1, 2,...)   The two-dimensional according to any one of claims 1 to 3, wherein a refractive index of the photonic crystal layer is larger than a refractive index of the cladding layer and lower than a refractive index of the light intensity distribution control layer. Photonic crystal surface emitting laser. A guide layer is provided between the lower cladding layer and the active layer,
5. The two-dimensional photonic crystal surface-emitting laser according to claim 1, wherein a refractive index of the light intensity distribution control layer is larger than a refractive index of the guide layer.

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