JP2003273455A - Two-dimensional photonic crystal face emitting laser and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a two-dimensional photonic crystal face emitting laser and its manufacturing method which improves the utilization efficiency of surface emitted light by 50% or more. <P>SOLUTION: There is provided two-dimensional photonic crystal face emitting laser which includes a photonic crystal periodic structure 21a in which there are laminated on a substrate a lower clad layer 12, an active layer for emitting light by doping a carrier, and an upper clad layer, and a refractive index period is arranged in the lower clad layer 12 two dimensionally, and in which light is surface-emitted from the upper surface of the upper clad layer by resonating it with the periodic structure 21a. The width of a cross sectional shape of the periodic structure 21a with respect to the crystal plane is gradually reduced in the direction of the light emission, whereby primary diffraction light L2 directed downward is suppressed, while the quantity of primary diffraction light L1 directed upward is correspondingly increased. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-dimensional photonic crystal surface emitting laser and a method of manufacturing the same, and more particularly to a photonic crystal in which a refractive index period is two-dimensionally arranged in or near an active layer emitting light by carrier injection. The present invention relates to a two-dimensional photonic crystal surface emitting laser that includes a periodic structure of a nick crystal and resonates with a photonic crystal to perform surface emission, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, various surface emitting lasers which emit laser light in a vertical direction from a substrate surface have been developed and studied. A surface-emitting laser can integrate (array) a large number of elements on the same substrate and emit coherent light from each element in parallel. Therefore, in the field of parallel optical pickup, parallel optical transmission, and optical parallel information processing. Applications are expected.

As a surface emitting laser of this type, a two-dimensional photonic crystal surface emitting laser utilizing a photonic crystal is disclosed in Japanese Patent Laid-Open No. 2000-332351. A photonic crystal is a crystal having a refractive index period that is about the same as or smaller than the wavelength of light. In a dielectric multidimensional periodic structure, the same principle as that in which a band gap occurs in the electronic state in a semiconductor crystal As a result, a wavelength band (photonic band gap) that suppresses the waveguiding of light is generated, and light can be confined in two dimensions or three dimensions.

The two-dimensional photonic crystal surface emitting laser described in the above publication is provided with a photonic crystal periodic structure in which a refractive index period is two-dimensionally arranged in the vicinity of an active layer which emits light when carriers are injected. The crystal resonates and emits surface light.

Specifically, as shown in FIG. 8, the two-dimensional photonic crystal surface emitting laser 10 is roughly composed of a substrate 1
1, a lower clad layer 12, an active layer 13, and an upper clad layer 14 are laminated on the lower clad layer 12.
A two-dimensional photonic crystal 20 is built in the vicinity of.

The substrate 11 is made of, for example, an n-type InP semiconductor material. The lower clad layer 12 and the upper clad layer 14 are, for example, n-type and p-type InP semiconductor layers, respectively, and have a lower refractive index than the active layer 13. The two-dimensional photonic crystal 20 is composed of holes (photonic crystal periodic structure 21) formed in the lower cladding layer 12,
The lower cladding layer 12 is composed of a square lattice or a triangular lattice in which media having different refractive indexes are arranged in a two-dimensional period.
The pores may be filled with SiN or the like. The active layer 13 is
For example, it has a multiple quantum well structure using an InGaAs / InGaAsP-based semiconductor material, and emits light when carriers are injected.

Lower clad layer 12 and upper clad layer 1
4 forms a double heterojunction with the active layer 13 sandwiched between them, thereby confining the carriers and concentrating the carriers contributing to light emission in the active layer 13.

A lower electrode 16 and an upper electrode 17 made of gold or the like are formed on the bottom surface of the substrate 11 and the upper surface of the upper cladding layer 14. The active layer 13 emits light by applying a voltage between the electrodes 16 and 17, and the light leaked from the active layer 13 enters the two-dimensional photonic crystal 20. Light whose wavelength matches the lattice spacing of the two-dimensional photonic crystal 20 is
It is resonated and amplified by the two-dimensional photonic crystal 20. Thereby, the upper surface of the upper clad layer 14 (the electrode 17
The coherent light is surface-emitted from the light emitting region 18) located around the area.

The resonance action of the two-dimensional photonic crystal 20 having a square lattice as shown in FIG. 9 will be described. The lattice shape is not limited to the square lattice, and may be a triangular lattice or the like.

The two-dimensional photonic crystal 20 is composed of a square lattice formed in the first medium 12 in the same period in two directions orthogonal to the second medium 21 such as holes. Square lattice is Γ
It has a representative direction of −X direction and Γ−M direction. Γ
When the distance between the second media 21 adjacent in the −X direction is a,
A basic lattice E, which is a square with one side of a, using the second medium 21 as a lattice point, is formed.

When the light L whose wavelength λ matches the lattice spacing a of the basic grating E travels in the Γ-X direction, the light L is second-order diffracted at the lattice points. Of these, 0 ° with respect to the traveling direction of the light L,
Only the light diffracted in the directions of ± 90 ° and 180 ° satisfies the Bragg condition. Further, since there are lattice points also in the traveling direction of the light diffracted in the directions of 0 °, ± 90 °, and 180 °, the diffracted light is again 0 °, ± 90 °, 1 with respect to the traveling direction.
Diffract in the 80 ° direction.

When the light L repeats the second-order diffraction once or a plurality of times, the diffracted light returns to the original lattice point and a resonance action occurs. In addition, the light that is first-order diffracted in the direction perpendicular to the paper also satisfies the Bragg condition. Therefore, the light amplified by resonance is emitted through the upper clad layer 14 and has a surface emitting function. Further, since this phenomenon occurs at all the lattice points, coherent laser oscillation is possible in the entire plane.

[0013]

By the way, in the two-dimensional photonic crystal surface emitting laser, the periodic structure 2 is used.
1 is formed in a cylindrical shape, an elliptic cylindrical shape, or a quadrangular prism shape, and as shown in FIG. 10, the cross-sectional shape in the direction perpendicular to the crystal plane is a quadrangular shape.

As described above, when the vertical cross-sectional shape of the periodic structure 21 is a quadrangle, the light due to the first-order diffraction has the same intensity (50% and 5) as the light L1 emitted upward and the light L2 emitted downward.
0%). The light used as the laser light is one of the emitted lights L1 and L2, and there is a problem that the light utilization efficiency is low.

Therefore, an object of the present invention is to provide a two-dimensional photonic crystal surface emitting laser capable of increasing the utilization efficiency of surface-emitted light to 50% or more and a manufacturing method thereof.

[0016]

In order to achieve the above objects, the two-dimensional photonic crystal surface emitting laser according to the present invention has an active layer which emits light by carrier injection sandwiched between clad layers, and the clad layers or the clad layers. In a two-dimensional photonic crystal surface emitting laser including a photonic crystal periodic structure in which a refractive index period is two-dimensionally arranged in an active layer, light emission whose cross-sectional shape with respect to a crystal plane of the photonic crystal periodic structure is the main It is characterized by gradually decreasing along the direction.

In this two-dimensional photonic crystal surface emitting laser, the cross-sectional shape of the photonic crystal periodic structure may be a multi-step shape approximate to a triangular shape. Further, the photonic crystal periodic structure may have a double cross structure in which substantially triangular cross-sections are stacked.

In the two-dimensional photonic crystal surface emitting laser according to the present invention, the light leaked from the active layer is second-order diffracted (resonated) and amplified by the periodic structure of the photonic crystal, and is amplified by the first-order diffraction. Surface emission from. Since the width of the vertical sectional shape of the periodic structure gradually decreases along the main light emitting direction, the first-order diffraction in the bottom direction is suppressed, and the first-order diffraction is performed more in the substantially triangular vertex direction. Therefore, by using the light that is first-order diffracted in the vertex direction as the surface emission, it is possible to obtain a light use efficiency of 50% or more.

On the other hand, in the two-dimensional photonic crystal surface emitting laser, when the photonic crystal periodic structure is processed into a substantially triangular shape having a step in a direction perpendicular to the crystal plane by a photolithography method, mass transport is performed. It can be manufactured by eliminating the step portion by the effect and forming an inclined surface.

A two-dimensional photonic crystal surface emitting laser having a photonic crystal periodic structure having a cross-section of substantially triangular cross-sections superposed on one another is a two-dimensional photonic crystal surface emitting laser, and the triangular bodies constituting the photonic crystal periodic structure are subjected to photolithography. It can be manufactured by eliminating the step portion by the mass transport effect and forming an inclined surface when processed in multiple steps by the method.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a two-dimensional photonic crystal surface emitting laser and a method of manufacturing the same according to the present invention will be described below with reference to the accompanying drawings.

(First Embodiment, See FIG. 1) A first embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention has a photonic crystal periodic structure as shown in FIG. 21a has a triangular cross-section in the direction perpendicular to the crystal plane, and the periodic structure 21a is formed in the lower cladding layer 12. The other structure has the same basic structure as the two-dimensional photonic crystal surface emitting laser 10 shown in FIG. 8, and is manufactured using the same kind of material.
Surface emission is performed by the same resonance action.

The periodic structure 21 shown in FIG. 8 has a cylindrical shape,
It consists of an elliptical shape and a quadrangular prism shape. The periodic structure 21a in the first embodiment has a conical shape, an elliptic cone shape, or a quadrangular pyramid shape corresponding to those shapes. The second-order diffraction is generated similarly to the conventional periodic structure 21, but the generation of the first-order diffracted light L2 in the bottom direction of the periodic structure 21 (triangular shape) is suppressed,
More first-order diffracted light L1 is emitted in the triangular vertex direction. This improves the light utilization efficiency.

(Second Embodiment, See FIG. 2) A second embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention is a photonic crystal periodic structure as shown in FIG. The cross-sectional shape of 21b in the direction perpendicular to the crystal plane is a three-step shape approximated to a triangular shape, and the periodic structure 21b is formed in the lower cladding layer 12. The other structure has the same basic structure as that of the two-dimensional photonic crystal surface emitting laser 10 shown in FIG. 8, is manufactured using the same kind of material, and emits surface light by the same resonance action.

The periodic structure 21b in the second embodiment also has a conical shape, an elliptic cone shape, and a quadrangular pyramid shape with a three-step pyramid shape. Compared with the first embodiment, the first-order diffracted light L
2 is slightly increased, and the first-order diffracted light L used for surface emission is used.
Although the utilization efficiency of No. 1 is slightly reduced, the utilization efficiency of light is improved as compared with the conventional periodic structure 21 having a rectangular vertical cross section.

(Third Embodiment, See FIG. 3) A two-dimensional photonic crystal surface emitting laser according to a third embodiment of the present invention has a photonic crystal periodic structure as shown in FIG. The cross-sectional shape of the 21c in the direction perpendicular to the crystal plane is a two-step shape approximated to a triangular shape, and the periodic structure 21c is formed in the lower cladding layer 12. The other structure has the same basic structure as that of the two-dimensional photonic crystal surface emitting laser 10 shown in FIG. 8, is manufactured using the same kind of material, and emits surface light by the same resonance action.

The periodic structure 21c in the third embodiment also has a two-step pyramid shape of a conical shape, an elliptic cone shape, and a quadrangular pyramid shape, and is also positioned as a modification of the second embodiment. Compared to the second embodiment, the first-order diffracted light L2 is slightly increased and the utilization efficiency of the first-order diffracted light L1 used for surface emission is slightly reduced, but compared with the conventional periodic structure 21 having a rectangular vertical cross section. And the utilization efficiency is improving.

(Manufacturing Method, See FIGS. 4 and 5) Here, in the manufacturing method of the two-dimensional photonic crystal surface emitting laser shown in the second embodiment, the photonic crystal periodic structure 21b, which is the main part thereof, is used. The processing steps (photolithography method, electron beam lithography method, etc.) will be described. The steps of forming the lower clad layer, the active layer, and the upper clad layer are the same as the conventional process.

First, a resist 31 is applied on the lower clad layer 12b (see FIG. 4A), the resist 31 is patterned (see FIG. 4B), and then the lower clad layer 12b is etched by a predetermined amount. (See FIG. 4C).

Next, the resist 31 is removed, and a new resist 31 is applied (see FIG. 4D).
Is patterned and is further etched by a predetermined amount (see FIG. 4E).

Next, the resist 31 is removed, and a new resist 31 is applied (see FIG. 4 (F)).
And patterned by a predetermined amount (see FIG. 4G) to remove the resist 31 (FIG. 4).
(See (H)). As a result, the three-step pyramid-shaped photonic crystal periodic structure 21b is formed in the lower cladding layer 12b.

Thereafter, the lower clad layer 12b is turned upside down (see FIG. 5A), and the lower clad layer 12b is fused on the lower clad layer 12a laminated on the substrate 11 (FIG. 5B). reference). The completed state is shown in Fig. 5 (C).
As shown in. The active layer 13 and the upper clad layer 14 are previously laminated on the lower clad layer 12b. After that, as shown in FIG. 8, the lower electrode 16 is provided on the lower surface of the substrate 11, and the upper electrode 17 is provided on the upper surface of the upper cladding layer 14.

Further, when the lower clad layer 12b is processed by the photolithography method, if the step portion is eliminated by the well-known mass transport effect to form the inclined surface, the vertical section shown in the first embodiment has a triangular shape. The periodic structure 21a can be formed.

InP, InGaAs, InGaP, In
III-V group semiconductors such as As, GaAs, GaP, AlGaAs, etc. strongly undergo mass transport by heat treatment at 450 ° C. or higher for 30 minutes or longer in an atmosphere of hydrogen gas, nitrogen gas or rare gas. This condition is almost the same in the inclined surface forming step in the fourth embodiment described below.

(Fourth Embodiment, See FIGS. 6 and 7) In the fourth embodiment of the two-dimensional photonic crystal surface emitting laser according to the present invention, as shown in FIG.
A two-dimensional photonic crystal 20 having a double cross structure is constituted by land portions 22a and 23a and groove portions 22b and 23b, which have triangular cross sections and are formed on the opposing surfaces of 2b in directions orthogonal to each other. Other configurations are the same as those of the two-dimensional photonic crystal surface emitting laser 10 shown in FIG.
It is manufactured using the same material. Therefore, in FIG. 6, the same members as those in FIG. 8 are designated by the same reference numerals.

Land portions 22a, 23a and groove portions 22b, 23
By joining b, the two-dimensional photonic crystal 20 having a double beam structure is formed. FIG. 7 is a plan view showing the two-dimensional photonic crystal 20. The land portions 22a, 23a are shown in FIG.
And the two-dimensional periodic structures 21d, 21 having different overlapping states of the groove portions 22b, 23b, that is, different refractive indexes.
e, 21f and 21g (shown by hatching) are arranged in a checkered pattern.

Light is second-order diffracted and resonated by such a two-dimensional periodic structure, and surface emission is performed by the first-order diffraction.
In this first-order diffraction, as shown in FIG. 6, generation of the first-order diffracted light L2 is suppressed, more first-order diffracted light L1 is emitted, and the light utilization efficiency is improved.

When a triangular body having a triangular cross-section that constitutes a double girder is processed in multiple steps by the photolithography method shown in FIG. 4, the step portion may be eliminated by the mass transport effect to form an inclined surface.

(Other Embodiments) The two-dimensional photonic crystal surface emitting laser and the method for manufacturing the same according to the present invention are not limited to the above embodiments, but may be variously modified within the scope of the invention. it can.

In particular, the materials for the semiconductor layer, the photonic crystal, the electrodes, the structure for aligning the polarization of light, the lattice shape, etc. are arbitrary. Further, in each of the above-described embodiments, the example in which the photonic crystal periodic structure is provided in the lower clad layer is shown, but it may be provided in the upper clad layer near the active layer or in the active layer.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of a two-dimensional photonic crystal surface emitting laser according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of a two-dimensional photonic crystal surface emitting laser according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing a main part of a two-dimensional photonic crystal surface emitting laser according to a third embodiment of the present invention.

FIG. 4 is an explanatory view showing a process of processing the photonic crystal periodic structure in the second embodiment.

FIG. 5 is an explanatory view showing a processing step of the photonic crystal periodic structure in the second embodiment, a continuation of FIG. 4;

FIG. 6 is a perspective view showing a two-dimensional photonic crystal surface emitting laser according to a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a two-dimensional photonic crystal according to the fourth embodiment.

FIG. 8 is a perspective view showing a two-dimensional photonic crystal surface emitting laser prior to the present invention.

FIG. 9 is an explanatory diagram showing a resonance action of a two-dimensional photonic crystal surface emitting laser.

10 is a sectional view showing a photonic crystal periodic structure in the surface emitting laser shown in FIG.

[Explanation of symbols]

10. Two-dimensional photonic crystal surface emitting laser 11 ... Substrate 12 ... Lower clad layer 13 ... Active layer 14 ... Upper clad layer 20 ... Two-dimensional photonic crystal 21a-21g ... Photonic crystal periodic structure

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yokoyama Hikaru             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. (72) Inventor Kojiro Sekine             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. F-term (reference) 5F073 AA63 AA74 AA75 AA89 AB17                       CA12 DA16

Claims (5)

[Claims] 1. An active layer that emits light by carrier injection is sandwiched between clad layers, and the clad layer or the active layer is provided with 2
A two-dimensional photonic crystal surface emitting laser including a photonic crystal periodic structure having a three-dimensionally arranged refractive index period, wherein the width of the cross-sectional shape of the photonic crystal periodic structure with respect to the crystal plane is along the main light emitting direction. A two-dimensional photonic crystal surface emitting laser characterized by being gradually reduced. 2. The two-dimensional photonic crystal surface emitting laser according to claim 1, wherein the cross-sectional shape of the photonic crystal periodic structure is a multi-step shape approximated to a triangular shape. 3. The two-dimensional photonic crystal surface emitting laser according to claim 1, wherein the photonic crystal periodic structure has a double-girder structure in which substantially triangular cross-sections are stacked. 4. The method of manufacturing a two-dimensional photonic crystal surface emitting laser according to claim 1, wherein the photonic crystal periodic structure is photolithographically formed into a substantially triangular cross-section having a step in a direction perpendicular to the crystal plane. A method for manufacturing a two-dimensional photonic crystal surface emitting laser, characterized in that when processed by the method, the step portion is eliminated by a mass transport effect to form an inclined surface. 5. The method for manufacturing a two-dimensional photonic crystal surface emitting laser according to claim 3, wherein a mass transformer is used when a triangular body forming the photonic crystal periodic structure is processed in multiple stages by photolithography. A method for manufacturing a two-dimensional photonic crystal surface emitting laser, characterized in that a step portion is eliminated by a port effect to form an inclined surface.