JP2000077776A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser that is possessed of a resonant structure and a light projection structure even if a substrate has a structure such that an excellent cleavage plane is hardly obtained. SOLUTION: An active layer 7 is formed of a multi-quantum well(MQW) that is formed by alternately laminating two kinds of InGaN layers that serve as a barrier layer and a well layer, and a variety of semiconductor layers which contain the active layer 7 are formed on a transparent sapphire substrate 1 for the formation of a semiconductor laser. A diffraction grating pattern that generates reflected waves is provided to the one surface of a clad layer 8 adjacent to the active layer 7 in an active region, and a diffraction grating pattern 8a that projects laser rays in a direction vertical to the sapphire substrate 1 is provided to the other surface of the clad layer 8 in the active region. A hologram 16 used for shaping the wavefront of laser rays is formed on the surface of the sapphire substrate 1 from which laser rays are projected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser used for optical information equipment and the like.

[0002]

2. Description of the Related Art A semiconductor laser realizes a resonator structure by using a pair of end faces of a substrate as cleavage planes and using the cleavage planes as mirrors. In a semiconductor laser such as a GaAs-based or InP-based laser, the mirror having such a cleavage plane can be easily obtained since the cleavage at the end face of the substrate is good.

[0003]

However, the GaN semiconductor laser of the sapphire substrate has a problem that the quality of the mirror is poor because the cleavage of the substrate end face is not so good, and the production yield is low. Therefore R
Although processing is performed to form a mirror by IE (reactive ion etching), as shown in FIG. 9, this mirror forming method has poor vertical accuracy of the end face and damage remains. And characteristic deterioration such as shortened life. In addition, since it is difficult to perform etching to a sufficient depth by RIE, a new problem such as deterioration of beam quality due to reflection and refraction on the substrate arises. Furthermore,
In some cases, such as when the end face of the substrate is wavy or chipped obliquely, the processing by RIE cannot be performed.

In view of the above circumstances, an object of the present invention is to provide a semiconductor laser capable of realizing a light emitting structure with a resonance structure even with a substrate structure in which it is difficult to obtain a good cleavage plane. I do.

[0005]

In order to solve the above-mentioned problems, a semiconductor laser according to the present invention comprises a semiconductor substrate comprising a transparent substrate on which various semiconductor layers including an active layer are formed. A diffraction grating pattern for generating a reflected wave is formed on one side of the active region adjacent to the active region, and a reflected wave is generated on the other side of the active region and perpendicular to the transparent substrate. A diffraction grating pattern for emitting laser light in various directions is formed, and an optical element for shaping the wavefront of the laser light is formed on the surface of the transparent substrate from which laser light is emitted. It is characterized by having. The transparent substrate in the present invention is a substrate through which the laser light can pass.

With the above configuration, even when the substrate end face does not have good cleavage properties, a resonance structure can be obtained by a pair of diffraction grating patterns sandwiching the active region, and the laser light emitted and stimulated can be emitted from the substrate. The light can be emitted not in the end face but in the direction perpendicular to the substrate. The laser light emitted from the transparent substrate side has a characteristic that it is not easy to make a minute spot, but the above optical element is formed on the surface of the substrate where the laser light is emitted. Therefore, the wavefront of the laser light is shaped, and for example, it can be used for an optical pickup or the like.

Further, according to the present invention, there is provided a semiconductor laser in which various semiconductor layers including an active layer are formed on a transparent substrate, wherein a resonance diffraction grating pattern formed adjacent to the active layer is formed. At least a portion has a pattern portion for emitting a laser beam in a direction perpendicular to the transparent substrate, and the surface of the transparent substrate from which the laser beam is to be emitted includes the laser An optical element for shaping the wavefront of light is formed. The transparent substrate in the present invention is a substrate through which the laser light can pass.

With the above configuration, even when the substrate end face does not have a good cleavage property, a resonance structure can be obtained by the diffraction grating pattern for resonance, and the laser light to be stimulated emitted is not emitted from the substrate end face. Light can be emitted in a direction perpendicular to the substrate. The laser light emitted from the transparent substrate side has a characteristic that it is not easy to make a minute spot, but the above optical element is formed on the surface of the substrate where the laser light is emitted. Therefore, the wavefront of the laser light is shaped, and for example, it can be used for an optical pickup or the like.

[0009]

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic front view showing the entire configuration of the semiconductor laser according to the first embodiment. This semiconductor laser has an i-type AlG on a transparent sapphire substrate 1.
aN buffer layer 2, i-type GaN layer 3, n-type GaN layer 4, n-type InGaN crack preventing layer 5, n-type AlG
Multiple quantum well (MQW) in which an aN cladding layer 6 and two types of InGaN layers serving as a barrier layer and a well layer are alternately stacked.
An active layer 7 comprising: a p-type AlGaN cladding layer 8;
A p-type GaN contact layer 9 is formed in this order. The p-type GaN contact layer 9
An insulating layer 10 is formed on the surface of the n-type AlGaN cladding layer 6 and the mesa-etched surface of the n-type AlGaN cladding layer 6, and the p-type GaN contact layer 9 is provided with a p-electrode through an opening formed in the insulating layer 10. 11 are formed, and an n-type electrode 12 is formed on the n-type AlGaN cladding layer 6. Further, a pad electrode 13 is formed on the p-electrode 11, and a pad electrode 14 is formed on the n-electrode 12. In FIG. 1, a region surrounded by a thick solid line circle is a light-emitting portion, but the light-emitting portion does not necessarily emit a laser beam in a direction perpendicular to the paper surface.

FIG. 2 is an enlarged sectional view showing a section taken along a dotted line passing through the light emitting section in FIG. 1, and a first end face side of the substrate is drawn on the left side of the figure. The right side of the figure is drawn as a fractured surface, and the second end surface side of the substrate is not shown. A first end face side of the substrate, wherein the p-type Al
The GaN cladding layer 8 includes a first diffraction grating pattern 8a
Are formed. The first diffraction grating pattern 8a is a second-order diffraction grating. The second-order diffraction light is used as feedback (reflection) light (generation of a reflected wave), and the first-order diffraction light is used as extraction light (emission light). It has become. On the other hand, on the second end face side of the substrate, that is, as shown in FIG. 3, the second diffraction grating pattern 8a is provided with an active region (gain region) 8c of a predetermined length from the first diffraction grating pattern 8a. A diffraction grating pattern 8b is formed. The second diffraction grating pattern 8b is composed of a first-order diffraction grating and functions for generating a reflected wave. That is, the unevenness period of the second diffraction grating pattern 8b is formed to be １ ／ of the wavelength of the laser light to be oscillated (about 80 nm in this embodiment), and The uneven period is set to be twice (about 160 nm) the uneven period of the second diffraction grating pattern 8b.

Since the pitch of the concave and convex portions of the diffraction grating patterns 8a and 8b is small, it is not easy to draw a pattern by a commonly used ultraviolet interference exposure method. Therefore, in this embodiment, the electron beam direct writing method is employed. Of course, a drawing method using interference exposure using ultraviolet rays or X-rays having a shorter wavelength can also be adopted.

By using the first diffraction grating pattern 8a, which is a second-order diffraction grating, the laser light is perpendicular to the sapphire substrate 1 as the first-order diffraction light, that is, in FIG.
Since the light is emitted in two directions, an upward direction and a downward direction (sapphire substrate 1 side), the efficiency is not good. Therefore, FIG.
In this embodiment, a reflection film 15 made of a dielectric multilayer film (SiO ₂ / TiO ₂ ) is provided above the first diffraction grating pattern 8a (on the side opposite to the sapphire substrate 1). Thus, almost all of the light guided perpendicularly to the substrate is emitted from the sapphire substrate 1 side. When the laser light is guided in the vertical direction of the substrate by the first diffraction grating pattern 8a, the laser light is emitted from the linear light source, so that it is difficult to condense the laser light on a minute spot. Therefore, as shown in FIG. 2, a hologram 1 for wavefront conversion is provided on the laser light emitting surface side of the sapphire substrate 1.
6 is formed, and the laser light is converted into a wavefront suitable for light collection such as a plane wave or a spherical wave and collected.

FIG. 4 schematically shows the positional relationship between the hologram 16 formed on the sapphire substrate 1 and the first diffraction grating pattern 8a and the second diffraction grating pattern 8b, and the manner in which laser light is focused. It is a perspective view. FIG. 5 is a schematic explanatory view showing a method of forming the hologram 16. In the method shown in FIG. 5, a photoresist 17 that is exposed to laser light is applied to the surface of the sapphire substrate 1 where a hologram 16 is to be formed.
The photoresist 17 is irradiated with laser light emitted from the sapphire substrate 1. Then, the laser light (0th-order diffracted light) leaking from the end face of the substrate is taken out by the single mode optical fiber 18, the tip of the optical fiber 18 is positioned as shown in the figure, and the laser light is applied from the tip to the photoresist 17 Irradiate toward Accordingly, in the photoresist 17, interference fringes are formed in the photoresist 17 by the laser light of the line light source emitted in the vertical direction of the substrate by the first diffraction grating pattern 8a and the laser light of the surface light source leaking from the end face of the substrate. Be recorded. When this is developed, the photosensitive (or non-photosensitive) portion is dissolved, and a grating groove is formed according to the intensity distribution of the interference fringes.

With the above configuration, a resonance structure can be obtained by the pair of diffraction grating patterns 8a and 8b sandwiching the active region, and the stimulated emission of laser light is not perpendicular to the sapphire substrate 1 but to the substrate end face. Can be emitted in any direction. Therefore, even when the substrate end face does not have a good cleavage property, it is possible to eliminate the trouble of processing for forming the mirror surface, or when there is an oblique crack or chip that cannot be dealt with by the processing. However, since the device can be operated normally, the yield can be improved. Furthermore, it is possible to use a cutting method such as dicing in which the end face is damaged but the processing is easy, and the production cost can be reduced. The laser light emitted from the transparent single crystal substrate side has a characteristic that it is not easy to form a minute spot, but the surface of the single crystal substrate from which the laser light is emitted has the hologram 16 above. Is formed, the wavefront of the laser light is shaped, and for example, it can be used for an optical pickup or the like.

In the above example, the laser light leaking from the end face of the semiconductor laser is used for exposing the photoresist 17, but this is not performed, but based on interference fringes created by computer graphics, for example. Exposure may be performed. Although the entire first diffraction grating pattern 8a is a secondary diffraction grating, only a part may be a secondary diffraction grating. In addition, the hologram 16 is formed to convert the laser light into a wavefront suitable for light collection such as a plane wave or a spherical wave, but a lenticular lens 19 may be formed as shown in FIG. is there. In addition, although a GaN-based semiconductor laser has been exemplified, the present invention can also be applied to semiconductor lasers having other structures.

(Embodiment 2) Next, this embodiment will be described with reference to FIGS. FIG. 7 is a perspective view schematically showing a portion where the diffraction grating pattern of the semiconductor laser of this embodiment is formed, and FIG. 8 is a graph showing the distribution of light intensity inside the semiconductor laser having such a structure. It is the graph which showed the light intensity and the position in the period direction of a diffraction grating pattern was taken on the horizontal axis.

Here, the semiconductor laser according to the first embodiment is a so-called DBR (Distributed Bragg Reflector).
on) The semiconductor laser according to the second embodiment has a DFB (Distributed Feed) structure.
back) It has a laser structure. The semiconductor laser according to the second embodiment also has various semiconductor layers including an active layer on a transparent single-crystal substrate, for example, as shown in FIG. Then, a resonance diffraction grating pattern is formed adjacent to the active layer. In order to emit stimulated emission laser light in a direction perpendicular to the substrate, as shown in FIG. A substantially central portion of the pattern 21 has a pattern portion 21a which is a secondary diffraction grating. The pattern portion 21a uses the second-order diffracted light as feedback (reflected) light (generation of a reflected wave) and the first-order diffracted light as extracted light (emitted light).

Further, although not shown, the surface of the transparent single crystal substrate from which laser light is to be emitted includes:
An uneven pattern (such as a hologram or a lenticular lens as described in Embodiment 1) for shaping the wavefront of the laser light is formed. Of course, the first embodiment
Similarly to the above, a reflection film made of a dielectric multilayer film (SiO ₂ / TiO ₂ ) is formed on the upper side of the pattern portion 21a (the side opposite to the single crystal substrate), and substantially all of the light guided perpendicularly to the substrate is The light may be emitted from the side.

In the semiconductor laser having such a structure, as in the first embodiment, even if the substrate structure has a difficulty in obtaining a good cleavage plane, a resonance structure can be obtained by the resonance diffraction grating pattern 21 and stimulated emission can be obtained. The laser light to be emitted can be emitted not in the substrate end face but in the direction perpendicular to the single crystal substrate. The laser light emitted from the transparent single crystal substrate side has a characteristic that it is not easy to make a minute spot, but the surface of the single crystal substrate from which the laser light is emitted has the above-mentioned uneven pattern. Is formed, the wavefront of the laser light is shaped.

[0021]

As described above, according to the present invention, even in the case of a substrate structure in which it is difficult to obtain a good cleavage plane, a light emitting structure with a resonance structure can be realized, and the product yield and the like can be improved. As a result, the production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a cross section taken along a dotted line in FIG.

FIG. 3 is a perspective view schematically showing a portion where a diffraction grating pattern of the semiconductor laser of FIG. 1 is formed.

FIG. 4 is a perspective view schematically showing a positional relationship between a hologram formed on a sapphire substrate and a diffraction grating pattern and a state of condensing laser light in the semiconductor laser of FIG. 1;

FIG. 5 is an explanatory view showing a method of forming the hologram of FIG. 2;

6 is a cross-sectional view showing an example in which a lenticular lens is used instead of the hologram in the semiconductor laser of FIG.

FIG. 7 is a perspective view schematically showing a portion where a diffraction grating pattern of a semiconductor laser according to a second embodiment of the present invention is formed.

8 is a graph showing the distribution of light intensity inside a semiconductor laser having the structure of FIG. 7, with the vertical axis representing the internal light intensity and the horizontal axis representing the position in the periodic direction of the diffraction grating pattern.

FIG. 9 is a diagram showing a defect of a conventional semiconductor laser.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sapphire substrate 2 i-type AlGaN buffer layer 3 i-type GaN layer 4 n-type GaN layer 5 n-type InGaN crack prevention layer 6 n-type AlGaN cladding layer 7 active layer 8 p-type AlGaN cladding layer 9 p-type GaN contact layer 10 insulating layer Reference Signs List 11 p electrode 12 n electrode 16 hologram 17 photoresist 18 optical fiber 19 lenticular lens 21 diffraction grating pattern for resonance 21a pattern portion

Claims (2)

[Claims] 1. A semiconductor laser comprising various semiconductor layers including an active layer formed on a transparent substrate, wherein a reflected wave is generated at a portion adjacent to the active layer and on one side of the active region. A diffraction grating pattern for forming a reflected wave on the other side of the active region and emitting a laser beam in a direction perpendicular to the transparent substrate is formed on the other side of the active region. A semiconductor laser characterized in that an optical element for shaping the wavefront of the laser light is formed on a surface of the substrate from which the laser light is emitted. 2. A semiconductor laser in which various semiconductor layers including an active layer are formed on a transparent substrate, wherein at least a part of a resonance diffraction grating pattern formed adjacent to the active layer has the structure described above. It has a pattern portion for emitting laser light in a direction perpendicular to the transparent substrate, and the surface of the transparent substrate where laser light is to be emitted is used to shape the wavefront of the laser light. A semiconductor laser, wherein the optical element is formed.