JP3635880B2 - Surface emitting semiconductor laser and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface emitting semiconductor laser that can stabilize the polarization plane of laser light.
[0002]
[Prior art and problems to be solved by the invention]
Conventionally, as a method for stabilizing the polarization plane of laser light of a surface emitting semiconductor laser, the present applicants disclosed a structure of a surface emitting semiconductor laser that stabilizes the polarization plane in Japanese Patent Laid-Open No. Hei 6-283818. Yes. This publication discloses that the polarization plane direction can be stabilized in one direction by making the cross-sectional shape of the vertical cavity portion of the surface emitting semiconductor laser rectangular.
[0003]
However, in the structure of a surface emitting semiconductor laser that has been studied extensively in recent years, the upper and lower portions of the surface mirror type semiconductor laser have a reflection mirror composed of a semiconductor multilayer film, and the length of the resonator in which the laser beam reciprocates multiple times is shortened to about one wavelength. Even when the structure disclosed in the above publication is used, it has been confirmed that as the laser output is increased, the polarization plane changes and unstable laser oscillation occurs.
[0004]
Japanese Laid-Open Patent Publication No. 9-83066 raises the problem that the plane of polarization of a surface emitting semiconductor laser having a resonator length of about one wavelength tends to become unstable during laser emission. Although a structure in which the polarization plane can be stabilized and externally controlled by changing the structure of the electrode part is disclosed, the structure becomes complicated, and in a surface-emitting type semiconductor laser that can produce a plurality of light emitting parts in the same substrate A new problem has arisen that it is difficult to produce stably.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a surface emitting semiconductor laser in which a reflecting mirror is formed of a semiconductor multilayer film on both the upper and lower sides, and the surface emitting semiconductor performs stable laser oscillation without changing the polarization plane even when the laser output is increased. The object is to provide a laser structure and a simple manufacturing method thereof.
[0006]
The surface-emitting type semiconductor laser of the present invention includes a substrate, a first reflection mirror having a semiconductor multilayer structure disposed on the substrate, an active layer disposed above the first reflection mirror, and the active layer A second reflecting mirror disposed above the layer and having a columnar portion having a rectangular cross-sectional shape parallel to the surface of the substrate, and an insulating layer disposed so as to cover a side surface of the columnar portion And an upper electrode arranged to cover a peripheral portion of the upper surface of the columnar part and a side surface of the columnar part via the insulating layer, and an upper electrode arranged to cover the upper surface of the columnar part, and A dielectric layer that extends from the upper surface of the columnar portion and is disposed so as to cover a side surface of the columnar portion via the insulating layer and the upper electrode .
[0007]
The upper electrode is covered with the dielectric layer. The columnar portion has a pair of first side surfaces facing each other and a pair of second side surfaces facing each other different from the first side surfaces, and the dielectric layer covering the first side surfaces; The dielectric layer covering the second side surface is different in film thickness .
[0008]
The dielectric layer is disposed so as to cover the first dielectric layer and the first dielectric layer, and a second dielectric layer made of a material different from the first dielectric layer; It is characterized by comprising.
[0009]
According to the method of manufacturing the surface emitting semiconductor laser of the present invention, the step of forming the first electrode on a part of the lower side of the semiconductor substrate and the first reflection by laminating semiconductor layers having different refractive indexes on the semiconductor substrate. Forming a mirror, forming a multilayer semiconductor layer including at least an active layer and a cladding layer on the first reflective mirror, and laminating semiconductor layers having different refractive indexes on the multilayer semiconductor layer. A step of forming a second reflection mirror, a step of etching at least half the thickness of the second reflection mirror from the surface side into a columnar shape, and an insulating layer and the columnar shape around the columnar portion The method includes a step of forming an upper electrode having an opening on the end face of the portion, and a step of depositing a dielectric material obliquely on the columnar portion so as to cover the opening and the upper electrode.
[0011]
[Action]
The surface emitting semiconductor laser of the present invention can have an optically anisotropic structure in the resonator by forming a part of the resonator into a columnar portion having a rectangular cross-sectional shape. However, in the surface emitting semiconductor laser of the present invention, since the distance between the pair of reflecting mirrors is as short as about one wavelength, the influence of the optical anisotropic structure in the resonator is small as it is, and the polarization plane of the laser light in the resonator The polarization plane becomes unstable as the laser light output increases.
[0012]
Therefore, in order to stabilize the polarization plane with a surface emitting semiconductor laser having a short resonator length, it is necessary to increase the influence of optical anisotropy in the resonator. It is well known that the optical properties of compound semiconductors change with temperature and pressure. Therefore, in order to give anisotropy to the optical characteristics in the resonator, it is necessary to have temperature and pressure distribution in the resonator, and a dielectric layer was formed around the columnar part of the resonator structure. . By using this structure, a dielectric layer having a thermal expansion coefficient different from that of the compound semiconductor is covered around the rectangular columnar portion, and the optical structure of the resonator is different due to the effect of distortion by the rectangular structure of the resonator and the dielectric layer. The isotropic effect is increased. Therefore, even in a surface emitting semiconductor laser as in the present invention where the distance between the pair of reflecting mirrors is as short as about one wavelength, the polarization plane direction of the laser beam can be aligned with the rectangular short side direction of the columnar portion. Even if the output is increased, the polarization plane can be stabilized.
[0013]
Further, it is defined that the dielectric layer of the present invention is composed of one or more layers of silicon oxide, tantalum oxide, titanium oxide, and zirconium oxide. Since these dielectric layers have a small absorption coefficient and a large thermal expansion coefficient in the wavelength band from about 0.6 μm to about 1.8 μm, which is the oscillation wavelength of the surface emitting semiconductor laser of the present invention, the effect on the columnar portion Has great features.
[0014]
Further, by combining a plurality of dielectric layers, it is also possible to control the thermal expansion coefficient and transmittance of the entire dielectric layer.
[0015]
Further, it is defined that B <A <2 × B, where A is the length in the major axis direction of the cross-sectional shape of the columnar portion and B is the length in the minor axis direction. This is because, in the structure of the present invention, the cross-sectional shape of the columnar portion is rectangular, so that the resonator has optical anisotropy. However, if the size of the rectangle is out of the above range, the long axis This is limited because the direction becomes too long and the laser oscillation transverse mode tends to become multimode.
[0016]
In the above structure, the vacuum deposition method is used in the step of forming the dielectric layer. Thus, it is only necessary to add a step of vacuum-depositing a dielectric on the substrate surface after the completion of laser fabrication without changing the conventional surface emitting semiconductor laser fabrication step. Further, since the surface emitting semiconductor laser is measured in the absence of a dielectric, and the deposition state of the dielectric can be changed using the result, the yield of polarization plane stability can be improved. For example, by depositing a dielectric on the columnar portion from an oblique direction, the thickness of the dielectric attached to the side surface of the columnar portion can be changed at the side surface position, thereby further increasing the optical anisotropy in the resonator. You can also.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
(Example 1)
FIG. 1 is a sectional view schematically showing a section of a surface emitting semiconductor laser capable of stabilizing the polarization plane in one embodiment of the present invention, and FIG. 2 is a schematic perspective view thereof. A cross section taken along the line AA 'shown in FIG. 2 is shown in FIG.
[0019]
The structure of the surface-emitting type semiconductor laser 100 shown in FIG. 1 will be described. The n-type GaAs buffer layer 103, the n-type AlAs layer, and the n-type Al _0.3 Ga _0.7 As layer are formed on the n-type GaAs substrate 102 at 780 nm. 40 pairs of distributed reflective semiconductor multilayer mirrors 104 having a reflectance of 99% or more with respect to the light in the vicinity, n-type Al _0.5 Ga _0.5 As cladding layer 105, n ⁻ -type Al _0.1 Ga _{0. A} multi-quantum well active layer 106 comprising a ₉ As well layer and an n ^- type Al _0.4 Ga _0.6 As barrier layer, and the well layer is composed of 5 layers, a p-type Al _0.5 Ga _0.5 As clad layer 107, p-type AlAs layers and p-type _Al 0.3 _{Ga 0.7} distributed reflection type 30 pairs with a reflectivity of more than 98.5% for light of 780nm around consists as layer semiconductor multilayer mirror 108 Fine p-type _Al 0.2 _{Ga 0.8} As contact layer 109 are sequentially stacked. For the production of this laminate, epitaxial growth by the MOVPE method was used. At this time, the total thickness of the n-type clad layer 105, the multiple quantum well active layer 106, and the p-type clad layer 107 was set to be about one wavelength of the laser wavelength in the resonator structure.
[0020]
Then, up to the upper layer of the p-type cladding layer 107, the columnar portion 114 is formed by etching into a rectangular shape when viewed from the upper surface of the semiconductor laminate. In this embodiment, the length of the long side A of the rectangle is 20 μm, and the length B of the short side is 15 μm. When resonators of various sizes were fabricated, the transverse mode of the laser beam was single mode and the output was 1 mW or more until the length of B was 5 to 20 μm, but when B was smaller than 5 μm Since the size is small, the output is small, and when B is larger than 20 μm, the transverse mode of the laser beam has become a multimode.
[0021]
By making the cross section of the columnar portion 114 parallel to the substrate 102 rectangular, the columnar portion 114 can have optical anisotropy.
[0022]
The periphery of the columnar portion 114 is buried with an insulating layer 110 made of a silicon oxide film (SiO _X film) such as SiO ₂ formed by a thermal CVD method.
[0023]
The insulating layer 110 is continuously formed along the side surfaces of the p-type semiconductor multilayer mirror 108 and the contact layer 109, and a contact metal layer (upper electrode) 111 made of, for example, Cr and a gold-zinc alloy is formed thereon. , Formed in contact with the contact layer 109 and serves as an electrode for current injection.
[0024]
The central portion of the columnar portion 114 is exposed without being covered with the upper electrode 111 (hereinafter, this portion is referred to as “opening 115”).
[0025]
A lower electrode 101 made of a gold-germanium alloy is formed below the substrate 102.
[0026]
Further, a dielectric layer 112 made of a silicon oxide film (SiO _X film) formed by an electron beam (EB) vacuum deposition method is formed on and around the columnar portion 114. The thickness of the dielectric layer 112 is set to about 2690 angstroms on the opening 115. The upper mirror of the surface emitting semiconductor laser is obtained by setting the wavelength in the air of the laser light emitted from the thickness of the dielectric layer 112 to an integral multiple of a value obtained by dividing the wavelength of the laser light by twice the refractive index of the dielectric layer Thus, the influence on the emission characteristics of the surface emitting semiconductor laser is reduced.
[0027]
By adopting the above structure, the optical anisotropy in the resonator 114 having a columnar structure can be increased. Therefore, even in a surface emitting semiconductor laser having a short wavelength of about 1 wavelength between a pair of reflecting mirrors, It has become possible to influence the optical anisotropy on multiple reciprocating laser beams. Thereby, in the surface emitting semiconductor laser of the present invention, the polarization plane direction can be aligned with the rectangular short side direction of the columnar portion, and the polarization plane can be stabilized even when the laser beam output is increased.
[0028]
Next, a method for manufacturing the dielectric layer 112 in this embodiment will be described.
[0029]
FIG. 3 is a schematic view of the inside of the EB vapor deposition apparatus used when the dielectric layer 112 is produced in this embodiment, and shows the positional relationship between the vapor deposition source 301 and the surface emitting semiconductor laser substrate 302.
[0030]
The vapor deposition material (SiO ₂ grains are used in this embodiment) in the vapor deposition source 301 is heated by the electron beam from the electron beam source 303 and evaporates as a vapor deposition beam on a hemispherical surface like 304. Here, when a surface emitting semiconductor laser having a columnar structure is installed facing the vapor deposition source 301 as in 302A, the vapor deposition beam 304 is isotropic, so the thickness of the dielectric attached to the side surface of the columnar portion is rectangular. The short side and the long side are the same. Therefore, the optical anisotropy in the resonator depends on the rectangular shape of the columnar part.
[0031]
On the other hand, when a surface emitting semiconductor laser having a columnar structure is deposited obliquely with respect to the vapor deposition beam 304 as in 302B when the dielectric layer is deposited, the columnar part is shaded, and the thickness of the dielectric depends on the location of the side of the columnar part. Can make a difference. Therefore, when installing a surface emitting semiconductor laser, the dielectric layer thickness on the side of the short side of the columnar part is set to the long side by setting the short side of the columnar part to be perpendicular and parallel to the vapor deposition beam 304. The thickness can be made thicker or thinner, and the optical anisotropy in the resonator, which has been dependent on the rectangular shape of the columnar part, can be increased or decreased. This has a great effect in suppressing variations in manufacturing each resonator structure in a surface emitting semiconductor laser having a plurality of resonator structures in the substrate.
[0032]
(Example 2)
FIG. 4 is a cross-sectional view schematically showing a cross section of a surface emitting semiconductor laser capable of stabilizing the polarization plane in the second embodiment of the present invention. This embodiment differs from the structure of the first embodiment in that the dielectric layer around the columnar portion is formed of two types of dielectrics.
[0033]
The structure of the surface emitting semiconductor laser 200 shown in FIG. 4 will be described. The n-type GaAs buffer layer 203, the n-type AlAs layer, and the n-type Al _0.3 Ga _0.7 As layer are formed on the n-type GaAs substrate 202 at 780 nm. 40 pairs of distributed reflection type semiconductor multilayer mirrors 204 having a reflectance of 99% or more with respect to the light in the vicinity, n-type Al _0.5 Ga _0.5 As cladding layer 205, n ⁻ -type Al _0.1 Ga _{0. A} multi-quantum well active layer 206 comprising a ₉ As well layer and an n ^- type Al _0.4 Ga _0.6 As barrier layer, and the well layer is composed of 5 layers, a p-type Al _0.5 Ga _0.5 As cladding layer 207, p-type AlAs layers and p-type _Al 0.3 _{Ga 0.7} as distributed reflection type 30 pairs will have a reflectivity of 98.5% or more with respect to light near 780nm from layer semiconductor multilayer mirror 208及p-type _Al 0.2 _{Ga 0.8} As contact layer 209 are successively laminated. For the production of this laminate, epitaxial growth by the MOVPE method was used. At this time, the total thickness of the n-type cladding layer 205, the multiple quantum well active layer 206, and the p-type cladding layer 207 was set to a length of about one wavelength of the laser wavelength in the resonator structure.
[0034]
Then, from the surface side of the p-type semiconductor multilayer mirror 208 to a half thickness, the columnar portion 214 is formed by etching into a rectangular shape as viewed from the top surface of the semiconductor laminate. In this embodiment, the long side A of the rectangle has a length of 30 μm, and the short side B has a length of 20 μm.
[0035]
By setting the height of the columnar portion 214 to a half of the thickness from the surface side of the p-type semiconductor multilayer mirror 208, the etching time at the time of columnar portion production is reduced and the variation in the etching rate in the substrate plane is suppressed. This is effective and leads to stabilization of the manufacturing process of the surface emitting semiconductor laser. However, since the length of the columnar portion 214 is short, there is a problem that diffusion of current injected from the upper electrode into the resonator is reduced. Therefore, after the columnar portion 214 is formed by etching, the p-type AlAs layer forming the p-type semiconductor multilayer mirror 208 is steam-oxidized by about 5 μm from the side surface to form an Al oxide insulating layer 213, and the current in the resonator is It is easy to cause diffusion.
[0036]
The periphery of the columnar portion 214 is buried with an insulating layer 210 made of a silicon oxide film (SiO _X film) such as SiO ₂ formed by a thermal CVD method.
[0037]
The insulating layer 210 is continuously formed along the side surfaces of the p-type semiconductor multilayer mirror 208 and the contact layer 209, and a contact metal layer (upper electrode) 211 made of, for example, Cr and a gold-zinc alloy is formed thereon. Are formed in contact with the contact layer 209 and serve as electrodes for current injection.
[0038]
The central portion of the columnar portion 214 is not covered with the upper electrode 211 and is an opening 215. A lower electrode 201 made of a gold-germanium alloy is formed under the substrate 202.
[0039]
Further, a dielectric layer 212 made of a silicon oxide film (SiO _X film) and a zirconium oxide film (ZrO _X film) formed by electron beam (EB) vacuum deposition is formed on and around the columnar portion 214. ing. The thickness of the dielectric layer 212 is set to about 2200 angstroms on the opening 215.
[0040]
Since the difference in the thermal expansion coefficient between the zirconium oxide film and the compound semiconductor is large, the optical anisotropy in the resonator 214 can be increased with only a zirconium oxide film of about 1000 angstroms. There was a problem that the film was easily peeled off. Therefore, a two-layer structure of a silicon oxide film and a zirconium oxide film prevents the film from peeling off, and reduces the dielectric thickness as compared with the thickness of the dielectric layer of only a single silicon oxide film described in the first embodiment. The body layer 212 has the effect of increasing the optical anisotropy.
[0041]
Therefore, also in this structure, the polarization plane direction can be aligned with the rectangular short side direction of the columnar portion, and the polarization plane can be stabilized even when the laser beam output is increased.
[0042]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist of the present invention.
[0043]
For example, the substrate is selected from the group consisting of Si, GaAlAs, GaInP, ZnSSe, and InGaN semiconductor substrates, or silicon oxide, aluminum oxide, nitride, depending on the material of the semiconductor layer that determines the oscillation wavelength of the surface emitting semiconductor laser. Either aluminum or a silicon nitride dielectric substrate may be used, and the present invention can be implemented even if the p-type and n-type semiconductor layers are replaced.
[0044]
【The invention's effect】
As described above in detail, by using the present invention, a surface emitting semiconductor laser capable of stabilizing the plane of polarization without impairing the laser emission characteristics can be obtained with a simple structure and an easy manufacturing method.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a cross section of a surface emitting semiconductor laser capable of stabilizing the plane of polarization in one embodiment of the present invention.
FIG. 2 is a schematic perspective view of the surface emitting semiconductor laser shown in FIG.
FIG. 3 is a schematic view of the inside of an EB vapor deposition apparatus used in Examples.
FIG. 4 is a cross-sectional view schematically showing a cross section of a surface emitting semiconductor laser capable of stabilizing the polarization plane in another embodiment of the present invention.
[Explanation of symbols]
101, 201 Lower electrode 102, 202 n-type GaAs substrate 103, 203 n-type GaAs buffer layer 104, 204, 108, 208 Distributed reflection type semiconductor multilayer mirror 105, 205 n-type Al _0.5 Ga _0.5 As cladding layer 106,206 Multiple quantum well active layers 107,207 p-type Al _0.5 Ga _0.5 As cladding layers 109,209 p-type Al _0.2 Ga _0.8 As contact layers 110,210 Insulating layers 111,211 Upper electrodes 112, 212 Dielectric layers 114, 214 Columnar portions 115, 215 Opening 213 Al oxide insulating layer 301 Deposition source 302A, 302B Surface emitting semiconductor laser substrate 303 Electron beam source 304 Deposition beam

Claims (5)

A substrate,
A first reflecting mirror having a semiconductor multilayer structure disposed on the substrate;
An active layer disposed above the first reflecting mirror;
A second reflecting mirror disposed above the active layer and having a columnar portion having a rectangular cross-sectional shape parallel to the surface of the substrate;
An insulating layer arranged to cover the side surface of the columnar part;
An upper electrode disposed so as to cover a peripheral portion of the upper surface of the columnar portion and a side surface of the columnar portion via the insulating layer;
A dielectric layer disposed so as to cover the upper surface of the columnar part and extending from the upper surface of the columnar part and disposed so as to cover a side surface of the columnar part via the insulating layer and the upper electrode; ,
A surface-emitting type semiconductor laser comprising:   2. The surface emitting semiconductor laser according to claim 1, wherein the upper electrode is covered with the dielectric layer. The columnar part according to claim 1 or 2, wherein the columnar portion has a pair of opposed first side surfaces and a pair of opposed second side surfaces different from the first side surface,
The surface emitting semiconductor laser, wherein the dielectric layer covering the first side surface and the dielectric layer covering the second side surface have different film thicknesses. In claim 1 or 2,
The dielectric layer is
A first dielectric layer;
A surface-emitting type semiconductor laser comprising: a second dielectric layer which is disposed so as to cover the first dielectric layer and is made of a material different from that of the first dielectric layer. In forming a surface emitting semiconductor laser on a semiconductor substrate,
Forming a first electrode on a lower portion of the semiconductor substrate;
Stacking semiconductor layers having different refractive indexes on the semiconductor substrate to form a first reflection mirror;
Forming a multilayer semiconductor layer including at least an active layer and a cladding layer on the first reflecting mirror;
Forming a second reflecting mirror by laminating semiconductor layers having different refractive indexes on the multilayer semiconductor layer;
A step of etching at least a half thickness of the second reflecting mirror from the surface side into a columnar shape;
Forming an insulating layer around the columnar portion and an upper electrode having an opening on the end face of the columnar portion;
Depositing a dielectric material obliquely on the columnar portion so as to cover the opening and the upper electrode;
A method of manufacturing a surface emitting semiconductor laser, comprising:

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