JP3685541B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device used for optical communication, optical information processing, and the like, and more particularly to a surface emitting semiconductor laser device and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, vertical cavity surface emitting semiconductor lasers, unlike edge-emitting semiconductor lasers, are superior in dynamic single wavelength characteristics and have features such as low threshold current operation and two-dimensional integration. In recent years, research and development has been actively conducted.
[0003]
FIGS. 7 and 8 are views showing an example of the structure of a conventional vertical cavity surface emitting semiconductor laser disclosed in Japanese Patent Laid-Open No. 5-37074. 7 is a cross-sectional view of the semiconductor laser, and FIG. 8 is a perspective view of an active layer of the semiconductor laser of FIG.
[0004]
Referring to FIGS. 7 and 8, this semiconductor laser device includes an n-type GaAs substrate 1, a reflection mirror layer 2, a n-type AlGaAs confinement layer 3, an n-type impurity-doped multilayer of GaAs and AlAs. An active layer 4, a p-type AlGaAs confinement layer 5, and a p-type impurity doped GaAs and AlAs layered with an undoped AlGaAs confinement layer 11 comprising a quantum wire periodic structure composed of InGaAs active fine wires 9 and InAlAs confinement fine wires 10. The reflective mirror layer 6 and AuZn metal electrode 7 made of a multilayer film are sequentially formed, and after all these layers are formed, mesa etching is performed up to the n-type multilayer reflective mirror layer 2, and the n-type multilayer reflective mirror layer 2 An AuGeNi metal electrode 8 is formed thereon.
[0005]
Here, the reflection mirror layers (multilayer mirror layers) 2 and 6 are composed of layers having a quarter wavelength thickness, and a reflectance of 99% or more can be obtained with about 10 to 20 layers. . Thereby, a resonator structure is formed by the p-type reflection mirror layer 6 and the n-type reflection mirror layer 2, and the resonance wavelength is about 950 nm, and light can be emitted (surface emission) from the substrate 1 side.
[0006]
The surface emitting semiconductor laser shown in FIGS. 7 and 8 has a structure in which a current flows through the reflecting mirror layers 2 and 6 of the semiconductor multilayer film. However, since the reflective mirror layers 2 and 6 of the semiconductor multilayer film are formed by laminating 10 to 20 semiconductor layers having different forbidden band widths, an energy barrier due to the forbidden band width difference is generated at each interface. End up. Therefore, in the p-type multilayer reflective mirror layer 6 that injects holes having a large effective mass and a low mobility, the series resistance increases, and therefore the operating voltage of the element increases or the element due to heat generation increases. There was a problem that deterioration occurred. Further, since the p-side electrode 7 is formed at the top of the mesa, when the mesa area is reduced for the purpose of reducing the laser threshold current, the contact area between the electrode and the semiconductor layer is reduced, and the contact resistance is increased. There is also a problem of becoming.
[0007]
On the other hand, Japanese Patent Laid-Open No. 6-196804 discloses a surface emitting semiconductor laser device in which the contact resistance of an element is reduced. FIG. 9 is a cross-sectional view of a semiconductor laser device disclosed in Japanese Patent Laid-Open No. 6-196804. This semiconductor laser device is an n-type semiconductor in which n-type AlGaAs and n-type AlAs are stacked on an n-type GaAs substrate 9 for 30 periods. A multilayer mirror 10, an n-type AlGaAs cladding layer 11, a p-type GaAs active layer 12, a p-type AlGaAs cladding layer 13, a p-type semiconductor multilayer reflector 14 made of p-type AlGaAs and AlAs, and a p-type AlGaAs contact layer 15 are provided. The p-type semiconductor multilayer mirror 14 is formed in sequence, and the H-type except for the central portion and the upper portion is formed on the p-type semiconductor multilayer mirror 14.⁺A current block portion 16 into which ions are implanted is formed. Reference numeral 17 denotes a p-side ohmic electrode formed on the upper surface of the contact layer excluding the laser emitting portion, and reference numeral 19 denotes an n-side ohmic electrode formed over the entire lower surface of the substrate.
[0008]
The surface emitting semiconductor laser of FIG. 9 has a planar structure instead of a mesa structure, unlike the surface emitting semiconductor lasers of FIGS. Thereby, the p-side electrode 17 can be formed on the entire surface except for the laser emitting portion, and the contact resistance between the electrode and the semiconductor can be reduced. However, the semiconductor laser device of FIG. 9 is the same as the semiconductor laser device of FIGS. 7 and 8 in that current injection is performed through the p-type semiconductor multilayer mirror 14, and through the p-type semiconductor multilayer mirror. Since current injection is performed, the series resistance is not reduced.
[0009]
FIG. 10 is a cross-sectional view of a surface emitting semiconductor laser disclosed in Japanese Patent Laid-Open No. 6-29612. 10 includes an n-type single crystal Bragg mirror 20 in which GaAs and AlGaAs are alternately stacked on an n-type GaAs substrate 19, a first epitaxial layer 21, a second epitaxial layer 22, and an active region. A second epitaxial layer 22 is formed.
[0010]
Here, the active region includes a plurality of quantum wells 23 and is separated from each other by the intermediate layer 24. A circular or rectangular protective mask 25 is formed on the upper second epitaxial layer 22, and p-type impurities are doped and diffused from the device surface not covered with the mask, and the impurities are diffused. The composition of the active region 26 is homogenized by mutual diffusion or migration of elements constituting each layer. Reference numeral 27 denotes an upper metal ohmic contact formed excluding the laser emitting portion, and reference numeral 28 denotes a lower metal ohmic contact. After these are formed, a translucent reflecting mirror 29 made of a dielectric multilayer film is formed. Are formed, the photon is confined in the resonator, and the laser beam is extracted to the outside.
[0011]
In the laser structure of FIG. 10, the current is injected from the region 26 homogenized by the p-type impurity diffusion around the translucent reflector 29 without passing through the p-type semiconductor multilayer film. Accordingly, an increase in series resistance due to the energy barrier is not caused, and a contact area between the electrode and the semiconductor can be increased, so that the contact resistance can be reduced. Further, since the forbidden band width of the compound homogenized by impurity diffusion is larger than the forbidden band width of the quantum well layer, injected carriers can be confined in the non-homogenized active region.
[0012]
FIG. 11 is a block diagram of a surface emitting laser disclosed in Japanese Patent Laid-Open No. 5-235473. The surface-emitting laser shown in FIG. 11 has, on an n-type GaAs substrate 30, a lower mirror 31 made of an n-type semiconductor multilayer film, a cavity region 32 including an active layer, and an upper mirror 35 made of a semiconductor multilayer film. Yes.
[0013]
Here, the upper mirror 35 has a shape having a convex portion, and an upper mirror lowermost layer 33 and a p-type current injection layer 34 are formed between the convex portion of the upper mirror 35 and the cavity region 32. . In addition, a semi-insulating film region 36 is formed in the vicinity of the active layer in the layer thickness direction in the peripheral part of the convex part, and an electrode 37 for current injection is provided in the peripheral part of the convex part of the upper mirror 35. Is formed.
[0014]
Also in the semiconductor laser of FIG. 11, since the current is injected into the active layer without passing through the p-type semiconductor multilayer film, the series resistance does not increase due to the energy barrier. In addition, since the contact area between the electrode and the semiconductor can be increased, the contact resistance can be reduced. The current can be confined below the convex portion of the upper mirror 35 by the semi-insulating region 36 formed in the vicinity of the active layer.
[0015]
[Problems to be solved by the invention]
By the way, in the surface emitting laser of FIG. 10, the injected carriers are confined in the homogenized active region, but p-type impurities are diffused in the lower second epitaxial layer 22, so that the p side A pn junction region extends below the electrode 27. For this reason, a surface emitting laser with a high injected carrier density has a problem that the oscillation threshold current increases due to a leakage current flowing through this interface.
[0016]
On the other hand, in the surface emitting laser of FIG. 11, a current confinement structure is formed by the semi-insulating region 36, but carriers injected into the active layer below the convex portion of the upper mirror 35 are adjacent to the active layer of the semi-insulating region 36. When it diffuses, non-radiative recombination occurs through crystal defects induced by ion implantation. In addition, the component that has undergone luminescence recombination does not contribute to laser oscillation because it is outside the cavity region. Therefore, extra carriers are injected, and there is a problem that the oscillation threshold current is increased.
[0017]
The present invention has been made to solve the above-described problem, and can provide a surface-emitting type semiconductor laser device capable of reducing element resistance and effectively preventing an increase in oscillation threshold current and its manufacture. It aims to provide a method.
[0018]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1HalfOn the conductor substrateHalfA conductor multilayer reflector, an n-type cladding layer, a quantum well active layer, a p-type cladding layer, and a p-type contact layer are formed;SaidOn the p-type contact layer, columnarUpper multilayer reflectorIs formed, andUpper multilayer reflectorA semi-insulating region is provided immediately below the n-type cladding layer in the region not covered withUpper multilayer reflectorThe region from the surface of the p-type contact layer not covered with the quantum well active layer to the quantum well active layer is a p-type impurity diffusion region in which p-type impurities are diffused and disordered, and the p-type impurities are diffused. Ohmic electrodes are formed on the p-type contact layer and the back surface of the substrate, respectively, so that laser oscillation is performed in a direction perpendicular to the substrate.
[0019]
  The invention according to claim 2HalfOn the conductor substrateHalfConductor multilayer mirror, n-type cladding layer,The forbidden bandwidth is narrower than the substrateA quantum well active layer, a p-type cladding layer, and a p-type contact layer are formed;SaidOn the p-type contact layer, columnarUpper multilayer reflectorIs formed, andUpper multilayer reflectorA semi-insulating region is provided immediately below the n-type cladding layer in the region not covered withUpper multilayer reflectorThe region from the surface of the p-type contact layer not covered with the quantum well active layer is a p-type impurity diffusion region in which p-type impurities are diffused and disordered,A p-side ohmic electrode is formed on the entire front surface of the substrate, and an n-side ohmic electrode is formed on the back surface of the substrate except for the laser beam emitting portion.The laser oscillates in a direction perpendicular to the substrate.
[0020]
  The invention according to claim 3 is the semiconductor laser device according to claim 1 or 2, wherein the columnar upper multilayer reflector isDielectricIt is characterized by being laminated alternately.
  According to a fourth aspect of the present invention, in the semiconductor laser device according to the first or second aspect, the columnar upper multilayer reflector is an undoped semiconductor.
[0021]
  Also,Claim 5The described inventionHalfOn the conductor substrateHalfConductor multilayer mirror, n-type cladding layer, quantum well active layer, p-type cladding layer, p-type contact layer,Upper multilayer reflectorSequentially laminating,Upper multilayer reflectorA mask with a predetermined shape is formed on the p-type contact layerUpper multilayer reflectorFrom the surface of the p-type contact layer to the quantum well active layer using the mask of the etching step, and the step of implanting proton ions immediately below the n-type cladding layer using the mask of the etching step The method includes a step of implanting and diffusing p-type impurities, and a step of forming ohmic electrodes on the p-type contact layer in which the p-type impurities are diffused and on the back surface of the substrate.
[0022]
  Also,Claim 6The described inventionHalfOn the conductor substrateHalfConductor multilayer mirror, n-type cladding layer, quantum well active layer, p-type cladding layer, p-type contact layer,Upper multilayer reflectorStep by step, and up to the p-type contact layerUpper multilayer reflectorFrom the surface of the p-type contact layer to the quantum well active layer using the mask of the etching step, and the step of implanting proton ions immediately below the n-type cladding layer using the mask of the etching step Self-aligned with the process of implanting and diffusing p-type impuritiesUpper multilayer reflectorThe method includes a step of forming a p-side ohmic electrode on the substrate surface excluding the top of the substrate and a step of forming an n-side ohmic electrode on the back surface of the substrate.
[0023]
  Claims 1 toClaim 4In the described invention, the current is applied to the upper multilayer reflector.(Upper multilayer reflector)Since the peripheral p-type impurity is implanted from the p-type contact layer, series resistance and contact resistance do not increase. Thereby, the operating voltage of the element can be reduced and heat generation can be suppressed, so that element deterioration can be prevented. Also, under the active layerHalfSince the region of the conductor multilayer reflector that is not covered by the upper multilayer reflector is a semi-insulating region, the current can be concentrated directly below the upper multilayer reflector.
[0024]
Further, the carrier of the p-type contact layer whose carrier concentration is lowered by proton ion implantation due to implantation and diffusion of p-type impurities from the p-type contact layer not covered by the upper multilayer mirror to the active layer region. The concentration is recovered so that the contact resistance with the p-side ohmic electrode does not increase. In addition, since the quantum well active layer in which the p-type impurity is diffused is disordered, the forbidden band width is larger than that of the quantum well active layer. Therefore, carriers can be confined directly below the upper multilayer mirror, and the emission threshold current can be reduced.
[0025]
  In particular, in the invention described in claim 2, since the forbidden band width of the quantum well active layer is smaller than the forbidden band width of the substrate, the laser light is not absorbed by the substrate, so that the laser light is extracted from the back surface of the substrate. Is possible. Accordingly, the p-side ohmic electrode does not need to be patterned, can be formed on the entire surface, and the p-side ohmic electrode can be used as a part of the reflecting mirror. Moreover, in the semiconductor laser device according to the second aspect, since it can be mounted by a junction down method, it is excellent in heat dissipation characteristics and the reliability of the element can be improved.
[0026]
  Further, in the invention according to claim 4, since the upper multilayer film reflector is a semiconductor multilayer film mirror rather than a dielectric multilayer film, a step of separately stacking the upper multilayer film mirror is not required, Up to the upper multilayer reflector can be formed by one-time semiconductor crystal growth, and the device manufacturing process can be simplified. In this case, since the upper semiconductor multilayer mirror does not need to be used as a current path, it can be formed undoped, thereby reducing free carrier absorption of light in the semiconductor multilayer reflector, and reflecting the semiconductor multilayer reflector. Decrease in the reflectance and transmittance of the mirror can be prevented. Therefore, the emission threshold current can be reduced and the external differential quantum efficiency can be improved.
[0027]
  Also,Claim 5In the described invention, up to the p-type contact layerUpper multilayer reflectorThe step of implanting proton ions directly under the n-type cladding layer and the step of injecting and diffusing p-type impurities for disordering the quantum well active layer from the surface of the p-type contact layer are performed using a mask for etching the substrate into a columnar shape. Therefore, the number of mask formations by the photolithography method can be reduced, and the manufacture becomes easy. In addition, since the optical resonator structure, the current confinement structure, and the carrier confinement structure are formed using the same mask, variations in device characteristics due to mask patterning deviation are not caused, and the yield can be improved.
[0028]
  Also,Claim 6In the described invention, p-side ohmic electrode pattern formation is performed by a self-alignment process.Upper multilayer reflectorSo that it can be formed on the surface of the substrate excluding the top of the substrate.To claim 5The described semiconductor laser device can be formed by one crystal growth and one photolithography process, which can further facilitate device manufacture.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration example of a semiconductor laser device (surface emitting semiconductor laser) according to the present invention. Referring to FIG. 1, this semiconductor laser device includes an n-type semiconductor multilayer reflector 102, an n-type AlGaAs cladding layer 103, an InGaAs strained quantum well active layer 104, and a p-type AlGaAs cladding layer 105 on an n-type GaAs substrate 101. , A p-type GaAs contact layer 106 and a dielectric multilayer reflector 107 are sequentially formed.
[0030]
Here, the n-type semiconductor multilayer mirror 102 is formed by alternately laminating AlAs and GaAs doped with n-type impurities at a thickness of λ / (4n) for about 20 periods (λ: oscillation wavelength). , N: Refractive index of each layer). The total thickness of the n-type cladding layer 103, the quantum well active layer 104, and the p-type cladding layer 105 is set to be a natural number multiple of the optical distance of λ / 2. The thickness of the p-type contact layer 106 is set to λ / (4n). In addition, the dielectric multilayer film reflecting mirror 107 has, for example, a cylindrical shape, and SiO 2₂And TiO₂Are stacked alternately with a thickness of λ / (4n). Thereby, the active layer 104 can be set at the antinode position of the standing wave without impairing the standing wave condition of the resonator.
[0031]
In the configuration example of FIG. 1, a semi-insulating region 108 is formed by proton ion implantation immediately below the n-type cladding layer 103 in a region not covered with the dielectric multilayer reflector 107. A p-type impurity (for example, Zn) is implanted and diffused from the surface of the p-type contact layer 106 not covered with the multilayer mirror 107 to the quantum well active layer 104, and a p-type impurity diffusion region 109 is formed. The quantum well active layer in which the p-type impurity (for example, Zn) is diffused, that is, the p-type impurity diffusion region 109 is disordered by the mutual diffusion of the constituent elements. The forbidden band width of the diffusion region 109 is larger than the forbidden band width of the quantum well active layer 104.
[0032]
A p-side ohmic electrode 110 made of AuZn / Au is formed on the p-type contact layer 106 in which the p-type impurity (Zn) is diffused, and n on the back surface of the substrate 101 is made of AuGe / Ni / Au. A side ohmic electrode 111 is formed.
[0033]
FIG. 2 is a view showing an example of a manufacturing process of the semiconductor laser device (surface emitting semiconductor laser) of FIG. Referring to FIG. 2, first, on an n-type GaAs substrate 101, an n-type semiconductor multilayer reflector 102, an n-type AlGaAs cladding layer 103, an InGaAs strained quantum well active layer 104, a p-type AlGaAs cladding layer 105, and a p-type. Crystal growth of the GaAs contact layer 106 is sequentially performed (FIG. 2A). The crystal growth methods include MBE (molecular beam epitaxy) and MOCVD (metal organic chemical vapor).
deposition) method or the like is used.
[0034]
Next, a dielectric multilayer reflecting mirror 107 is laminated on the entire surface of the p-type GaAs contact layer 106 (FIG. 2B). The dielectric multilayer reflecting mirror 107 can be manufactured by, for example, an electron beam evaporation method while optically monitoring the film thickness.
[0035]
After forming the dielectric multilayer film reflecting mirror 107 in this way, a circular resist 201 having a diameter of several μm is formed on the dielectric multilayer film reflecting mirror 107 by a photolithography technique. Then, the dielectric multilayer film 107 is etched to the upper surface of the p-type contact layer 106 by the RIE (reactive ion etching) method using the circular resist 201 as a mask (FIG. 2C). Thereby, the cylindrical dielectric multilayer film reflecting mirror 107 can be formed. Note that the shape of the mask is not necessarily circular, and may be rectangular or the like. When a rectangular mask is used, the dielectric multilayer film reflecting mirror 107 can be formed in a prismatic shape.
[0036]
Thereafter, proton ions are implanted using the resist 201 and the dielectric multilayer film 107 as a mask. At this time, the semi-insulating region 108 is formed in the n-type semiconductor multilayer reflector 102 immediately below the n-type cladding layer 103 by controlling the acceleration voltage to be implanted (FIG. 2D).
[0037]
Further, using the resist 201 and the dielectric multilayer film 107 as a mask, Zn ions that are p-type impurities are implanted to the vicinity of the active layer 104. Thereafter, the p-type impurity (Zn) is diffused by lamp annealing to disorder the region of the quantum well active layer 104 in which the p-type impurity is diffused, that is, the p-type impurity diffusion region 109 (FIG. 2E).
[0038]
Finally, the resist mask 201 is removed, a p-side electrode 110 is formed on the p-type contact layer 106, and an n-side electrode 111 is formed on the back surface of the substrate 101 (FIG. 2 (f)). The p-side electrode 110 is formed by a lift-off method using a circular mask that is one size larger than the resist mask 201, except for the dielectric multilayer film reflecting mirror 107 and its surroundings.
[0039]
In the surface emitting semiconductor laser shown in FIG. 1, a resonator is formed by the n-type semiconductor multilayer reflector 102 and the dielectric multilayer reflector 107 so that the laser light is extracted from the dielectric multilayer reflector 107 side. It has become. At this time, the p-type GaAs contact layer 106 in the resonator has a layer thickness of λ / (4n) and is a part of the multilayer reflector 107, and the p-type GaAs contact layer 106 is forbidden. Since the band width is larger than the forbidden band width of the InGaAs strained quantum well active layer 104, there is no light absorption loss in the p-type GaAs contact layer 106 in the resonator.
[0040]
Further, in the surface emitting semiconductor laser of FIG. 1, current is injected from the p-type contact layer 106 around the dielectric multilayer reflector 107, so that carriers (holes) are generated in the semiconductor multilayer reflector. The series resistance does not increase because it does not pass through. That is, the series resistance can be reduced. Further, since the contact area between the p-side electrode 110 and the p-type contact layer 106 can be increased, the contact resistance can also be reduced.
[0041]
Further, in the surface emitting semiconductor laser of FIG. 1, a semi-insulating region 108 is formed in the region of the n-type semiconductor multilayer reflector 102 immediately below the n-type cladding layer 103 that is not covered by the dielectric multilayer reflector 107. As a result, the current injected from the p-type contact layer 106 can be concentrated directly below the dielectric multilayer film reflecting mirror 107.
[0042]
Further, in the surface-emitting semiconductor laser of FIG. 1, since the p-type impurity Zn is implanted and diffused from the p-type contact layer 106 not covered with the dielectric multilayer reflector 107 to the active region, proton ions The carrier concentration of the p-type contact layer 106 whose carrier concentration has been lowered by the implantation is recovered so that the contact resistance with the p-side ohmic electrode 110 does not increase. Further, the region of the quantum well active layer in which the p-type impurity (Zn) is diffused and disordered, that is, the p-type impurity diffusion region 109 has a larger forbidden band than the quantum well active layer 104 that is not disordered. The carrier can be confined immediately below the dielectric multilayer film reflecting mirror 107. Therefore, the oscillation threshold current can be reduced.
[0043]
In addition, according to the example of the manufacturing process shown in FIG. 2, after the dielectric multilayer film reflecting mirror 107 is etched and formed into a predetermined shape, proton ions and p are formed using the resist mask 201 and the etched dielectric multilayer film as a mask. Since type impurity (Zn) ions are implanted, the number of mask formations by photolithography can be reduced, and manufacturing is facilitated. Furthermore, since the optical resonator structure, the current confinement structure, and the carrier confinement structure are formed with the same mask, it is not necessary to cause variations in element characteristics due to mask pattern misalignment.
[0044]
FIG. 3 is a diagram showing another configuration example of the semiconductor laser device (surface emitting semiconductor laser) according to the present invention. Referring to FIG. 3, in this semiconductor laser device, as in the semiconductor laser device of FIG. 1, an n-type semiconductor multilayer mirror 102, an n-type AlGaAs cladding layer 103, and an InGaAs strain quantum are formed on an n-type GaAs substrate 101. A well active layer 104, a p-type AlGaAs cladding layer 105, and a p-type GaAs contact layer 106 are sequentially formed.
[0045]
In the semiconductor laser device of FIG. 3, an AlGaInP etching stop layer 301 formed in, for example, a columnar shape and an undoped semiconductor multilayer film reflecting mirror 302 are sequentially stacked on the p-type contact layer 106. Here, the layer thickness of the AlGaInP etching stop layer 301 is set to λ / (4n), and the undoped semiconductor multilayer reflector 302 alternately stacks AlAs and GaAs with a thickness of λ / (4n). Is formed.
[0046]
In the semiconductor laser device of FIG. 3, a semi-insulating region 108 is formed by proton ion implantation in a region immediately below the n-type cladding layer 103 that is not covered by the undoped semiconductor multilayer reflector 302, and further, an undoped semiconductor. A p-type impurity (for example, Zn) is implanted and diffused from the surface of the p-type contact layer 106 not covered by the multilayer reflector 302 to the quantum well active layer 104, and a p-type impurity diffusion region 109 is formed.
[0047]
A p-side ohmic electrode 110 is formed on the surface of the substrate except for the top of the undoped semiconductor multilayer film reflecting mirror 302 that is a laser beam emitting portion. An n-side ohmic electrode is formed on the back surface of the substrate 101. 111 is formed.
[0048]
4 and 5 are views showing an example of a manufacturing process of the semiconductor laser device (surface emitting semiconductor laser) shown in FIG. 4 and 5, first, an n-type semiconductor multilayer mirror 102, an n-type AlGaAs cladding layer 103, and an InGaAs strained quantum well active layer 104 are formed on an n-type GaAs substrate 101 by MBE or MOCVD. , A p-type AlGaAs cladding layer 105, a p-type GaAs contact layer 106, an AlGaInP etching stop layer 301, and an undoped semiconductor multilayer reflector 302 are sequentially formed by a single crystal growth (FIG. 4A).
[0049]
Next, on the undoped semiconductor multilayer mirror 302, Si_ThreeN_FourLayer 401 is formed. Then, using a circular resist 201 having a diameter of several μm formed by photolithography as a mask, Si_ThreeN_FourThe layer 401 is dry etched by RIE. Furthermore, Si_ThreeN_FourUsing the layer 401 as a mask, the undoped semiconductor multilayer mirror 302 is dry-etched up to the AlGaInP etching stop layer 301 (FIG. 4B).
[0050]
At this time, for example, by using an ECR-RIBE (electron cyclotron resonance-reactive ion beam etching) method as an etching method, a substantially vertical etching shape can be obtained, and the cylindrical semiconductor multilayer reflector 302 can be formed. Here, since the AlGaInP crystal has a slower dry etching rate than AlAs or GaAs, the AlGaInP layer 301 was used as an etching stop layer.
[0051]
Thereafter, the exposed AlGaInP etching stop layer 301 is removed by chemical etching with a sulfuric acid etchant to expose the p-type GaAs contact layer 106. Sulfuric acid etches AlGaInP crystals selectively without etching AlGaAs crystals. And Si_ThreeN_FourProton ions are implanted using the layer 401 as a mask to form a semi-insulating region 108 in the n-type semiconductor multilayer reflector 102 immediately below the n-type cladding layer 103. Furthermore, Si_ThreeN_FourUsing the layer 401 as a mask, Zn ions, which are p-type impurities, are implanted to the vicinity of the active layer 104, and p-type impurities (Zn) are diffused by lamp annealing to form a p-type impurity diffusion region 109 (FIG. 4C). ). At this time, the region of the quantum well active layer 104 in which the p-type impurity (Zn) is diffused, that is, the p-type impurity diffusion region 109 is disordered.
[0052]
Next, after removing the resist mask 201, a p-side electrode 110 made of AuZn / Au is formed on the entire front surface of the substrate by vacuum deposition (FIG. 4D).
[0053]
Then, a resist 402 is applied on the p-side electrode 110 by spin coating. At this time, if a resist 402 having a relatively low viscosity is used, the resist film thickness at the top of the cylinder can be made thinner than other portions (FIG. 5E).
[0054]
Next, after hard baking the resist 402, the entire surface of the resist 402 is O.₂Ashing with plasma exposes the p-side electrode 110 at the top of the cylinder (FIG. 5 (f)).
[0055]
Then, using the resist 402 as a mask, the p-side electrode at the top of the cylinder is etched away by sputter etching (FIG. 5G). At this time, Si_ThreeN_FourLayer 401 serves as an etch stop layer.
[0056]
Finally, resist 402 and Si_ThreeN_FourAfter removing the layer 401, an n-side electrode 111 made of AuGe / Ni / Au is formed on the back surface of the substrate (FIG. 5 (h)).
[0057]
In the surface emitting semiconductor laser shown in FIG. 3, similarly to the surface emitting semiconductor laser shown in FIG. 1, the n-type semiconductor multilayer reflector 102 and the undoped semiconductor multilayer reflector 302 form a resonator, and the laser Light can be extracted from the undoped semiconductor multilayer film reflector 302 side. At this time, the p-type GaAs contact layer 106 and the AlGaInP etching stop layer 301 in the resonator are respectively set to λ / (4n) and are part of the multilayer reflector 302. Since the forbidden band width of the type GaAs contact layer 106 and the AlGaInP etching stop layer 301 is larger than the forbidden band width of the InGaAs strained quantum well active layer 104, there is no light absorption loss in the resonator.
[0058]
Also in the semiconductor laser device of FIG. 3, the p-side ohmic electrode structure, current confinement structure, and carrier confinement structure are the same as those of the semiconductor laser device of FIG.
[0059]
The surface emitting semiconductor laser of FIG. 3 is different from the surface emitting semiconductor laser of FIG. 1 in that an undoped semiconductor multilayer reflector 302 is used instead of a dielectric multilayer as an upper reflector. Therefore, in the semiconductor laser device of FIG. 3, it is not necessary to stack the dielectric multilayer film separately from the semiconductor layer, and the n-type semiconductor multilayer mirror 102, the n-type AlGaAs cladding layer 103, and the InGaAs can be obtained by a single crystal growth. Since not only the strained quantum well active layer 104, the p-type AlGaAs cladding layer 105, and the p-type GaAs contact layer 106 but also the upper reflecting mirror 302 can be formed, the production can be simplified. Further, the semiconductor multilayer film reflecting mirror 302 is made of SiO in the semiconductor laser device of FIG.₂/ TiO₂Compared with the dielectric multilayer film reflecting mirror 107, the thermal conductivity is large, and the heat dissipation characteristics are excellent. The semiconductor multilayer reflector 302 does not need to be used as a current path, and can be formed undoped. Therefore, when the semiconductor multilayer film reflector 302 is formed undoped, free carrier absorption of light in the semiconductor multilayer film reflector 302 can be reduced, thereby preventing a decrease in reflectance and transmittance. .
[0060]
Also, according to the manufacturing process example shown in FIGS. 4 and 5, the p-side ohmic electrode 101 is formed by a self-alignment process. Therefore, the surface emitting laser of FIG. And a single photolithographic process. This further facilitates device manufacture. In particular, when the circular mask pattern is miniaturized for the purpose of reducing the threshold current, it is effective because patterning deviation of the p-side electrode does not occur.
[0061]
FIG. 6 is a diagram showing another configuration example of the semiconductor laser device (surface emitting semiconductor laser) according to the present invention. Referring to FIG. 6, in this semiconductor laser device, as in the semiconductor laser device of FIGS. 1 and 3, an n-type semiconductor multilayer reflector 102, an n-type AlGaAs cladding layer 103, An InGaAs strained quantum well active layer 104, a p-type AlGaAs cladding layer 105, and a p-type GaAs contact layer 106 are sequentially formed.
[0062]
In the semiconductor laser device of FIG. 6, on the p-type contact layer 106, for example, an AlGaInP etching stop layer 301 formed in a columnar shape, a semiconductor multilayer reflector 302 made of undoped AlAs and GaAs, and Si_ThreeN_FourThe layer 401 is sequentially stacked. Here, the AlGaInP etching stop layer 301 and Si_ThreeN_FourThe layer thickness of the layer 401 is set to λ / (4n), respectively. Further, the undoped semiconductor multilayer mirror 302 is formed by alternately laminating AlAs and GaAs with a thickness of λ / (4n).
[0063]
In the semiconductor laser device of FIG. 6, a semi-insulating region 108 is formed by proton ion implantation in a region immediately below the n-type cladding layer 103 that is not covered by the undoped semiconductor multilayer mirror 302, and further, an undoped semiconductor. A p-type impurity (for example, Zn) is implanted and diffused from the surface of the p-type contact layer 106 not covered by the multilayer reflector 302 to the quantum well active layer 104, and a p-type impurity diffusion region 109 is formed.
[0064]
A p-side ohmic electrode 110 made of AuZn / Au is formed on the entire front surface of the substrate, and an n-side ohmic electrode 111 made of AuGe / Ni / Au is formed on the back surface of the substrate except for the laser beam emitting portion. Is formed.
[0065]
In the surface emitting semiconductor laser shown in FIG. 6, similarly to the surface emitting semiconductor laser shown in FIGS. 1 and 3, a resonator is formed by the n-type semiconductor multilayer reflector 102 and the undoped semiconductor multilayer reflector 302. In the semiconductor laser device of FIG. 6, the p-side ohmic electrode structure, current confinement structure, and carrier confinement structure are the same as those of the semiconductor laser device of FIGS. In the surface emitting semiconductor laser shown in FIG. 6, unlike the laser shown in FIGS. 1 and 3, the laser light is extracted through the substrate 101 from the n-type semiconductor multilayer reflector 102 side. At this time, since the forbidden band width of the InGaAs strained quantum well active layer 103 is smaller than the forbidden band width of the GaAs substrate 101, the laser light is not subjected to absorption loss in the GaAs substrate 101.
[0066]
In the surface-emitting type semiconductor laser shown in FIG._ThreeN_FourA p-side electrode 110 is formed through the layer 401, and this Si_ThreeN_FourBy setting the layer thickness of the layer 401 to λ / (4n), Au used for the p-side electrode 110 can be used as a part of the reflecting mirror. Si_ThreeN_FourSince AuZn and the semiconductor layer are stacked via the layer 401, the reflectance does not decrease due to annealing.
[0067]
The surface-emitting type semiconductor laser shown in FIG. 6 can be mounted by a junction down method, and thus has a feature of excellent heat dissipation characteristics. Therefore, the reliability of the element can be improved. In addition, Si between the p-side electrode 110 and the undoped semiconductor multilayer reflector 301_ThreeN_FourSince the layer 401 is a material having a relatively high thermal conductivity, the heat dissipation characteristics are not impaired.
[0068]
In each of the above-described configuration examples, the upper multilayer film reflecting mirror is etched to the lowermost layer to produce a cylindrical shape, but the number of layers between the p-type cladding layer 105 and the p-type contact layer 106 is small. A semiconductor multilayer film reflecting mirror may be formed. In this case, since the region of the semiconductor multilayer reflector in which the p-type impurity (for example, Zn) is diffused from the p-type contact layer 105 is disordered, there is no hetero barrier. Therefore, the series resistance can be kept low even if current passes through this portion.
[0069]
Further, in each of the above-described configuration examples, the dielectric multilayer film reflector 107 and the semiconductor multilayer film reflector 302 are formed in a columnar or prismatic shape. , It can be formed in any shape, not limited to a prismatic shape.
[0070]
In each of the above-described configuration examples, the AlGaAs-based material has been described as an example.
[0071]
【The invention's effect】
  As explained above, claims 1 toClaim 4According to the described inventionHalfOn the conductor substrateHalfA conductor multilayer mirror, an n-type cladding layer, a quantum well active layer, a p-type cladding layer, and a p-type contact layer are formed, and a columnar shape is formed on the p-type contact layer.Upper multilayer reflectorIs formed, andUpper multilayer reflectorA semi-insulating region is provided immediately below the n-type cladding layer in the region not covered withUpper multilayer reflectorThe region from the surface of the p-type contact layer not covered with the quantum well active layer to the quantum well active layer is a p-type impurity diffusion region in which p-type impurities are diffused and disordered, and the p-type impurity is diffused. Ohmic electrodes are formed on the contact layer and the back surface of the substrate, respectively, so that laser oscillation occurs in a direction perpendicular to the substrate, and current diffuses p-type impurities around the upper multilayer reflector. Since it is injected from the p-type contact layer, the series resistance and contact resistance do not increase. Thereby, the operating voltage of the element can be reduced and heat generation can be suppressed, so that element deterioration can be prevented. Also, under the active layerHalfSince the region of the conductor multilayer reflector that is not covered by the upper multilayer reflector is a semi-insulating region, the current can be concentrated directly below the upper multilayer reflector.
[0072]
Further, the carrier of the p-type contact layer whose carrier concentration is lowered by proton ion implantation due to implantation and diffusion of p-type impurities from the p-type contact layer not covered by the upper multilayer mirror to the active layer region. The concentration is recovered so that the contact resistance with the p-side ohmic electrode does not increase. In addition, since the quantum well active layer in which the p-type impurity is diffused is disordered, the forbidden band width is larger than that of the quantum well active layer. Therefore, carriers can be confined directly below the upper multilayer mirror, and the emission threshold current can be reduced.
[0073]
  In particular, in the invention described in claim 2, since the forbidden band width of the quantum well active layer is smaller than the forbidden band width of the substrate, the laser light is not absorbed by the substrate, so that the laser light is extracted from the back surface of the substrate. Is possible. Accordingly, the p-side ohmic electrode does not need to be patterned, can be formed on the entire surface, and the p-side ohmic electrode can be used as a part of the reflecting mirror. Moreover, in the semiconductor laser device according to the second aspect, since it can be mounted by a junction down method, it is excellent in heat dissipation characteristics and the reliability of the element can be improved.
[0074]
  According to the invention described in claim 4, since the upper multilayer reflector is a semiconductor multilayer reflector rather than a dielectric multilayer, there is no need to separately stack the upper multilayer reflector. Thus, up to the upper multilayer reflector can be formed by one-time semiconductor crystal growth, and the device manufacturing process can be simplified. In this case, since the upper semiconductor multilayer mirror does not need to be used as a current path, it can be formed undoped, thereby reducing free carrier absorption of light in the semiconductor multilayer reflector, and reflecting the semiconductor multilayer reflector. Decrease in the reflectance and transmittance of the mirror can be prevented. Therefore, the emission threshold current can be reduced and the external differential quantum efficiency can be improved.
[0075]
  Also,Claim 5According to the described invention, up to the p-type contact layerUpper multilayer reflectorThe step of implanting proton ions directly under the n-type cladding layer and the step of injecting and diffusing p-type impurities for disordering the quantum well active layer from the surface of the p-type contact layer are performed using a mask for etching the substrate into a columnar shape. Therefore, the number of mask formations by the photolithography method can be reduced, and the manufacture becomes easy. In addition, since the optical resonator structure, the current confinement structure, and the carrier confinement structure are formed using the same mask, variations in device characteristics due to mask patterning deviation are not caused, and the yield can be improved.
[0076]
  Also,Claim 6According to the described invention, pattern formation of the p-side ohmic electrode is performed by a self-alignment process.Upper multilayer reflectorSo that it can be formed on the surface of the substrate excluding the top of the substrate.Thru claim 4The described semiconductor laser device can be formed by one crystal growth and one photolithography process, which can further facilitate device manufacture.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of a semiconductor laser device according to the present invention.
FIG. 2 is a diagram showing an example of a manufacturing process of the semiconductor laser device of FIG.
FIG. 3 is a diagram showing another configuration example of the semiconductor laser device according to the present invention.
4 is a diagram showing a manufacturing process example of the semiconductor laser device of FIG. 3; FIG.
5 is a diagram showing a manufacturing process example of the semiconductor laser device of FIG. 3; FIG.
FIG. 6 is a diagram showing another configuration example of the semiconductor laser device according to the present invention.
FIG. 7 is a diagram showing a configuration example of a conventional vertical cavity surface emitting semiconductor laser.
8 is a perspective view of an active layer of the semiconductor laser of FIG.
FIG. 9 is a diagram showing a configuration example of a conventional vertical cavity surface emitting semiconductor laser.
FIG. 10 is a diagram showing a configuration example of a conventional vertical cavity surface emitting semiconductor laser.
FIG. 11 is a diagram showing a configuration example of a conventional vertical cavity surface emitting semiconductor laser.
[Explanation of symbols]
101 n-type GaAs substrate
102 n-type semiconductor multilayer reflector
103 n-type AlGaAs cladding layer
104 Quantum well active layer
105 p-type AlGaAs cladding layer
106 p-type GaAs contact layer
107 dielectric multilayer reflector
108 Semi-insulating region
109 p-type impurity diffusion region
110 p-side electrode
111 n-side electrode
201 resist mask
301 AlGaInP etching stop layer
302 Undoped Semiconductor Multilayer Reflector
401 Si_ThreeN_Fourlayer
402 resist

Claims (6)

On a semi-conductor substrate, a semi-conductive multilayer mirror, n-type cladding layer, a quantum well active layer, p-type cladding layer, p-type contact layer is formed, the said p-type contact layer, columnar upper multilayer reflector is formed, wherein the right under the upper multilayer mirror not covered with the region n-type cladding layer, and the semi-insulating region is provided, also covered with the upper multilayer mirror The region from the p-type contact layer surface to the quantum well active layer is a p-type impurity diffusion region in which p-type impurities are diffused and disordered, and the p-type contact layer in which p-type impurities are diffused A semiconductor laser device, wherein an ohmic electrode is formed on each of an upper surface and a back surface of the substrate, and laser oscillation is performed in a direction perpendicular to the substrate. On a semi-conductor substrate, a semi-conductive multilayer mirror, n-type cladding layer, a narrow quantum well active layer than the forbidden band width of the substrate, p-type cladding layer, p-type contact layer is formed, the p-type contact layer A columnar upper multilayer reflector is formed, a semi-insulating region is provided immediately below the n-type cladding layer in a region not covered by the upper multilayer reflector , and the upper multilayer film A region from the surface of the p-type contact layer not covered by the reflecting mirror to the quantum well active layer is a p-type impurity diffusion region in which p-type impurities are diffused to be disordered. A p-side ohmic electrode is formed, and an n-side ohmic electrode is formed on the back surface of the substrate except for a laser beam emitting portion, so that laser oscillation occurs in a direction perpendicular to the substrate. Laser device. 3. The semiconductor laser device according to claim 1, wherein the columnar upper multilayer reflector is formed by alternately laminating dielectrics . 3. The semiconductor laser device according to claim 1, wherein the columnar upper multilayer reflector is an undoped semiconductor . On a semi-conductor substrate, a semi-conductive multilayer mirror, n-type cladding layer, a quantum well active layer, p-type cladding layer, p-type contact layer, and a step of laminating the upper multilayer mirror sequentially, upper multilayer A step of forming a mask having a predetermined shape on the mirror and etching the upper multilayer reflector into a columnar shape up to the p-type contact layer, and implanting proton ions directly below the n-type cladding layer using the mask of the etching step A step of implanting and diffusing p-type impurities from the surface of the p-type contact layer to the quantum well active layer using the mask of the etching step, and on the p-type contact layer in which the p-type impurities are diffused and on the back surface of the substrate And a step of forming ohmic electrodes, respectively, for manufacturing a semiconductor laser device. On a semi-conductor substrate, a semi-conductive multilayer mirror, n-type cladding layer, a quantum well active layer, p-type cladding layer, p-type contact layer, and a step of laminating the upper multilayer mirror sequentially, p-type contact layer A step of etching the upper multilayer reflector in a columnar shape up to the top, a step of implanting proton ions directly under the n-type cladding layer using the mask of the etching step, and a p-type contact layer using the mask of the etching step Injecting and diffusing p-type impurities from the surface to the quantum well active layer, forming a p-side ohmic electrode on the substrate surface excluding the top of the upper multilayer reflector in a self-aligned manner, and forming n on the back surface of the substrate Forming a side ohmic electrode. A method for manufacturing a semiconductor laser device, comprising:

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