JP3708213B2 - Semiconductor light emitting device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device such as a semiconductor laser or a light emitting diode used for an optical disc.
[0002]
[Prior art]
Since ZnSe II-VI compound semiconductors are semiconductor materials with a direct transition and a wide band gap, in recent years, semiconductor lasers that emit blue laser light using these materials (hereinafter referred to as “blue semiconductor lasers”) Is being actively developed. FIG. 13 is a cross-sectional view showing an example of the structure of a conventional blue semiconductor laser 1300 using a ZnSe-based II-VI group semiconductor material.
[0003]
Specifically, on an n-type GaAs substrate 131 doped with Si, an n-type ZnSe epitaxial layer 132 doped with Cl, an n-type ZnMgSSe cladding layer 133 doped with Cl, and an n-type ZnSSe optical waveguide layer doped with Cl 134, a ZnCdSe active layer 135, a p-type ZnSSe optical waveguide layer 136 doped with N, and a p-type ZnMgSSe cladding layer 137 doped with N are sequentially stacked. The p-type ZnMgSSe cladding layer 137 is formed so that a part thereof has a stripe shape, and a p-type ZnTe contact layer 138 doped with N is formed on the stripe portion. On the other hand, on the p-type ZnMgSSe cladding layer 137 other than the stripe portion, a polycrystalline SiO2 buried layer 139 is provided so as to sandwich the stripe portion from both sides. Further, a p-type AuPd electrode 1310 is provided on the p-type ZnTe contact layer 138 and the polycrystalline SiO 2 buried layer 139. On the other hand, an n-type In electrode 1311 is provided under the n-type GaAs substrate 131.
[0004]
[Problems to be solved by the invention]
The conventional blue semiconductor laser 1300 having the above structure has the following problems to be solved.
[0005]
First, the polycrystalline SiO 2 buried layer 139 used in the conventional blue semiconductor laser 1300 is formed by chemical vapor deposition or the like. However, the crystal growth temperature of ZnSe II-VI compound semiconductor materials is generally as low as about 250 ° C. Therefore, in the step of forming the polycrystalline SiO 2 buried layer 139 performed after the formation of the layer made of the ZnSe II-VI group compound semiconductor material, the crystal degradation of the ZnSe II-VI group compound semiconductor layer previously formed is performed. In order to prevent the occurrence of the above, the polycrystalline SiO 2 buried layer 139 must be formed at a temperature lower than the growth temperature of the ZnSe II-VI compound semiconductor layer.
[0006]
However, SiO2 formed at such a low temperature becomes a porous polycrystal. As a result, adhesion to a ZnSe layer or the like is extremely deteriorated, and peeling easily occurs. Therefore, there are many problems in using SiO2 as the insulating buried layer. Also, when the polycrystalline SiO2 buried layer 139 is used as a mask in etching, side etching or the like is likely to occur due to poor adhesion and its porous properties, and its utility value as a mask material is low.
[0007]
Secondly, since the thermal conductivity of polycrystalline SiO2 is very low, the generated heat cannot be efficiently dissipated. As a result, the laser oscillation threshold is increased and the lifetime of the light emitting element is shortened.
[0008]
The present invention has been made in view of the above problems, and its object is to (1) be formed on the epitaxial layer of the II-VI group semiconductor laser structure with good adhesion, and have high thermal conductivity and optical confinement. A semiconductor light emitting device that forms a buried layer using a material having a low refractive index that can be used for (2), and (2) a method of manufacturing such a semiconductor light emitting device.
[0009]
[Means for Solving the Problems]
The semiconductor light emitting device of the present invention includes a II-VI group semiconductor epitaxial layer, a ZnO layer provided on the II-VI group semiconductor epitaxial layer, and an oxide XO layer (insulator) other than ZnO on the ZnO layer. Layer) or a zinc compound ZnX layer, whereby the above object is achieved. In one embodiment, the II-VI group semiconductor epitaxial layer has a laser structure.
[0010]
According to another aspect of the present invention, a semiconductor light emitting device is provided with an active layer made of a II-VI group compound semiconductor, and the active layer sandwiched from above and below, and is made of a II-VI group compound semiconductor. First and second cladding layers, a ZnO buried layer formed on the first cladding layer, and an oxide XO layer (insulator layer) other than ZnO on the ZnO layer Or a zinc compound ZnX layer, whereby the above object is achieved.
[0011]
According to still another aspect of the present invention, a semiconductor light-emitting device includes a substrate, and an n-type cladding layer, an active layer, and a p-type cladding layer, each of which is sequentially epitaxially grown on the substrate and made of a II-VI group compound semiconductor. And the p-type contact layer, wherein the p-type contact layer is formed in a stripe shape, and the p-type clad layer has a portion on both sides of the striped p-type contact layer. Further, a buried layer made of an oxide XO layer other than ZnO and ZnO or a zinc compound ZnX layer is further formed, whereby the above object is achieved.
[0012]
According to still another aspect of the present invention, a semiconductor light emitting device includes a II-VI group semiconductor epitaxial layer, and the II-VI group semiconductor epitaxial layer includes a buried layer containing 1 × 10 14 cm −3 or more of oxygen atoms. Further, an oxide XO layer or a zinc compound ZnX layer is provided on the buried layer, thereby achieving the above object. In one embodiment, the II-VI group semiconductor epitaxial layer has a laser structure.
[0013]
The method for producing a semiconductor light emitting device of the present invention includes a step of forming a ZnO layer using plasma oxygen on the II-VI group semiconductor epitaxial layer, thereby achieving the above object.
[0014]
According to another aspect of the present invention, a method of manufacturing a semiconductor light emitting device includes immersing a metal member and a II-VI group semiconductor member in a solvent containing a NO3 compound, and the metal member is used as a positive electrode and the II-VI. Including a step of forming a ZnO layer on the surface of the II-VI group semiconductor member by applying a voltage between the two members using the group group semiconductor member as a negative electrode, thereby achieving the above object. The
[0015]
According to still another aspect of the present invention, a method for manufacturing a semiconductor light emitting device includes: an n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer each made of a II-VI group compound semiconductor on a substrate. A step of sequentially epitaxially growing, a step of etching the p-type contact layer in a stripe shape, and ZnO and ZnO on regions of the p-type cladding layer located on both sides of the stripe-shaped p-type contact layer. Forming a buried layer composed of an oxide XO layer or a zinc compound ZnX layer other than the above, thereby achieving the above object. In one embodiment, oxygen converted into plasma in the step of forming the buried layer is used. In another embodiment, in the step of forming the buried layer, the metal member and the II-VI group semiconductor member are immersed in a solvent containing a NO3 compound, and the metal member is used as the positive electrode and the II-VI group semiconductor member. As a negative electrode, a voltage is applied between the two members, thereby forming a ZnO layer on the surface of the II-VI group semiconductor member, and the ZnO layer is used as the buried layer.
[0016]
According to still another aspect of the present invention, a semiconductor light emitting device is provided with an active layer made of a II-VI group compound semiconductor and the active layer sandwiched from above and below, and the II-VI group compound semiconductor An upper clad layer and a lower clad layer, a buried layer formed by implanting oxygen ions formed on the upper clad layer, an oxide XO layer or a zinc compound ZnX layer on the buried layer; , Thereby achieving the above object.
[0017]
According to still another aspect of the present invention, a semiconductor light-emitting device includes a substrate, and an n-type cladding layer, an active layer, and a p-type cladding layer, each of which is sequentially epitaxially grown on the substrate and made of a II-VI group compound semiconductor. And the p-type contact layer, wherein the p-type contact layer is formed in a stripe shape, and the p-type clad layer has a portion on both sides of the striped p-type contact layer. A buried layer into which oxygen ions are implanted is further formed, and the above object is achieved by the oxide XO layer or the zinc compound ZnX layer on the buried layer.
[0018]
According to still another aspect of the present invention, the method for manufacturing a semiconductor light emitting device includes a step of implanting oxygen ions into a predetermined region of the II-VI group semiconductor epitaxial layer to form a buried layer, This achieves the above object.
[0019]
According to still another aspect of the present invention, a method for manufacturing a semiconductor light emitting device includes: an n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer each made of a II-VI group compound semiconductor on a substrate. A step of sequentially epitaxially growing, a step of etching the p-type contact layer in a stripe shape, and implanting oxygen ions into predetermined regions located on both sides of the stripe-shaped p-type contact layer in the p-type cladding layer Forming the buried layer and forming the oxide XO layer or the zinc compound ZnX layer on the buried layer, thereby achieving the above object.
[0020]
Specifically, in the present invention, a ZnO layer is formed on the II-VI group semiconductor epitaxial structure included in the blue semiconductor laser structure, and an oxide XO layer other than ZnO or a zinc compound ZnX layer is formed thereon. This is used as an insulating buried layer. This ZnO layer can be formed, for example, by using plasma oxygen. Alternatively, a metal member and a II-VI group semiconductor member are immersed in a solvent containing a NO3 compound, a voltage is applied between both members using the metal member as a positive electrode and a II-VI group semiconductor member as a negative electrode, Thereby, a ZnO layer can be formed on the surface of the II-VI group semiconductor member.
[0021]
Alternatively, according to the present invention, a layer containing 1 × 10 14 cm −3 or more of oxygen is provided in the II-VI group semiconductor epitaxial structure included in the blue semiconductor laser structure, and an oxide XO layer or a zinc compound ZnX is formed thereon. It is also possible to form a layer and make it an insulating buried layer. In this case, oxygen can be added using accelerated oxygen ions.
[0022]
The operation will be described below.
The ZnO layer used as a material for the insulating buried layer in the present invention is one of II-VI group compound semiconductor materials and has extremely good adhesion to materials such as ZnSe, ZnSSe, and ZnMgSSe. Further, since it is an oxide, it has good adhesion to oxides such as Al2O3 and SiO2. Moreover, it is excellent in acid resistance and oxidation resistance. Furthermore, there is almost no water absorption and it is excellent in stability of a shape and a dimension.
[0023]
ZnO has extremely good thermal conductivity, and its thermal conductivity value is nearly 30 times that of SiO2. Therefore, by using ZnO as the insulating buried layer, the heat generated in the active layer is efficiently dissipated through the ZnO insulating buried layer.
[0024]
Furthermore, although ZnO has a lower refractive index than ZnSe, ZnSSe, ZnMgSSe, etc., the difference is in an appropriate range.
[0025]
Specifically, for example, the refractive index of the cladding layer is typically about 2.5 to 2.6, whereas the refractive index of the ZnO layer constituting the insulating buried layer is about 2.2. . When the difference in refractive index existing between the cladding layer and the insulating buried layer is such a value, the single transverse mode can be obtained even if the width of the stripe portion of the cladding layer is increased to about 5 to 10 μm. Laser oscillation is realized satisfactorily. On the other hand, the conventional insulating buried layer made of SiO2 has a refractive index of about 1.4, and the refractive index difference with the cladding layer is large. Therefore, in order to realize stable single transverse mode laser oscillation, the stripe width formed in the cladding layer must be reduced to about 2 μm. However, it is difficult to form such a small stripe.
[0026]
Thus, the insulating buried layer made of the ZnO layer effectively functions as a lateral light confinement layer.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings.
[0028]
FIG. 1 is a sectional view showing the structure of a blue semiconductor laser 100 using a ZnSe II-VI group semiconductor according to the first embodiment of the present invention.
[0029]
In the semiconductor laser 100, an n-type ZnSe epitaxial layer 12 (thickness 0.03 μm) doped with Cl and an n-type ZnMgSSe cladding layer 13 (Zn0.9Mg0) doped with Cl are formed on an n-type GaAs substrate 11 doped with Si. 0.1S0.1Se0.9, thickness 1.0 μm), Cl-doped n-type ZnSSe optical waveguide layer 14 (ZnS0.06Se0.94, thickness 0.12 μm), ZnCdSe active layer 15 (Zn0.8Cd0.2Se, And a p-type ZnSSe optical waveguide layer 16 doped with N (ZnS0.06Se0.94, thickness 0.12 μm) are sequentially stacked.
[0030]
A p-type ZnMgSSe cladding layer 17 is formed on the p-type ZnSSe optical waveguide layer 16 so that a part thereof has a stripe shape, and p is doped with N on the stripe portion. A type ZnTe contact layer 18 is formed. On the other hand, on the p-type ZnMgSSe cladding layer 17 other than the stripe portion, a buried layer 19 having a laminated structure of polycrystalline ZnO and Al2O3 is provided so as to sandwich the stripe portion from both sides. Further, a p-type AuPd electrode 110 is provided on the p-type ZnTe contact layer 18 and the buried layer 19 having a multilayer structure of polycrystalline ZnO 19z (2000A) and Al2O3 19a (2000A). On the other hand, an n-type In electrode 111 is provided under the n-type GaAs substrate 11.
[0031]
Of the layers stacked as described above, the n-type ZnSe epitaxial layer 12 is not lattice-matched to the GaAs substrate 11, but is between the GaAs substrate 11 and the upper structure composed of a II-VI group semiconductor material. Functions as a buffer layer. On the other hand, the n-type ZnMgSSe cladding layer 13 and the n-type ZnSSe optical waveguide layer 14 stacked on the n-type ZnSe epitaxial layer 12 are lattice-matched with the GaAs substrate 11. The ZnCdSe active layer 15 laminated on the n-type ZnSSe optical waveguide layer 14 does not lattice match with the GaAs substrate 11, but its thickness is as small as 0.006 μm and less than the critical film thickness. The dislocation caused by is not generated.
[0032]
As described above, in the semiconductor laser 100 of the present embodiment, the buried layer 19 having a laminated structure composed of polycrystalline ZnO and Al2O3 is provided, and plays a role of current confinement and light confinement. Since ZnO and Al2O3 have good heat dissipation, it is possible to reduce the threshold current density and extend the lifetime of the device. Moreover, single transverse mode laser oscillation can be obtained by effective light confinement.
[0033]
In the present embodiment, the buried layer 19 is made of polycrystalline ZnO and Al2O3, but the same effect can be obtained even if it is made of single crystal ZnO and Al2O3. Similar effects can be obtained by using oxides such as SiO2, ZnO, TiO2, and ZrO2 instead of Al2O3. In short, any insulating layer may be used. Further, similar effects can be obtained by using a zinc compound such as ZnS, ZnSe, ZnTe or the like instead of Al2O3.
[0034]
Furthermore, although ZnO is used as the material of the buried layer 19 in the above description, polycrystalline ZnS can also be used as the material of the buried layer 19. However, polycrystalline ZnS is highly water-absorbing and tends to be altered by water absorption. Moreover, since it is fragile in terms of material strength, it has poor adhesion to ZnSe and the like. Therefore, it cannot be said that the utility value as an insulating buried layer or an etching mask material is very high. On the other hand, by forming the buried layer 19 from ZnO as in the present embodiment described above, the buried layer 19 having low water absorption and good adhesion to the II-VI group compound semiconductor material is obtained. Therefore, a semiconductor laser having a low threshold can be realized.
[0035]
Next, an example of a manufacturing process of the semiconductor laser 100 in the present embodiment will be described with reference to FIGS. 2 (a) to 2 (e). In the manufacturing process in the present embodiment described below, a molecular beam epitaxy method is used as a growth method of the ZnSe II-VI group semiconductor material.
[0036]
First, an n-type GaAs substrate 11 is prepared as shown in FIG. 2A, and an n-type ZnSe epitaxial layer 12 doped with Cl and Cl are formed on the GaAs substrate 11 as shown in FIG. 2B. Doped n-type ZnMgSSe cladding layer 13, Cl-doped n-type ZnSSe optical waveguide layer 14, ZnCdSe active layer 15, N-doped p-type ZnSSe optical waveguide layer 16, N-doped p-type ZnMgSSe cladding layer 17, and A p-type ZnTe contact layer 18 doped with N is sequentially epitaxially grown.
[0037]
Next, a pattern of the striped resist 112 is formed on the epitaxial layer obtained by epitaxial growth, specifically on the uppermost p-type ZnTe contact layer 18 by photolithography, and used as a mask. Then, the epitaxial layer is etched in a stripe shape. Specifically, as shown in FIG. 2C, the p-type ZnMgSSe cladding layer 17 doped with N and the p-type ZnTe contact layer 18 doped with N are saturated in a region not covered with the resist mask 112. Etch with bromine solution. The etchant is a mixed solution of saturated bromine water: phosphoric acid: water = 1: 2: 3.
[0038]
Thereafter, a buried layer 19 is formed by depositing a ZnO layer and then an Al2O3 layer on the entire surface of the wafer at room temperature using a sputtering method. After forming the buried layer 19 having a laminated structure of polycrystalline ZnO and Al2O3, the ZnO and Al2O3 layers deposited on the resist layer 112 and the resist layer 112 are removed using lift-off with acetone (FIG. 2D )reference). Thereafter, the p-type AuPd electrode 110 is formed over the entire upper surface of the wafer by vapor deposition as shown in FIG. Further, after that, an n-type In electrode 111 is deposited on the back side of the GaAs substrate 11 by vapor deposition. Thereby, the semiconductor laser 100 is formed.
[0039]
In the above description, the sputtering method is used to form the ZnO and Al2O3 layers.However, in order to increase the deposition rate of the ZnO and Al2O3 layers even when the process temperature is sufficiently low, plasma oxygen is used in the sputtering apparatus. It is effective to introduce. FIG. 3 shows a schematic diagram of an apparatus 300 used in forming ZnO and Al2O3 layers using plasmatized oxygen.
[0040]
In the configuration of FIG. 3, a wafer 31 made of a II-VI group semiconductor material is placed on an electrode 36 provided in a vacuum vessel 30. Further, a ZnO or Al 2 O 3 target 32 is disposed on the other electrode 37 so as to face the wafer 31. Further, the vacuum container 30 is provided with an argon gas introduction pipe 33, an oxygen gas introduction pipe 34, and an exhaust system 35.
[0041]
Specifically, in a state where the ZnO or Al2O3 target 32 is kept at a negative potential with respect to the wafer 31, a discharge gas, for example, Ar gas introduced into the vacuum vessel 30 is decompressed to cause discharge. As a result, Ar ions are accelerated and collided toward the ZnO or Al2O3 target 32 maintained at a negative potential. In this collision, ZnO or Al2O3 detached from the target 32 is deposited on the II-VI group semiconductor wafer (substrate) 31 located nearby.
[0042]
In the configuration of the apparatus 300 shown in FIG. 3, Ar gas is introduced into the vacuum vessel 30 from the argon gas introduction tube 33, and oxygen is introduced into the vacuum vessel 30 from the oxygen gas introduction tube 34. Oxygen converted into plasma by the discharge is taken into a ZnO or Al2O3 film deposited on the II-VI group semiconductor substrate 31. As a result, the escape of oxygen in the deposited ZnO or Al2O3 film can be prevented, and a high-quality ZnO or Al2O3 film can be obtained. Furthermore, even at low process temperatures, the deposition rate of ZnO or Al2O3 films increases several times compared to prior art deposition methods.
[0043]
In the manufacturing method according to the first embodiment of the present invention described above, the sputtering method is used to form the ZnO film. However, a method of obtaining a ZnO film by electrochemically oxidizing a II-VI group semiconductor substrate. Is also effective.
[0044]
FIG. 4 is a schematic diagram of an apparatus 400 used for electrochemical formation of a ZnO film.
The II-VI group semiconductor wafer (substrate) 41 and the electrode 43 are immersed in the electrolytic solution 42. As the electrolytic solution 42, a solution obtained by adding a salt such as KNO3 or NH4NO3 to a solvent such as ethylene glycol or N-methylacetamide is used. A voltage is applied between the electrodes 41 and 43 using the II-VI group semiconductor substrate 41 as a negative electrode and the electrode 43 made of a metal such as platinum as a positive electrode, and the surface of the semiconductor substrate 41 is oxidized.
[0045]
The oxidation mechanism is such that Zn ions leaving the interface between ZnSe and ZnO move and diffuse in the ZnO film by an electric field, and react with oxygen on the surface of the oxide film. The growth rate of the oxide film is almost proportional to the current density flowing through the circuit. Therefore, when oxidation is performed at a constant current, the voltage between the electrodes 41 and 43 gradually increases and dielectric breakdown of the ZnO film occurs, so that the film thickness that can be grown is limited. Typically, the limit is about 200 nm.
[0046]
By this method, a good quality ZnO film can be formed at room temperature without damaging the II-VI group semiconductor substrate 41.
[0047]
(Second Embodiment)
Below, the 2nd Embodiment of this invention is described with reference to drawings.
[0048]
FIG. 5 is a cross-sectional view showing the structure of the blue semiconductor laser 500 of this embodiment using a ZnSe II-VI group semiconductor.
[0049]
In the semiconductor laser 500, an n-type ZnSe epitaxial layer 52 doped with Cl, an n-type ZnMgSSe clad layer 53 doped with Cl, and an n-type ZnSSe optical waveguide layer doped with Cl on an Si-doped n-type GaAs substrate 51. 54, a ZnCdSe active layer 55, a p-type ZnSSe optical waveguide layer 56 doped with N, and a p-type ZnMgSSe clad layer 57 doped with N are sequentially stacked.
[0050]
The p-type ZnMgSSe cladding layer 57 is formed so that a part thereof has a stripe shape, and a p-type ZnTe contact layer 58 doped with N is formed on the stripe portion. On the other hand, on the p-type ZnMgSSe cladding layer 57 other than the stripe portion, a buried layer 59 in which oxygen ions are implanted so as to sandwich the stripe portion from both sides is provided. An Al2O3 layer 514 is formed on the buried layer 59 into which oxygen is ion-implanted. Further, a p-type AuPd electrode 510 is provided on the p-type ZnTe contact layer 58 and the buried layers 59 and 514. On the other hand, an n-type In electrode 511 is provided under the n-type GaAs substrate 51.
[0051]
As described above, in the semiconductor laser 500 of this embodiment, the oxygen ion-implanted layer 59 and the Al2O3 layer 514 are provided as buried layers, and play a role of current confinement and light confinement. Since such a layer has good heat dissipation, it is possible to reduce the threshold current density and extend the lifetime of the device.
[0052]
In addition, as in the case of the buried layer of the ZnO layer in the first embodiment, it is possible to ensure an appropriate range of refractive index difference with respect to the cladding layer. As a result, effective light confinement is realized, and good single transverse mode laser oscillation can be obtained.
[0053]
In this embodiment, the buried layer 514 is made of polycrystalline Al 2 O 3, but the same effect can be obtained even if it is made of single crystal Al 2 O 3. Similar effects can be obtained by using oxides such as SiO2, ZnO, TiO2, and ZrO2 instead of Al2O3. Further, similar effects can be obtained by using a zinc compound such as ZnS, ZnSe, ZnTe or the like instead of Al2O3.
[0054]
In the semiconductor laser 500 having this structure, continuous oscillation at room temperature is realized at a wavelength of about 500 nm. FIG. 6 is an example of a graph of current-light output characteristics obtained when continuous oscillation is performed at room temperature when the stripe width of the cladding layer 57 is 5 μm.
[0055]
Next, an example of a manufacturing process of the semiconductor laser 500 in the present embodiment will be described with reference to FIGS. 7 (a) to 7 (d). In the manufacturing process in the present embodiment described below, a molecular beam epitaxy method is used as a growth method of the ZnSe II-VI group semiconductor material.
[0056]
First, an n-type GaAs substrate 51 is prepared as shown in FIG. 7A, and an n-type ZnSe epitaxial layer 52 doped with Cl is formed on the GaAs substrate 51 as shown in FIG. A doped n-type ZnMgSSe cladding layer 53, a Cl-doped n-type ZnSSe optical waveguide layer 54, a ZnCdSe active layer 55, an N-doped p-type ZnSSe optical waveguide layer 56, an N-doped p-type ZnMgSSe cladding layer 57, and A p-type ZnTe contact layer 58 doped with N is sequentially epitaxially grown.
[0057]
Next, a striped resist 512 pattern is formed on the epitaxial layer obtained by epitaxial growth, specifically on the uppermost p-type ZnTe contact layer 58 by photolithography, and used as a mask. Then, as shown in FIG. 7C, oxygen ions 513 are implanted into the epitaxial layer.
[0058]
Thereafter, an Al2O3 layer 514 is deposited and formed on the entire surface of the wafer at room temperature using a sputtering method. After the formation of the polycrystalline Al2O3 layer 514, the Al2O3 layer 514 deposited on the resist layer 512 and the resist layer 512 is removed by using lift-off with acetone (see FIG. 7D). Thereafter, a p-type AuPd electrode 510 is formed over the entire upper surface of the wafer by vapor deposition as shown in FIG. Further, an n-type In electrode 511 is deposited on the back side of the GaAs substrate 51 by vapor deposition. Thereby, the semiconductor laser 500 is formed.
[0059]
The ion implantation conditions are set, for example, at an acceleration voltage of 90 V and a dose of 1 × 10 13 cm −2. In this case, the range calculated from the LSS theory is Rp = 0.14 μm. As a result, oxygen ions 513 are implanted into portions of the p-type ZnMgSSe cladding layer 57 and the p-type ZnTe contact layer 58 that are not covered with the resist 512, thereby forming an implanted layer 59.
[0060]
When oxygen is ion-implanted into a ZnSe II-VI group semiconductor, the dose is preferably 1 × 10 14 cm −2 or less and 5 × 10 12 cm −2 or more. If the dose is in this range, the oxygen impurity concentration in the region having a depth of 2Rp (0.28 μm) is 1 × 10 14 cm −3 or more, and this region has a high resistance. However, at doses larger than this range, the effect on the active layer due to irradiation damage defects peculiar to II-VI group semiconductor materials increases, making it difficult to obtain laser oscillation. Further, when the dose is smaller than this range, it is difficult to increase the resistance, and it cannot be used as an insulating buried layer.
[0061]
FIG. 8 shows the current-voltage characteristics of the layer 59 for the purpose of showing the insulating property of the layer 59 into which oxygen ions are implanted. From this, it can be seen that even when a voltage in the range of −20 V to +20 V is applied to the layer 59, no current flows and effective insulation is provided. In this embodiment, heat treatment is performed at 275 ° C. for 10 minutes after ion implantation, but this may be omitted depending on the dose.
[0062]
(Third embodiment)
The blue-green semiconductor laser is required to realize a stable fundamental transverse mode laser oscillation with a small astigmatic difference in order to be applied to a high-density optical disk memory or a laser printer. The index guide effect in the buried ridge structure is effective for realizing such characteristics. In the following, as a third embodiment of the present invention, an actual index guide type blue-green semiconductor laser that realizes stable transverse mode laser oscillation by using a ZnO buried layer to reduce the beam astigmatism will be described.
[0063]
FIG. 9A is a cross-sectional view showing a configuration of the ZnCdSe / ZnSSe / ZnMgSSeSCH index guide type laser 900 of the present embodiment.
[0064]
In the semiconductor laser 900, a Cl-doped n-type ZnSe epitaxial layer 92 (thickness 0.01 μm) and a Cl-doped n-type ZnMgSSe cladding layer 93 (Zn0.9Mg0) are formed on an Si-doped n-type GaAs substrate 91. .1S0.1Se0.9, thickness 2.0 μm), Cl-doped n-type ZnSSe optical waveguide layer 94 (ZnS0.06Se0.94, thickness 0.11 μm), ZnCdSe active layer 95 (Zn0.8Cd0.2Se, A p-type ZnSSe optical waveguide layer 96 (ZnS0.06Se0.94, thickness 0.12 μm) doped with N and a p-type ZnMgSSe cladding layer 97 are sequentially laminated.
[0065]
The p-type ZnMgSSe cladding layer 97 is formed so that a part thereof has a stripe shape. The thickness of the stripe portion is 0.74 μm, and the thickness of the other portions is 0.23 μm. On the stripe portion, a p-type ZnSSe layer 98 (ZnS0.06Se0.94, thickness 0.45 μm) lattice-matched to the GaAs substrate 91, a p-type ZnSe layer 99, and a multiplexing of p-type ZnTe and p-type ZeSe. A p-type ZnTe contact layer 912 doped with N is formed via the quantum well layer 911. On the other hand, a buried layer 913 made of ZnO and Al2O3 is provided on the p-type ZnMgSSe cladding layer 97 other than the stripe portion and on the side surface of the stripe portion. Further, a p-type AuPd electrode 914 is provided on the p-type ZnTe contact layer 912 and the buried layer 913 of polycrystalline ZnO and Al 2 O 3. On the other hand, an n-type In electrode 915 is provided under the n-type GaAs substrate 91.
[0066]
Among the layers stacked as described above, the n-type ZnSe epitaxial layer 92 is not lattice-matched to the GaAs substrate 91, but between the GaAs substrate 91 and the upper structure composed of a II-VI group semiconductor material. Functions as a buffer layer. On the other hand, the n-type ZnMgSSe cladding layer 93 and the n-type ZnSSe optical waveguide layer 94 stacked on the n-type ZnSe epitaxial layer 92 are lattice-matched with the GaAs substrate 91. In addition, the ZnCdSe active layer 95 laminated on the n-type ZnSSe optical waveguide layer 94 does not lattice match with the GaAs substrate 91, but its thickness is as small as 0.006 μm and less than the critical film thickness. The dislocation caused by is not generated.
[0067]
Further, the p-type ZnSSe layer 98 on the p-type ZnMgSSe cladding layer 97 is inserted to alleviate a sudden band offset change between the P-type ZnMgSSe layer 97 and the P-type ZnSe layer 99. In the multiple quantum well layer 911, as shown in FIG. 9B, ZnSe layers and ZnTe layers are alternately stacked. As a result, the composition change from the lower ZnSe layer 99 to the upper ZeTe layer 912 occurs. It is gradually happening.
[0068]
Thus, in the semiconductor laser 900 of this embodiment, the buried layer 913 made of ZnO and Al2O3 having a refractive index of about 2.2 is provided, and plays a role of current confinement and light confinement. Since ZnO has good heat dissipation, it is possible to reduce the threshold current density and extend the lifetime of the device. Moreover, single transverse mode laser oscillation can be obtained by effective light confinement.
[0069]
The epitaxial growth of each of the above layers is performed at a growth temperature of about 270 ° C. The ridge-type waveguide structure is formed using a load-locked electron cyclotron resonance (ECR) plasma etching system. The laser structure is formed using a discharge of Cl2 gas and H2 gas. Due to the anisotropic characteristics of ECR plasma etching, the side walls of the ridge portion can be made vertical and the surface can be smoothed, and a ridge pattern can be formed with high accuracy.
[0070]
The characteristics when the semiconductor laser 900 of this embodiment is pulse-driven at room temperature will be described below. Typically, the light output-current characteristics are kink free up to a range of 200 mA or higher. The threshold current value is about 200 mA.
[0071]
Further, the results of studying the far field pattern in the laser oscillation mode are described below. FIG. 10 is a graph showing lateral far-field pattern characteristics when a ridge having a width of 5 μm is provided.
[0072]
From this, it can be seen that even when the output is changed by changing the injection current over a wide range, the output beam has no astigmatic difference and has a constant far-field full angle. This shows that the actual index guide mode in the horizontal direction is established. Furthermore, the fact that the shape in the lateral direction is constant even when the injection current changes means that single transverse mode laser oscillation has been established in the range up to an output of 18 mW. The far-field radiation angle in the lateral direction is as narrow as about 7 degrees in the range above the threshold value.
[0073]
FIG. 11 shows the laser spot size in the vicinity of the laser output end, measured in a plane parallel to the bonding surface when the output is 3 mW.
[0074]
In general, the distance between the laser beam beam waist (that is, the portion where the laser spot diameter is the smallest) and the laser output end is referred to as an astigmatic difference. As shown in FIG. 11, in the semiconductor laser having the structure according to the prior art, the astigmatic difference is about 25 μm, whereas in this embodiment, the astigmatic difference is 0.5 μm or less due to the actual index guide type structure. is there. Therefore, according to the present embodiment, as shown in FIGS. 12A and 12B, the laser beam can be viewed from the side (FIG. 12A) or from the top (FIG. 12B). The beam waist is located on the laser emission end face. This makes it possible to minimize the beam spot diameter when the laser is focused by a lens.
[0075]
In the semiconductor laser in each embodiment described above, the width of the stripe provided in the cladding layer is typically about 5 μm.
[0076]
In the above description of the present embodiment, a ZnSe II-VI group semiconductor laser is shown as an example, but it goes without saying that the present invention can also be used in a ZnS II-VI group semiconductor laser.
[0077]
Further, the composition and thickness of each layer are not limited to the specific values mentioned in the above description.
[0078]
【The invention's effect】
In the present invention, a ZnO layer or a ZnSe-based semiconductor layer to which oxygen is added is used as a buried layer of a semiconductor laser. Thereby, the adhesion of the buried layer to the ZnSe-based semiconductor layer is improved, and heat dissipation is improved. Therefore, in the ZnSe blue semiconductor laser, unprecedented low threshold current density, long life, high power, high temperature operation, etc. are obtained, and the industrial value is extremely high.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a blue semiconductor laser according to a first embodiment of the present invention.
FIGS. 2A to 2E are cross-sectional views showing manufacturing steps of the blue semiconductor laser shown in FIG.
FIG. 3 is a cross-sectional view showing a configuration of a ZnO film forming apparatus using plasmad oxygen used in an embodiment of the present invention.
FIG. 4 is a cross-sectional view showing the configuration of an electrochemical ZnO film forming apparatus used in an embodiment of the present invention.
FIG. 5 is a sectional view showing a structure of a blue semiconductor laser according to a second embodiment of the present invention.
6 is a graph showing current-light output characteristics of the blue semiconductor laser shown in FIG.
7A to 7D are cross-sectional views showing manufacturing steps of the blue semiconductor laser shown in FIG.
8 is a graph showing current-voltage characteristics in a layer (buried layer) into which oxygen contained in the semiconductor laser shown in FIG. 5 is ion-implanted.
FIG. 9A is a sectional view of a blue semiconductor laser according to a third embodiment of the present invention.
(B) is the expanded sectional view which shows the structure of the multiple quantum well layer contained in the semiconductor laser shown to (a)
FIG. 10 is a diagram showing lateral far-field pattern characteristics in the semiconductor laser shown in FIG.
11 is a graph showing a change in beam spot diameter when the output is 3 mW measured on a plane parallel to the bonding surface in the vicinity of the laser end face of the semiconductor laser shown in FIG.
12 is a diagram schematically showing the shape of a beam waist in the semiconductor laser of the present invention shown in FIG. 9 (a).
(A) is a side view of the beam
(B) View of the beam from above
FIG. 13 is a sectional view showing the structure of a conventional blue semiconductor laser.
[Explanation of symbols]
100 Semiconductor laser
11 n-type GaAs substrate doped with Si
12 Cl doped n-type ZnSe epitaxial layer
13 Cl doped n-type ZnMgSSe cladding layer
14 Cl doped n-type ZnSSe optical waveguide layer
15 ZnCdSe active layer
16 N doped p-type ZnSSe optical waveguide layer
17 N doped p-type ZnMgSSe cladding layer
18 N doped p-type ZnTe contact layer
19 Buried layer consisting of multilayer structure of polycrystalline ZnO and Al2O3
110 p-type AuPd electrode
111 n-type In electrode
112 resist
31 II-VI group semiconductor wafer (substrate)
32 ZnO or Al2O3 target
33 Argon gas inlet tube
34 Oxygen gas introduction pipe
35 Exhaust system
36, 37 electrodes
41 II-VI group semiconductor wafer (substrate)
42 Electrolyte
43 Platinum electrode
500 Semiconductor laser
51 Si doped n-type GaAs substrate
52 Cl doped n-type ZnSe epitaxial layer
53 Cl doped n-type ZnMgSSe cladding layer
54 Cl doped n-type ZnSSe optical waveguide layer
55 ZnCdSe active layer
56 N doped p-type ZnSSe optical waveguide layer
57 N doped p-type ZnMgSSe cladding layer
58 N doped p-type ZnTe contact layer
59 Oxygen-implanted layer
510 p-type AuPd electrode
511 n-type In electrode
512 resist
513 oxygen ion
514 Al2O3 layer
900 Semiconductor laser
91 n-type GaAs substrate doped with Si
92 Cl doped n-type ZnSe epitaxial layer
93 Cl doped n-type ZnMgSSe cladding layer
N-type ZnSSe optical waveguide layer doped with 94 Cl
95 ZnCdSe active layer
96 N doped p-type ZnSSe optical waveguide layer
97 N doped p-type ZnMgSSe cladding layer
911 p-type ZnTe / ZnSe multiple quantum well layer
912 N doped p-type ZnTe contact layer
913 ZnO buried layer
914 p-type AuPd electrode
915 n-type In electrode

Claims (15)

II-VI semiconductor epitaxial layer,
A ZnO layer provided on the II-VI semiconductor epitaxial layer;
An insulator layer other than ZnO provided on the ZnO layer;
A semiconductor light emitting device , wherein the II-VI group semiconductor epitaxial layer has a laser structure . An active layer made of a II-VI compound semiconductor;
A first clad layer and a second clad layer which are provided so as to sandwich the active layer from above and made of a II-VI group compound semiconductor;
A ZnO buried layer formed on the first cladding layer;
An insulator layer other than ZnO formed on the ZnO buried layer;
A semiconductor light emitting device comprising: A substrate,
An n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer, each of which is sequentially epitaxially grown on the substrate and made of a II-VI group compound semiconductor,
The p-type contact layer is formed in a stripe shape,
A semiconductor light emitting element, wherein a buried layer made of an insulating layer other than ZnO and ZnO is further formed on portions of the p-type cladding layer located on both sides of the striped p-type contact layer.   The semiconductor light emitting element according to claim 2, wherein the insulator layer is an oxide of Si, Al, Ti, and Zr.   A method for manufacturing a semiconductor light emitting device, comprising a step of forming a ZnO layer and an insulator layer other than ZnO using plasma-ized oxygen on a II-VI group semiconductor epitaxial layer. A metal member and a II-VI semiconductor member are immersed in a solvent containing a NO ₃ compound, and a voltage is applied between the two members using the metal member as a positive electrode and the II-VI group semiconductor member as a negative electrode. And thereby forming a ZnO layer on the surface of the II-VI group semiconductor member;
Forming an insulating layer other than ZnO on the ZnO layer. A step of sequentially epitaxially growing an n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer each made of a II-VI group compound semiconductor on the substrate;
Etching the p-type contact layer in stripes;
Forming a buried layer made of an insulator other than ZnO and ZnO on regions of the p-type cladding layer located on both sides of the striped p-type contact layer;
A method for manufacturing a semiconductor light emitting device, comprising:   The method for manufacturing a semiconductor light emitting element according to claim 7, wherein plasmaized oxygen is used in the step of forming the buried layer. II-VI semiconductor epitaxial layer,
A ZnO layer provided on the II-VI semiconductor epitaxial layer;
An insulating zinc compound ZnX layer other than ZnO provided on the ZnO layer; and
A semiconductor light emitting device , wherein the II-VI group semiconductor epitaxial layer has a laser structure . An active layer made of a II-VI compound semiconductor;
A first clad layer and a second clad layer which are provided so as to sandwich the active layer from above and made of a II-VI group compound semiconductor;
A semiconductor light emitting device comprising: a ZnO buried layer formed on the first cladding layer; and an insulating zinc compound ZnX layer other than ZnO provided on the ZnO layer. A substrate,
An n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer, each of which is sequentially epitaxially grown on the substrate and made of a II-VI group compound semiconductor;
With
The p-type contact layer is formed in a stripe shape,
A buried layer made of ZnO and an insulating zinc compound ZnX layer other than ZnO is further formed on portions of the p-type cladding layer located on both sides of the striped p-type contact layer. , Semiconductor light emitting device. The semiconductor light emitting element according to claim 10 or 11, wherein the zinc compound ZnX layer is ZnS, ZnSe, or ZeTe . A step of sequentially epitaxially growing an n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer each made of a II-VI group compound semiconductor on the substrate;
Etching the p-type contact layer in stripes;
Forming a buried layer made of an insulating zinc compound ZnX other than ZnO and ZnO on regions of the p-type cladding layer located on both sides of the striped p-type contact layer. A method for manufacturing a semiconductor light emitting device.   The method for manufacturing a semiconductor light emitting element according to claim 13, wherein plasmaized oxygen is used in the step of forming the buried layer. In the step of forming the buried layer, the metal member and the II-VI group semiconductor member are immersed in a solvent containing a NO ₃ compound, and both the metal member is used as a positive electrode and the II-VI group semiconductor member is used as a negative electrode. A voltage is applied between the members, whereby a ZnO layer is formed on the surface of the II-VI group semiconductor member, and the insulating zinc compound ZnX layer other than ZnO layer and ZnO is used as the buried layer. A method for manufacturing a semiconductor light emitting device according to claim 13.

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