JP4192324B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device and a manufacturing method thereof.
[0002]
[Prior art]
Semiconductor laser elements are currently widely used in fields such as optical communication, optical recording, and optical information processing. One of the waveguide structures of such a semiconductor laser device is a ridge waveguide structure. The ridge waveguide structure has been widely used as a structure of various types of semiconductor laser elements since it has a practical level of good characteristics with a relatively simple manufacturing process.
[0003]
On the other hand, a refractive index waveguide structure frequently used in a long-wavelength laser element using an InP substrate has a structure in which the active layer is etched in a stripe shape and then the periphery thereof is buried with another semiconductor layer. If this structure is adopted in a semiconductor laser device having a wavelength of 1 μm or less manufactured using a GaAs substrate, a characteristic failure often occurs due to the etching interface of the active layer. There are various ridge waveguide structures. Examples of such a semiconductor laser element include a red visible light laser and a 0.98 μm band laser for exciting an erbium-doped optical fiber amplifier.
[0004]
In the ridge waveguide structure, the cladding layer is etched into a mesa structure for ridge formation. The depth at which the clad layer is etched during this mesa etching defines the strength of confinement in the transverse waveguide mode, and is a factor that determines the laser element characteristics. For this reason, the reproducibility of the etching depth and the in-plane uniformity of the etching depth have a great influence on the uniformity of the device characteristics and the manufacturing yield. As described above, since the mesa etching depth is required to have high reproducibility and in-plane uniformity, sufficient care is taken in handling the etching solution that affects the etching characteristics.
[0005]
[Problems to be solved by the invention]
This etching solution is susceptible to the etching rate if the temperature, concentration, chemical mixing ratio, etc. of the solution slightly vary. In addition, due to the difference in the stirring rate of the etching solution between the central portion and the peripheral portion of the wafer, a non-negligible difference occurs in the etching rate within the wafer surface.
[0006]
In order to improve the non-uniformity of the etching depth due to these reasons and the poor reproducibility, a method of providing an etching stop layer at a desired position in the cladding layer is usually used. The etching stop layer is a thin semiconductor layer formed using a material having a sufficiently low etching rate with respect to the etching solution of the cladding layer, that is, a high etching selectivity. When an etching stop layer is inserted, a large rate difference can be provided in the etching rate of the etching stop layer with respect to the etching rate of the clad layer to be etched. For this reason, even if fluctuations and in-plane differences occur in the etching rate of the cladding layer, the etching rate is very slow when the mesa etching reaches the etching stop layer, so that the etching is substantially stopped. As a result, good reproducibility and in-plane uniformity with respect to the etching depth can be obtained.
[0007]
In a short-wave laser element manufactured using a GaAs substrate, a semiconductor such as AlGaInP or GaInP that can be lattice-matched to the GaAs substrate is used as one of typical cladding materials. Conventionally, as a material for an etching stop layer that can ensure a selection ratio with respect to such an etching solution of a clad material (hydrochloric acid-based etching solution), for the reasons of lattice matching and ease of crystal growth, JP-A-3- As described in Japanese Patent No. 222488, a GaAs semiconductor was exclusively used.
[0008]
Since the difference between the band gap of the AlGaInP semiconductor or GaInP semiconductor used for the cladding layer and the band gap of the GaAs semiconductor used for the etching stop layer is large, when the GaAs semiconductor layer is used as the etching stop layer, the cladding layer And a large hetero-barrier generated due to the difference in the band gap is formed at each interface of the etching stopper layer.
[0009]
In other words, when two semiconductor layers with different band gaps are crystallographically coupled, a band structure is formed in which the Fermi levels in each layer coincide with each other, resulting in band edge energy discontinuities at the heterojunction interface. Is done. These are called spikes and notches, projecting in a wedge shape toward the conduction band and valence band of the energy band diagram, forming a heterobarrier, and this part is against the electrons in the conduction band and in the valence band. Acts as an electrical resistance to the holes because they become barriers ΔEc and ΔEv, respectively. Reference 1 (M. Ohkubo et.al. IEEE J. Quantum Electron., Vol. 30, No. 2, pp. 408 to 414, 1994) describes that a GaInP semiconductor or an AlGaInP semiconductor is used for the cladding and GaAs is used for the etching stop layer. It has been reported that when a semiconductor is used, a large hetero barrier is generated particularly for holes.
[0010]
In order to further increase the output and reliability of the semiconductor laser device having such a structure, it is necessary to reduce the electric resistance caused by such a hetero barrier. As a material capable of lowering the hetero barrier, a semiconductor material having a larger band gap than a GaAs semiconductor is preferable. As such a material, a GaInAsP semiconductor described in JP-A-7-111363 can be considered.
[0011]
However, in the case of GaInAsP semiconductors, there are so-called miscibility gaps. In the non-miscible region, since the crystal system to be grown is thermodynamically unstable, the constituent elements do not easily melt together during the growth of the semiconductor crystal. According to Reference 2 (K. Onabe, Japanese Journal of Applied Physics, vol. 21, No. 5, pp 797-798, 1982), in the case of a GaInAsP semiconductor lattice-matched to a GaAs substrate, it is used for normal crystal growth 600. In the temperature range of ˜700 ° C., an immiscible region exists in the range of the band gap of 1.6 to 1.8 eV which is optimum as an etching stop layer. Therefore, it is more difficult than usual to form a good GaInAsP semiconductor crystal having a band gap in such a range, and strict control of temperature, pressure, raw material flow rate, etc. during crystal growth is required. For this reason, much labor is required to determine suitable conditions for crystal growth. In addition, since the GaInAsP semiconductor has many constituent elements such as quaternary elements, it is necessary to determine a large number of parameters according to the number of constituent elements for crystal growth. Therefore, it took much time to optimize the growth conditions.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser device including an etching stop layer including a semiconductor material that has fewer constituent elements than a GaInAsP semiconductor and does not have any restrictions due to an immiscible region with respect to a band gap, and a method for manufacturing the same. That is.
[0013]
[Means for Solving the Problems]
In the semiconductor laser device that achieves such an object, since there is no immiscible region in the phase diagram of the semiconductor material of the intermediate layer to be grown, there is a band gap range that can be formed regardless of the limitations caused by the immiscible region. Has been extended. For this reason, in the semiconductor laser device having such an etching stop layer, the degree of freedom in setting the band gap value is increased, so that the internal resistance due to the hetero barrier can be reduced more easily than in the past. Therefore, the heat generation of the semiconductor laser element can be reduced more than ever before.
[0014]
In order to achieve such an object and to lower the heterobarrier, a material having a band gap larger than that of a GaAs semiconductor and having no immiscible region and capable of easily crystal growth on a cladding layer is required.
[0015]
As such a semiconductor material, conventionally, a semiconductor material having a composition that lattice-matches with a substrate or an underlying semiconductor has been adopted. However, what is required of the semiconductor material to be adopted is that the band gap required by the semiconductor laser element is practically not a lattice defect such as misfit transition, rather than having a lattice matching composition within the range of the composition used. It is within the range of the composition that does not cause crystal defects due to matching. Therefore, the present invention has the following configuration.
[0016]
The semiconductor laser device of the present invention includes (1) an active layer provided on a semiconductor substrate, and (2) a first cladding layer provided on the active layer and including at least one of an AlGaInP semiconductor and a GaInP semiconductor; (3) an intermediate layer provided on the first cladding layer and including a GaAsP semiconductor; and (4) a second cladding layer provided on the intermediate layer and including at least one of an AlGaInP semiconductor and a GaInP semiconductor; With The band gap of the intermediate layer is substantially the same as at least one of the band gaps of the first and second cladding layers. The
[0017]
In this way, the first and second cladding layers are formed of at least one of the AlGaInP semiconductor and the GaInP semiconductor, and GaAsP (GaAs _x P _1-x ) An intermediate layer containing a semiconductor is provided between the first and second cladding layers. Therefore, the band gap of the intermediate layer can be made larger than the band gap of the GaAs semiconductor by changing the composition ratio x of As and P of the intermediate layer. Therefore, compared to the case where a GaAs semiconductor is used for the intermediate layer, the hetero barrier formed at the interface between the first and second cladding layers and the intermediate layer is reduced.
[0018]
In addition, the GaAsP semiconductor used for the intermediate layer does not have an immiscible region as seen in the GaInAsP semiconductor at a temperature range of 200 ° C. or higher as described in, for example, Document 1. Since the formation of the GaAsP semiconductor is not performed below 200 ° C., there is no restriction due to the immiscible region found in the GaInAsP semiconductor when adopting a band gap suitable for the intermediate layer. Therefore, as compared with a GaInAsP semiconductor, it is much easier to find conditions for obtaining a good crystal.
[0019]
In the semiconductor laser device of the present invention, the intermediate layer may have a lattice irregularity within a range of ± 2% with respect to the semiconductor substrate.
[0020]
Since the thickness of the intermediate layer is thin, the generation of crystal defects due to lattice mismatch can be suppressed if the lattice constant of the intermediate layer is included in such a range. In this case, since the lattice matching condition is relaxed to such a range, the degree of freedom in selecting the band gap value of the intermediate layer is further increased. For example, the thickness of such an intermediate layer is preferably about 5 to 10 nm, particularly about 5 nm.
[0021]
For example, in a short-wave semiconductor laser element, a GaAs semiconductor is used as a substrate. GaAs _x P _1-x A semiconductor has a smaller lattice constant than a GaAs semiconductor except for x = 1. For this reason, it has a negative (tensile) strain with respect to the GaAs semiconductor. Since the GaAsP semiconductor can take a wide band gap value from about 1.42 to about 2 eV within the range of the strain amount within −2%, the degree of freedom in selecting the band gap value of the intermediate layer is increased.
[0022]
In the semiconductor laser device of the present invention, the band gap of the intermediate layer may be substantially the same as at least one of the band gaps of the first and second cladding layers.
[0023]
By adjusting the band gap of the intermediate layer in this way, the hetero barrier can be reduced to nearly zero, and the resistance due to this barrier is further reduced.
[0024]
In the semiconductor laser device of the present invention, the active layer may include at least one of a GaInAs semiconductor and a GaInAsP semiconductor and have a strained quantum well structure.
[0025]
As described above, when the active layer is formed of a strained quantum well structure of a GaInAs semiconductor, the present invention can be applied to a semiconductor laser having a wavelength of 0.98 μm where high output is indispensable for exciting an erbium-doped optical fiber amplifier. In this semiconductor laser, laser oscillation conditions such as threshold gain are improved by the effect of compressive strain applied to the GaInAs semiconductor. This improvement works synergistically with the effect of reducing the hetero-barrier between the clad and the intermediate layer by using the GaAsP semiconductor for the intermediate layer, so that the output characteristics are greatly improved and the output of the semiconductor laser device is increased. In addition, in the case of using a strained quantum well structure of a GaInAsP semiconductor, in addition to the same function, the number of constituent elements in the GaInAsP semiconductor is larger than that in the GaInAs semiconductor. It can be changed greatly depending on the situation. For this reason, the freedom degree of design can further be increased.
[0026]
A method of manufacturing a semiconductor laser device according to the present invention is a method of manufacturing a semiconductor laser device including a first cladding layer and a second cladding layer on an active layer provided on a substrate, and (1) on the active layer Providing a first cladding layer, (2) providing an intermediate layer on the first cladding layer, and (3) providing a second cladding layer on the intermediate layer, The band gap of the intermediate layer is substantially the same as at least one of the band gaps of the first and second cladding layers, The first cladding layer and the second cladding layer include at least one of an AlGaInP semiconductor and a GaInP semiconductor, and the intermediate layer includes a GaAsP semiconductor.
[0027]
Conventionally, when an GaAs layer is grown as an etching stop layer on a clad layer made of a semiconductor such as AlGaInP or GaInP, for example, using an OMVPE growth apparatus, an arsenic GaAs semiconductor is formed on the phosphorous AlGaInP or GaInP semiconductor layer. Since the layer is directly grown, it is necessary to discontinuously switch the source element from phosphorus to arsenic when starting the growth of the GaAs etching stop layer. For this reason, crystallinity such as so-called surface turbidity is likely to be deteriorated, and in order to obtain a semiconductor layer with good crystallinity, growth conditions such as the growth temperature and the timing of changing the raw material must be fully studied. Alternatively, a buffer layer must be inserted between the AlGaInP and GaInP semiconductor layers and the GaAs semiconductor layer to prevent the deterioration of crystallinity.
[0028]
However, the GaAsP semiconductor constituting the intermediate layer contains both As and P. For this reason, when starting the formation of the intermediate layer on the clad layer containing either one of the AlGaInP semiconductor and the GaInP semiconductor, and when starting the formation of the clad layer on the intermediate layer, discontinuity of the raw materials of phosphorus and arsenic Switching is not necessary, and the above-described crystal deterioration does not occur. Therefore, it becomes easy to form the intermediate layer directly on the cladding layer without adopting a troublesome process such as insertion of the buffer layer. In addition, since there is no immiscible region in the GaAsP semiconductor that is a problem in the GaInAsP semiconductor in the normal growth temperature range, it is possible to more easily determine suitable crystal growth conditions. Further, since the number of constituent elements of the GaAsP semiconductor is smaller than that of the GaInAsP semiconductor, the parameters to be controlled at the time of crystal growth are reduced, so that the growth conditions can be easily determined.
[0029]
The semiconductor laser device manufacturing method of the present invention may further include a step of selectively etching the second cladding layer with respect to the intermediate layer.
[0030]
As described above, when the second cladding layer is selectively etched with respect to the intermediate layer, a clad layer having a predetermined depth, for example, a mesa stripe shape is formed with good uniformity and reproducibility.
[0031]
Further, a step of selectively etching the intermediate layer with respect to the first cladding layer may be further provided.
[0032]
As described above, when the intermediate layer is etched, carriers injected through the second upper clad layer are prevented from leaking to other than the central mesa stripe region through the intermediate layer. For this reason, a good current confinement is realized toward the stripe portion which becomes the light emitting region.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail while showing a case where a semiconductor laser element is formed on a semiconductor substrate. This embodiment is merely an example, and the present invention is not limited to this. Where possible, the same parts are denoted by the same reference numerals, and redundant description is omitted.
[0034]
FIG. 1 is a perspective view showing an embodiment representing the structure of a semiconductor laser device 1 according to the present invention. Referring to FIG. 1, a first conductivity type lower cladding layer 4 is provided on a first conductivity type semiconductor substrate (hereinafter referred to as a substrate) 2, and an undoped first separation is provided on the first conductivity type lower cladding layer 4. A confinement heterostructure layer (hereinafter referred to as a lower SCH layer) 6 is provided, an undoped active layer 8 is provided on the lower SCH layer 6, and an undoped second separated confinement heterostructure layer (hereinafter referred to as an “undoped” active layer 8). 10 (referred to as the upper SCH layer). The active layer 8 is provided between the lower SCH layer 6 and the upper SCH layer 10, and one surface of each of the SCH layer 6 and the SCH layer 10 is in contact with each of the two opposing surfaces of the active layer. The SCH layers 6 and 10 act to confine carriers (electrons and holes) to the active layer 8 by the respective band gaps.
[0035]
On the active layer 8, a second conductivity type first upper clad layer 12, a second conductivity type second upper clad portion 20, and a second conductivity type intermediate layer portion 22 are provided. The first upper cladding layer 12 is provided on the active layer 8, the intermediate layer part 22 is provided on the first upper cladding layer 12, and the second upper cladding part 20 is provided on the intermediate layer part 22. Yes. One surface of each of the first upper clad layer 12 and the second upper clad portion 20 is in contact with a pair of opposed surfaces of the intermediate layer portion 22. The other surface facing one surface of the lower SCH layer 6 is in contact with one surface of the lower cladding layer 4. The other surface facing the one surface of the upper SCH layer 10 is in contact with the one surface of the first upper clad layer 12. Therefore, the clad layers 4 and 12 have a smaller refractive index than the layers sandwiched between these layers 4 and 12 (the lower SCH layer 6, the active layer 8, and the upper SCH layer 10). The active layer 8 and the upper SCH layer 10 act to confine light. In the active layer 8, electrons and holes injected from the upper and lower cladding layers 4 and 12 through the upper and lower SCH layers 6 and 10 are recombined to generate light.
[0036]
Since the material of the intermediate layer part 22 is larger than the band gap value of the GaAs semiconductor, the hetero barrier between the intermediate layer part 22 and the first upper clad layer 12 and the second upper clad part 20 sandwiching the intermediate layer part 22 is made of GaAs semiconductor. Compared to the case where it is used as the material of the intermediate layer, it is reduced. For this reason, the resistance resulting from these interfaces is reduced. It is particularly preferable that the band gap value of the intermediate layer portion 22 is the same value as the band gap values of the first upper cladding layer 12 and the second upper cladding portion 20, and this resistance can be reduced to near zero.
[0037]
Further, the second upper clad part 20 and the intermediate layer part 22 extend along the layer in which carriers are to be injected into the active layer 8 and are provided in a mesa shape on the first upper clad layer 12. . That is, these portions 20 and 22 are provided along an axis that reaches the reflection end face 42 facing the end face from the emission end face 40 of the semiconductor laser element 1 on the waveguide where light is generated by recombination of injected carriers. This axis is orthogonal to the respective end faces 40, 42. The emission end face 40 and the reflection end face 42 constitute an optical resonator of the semiconductor laser element.
[0038]
The second upper clad portion 20 and the intermediate layer portion 22 extending in a stripe shape in this way extend in the axial direction and are opposed to the surface facing the active layer 8. Is in contact with. The first conductivity type current blocking layer 24 is provided on the first upper cladding layer 12. A second conductivity type contact layer 26 is provided on the second upper clad portion 20 and the current blocking layer 24. On the contact layer 26, an ohmic electrode 28 for the second conductivity type semiconductor layer is provided. On the back surface of the first conductivity type substrate 2, an ohmic electrode 30 for the first conductivity type semiconductor layer is provided.
[0039]
The operation of such a semiconductor laser device 1 will be described below. The carriers from the ohmic electrode 28 are provided with the current blocking layer 24 sandwiching the second upper clad portion 20 and the conductivity type opposite to that of the first upper clad layer 12 and the second upper clad portion 20. Therefore, under the forward bias condition of the semiconductor laser element 1, it passes through the region of the second upper cladding layer 20 having a width of several μm and reaches the active layer 8. That is, a ridge structure is employed so as to realize current confinement. For this reason, the thickness of the second upper cladding portion 20 is determined according to the characteristics of the semiconductor laser element 1.
[0040]
The thickness of the main semiconductor layer of such a semiconductor laser device 1 is exemplarily shown below.
Lower cladding layer 4: 1.5 μm
Active layer 8: 8 nm
Lower SCH layer 6: 47 nm
Upper SCH layer 10: 47 nm
First upper cladding layer 12: 0.6 μm
Second upper clad portion 20: 0.9 μm
Intermediate layer part 22: 5 nm
It is.
[0041]
Next, a method for manufacturing the semiconductor laser device 1 according to the present invention will be described in detail with reference to the process cross-sectional views shown in FIGS. The following description is made on the case of using an n-type GaAs substrate and a GaInAs semiconductor as the active layer material, but the present invention is not limited to this.
[0042]
A stacked structure of semiconductor layers is formed on the n-type GaAs substrate 52 (semiconductor layer deposition step). Referring to FIG. 2A, an n-type GaInP lower cladding layer 54 is formed on an n-type GaAs substrate 52. The lower cladding layer 54 is a semiconductor layer deposited so as to cover the substrate 52. On the lower cladding layer 54, an undoped GaInAsP lower SCH layer 56, an undoped GaInAs active layer 58, and an undoped GaInAsP upper SCH layer 60 are sequentially formed. The undoped GaInAsP lower SCH layer 56 is a semiconductor layer deposited over the lower cladding layer 54, the undoped GaInAs active layer 58 is a semiconductor layer deposited over the lower SCH layer 56, and the undoped GaInAsP upper SCH layer 60 is A semiconductor layer deposited over the active layer 58.
[0043]
Next, a p-type GaInP upper first cladding layer 62, a p-type GaAsP intermediate layer 64, and a p-type GaInP upper second cladding layer 66 are sequentially formed. The upper first cladding layer 62 is a semiconductor layer deposited over the upper SCH layer 60, and the p-type GaAsP intermediate layer 64 is a semiconductor layer deposited over the upper first cladding layer 62, and is p-type. The GaInP upper second cladding layer 66 is a semiconductor layer deposited so as to cover the p-type GaAsP intermediate layer 64.
[0044]
These semiconductor layers are grown using, for example, metal organic vapor phase epitaxy (OMVPE). The n-type GaInP lower clad layer 54, the undoped GaInAsP lower SCH layer 56, the undoped GaInAsP upper SCH layer 60, the p-type GaInP first upper clad layer 62, and the p-type GaInP second upper clad layer 66 are respectively connected to the GaAs substrate. The lattice constants are preferably matched. In this way, a semiconductor with good crystallinity can be obtained. On the other hand, the undoped GaInAs active layer 58 has a lattice constant of about 1% relative to the n-type GaAs substrate 52 so that compressive strain is applied to the respective semiconductor layers of the undoped GaInAsP lower SCH layer 56 and the undoped GaInAsP upper SCH layer 60. Is determined to have a large composition. In this way, since an active layer having a strained single quantum well structure is formed, a laser light oscillation wavelength in the 0.98 μm band can be obtained. An active layer having a multiple quantum well structure may be formed. The active layer 58 can also be formed so as to be lattice-matched to the substrate.
[0045]
The p-type GaAsP intermediate layer 64 is determined to have a composition containing a strain of up to −2% corresponding to the band gap value required as an etching stop layer. Since the etching stop layer is a thin semiconductor layer, for example, a 5 nm semiconductor layer, a crystal defect caused by lattice mismatch does not occur if the strain is within ± 2%. Therefore, a semiconductor layer having a band gap value that can be formed in the range of the lattice irregularity is formed.
[0046]
In the above embodiment, the case where a GaInP semiconductor is used as the semiconductor material of the clad layer is exemplified, but an AlGaInP semiconductor can also be used. When a GaInP semiconductor is used, the number of constituent elements is as small as 3 elements, so that it is easy and easy to determine the growth conditions, and a semiconductor layer having good crystallinity can be obtained relatively easily using a normal crystal growth apparatus. In addition, it has already been widely used in visible light semiconductor lasers, etc., and has a track record as a material. In addition, when an AlGaInP semiconductor is used, a larger band gap can be realized as compared with a GaInP semiconductor. Therefore, when this is used as a clad material, the confinement of carriers in the light emitting region is further improved, and laser characteristics such as higher output are obtained. Further improvement is expected. In addition, it has already been widely used in visible light semiconductor lasers, etc., and has a track record as a material.
[0047]
p-type GaAs _x P _1-x In this embodiment, the intermediate layer 64 has a tensile strain of about −0.8% at x = 0.78, and the band gap value is about 1.68 eV if the lattice strain and the quantum size effect are ignored. . Actually, the band gap value is reduced by the contradictory actions of the decrease in the band gap value due to the lattice irregularity (decrease due to the pulling effect) and the increase in the band gap value due to the fact that the intermediate layer is a thin film (increase due to the quantum size effect). However, a semiconductor layer having a larger bandgap value than a GaAs semiconductor conventionally used for an intermediate layer is formed. Therefore, the hetero barrier generated between the cladding layer and the intermediate layer can be greatly reduced.
[0048]
In addition, p-type GaAs _x P _1-x Since the intermediate layer 64 may be very thin, if the lattice mismatch with respect to the GaAs substrate is within −2%, good crystallinity is maintained without inducing the occurrence of crystal defects such as misfit dislocations. The thickness of such an intermediate layer is preferably in the range of 5 nm to 10 nm, particularly about 5 nm. If lattice mismatch is allowed in such a range, the degree of freedom in designing the band gap value of the intermediate layer increases. For this reason, almost the same band gap value can be realized for GaInP and AlGaInP. As an example of the composition for realizing the same band gap value of 1.88 eV as that of the GaInP cladding layer, a semiconductor layer having a lattice mismatch of −1.4% is formed when x = 0.61. For this reason, the hetero barrier between the cladding layer and the intermediate layer can be substantially eliminated. Therefore, the series resistance in the semiconductor laser element can be further reduced. In actual manufacturing, the band gap value of GaAsP slightly varies depending on the tensile strain and the quantum size effect, but by adjusting the composition ratio x, it is possible to realize a band gap substantially the same as that of the cladding layer.
[0049]
The GaAsP semiconductor constituting the intermediate layer includes both As and P. For this reason, when starting the formation of the intermediate layer on the clad layer including any one of the AlGaInP semiconductor and the GaInP semiconductor, and when starting the formation of the clad layer on the intermediate layer, phosphorus and arsenic which are raw material elements Discontinuous switching becomes unnecessary. For this reason, the deterioration of crystallinity such as so-called surface turbidity, which has occurred in the case of using a conventional GaAs semiconductor layer as an intermediate layer, the growth temperature and the timing of material switching in order to obtain a semiconductor layer with good crystallinity, etc. Problems such as sufficient examination of the growth conditions or insertion of a buffer layer between the AlGaInP and GaInP semiconductor layers and the GaAs semiconductor layer are eliminated. In addition, since there is no immiscible region in the GaAsP semiconductor, there is no restriction on the band gap value required for the intermediate layer. In this respect, the GaInAsP semiconductor is superior. Furthermore, since the number of constituent elements in a GaAsP semiconductor is smaller than that in a GaInAsP semiconductor, parameters to be controlled during crystal growth are reduced. For this reason, it has the advantage that determination of the optimized growth conditions becomes easy.
[0050]
Next, an etching mask layer 68 is formed on the second upper cladding layer 66 (mask forming process). Referring to FIG. 2B, the etching mask layer 68 is formed by depositing a mask material on the second upper cladding layer 66 and etching the mask material into a predetermined shape by a photolithography technique. . The mask layer 68 is formed in a strip shape extending from the laser light emitting end face to the laser light reflecting end face along the current injection region of the active layer 58. As the mask material, a material that has sufficient etching resistance in the subsequent ridge formation process and can withstand the environment during crystal growth of the current blocking layer is employed. For example, silicon dioxide (SiO ₂ ) Or silicon nitride (SiN) can be used.
[0051]
A ridge structure is formed using this mask layer 68 (ridge forming step). Referring to FIG. 3A, the process after the second upper cladding layer 66 is etched is shown. This ridge structure is formed as follows. First, the second upper cladding layer 66 is etched. In this etching, an etching method is employed in which the etching rate of the second upper clad layer 66 is sufficiently larger than the etching rate of the intermediate layer 64. As such a method, for example, an etching solution containing hydrochloric acid, phosphoric acid, and water is preferably used, and the volume ratio of 36% hydrochloric acid, 85% phosphoric acid, and pure water expressed by weight percentage is 4: 2: 3. It is particularly preferable to use an etching solution mixed in When this etching solution is employed, the etching selectivity of the p-type GaInP semiconductor to the p-type GaAsP semiconductor is 130 times or more. For this reason, the intermediate layer 64 functions as an etching stop layer. Therefore, the depth of the second upper clad portion 70 having the mesa stripe shape is determined by the thickness of the semiconductor layer on which the second upper clad layer 66 is deposited, regardless of the etching conditions. Whether the mesa shape is forward mesa or reverse mesa
It depends on the plane orientation of the crystal used. FIG. 3A exemplarily shows a second upper clad portion 70 having an inverted mesa shape.
[0052]
Thus, the intermediate layer 64 is preferably formed to a thickness that functions as an etching stop layer, and is preferably thinner than the thicknesses of the first and second cladding layers.
[0053]
Next, referring to FIG. 3B, the process after the intermediate layer 64 is etched is shown. In the etching of the intermediate layer 64, an etching method that can make the etching rate of the intermediate layer 64 sufficiently higher than the etching rate of the first upper cladding layer 62 is employed. As such a method, for example, an etching solution containing phosphoric acid, hydrogen peroxide, and water is preferably used, and the volume ratio of 85% phosphoric acid, 30% hydrogen peroxide, and pure water expressed by weight percentage is used. It is particularly preferred to use an etching solution mixed at 5: 1: 40. When this etching solution is employed, the etching selectivity of the p-type GaAsP semiconductor to the p-type GaInP semiconductor becomes 100 times or more. For this reason, the first upper cladding layer 62 functions as an etching stop layer. Accordingly, the etching of the second upper cladding portion 70 does not proceed, and even if a portion of the intermediate layer 64 is etched to reach the first upper cladding layer 62, the cladding layer 62 is not etched.
[0054]
Thus, when the second upper cladding layer 66 and the intermediate layer 64 are etched using the mask layer 68, a ridge structure including the second upper cladding part 70 and the intermediate layer part 72 is formed.
[0055]
Since the intermediate layer 64 is a p-type semiconductor into which impurities are introduced at a high concentration, the intermediate layer 64 is a low-resistance semiconductor layer. When this is etched into a mesa shape, it is possible to prevent the injected carriers from spreading outside the mesa stripe region (that is, the light emitting region) through this low resistance layer. For this reason, the favorable narrowing of a carrier is realizable.
[0056]
Thereafter, an n-type AlGaInP current blocking layer 74 is formed on the first upper cladding layer 62 with the second upper cladding portion 70 interposed therebetween (current blocking layer forming step). Referring to FIG. 4A, the semiconductor layer 74 is not deposited on the mask material 68 but selectively grows only on the first upper clad layer 62, and the second upper clad portion 70 and the intermediate layer 74 are intermediate. The both side surfaces of the layer part 72 are covered. The current blocking layer 74 has a thickness corresponding to the sum of the depths of the etched intermediate layer 64 and second upper cladding layer 66. Thus, the portion left behind by etching is buried, providing a planarized surface.
[0057]
Subsequently, the mask material 68 is removed, and a p-type GaAs contact layer 76 is formed. Referring to FIG. 4B, the contact layer 76 is a semiconductor layer deposited so as to cover the second cladding part 70 and the current blocking layer 74. The back surface of the substrate 52 is chemically etched until the thickness of the substrate reaches about 100 μm. Thereafter, an ohmic electrode 78 is formed covering the p-type GaAs contact layer 76, and an ohmic electrode 80 is formed covering the back surface of the substrate 52.
[0058]
As a result of these steps, the semiconductor laser device according to the present invention is manufactured on the substrate.
[0059]
As described above, the embodiment according to the present invention has been described in detail with reference to the drawings. The semiconductor laser device according to the present invention is provided with an active layer 58 provided on a semiconductor substrate 52 and an active layer 58. A first clad layer 62; an intermediate layer portion 72 provided on the first clad layer 62; and a second clad layer portion 70 provided on the intermediate layer portion 72. The band gap is larger than the band gap of the GaAs semiconductor and is equal to or smaller than the band gaps of the semiconductors of the first cladding layer 62 and the second cladding layer portion 70. The second cladding layer portion 70 is made of a material that can be selectively etched with respect to the intermediate layer portion 72, and the intermediate layer portion 72 is made of a material that can be selectively etched with respect to the first cladding layer 62. It is configured.
[0060]
The first cladding layer 62 and the second cladding layer part 70 preferably include at least one of an AlGaInP semiconductor and a GaInP semiconductor. The intermediate layer portion 72 preferably includes a GaAsP semiconductor.
[0061]
When the present invention is applied to a semiconductor laser having a wavelength of 0.98 μm for exciting an erbium-doped optical fiber amplifier, a particularly great effect can be expected. That is, in a semiconductor laser having a wavelength of 0.98 μm, when a strained quantum well structure of at least one of a GaInAs semiconductor and a GaInAsP semiconductor is adopted as an active layer, the action of compressive strain applied to the semiconductor region constituting the active layer There is an effect that laser oscillation conditions such as threshold gain are improved. This effect also works synergistically with the effect of reducing the hetero barrier (clad-inter layer hetero barrier) by using a GaAs semiconductor for the intermediate layer, and greatly improves the high output characteristics and long-term reliability of the semiconductor laser. Is possible.
[0062]
In addition, since the GaAsP intermediate layer is a thin film, no crystal defects are generated within the allowable lattice mismatch within about −2%, and good crystallinity is maintained. In this case, the degree of freedom in selecting the band gap value is further increased by appropriately controlling the strain of the GaAsP intermediate layer within the above range. In particular, when the strain amount of the GaAsP intermediate layer is controlled so that the band gap value is substantially the same as that of the AlGaInP semiconductor and GaInP semiconductor used as the cladding layer, the hetero barrier is Can be removed to near zero. For this reason, the internal resistance of the semiconductor laser is further reduced.
[0063]
When an active layer having a strained quantum well structure is formed using a GaInAsP semiconductor, in addition to the above effects, the GaInAsP semiconductor has a larger number of constituent elements than the GaInAs semiconductor. Since it can be changed, the degree of freedom in designing the semiconductor laser is further increased.
[0064]
In addition, by using the etching solution shown in the embodiment, the P-type AlGaInP semiconductor as the second upper cladding layer and the P-type GaInP semiconductor are selectively etched with respect to the P-type GaAsP semiconductor as the intermediate layer. Therefore, the P-type GaAsP semiconductor functions as an etching stop layer, and the mesa stripe-shaped second upper clad portion having a predetermined depth is formed with good uniformity and reproducibility.
[0065]
Furthermore, by using the etching solution shown in the embodiment, the P-type GaAsP semiconductor that is the intermediate layer is selectively etched with respect to the P-type AlGaInP semiconductor or the P-type GaInP semiconductor that is the first upper cladding layer. Therefore, carriers injected through the second upper clad layer are prevented from leaking to other than the central mesa stripe region via the intermediate layer. For this reason, a good current confinement is realized toward the stripe portion which becomes the light emitting region.
[0066]
【The invention's effect】
As described above in detail with reference to the drawings, according to the semiconductor laser device of the present invention, the first and second cladding layers are formed of at least one of the AlGaInP semiconductor and the GaInP semiconductor. Since the intermediate layer containing the GaAsP semiconductor is sandwiched between the first and second cladding layers, the band gap of the intermediate layer is compared with the band gap of the GaAs semiconductor by changing the composition ratio of As and P in the intermediate layer. Can be bigger. For this reason, the hetero barrier at the interface between the first and second cladding layers and the intermediate layer is reduced as compared with the case where a GaAs semiconductor is used for the intermediate layer.
[0067]
In addition, since there is no immiscible region in the normal growth temperature range in the GaAsP semiconductor, which is a problem in the GaInAsP semiconductor, the etching stop having a band gap value suitable as an intermediate layer can be achieved by arbitrarily changing the composition of the constituent elements. A layer is obtained.
[0068]
Therefore, since the internal resistance of the semiconductor laser element can be reduced, it is possible to provide a semiconductor laser element in which heat generation of the element is suppressed and high light output characteristics and reliability are improved.
[0069]
According to the method of manufacturing a semiconductor laser device according to the present invention, the GaAsP semiconductor constituting the intermediate layer includes both As and P. For this reason, when starting the formation of the intermediate layer on the clad layer containing either one of the AlGaInP semiconductor and the GaInP semiconductor, and when starting the formation of the clad layer on the intermediate layer, discontinuity of the raw materials of phosphorus and arsenic Switching is not necessary.
[0070]
For this reason, the occurrence of crystallinity deterioration such as so-called surface turbidity is suppressed, and in order to obtain a semiconductor layer with good crystallinity, sufficient study on the growth conditions such as the growth temperature and the timing of material switching becomes unnecessary. Furthermore, it is not necessary to insert a buffer layer between the AlGaInP and GaInP semiconductor layers and the intermediate layer.
[0071]
In addition, since the GaAsP semiconductor does not have an immiscible region that is a problem in the GaInAsP semiconductor in the normal growth temperature range, it is possible to simply determine suitable crystal growth conditions.
[0072]
Furthermore, since the GaAsP semiconductor is a ternary semiconductor and is smaller than the number of constituent elements of the GaInAsP semiconductor, it is easier to optimize the crystal growth conditions.
[0073]
Accordingly, there is provided a semiconductor laser device including an etching stop layer including a semiconductor material in which no limitation caused by an immiscible region exists with respect to a band gap, and a method for manufacturing the same.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating one embodiment showing the structure of a semiconductor laser device according to the present invention.
2A and 2B are process cross-sectional views illustrating an embodiment of a method for manufacturing the semiconductor laser device shown in FIG.
FIGS. 3A and 3B are process cross-sectional views illustrating an embodiment of a method of manufacturing the semiconductor laser device shown in FIG.
4 (a) and 4 (b) are process cross-sectional views illustrating an embodiment of a method of manufacturing the semiconductor laser device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser element, 2 ... 1st conductivity type GaAs substrate, 4 ... 1st conductivity type lower clad layer, 6 ... Undoped 1st isolation | separation confinement heterostructure layer (lower SCH layer),
8 ... Undoped active layer, 10 ... Undoped second separated confinement heterostructure layer (upper SCH layer), 12 ... Second conductivity type first upper cladding layer,
DESCRIPTION OF SYMBOLS 20 ... 2nd conductivity type 2nd upper clad part, 22 ... 2nd conductivity type intermediate | middle layer part, 24 ... 1st conductivity type current block layer, 28, 30 ... Ohmic electrode
40... End face of the semiconductor laser element 42. Reflection end face of the semiconductor laser element
52 ... n-type GaAs substrate, 54 ... n-type GaInP lower clad layer,
56 ... Undoped GaInAsP lower SCH layer, 58 ... Undoped GaInAs active layer, 60 ... Undoped GaInAsP upper SCH layer,
62... P-type GaInP upper first cladding layer, 64... P-type GaAsP intermediate layer,
66 ... p-type GaInP upper second cladding layer, 68 ... etching mask layer,
70 ... p-type GaInP second upper cladding part, 72 ... p-type GaAsP intermediate layer part
74 ... n-type AlGaInP current blocking layer, 76 ... p-type GaAs contact layer,
78, 80 ... Ohmic electrode

Claims (6)

An active layer provided on a semiconductor substrate;
A first cladding layer provided on the active layer and including at least one of an AlGaInP semiconductor and a GaInP semiconductor;
An intermediate layer provided on the first cladding layer and including a GaAsP semiconductor;
A second clad layer provided on the intermediate layer and including at least one of an AlGaInP semiconductor and a GaInP semiconductor ;
The semiconductor laser device bandgap of the intermediate layer, Ru least one substantially identical der bandgap of said first and second cladding layers.   2. The semiconductor laser device according to claim 1, wherein the intermediate layer has a lattice irregularity within a range of ± 2% with respect to the semiconductor substrate. The active layer, a semiconductor laser device according to claim 1 or claim 2 having a strained quantum well structure comprises at least one of GaInAs semiconductor and GaInAsP semiconductor, characterized in that. A method of manufacturing a semiconductor laser device comprising a first cladding layer and a second cladding layer on an active layer provided on a substrate,
Providing the first cladding layer on the active layer;
Providing an intermediate layer on the first cladding layer;
Providing the second cladding layer on the intermediate layer, and
The band gap of the intermediate layer is substantially the same as at least one of the band gaps of the first and second cladding layers,
The first cladding layer and the second cladding layer include at least one of an AlGaInP semiconductor and a GaInP semiconductor,
The method for manufacturing a semiconductor laser device, wherein the intermediate layer includes a GaAsP semiconductor. 5. The method of manufacturing a semiconductor laser device according to claim 4 , further comprising a step of selectively etching the second cladding layer with respect to the intermediate layer. The method of manufacturing a semiconductor laser device according to claim 4 or claim 5 wherein the intermediate layer further comprises a step of selectively etching with respect to the first cladding layer, it is characterized.

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