JP2000058973A - Semiconductor laser element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element, which can suppress the inner resistance of the semiconductor laser element and decrease the heating of the element, and the manufacturing method thereof. SOLUTION: This semiconductor laser element has an active layer 8 provided on a substrate 2, a first clad layer 20, which includes at least either of an AlGaInP semiconductor and a GaInP semiconductor and is provided along the active layer 8, an intermediate layer 22, which is held between the active layer 8 and a second clad layer 20 and includes a GaInAsP semiconductor, and a first clad layer 12, which is held between the intermediate layer 22 and the active layer 8 and includes at least either of the AlGaInP semiconductor and the GaInP semiconductor. Since the band gap of the intermediate layer can be changed by changing the compositional ratio, the hetero-barrier of the interface between the first and second clad layers and the intermediate layer can be shortened in comparison with the case of using the GaAs semiconductor for the intermediate layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device and a method for manufacturing the same.

[0002]

2. Description of the Related Art Semiconductor laser devices are used for optical communication, optical recording,
Used in fields such as 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 devices since a ridge waveguide structure can provide practically good characteristics in a relatively simple manufacturing process.

On the other hand, a refractive index waveguide structure often used in a long-wavelength laser device using an InP substrate has a structure in which an active layer is etched in a stripe shape and then embedded in another semiconductor layer. If this structure is adopted in a short-wavelength semiconductor laser device having a wavelength of 1 μm or less manufactured using a GaAs substrate, characteristic failure may occur due to the etching interface of the active layer. A ridge waveguide structure is employed. Such a semiconductor laser device is used in a red visible light laser and a laser for exciting an erbium-doped optical fiber amplifier.

In a ridge waveguide structure, a cladding layer is etched into a mesa structure to form a ridge. The depth at which the cladding layer is etched during the mesa etching is a factor that determines the characteristics of the laser device. Therefore, the reproducibility of the etching depth and the in-plane uniformity of the etching depth greatly affect the uniformity of the device characteristics and the manufacturing yield. As described above, since the depth of the mesa etching is required to have high reproducibility and in-plane uniformity, sufficient attention is paid to the handling of the etching solution which affects the etching characteristics.

[0005] However, the etching rate of the etching solution is easily affected when the temperature, concentration, mixing ratio of chemicals and the like of the solution slightly fluctuate. Further, due to the difference in the stirring speed of the etching solution between the central portion and the peripheral portion of the wafer, a non-negligible difference occurs in the etching rate in the wafer surface.

In order to improve the uniformity and reproducibility of the etching depth due to these reasons, there is a method of providing an etching stop layer in a cladding layer.
No. 22488. This etching stop layer is a thin layer formed using a material having a high selectivity to the etching solution of the cladding layer. Since a large difference can be provided to the etching rate of the clad layer to be etched, even if the etching rate fluctuates or an in-plane difference occurs, the mesa etching substantially stops when it reaches the etching stop layer. As a result, good reproducibility and in-plane uniformity of the etching depth are achieved.

As a clad material used in a short-wave laser device, there is a semiconductor such as AlGaInP or GaInP. A GaAs semiconductor is used as a material of the etching stop layer that can secure a selectivity with respect to the etching solution (hydrochloric acid type etching solution) of such a clad material.

[0008]

SUMMARY OF THE INVENTION The inventor has been studying to reduce heat generation of a semiconductor laser device having such a structure. For this purpose, it is necessary to reduce the series resistance inside and outside the element. In this study, the inventor has found that the resistance caused by the hetero-barrier exists at the interface between the cladding layer and the etching stop layer, and that by reducing this, the device characteristics such as high output characteristics can be improved.

An object of the present invention is to provide a semiconductor laser device capable of suppressing the internal resistance of the semiconductor laser device and improving the heat generation of the device in order to improve high output characteristics and the like, and a method of manufacturing the same. It is.

[0010]

Means for Solving the Problems In order to solve such an object, the inventor has conducted further studies, and as a result, has reached the following conclusion.

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. At the interface between the cladding layer and the etching stop layer, a large hetero barrier generated due to the band gap difference is formed.

That is, when two semiconductor layers having different band gaps are crystallographically coupled, the Fermi level in each layer coincides, so that a discontinuity in band edge energy is formed at the heterojunction interface. These are called spikes, notches, and project in a wedge-like manner toward the conduction band and the valence band of the energy band diagram, forming barriers, which are for electrons in the conduction band and for the valence band. For the holes, barriers {E _c , そ れ ぞ れ} respectively
Since it becomes _Ev , it acts as an electric resistance. Experimentally △
E _c and ΔE _v are obtained as being proportional to the difference in energy gap between the semiconductor layers forming the heterojunction.

Therefore, it has been found that a material having a larger band gap than the GaAs semiconductor and capable of easily growing crystals on the cladding layer can be used to lower the hetero barrier. Therefore, the present invention has the following configuration.

A semiconductor laser device according to the present invention comprises: an active layer provided on a semiconductor substrate; and an AlG layer provided on the active layer.
a first cladding layer containing at least one of an aInP semiconductor and a GaInP semiconductor, an intermediate layer provided on the first cladding layer and containing a GaInAsP semiconductor, and an AlGaInP semiconductor and a GaInP semiconductor provided on the intermediate layer. Second containing at least one of
And a cladding layer.

As described above, the first and second cladding layers are formed of at least one of the AlGaInP semiconductor and the GaInP semiconductor, and the GaInA
An intermediate layer containing an sP semiconductor is provided between the first and second cladding layers. Therefore, Ga and I in the intermediate layer
By changing n and the composition ratio of As and P, the band gap of the intermediate layer can be made larger than the band gap of the GaAs semiconductor. Therefore, compared to the case where a GaAs semiconductor is used for the intermediate layer,
The hetero barrier at the interface between the first and second cladding layers and the intermediate layer is reduced.

In the semiconductor laser device of the present invention, the intermediate layer may have a lattice misalignment within a range of ± 2% with respect to the semiconductor substrate.

Since the thickness of the intermediate layer is small, the occurrence of crystal defects due to the lattice mismatch can be suppressed if the lattice is matched 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 desirably about 5 to 10 nm, particularly 5 n
m is preferred.

In the semiconductor laser device of the present invention, the band gap of the intermediate layer may be substantially equal to at least one of the band gaps of the first and second cladding layers.

By adjusting the band gap of the intermediate layer as described above, the resistance caused by the hetero barrier is further reduced.

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.

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 in a wavelength of 0.98 μm where high output is indispensable for pumping an erbium-doped optical fiber amplifier. Become. 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 is due to GaInAsP
The use of a semiconductor for the intermediate layer works synergistically with the effect of reducing the hetero-barrier between the cladding and the intermediate layer, so that the high-output characteristics are greatly improved. When a strained quantum well structure of a GaInAsP semiconductor is used, in addition to the same effect,
Since the number of constituent elements of the aInAsP semiconductor is larger than that of the GaInAs semiconductor, the amount of strain can be largely changed depending on the purpose as compared with the case of the GaInAs semiconductor. For this reason, the degree of freedom in design can be further increased.

The method for manufacturing a semiconductor laser device according to the present invention comprises:
A method for manufacturing a semiconductor laser device comprising a first cladding layer and a second cladding layer on an active layer provided on a substrate, comprising: providing a first cladding layer on the active layer; A step of providing an intermediate layer on the clad layer; and a step of providing a second clad layer on the intermediate layer.
The cladding layer and the second cladding layer are made of AlGaIn
The intermediate layer includes at least one of a P semiconductor and a GaInP semiconductor, and the intermediate layer includes a GaInAsP semiconductor.

Conventionally, AlGaInP, GaI
When a GaAs layer is grown as an etching stop layer on a cladding layer made of a semiconductor such as nP using, for example, an OMVPE growth apparatus, phosphorus-based AlGaInP, Ga
Since an arsenic-based GaAs semiconductor layer is directly grown on the InP semiconductor layer, it is necessary to discontinuously switch the source element from phosphorus to arsenic when starting to grow the GaAs etching stop layer. Therefore, deterioration of crystallinity such as so-called surface turbidity is likely to occur, and growth conditions such as growth temperature and timing of material switching have to be sufficiently studied in order to obtain a semiconductor layer with good crystallinity. Alternatively, a buffer layer must be inserted between the AlGaInP or GaInP semiconductor layer and the GaAs semiconductor layer to prevent the deterioration of crystallinity.

However, the GaIn
AsP semiconductors include both As and P. Therefore, when starting the formation of the intermediate layer on the cladding layer containing either the AlGaInP semiconductor or the GaInP semiconductor, and when starting the formation of the cladding layer on the intermediate layer, the discontinuity of the raw material of phosphorus and arsenic occurs. It is not necessary to perform a proper switching, and the accompanying crystal deterioration does not occur.

The method of manufacturing a semiconductor laser device according to the present invention may further include a step of selectively etching the second clad layer with respect to the intermediate layer.

As described above, when the second clad layer is selectively etched with respect to the intermediate layer, a clad layer having a predetermined depth is formed with good uniformity and reproducibility.

The method may further include a step of selectively etching the intermediate layer with respect to the first cladding layer.

As described above, when the intermediate layer is etched,
Carriers injected through the second upper cladding layer are prevented from leaking to the region other than the central mesa stripe region via the intermediate layer. Therefore, good current confinement is realized toward the stripe portion serving as the light emitting region.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to a case where a semiconductor laser device is formed on a semiconductor substrate. The present embodiment is merely an example, and the present invention is not limited to this. If possible,
The same portions are denoted by the same reference numerals, and duplicate description will be omitted.

FIG. 1 shows a semiconductor laser device 1 according to the present invention.
FIG. 2 is a perspective view illustrating an embodiment of the present invention. FIG.
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.
An undoped first isolation / confinement heterostructure layer (hereinafter, referred to as a lower SCH layer) is provided on the first conductivity type lower cladding layer 4.
An undoped active layer 8 is provided on the lower SCH layer 6, and an undoped second isolation / confinement heterostructure layer (hereinafter, referred to as an upper SCH layer) 10 is provided on the active layer 8. The active layer 8 includes a lower SCH layer 6 and an upper S
The SCH layer 6 and the SCH
Since one side of each of the layers 10 contacts each of the two opposing sides of the active layer, both SCH layers 6 and 10 act to confine carriers to the active layer 8.

On the active layer 8, a first upper clad layer 12 of the second conductivity type, a second upper clad portion 20 of the second conductivity type, and an intermediate layer portion 22 of the second conductivity type are provided, respectively. ing. The first upper cladding layer 12 is provided on the active layer 8, the intermediate layer 22 is provided on the first upper cladding layer 12, and the second upper cladding 20 is provided on the intermediate layer 22.
It is provided above. One surface of each of the first upper cladding layer 12 and the second upper cladding portion 20 is in contact with two opposing surfaces of the intermediate layer portion 22. Lower SCH
The other surface facing one surface of the layer 6 is in contact with one surface of the lower cladding layer 4, and the other surface facing the one surface of the upper SCH layer 10 is one surface of the first upper cladding layer 12. Therefore, the cladding layers 4 and 12 act to confine light to the lower SCH layer 6, the active layer 8 and the upper SCH layer 10. The active layer 8 includes upper and lower SCs.
Upper and lower cladding layers 4 and 12 via H layers 6 and 10
The electrons and holes injected from the electron recombine to generate light.

Since the material of the intermediate layer portion 22 is larger than the band gap value of the GaAs semiconductor, the hetero barrier between the intermediate layer portion 22 and the first upper clad layer 12 and the second upper clad portion 20 sandwiching the intermediate layer portion 22 is as follows. The size is reduced as compared with the case where the GaAs semiconductor is used as the material of the intermediate layer. Therefore, resistance due to these interfaces is reduced. The band gap value of the intermediate layer part 22 is set to the first upper clad layer 12.
It is particularly preferable that the resistance value be the same as the band gap value of the second upper clad portion 20, and the resistance can be made substantially zero.

Further, the second upper cladding portion 20 and the intermediate layer portion 22 extend along the layer into which carriers are to be injected into the active layer 8 and are provided in a mesa shape on the first upper cladding layer 12. Have been. That is, these parts 20,
Numeral 22 is provided on the waveguide on which light is generated by the recombination of the injected carriers, along the axis extending from the emission end face 40 of the semiconductor laser device 1 to the reflection end face 42 facing this end face. , 42.

The second upper cladding portion 20 and the intermediate layer portion 22 extending in a stripe shape as described above have a first conductivity type current on two opposite surfaces different from the surface extending in the axial direction and facing the active layer 8. It is in contact with the block layer 24. First
The conduction type current blocking layer 24 is formed of the first upper clad layer 1.
2 is provided. A second conductivity type contact layer 26 is provided on the second upper clad portion 20 and the current block layer 24. An ohmic electrode 28 for the second conductivity type semiconductor layer is provided on the contact layer 26. On the back surface of the first conductivity type substrate 2, an ohmic electrode 30 for the first conductivity type semiconductor layer is provided.

The operation of such a semiconductor laser device 1 will be described below. The carriers from the ohmic electrode 28 are supplied to the current blocking layer 24 by the second upper cladding part 20.
And the conductive type is opposite to the conductive type of the first upper clad layer 12 and the second upper clad portion 20, so that the semiconductor laser device 1 has a width of several μm under the forward bias condition. Through the region of the second upper cladding layer 20 to reach the active layer 8. That is, a ridge structure is employed so as to realize current constriction. For this reason, the thickness of the second upper cladding part 20 is
Is determined according to the characteristics of

The thickness of the main semiconductor layer of such a semiconductor laser device 1 is illustratively 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 cladding part 20: 0.9 μm Intermediate layer part 22: 5 nm.

Next, a method of manufacturing the semiconductor laser device 1 according to the present invention will be described in detail with reference to the sectional views shown in FIGS. The following description is based on an n-type GaAs substrate and GaI as an active layer material.
This is performed in the case where an nAs semiconductor is used, but the present invention is not limited to this.

A laminated 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
A semiconductor layer deposited over the substrate 52. An undoped GaInAsP lower SC is formed on the lower cladding layer 54.
An H 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, and the undoped GaInAs active layer 58 is a semiconductor layer deposited over the lower SCH layer 56, and undoped GaIn
The AsP upper SCH layer 60 is a semiconductor layer deposited over the active layer 58.

Next, a p-type GaInP upper first cladding layer 62, a p-type GaInAsP intermediate layer 64, a p-type GaI
An nP upper second cladding layer 66 is formed sequentially. The upper first cladding layer 62 is a semiconductor layer deposited over the upper SCH layer 60, and includes a p-type GaInAsP intermediate layer 64.
Is a semiconductor layer deposited over the upper first cladding layer 62, and the p-type GaInP upper second cladding layer 66 is a semiconductor layer deposited over the p-type GaInAsP intermediate layer 64.

These semiconductor layers are formed, for example, by metalorganic vapor phase epitaxy (OMVPE, Organometallic Vapor Pha
se Epitaxy). n-type GaInP lower cladding layer 54, undoped GaInAsP lower SCH
Layer 56, undoped GaInAsP top SCH layer 60,
p-type GaInP first upper cladding layer 62, p-type GaI
It is preferable that the nAsP intermediate layer 64 and the p-type GaInP second upper cladding layer 66 have matching lattice constants with respect to the GaAs substrate. In this manner, a semiconductor with good crystallinity can be obtained. On the other hand, the undoped GaInAs active layer 58 is made of undoped GaInAs.
The compositions of the lattice constants are different from each other by about 1% so that compressive strain is applied to each of the semiconductor layers of the P lower SCH layer 56 and the undoped GaInAsP upper SCH layer 60. 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. Further, an active layer having a multiple quantum well structure may be formed. Note that the active layer 58 may be formed so as to be lattice-matched to the substrate.

In the above embodiment, the case where a GaInP semiconductor is used as the semiconductor material of the cladding layer has been exemplified, but an AlGaInP semiconductor can also be used. When a GaInP semiconductor is used, the number of constituent elements is as small as ternary, so that the conditions for growth are simple and easy, and a semiconductor layer having good crystallinity can be obtained relatively easily using an ordinary crystal growth apparatus. In addition, it is already widely used in visible light semiconductor lasers and the like, and has a track record as a material. When an AlGaInP semiconductor is used, Ga
Since a larger band gap can be realized as compared with an InP semiconductor, using this as a cladding material further improves the confinement of carriers in the light emitting region, and is expected to further improve laser characteristics such as high output. In addition, it is already widely used in visible light semiconductor lasers and the like, and has a track record as a material.

[0042] p-type _{Ga x In 1-x As y} P 1-y intermediate layer 64
In the present embodiment, x = 0.78 and y = 0.56
And is lattice-matched to the semiconductor layer of the GaAs substrate, and has a band gap value of about 1.59 eV. Under the condition of lattice matching with the semiconductor layer of the GaAs substrate, 1.41 eV (x = 1, y = 1) to 1.88 eV
A band gap value can be selected in a range up to (x = 0.52, y = 0). Therefore, a semiconductor layer larger than the band gap value of the GaAs semiconductor can be formed.

[0043] Further, since it a p-type _{Ga x In 1-x As y} P 1-y intermediate layer 64 is very thin, if the lattice mismatch within about ± 2% with respect to the GaAs substrate, misfit dislocation or the like Good crystallinity is maintained without inducing the occurrence of crystal defects. The thickness of such an intermediate layer is 5n
The range is preferably from m to 10 nm, and particularly preferably about 5 nm. If the lattice mismatch is allowed in such a range, the degree of freedom in designing the band gap value of the intermediate layer increases. Therefore, substantially the same band gap value can be realized for GaInP and AlGaInP. As an example of a composition for realizing the same band gap value of 1.88 eV as the GaInP cladding layer, x = 0.83 and y = 0.
When it is set to about 38, a semiconductor layer having a lattice irregularity of about -1% can be formed. Therefore, the hetero barrier between the cladding layer and the intermediate layer can be substantially eliminated. Therefore, the series resistance in the semiconductor laser device can be further reduced. In actual production, tensile strain and quantum well effects cause GaI
Although the band gap of nAsP slightly varies, by adjusting the composition ratios x and y, the same band gap as that of the cladding layer can be realized.

Further, the GaInAsP semiconductor constituting the intermediate layer contains both As and P. For this reason, AlG
When starting the formation of the intermediate layer on the cladding layer containing one of the aInP semiconductor and the GaInP semiconductor, and starting the formation of the cladding layer on the intermediate layer, the discontinuous formation of the raw material elements phosphorus and arsenic occurs. No special switching is required. Therefore, degradation of crystallinity such as so-called surface turbidity, which has occurred when a GaAs semiconductor layer is used as an intermediate layer in the related art, and a growth temperature and a timing of material switching in order to obtain a semiconductor layer with good crystallinity. Careful consideration of the growth conditions or AlGaInP and GaIn
Inserting a buffer layer between the P semiconductor layer and the GaAs semiconductor layer,
Such disadvantages are eliminated.

Next, an etching mask layer is formed on the second upper cladding layer 66 (mask forming step). FIG.
Referring to (b), the etching mask layer 68 has a second shape.
Is formed by depositing a mask material over the upper cladding layer 66 and etching the mask material into a predetermined shape by photolithography. Mask layer 6
Numeral 8 is formed in a rectangular 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 forming step and that can withstand the environment during the crystal growth of the current blocking layer is used.
For example, silicon dioxide (SiO ₂ ) or silicon nitride (SiN) can be used.

A ridge structure is formed using this mask layer 68 (ridge forming step). Referring to FIG. 3A, a step 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 that allows the etching rate of the second upper cladding layer 66 to be sufficiently higher than the etching rate of the intermediate layer 64 is employed. As such a method, for example, it is preferable to use an etching solution containing hydrochloric acid, phosphoric acid, and water, 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. When this etching solution is adopted, the p-type GaInP
The selectivity of semiconductor etching is 130 times or more.
Thus, the intermediate layer 64 functions as an etching stop layer. Therefore, the depth of the second upper cladding portion 70 having the mesa stripe shape is determined by the thickness of the semiconductor layer on which the second upper cladding layer 66 is deposited, regardless of etching conditions. If the mesa shape becomes a regular mesa,
Alternatively, whether or not an inverted mesa is formed is determined depending on the plane orientation of the crystal used. FIG. 3A exemplarily shows the second upper clad portion 70 having an inverted mesa shape.

As described above, 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.

Next, referring to FIG. 3B, a step after the etching of the intermediate layer 64 is shown. In the etching of the intermediate layer 64, an etching method that allows the etching rate of the intermediate layer 64 to be sufficiently higher than the etching rate of the first upper cladding layer 62 is employed. As such a method, for example, it is preferable to use an etching solution containing phosphoric acid, hydrogen peroxide, and water, and the volume of 85% phosphoric acid, 30% hydrogen peroxide, and pure water expressed by weight percentage is preferable. It is particularly preferred to use an etching solution mixed at a ratio of 5: 1: 40. When this etching solution is employed, the p-type GaI
The etching selectivity of the nAsP semiconductor becomes 100 times or more. For this reason, the first upper cladding layer 62 functions as an etching stop layer. Therefore, the etching of the second upper cladding portion 70 does not proceed, and even if a part of the intermediate layer 64 is etched to reach the first upper cladding layer 62, the cladding layer 62 is not etched.

Thus, the second layer is formed using the mask layer 68.
When the upper clad layer 66 and the intermediate layer 64 are etched, a ridge structure including the second upper clad part 70 and the intermediate layer part 72 is formed.

The intermediate layer 64 is a low-resistance semiconductor layer because it is a p-type semiconductor into which impurities are introduced at a high concentration. When this is etched into a mesa shape, the injected carriers can be prevented from spreading to other than the mesa stripe region (that is, the light emitting region) through the low resistance layer. Therefore, good narrowing of the carrier can be realized.

Thereafter, an n-type AlGaInP current block layer 74 is formed on the first upper clad portion 62 with the second upper block layer 70 interposed therebetween (current block layer forming step). Referring to FIG. 4A, the semiconductor layer 74 includes:
It is not deposited on the mask material 68 but selectively grows only on the first upper cladding layer 62 to cover both side surfaces of the second cladding part 70 and the intermediate layer part 72. Current block layer 74
Has a thickness corresponding to the sum of the depths of the etched intermediate layer 64 and the second upper cladding layer 66. For this reason, the portions left by the etching are buried to provide a flattened surface.

Subsequently, the mask material 68 is removed, and the p-type G
An aAs contact layer 76 is formed. Contact layer 76
Is a semiconductor layer deposited to cover the second cladding part 70 and the current blocking layer 74. The back surface of the substrate 52
It is chemically etched until the thickness of the substrate becomes about 100 μm. Thereafter, an ohmic electrode 78 is formed to cover the p-type contact layer 76, and an ohmic electrode 80 is formed to cover the back surface of the substrate 52.

As a result of these steps, a semiconductor laser device according to the present invention is manufactured.

As described above, the embodiment according to the present invention has been described in detail with reference to the accompanying drawings. As described above, the semiconductor laser device according to the present invention comprises an active layer 5 provided on a semiconductor substrate 52.
8 and a first cladding layer 62 provided on the active layer 58.
And an intermediate layer 72 provided on the first cladding layer 62.
And a second cladding layer portion 70 provided on the intermediate layer portion 72. The band gap of the intermediate layer portion 72 is G
larger than the band gap of the aAs semiconductor and the first
Of the semiconductor in the cladding layer 62 and the second cladding layer 70 of the second embodiment. The second clad 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 clad layer 62. It is configured.

The first cladding layer 62 and the second cladding layer 70 are made of an AlGaInP semiconductor and a GaInP
It is preferable to include at least one of semiconductors. The intermediate layer 72 preferably contains a GaInAsP semiconductor.

When the present invention is applied to a semiconductor laser having a wavelength of 0.98 μm for pumping an erbium-doped optical fiber amplifier, a particularly large effect can be expected. That is, in a semiconductor laser having a wavelength of 0.98 μm, GaInAs
When a strained quantum well structure of a semiconductor of at least one of GaInAsP and GaInAsP is used for the active layer, there is an effect that laser oscillation conditions such as a threshold gain are improved by the action of compressive strain applied to a semiconductor region forming the active layer. . Also,
This effect and the effect of reducing the hetero-barrier between the cladding and the intermediate layer by using the GaInAsP semiconductor for the intermediate layer act synergistically, and the high output characteristics of the semiconductor laser can be greatly improved.

When an active layer having a strained quantum well structure is formed by using a GaInAsP semiconductor, in addition to the above-described effects, the GaInAsP semiconductor has a larger number of constituent elements than the GaInAs semiconductor, so that the amount of strain is reduced. Since it can be largely changed in response to the change, there is an effect that the degree of freedom in designing the semiconductor laser is further increased.

[0058]

As described above in detail with reference to the drawings, according to the semiconductor laser device of the present invention,
Since the first and second cladding layers are formed of at least one material of an AlGaInP semiconductor and a GaInP semiconductor, the intermediate layer containing the GaInAsP semiconductor is sandwiched between the first and second cladding layers. The band gap of the intermediate layer is changed to G by changing the composition ratios of Ga and In and As and P, respectively.
It can be larger than the band gap of an aAs semiconductor.
Therefore, 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 the GaAs semiconductor is used for the intermediate layer. Therefore, since the internal resistance of the semiconductor laser device can be reduced, heat generation of the device can be suppressed, and a semiconductor laser device having high light output characteristics and improved reliability can be provided.

If a GaInAsP intermediate layer containing a strain caused by a slight irregularity of the crystal lattice is used, the AlGaInP used as the cladding layer can be used.
Since the semiconductor and the GaInP semiconductor can have almost the same band gap, the hetero barrier can be almost removed. Therefore, the internal resistance of the semiconductor laser device is further reduced.

According to the method of manufacturing a semiconductor laser device according to the present invention, the GaInAsP semiconductor constituting the intermediate layer contains both As and P. For this reason, AlGaI
When starting the formation of the intermediate layer on the cladding layer containing any one of the nP semiconductor and the GaInP semiconductor, and when starting the formation of the cladding layer on the intermediate layer, discontinuous switching of phosphorus and arsenic raw materials is performed. Becomes unnecessary.

For this reason, the occurrence of deterioration in crystallinity such as so-called surface turbidity is suppressed, and sufficient study on growth conditions such as growth temperature and timing of material switching is not required to obtain a semiconductor layer with good crystallinity. And,
There is no need to insert a buffer layer between the AlGaInP or GaInP semiconductor layer and the etching stop layer.

Therefore, GaIn is directly formed on the cladding layer.
It is possible to provide a method of manufacturing a semiconductor laser device in which an etching stop layer made of an AsP semiconductor can be formed and the examination of manufacturing conditions is simplified.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an embodiment showing a structure of a semiconductor laser device according to the present invention.

FIGS. 2A and 2B are process cross-sectional views illustrating one embodiment of a method of manufacturing the semiconductor laser device shown in FIG.

FIGS. 3A and 3B are process cross-sectional views illustrating one embodiment of a method for manufacturing the semiconductor laser device shown in FIG.

FIGS. 4A and 4B are process cross-sectional views illustrating one embodiment of a method for manufacturing the semiconductor laser device shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser element, 2 ... First conductivity type GaAs substrate,
4 a first conductivity type lower cladding layer, 6 undoped first separated confinement heterostructure layer (lower SCH layer), 8 undoped active layer, 10 undoped second separated confinement heterostructure layer (upper SCH layer), 12: second conductive type first upper clad layer, 20: second conductive type second upper clad part, 22: second conductive type intermediate layer part, 24: first conductive type current blocking layer, 28, 30 ... Ohmic electrode, 40: emission end face of semiconductor laser element, 42: reflection end face of semiconductor laser element, 52: n-type GaAs substrate, 54: n-type GaIn
P lower cladding layer, 56 undoped GaInAsP lower SCH layer, 58 undoped GaInAs active layer, 6
0: Undoped GaInAsP upper SCH layer, 62: p
GaInP upper first cladding layer, 64... P-type GaI
nAsP intermediate layer, 66: p-type GaInP upper second cladding layer, 68: etching mask layer, 70: p-type GaI
nP second upper cladding part, 72... p-type GaInAsP
Intermediate layer portion, 74... N-type AlGaInP current blocking layer,
76: p-type contact layer, 78, 80: ohmic electrode

Claims (6)

[Claims] An active layer provided on a semiconductor substrate; and a first layer provided on the active layer and containing at least one of an AlGaInP semiconductor and a GaInP semiconductor.
A middle layer provided on the first cladding layer and containing a GaInAsP semiconductor; and a second layer provided on the middle layer and containing at least one of an AlGaInP semiconductor and a GaInP semiconductor.
A semiconductor laser device comprising: 2. The semiconductor laser device according to claim 1, wherein the intermediate layer has a lattice misalignment within ± 2% with respect to the semiconductor substrate. 3. The semiconductor according to claim 1, wherein 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. Laser element. 4. The semiconductor laser device according to claim 1, wherein said active layer includes at least one of a GaInAs semiconductor and a GaInAsP semiconductor and has a strained quantum well structure. 5. A method for manufacturing a semiconductor laser device comprising: a first cladding layer and a second cladding layer on an active layer provided on a substrate, wherein the first cladding layer is formed on the active layer. Providing; providing an intermediate layer on the first cladding layer; providing the second cladding layer on the intermediate layer;
The first cladding layer and the second cladding layer,
A method for manufacturing a semiconductor laser device, including at least one of an AlGaInP semiconductor and a GaInP semiconductor, wherein the intermediate layer includes a GaInAsP semiconductor. 6. The method according to claim 5, further comprising a step of selectively etching the second cladding layer with respect to the intermediate layer.