JPH0946002A - Semiconductor optical element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a selective growth method which can change a crystalline layer thickness largely without change a crystalline strain amount almost at all in regions of different mask widths. SOLUTION: A growth blocking mask of a large number of strip-like dielectric thin films which are formed to an array shape at a period A which is shorter than a diffusion length of raw material species in vapor phase inside a reaction tube is introduced in selective growth and selective growth wherein crystal formed in an optical waveguide region between dielectric masks can largely change the thickness of a crystalline layer without changing a crystalline strain amount almost at all to change of a mask width can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor optical device and a semiconductor optical device.

[0002]

2. Description of the Related Art Selective growth using a striped dielectric mask in metal organic chemical vapor deposition (MOVPE) is
Since it is possible to change the composition and layer thickness of the semiconductor crystal grown in the growth region sandwiched by the dielectric mask only by changing the width of the dielectric mask, research as a basic technique for manufacturing an optical integrated device, etc. Is being actively conducted.

FIG. 10A is a plan view schematically showing a pattern of a dielectric mask used in conventional selective growth. With reference to FIG. 10A, in the conventional selective growth method,
On a semiconductor substrate 1 of InP or the like, a pair of stripe-shaped dielectric thin film masks (also simply referred to as “dielectric masks”) 5 facing each other with a growth region 2 having a width of about 1.5 μm therebetween is formed, and MOVPE is used. Then, a quaternary crystal such as InGaAsP is selectively grown in the growth region 2.

At this time, the crystal composition wavelength to be grown and the crystal layer thickness can be controlled only by changing the width of the dielectric mask 5, and an optical device in which optical elements such as a semiconductor laser, an optical modulator and an optical amplifier are integrated is integrated. Since integrated devices can be formed at one time, it is a very promising method for manufacturing an optical integrated device. References relating to this prior art include, for example, Document 1 (Journal of Crystal Growth (JCG), Vol. 132, No. 43).
Pp. 5-443, 1993).

In the selective growth, when the width of the dielectric mask 5 is wider, the crystal composition grown in the growth region 2 shifts to the longer wavelength side. For example, when crystal growth of a multiple quantum well is performed using the dielectric mask 5 shown in FIG. 10A, the quantum well composition wavelength of a region a having a wide width (also referred to as “mask width”) of the dielectric mask 5 is 1. 55 μm, the quantum well composition wavelength of the region b having a narrow mask width can be set to 1.48 μm. By using the region a as the semiconductor laser and the region b as the optical modulator, the semiconductor laser / optical modulator can be easily manufactured. An integrated light source can be produced.

[0006]

However, when the crystal composition or the crystal layer thickness is changed by the selective growth, the crystal strain amount also changes at the same time. For example, in the growth region 2 sandwiched between the dielectric masks 5 having mask widths of 30 μm and 4 μm, the crystal composition is 1.3.
When a GaInAsP layer of μm is selectively grown at a growth pressure of 150 torr, the mask width is 30 μ as a crystal layer thickness ratio.
The layer thickness in the mask width 4 μm region is 1 with respect to the layer thickness in the m region.
/ 2 or less.

However, if the crystal strain amount in the mask width 30 μm region is 0, the crystal strain amount is −0.
It will be about 5%. Therefore, the crystal layer thickness in the mask width region of 4 μm cannot be made too thick.

That is, the conventional selective growth has a problem that the layer thickness cannot be increased while maintaining the crystal layer thickness ratio.

For example, a variable wavelength stepped waveguide structure (T with a single current that enables continuous wavelength control without mode jumping)
The SG) DBR laser is designed as a DBR
The layer thickness of the light confinement layer in the phase adjustment region must be twice or more the layer thickness of the light confinement layer in the (distributed Bragg reflection) region. This requirement can be satisfied by using the above selective growth.

However, even if the layer thickness ratio is taken, the absolute value of the layer thickness in the DBR region cannot be increased due to the influence of strain, and the wavelength tunable width of the TSG-DBR laser cannot be sufficiently widened. There was a problem. This TSG-D
References regarding BR lasers include Document 2 (Proceedings of the Institute of Electronics, Information and Communication Engineers Electronics 1, C-39).
0, p. 390, spring 1995).

Therefore, an object of the present invention is to provide a striped dielectric thin film formed in parallel with a period Λ shorter than the diffusion length of the raw material species in the gas phase in the reaction tube in the selective growth using MOVPE. By introducing a mask, the selective growth method in which the crystal layer thickness of the crystal grown in the growth region of the dielectric thin film sandwiched by the mask is largely changed with respect to the dielectric mask width, and at the same time the crystal strain amount is small To provide. Another object of the present invention is to solve the above-mentioned problems of the prior art and to provide a semiconductor optical device in which the crystal layer thickness of the optical waveguide layer is largely changed and at the same time the crystal strain amount is small.

[0012]

In order to achieve the above object, the present invention selectively selects a semiconductor multi-layer structure composed of a quantum well layer or a bulk layer into an optical waveguide region sandwiched between striped dielectric thin films. A method for manufacturing a semiconductor optical device, comprising a step of growing a crystal, wherein a plurality of the striped dielectric thin films are formed in parallel.

In the present invention, preferably, a plurality of the striped dielectric thin films are formed in parallel at a period Λ shorter than the diffusion length of the raw material species in the reaction tube during crystal growth.

[0014]

The principle of the method for manufacturing a semiconductor optical device of the present invention will be described below.

FIG. 10B shows a schematic diagram of the lateral concentration gradient of the group III source species in the vapor phase when the conventional selective growth mask pattern of FIG. 10A is used.

In the selective growth of the GaInAsP quaternary system, the change in the crystal layer thickness with respect to the width of the dielectric mask 5 is mainly caused by the lateral diffusion of the group III source species such as Ga and In in the vapor phase in the reaction tube. That is, since the raw material species are not consumed (grown) on the dielectric mask 5 in FIG. 10A, the concentration becomes high and the growth region 2 sandwiched between the dielectric masks 5 is formed.
In this case, the raw material species are consumed (grown), resulting in a low concentration.

As a result, a concentration gradient of the raw material species is produced in the lateral direction, and lateral diffusion occurs (see FIG. 10 (B)). At this time, as the width of the dielectric mask 5 is wider, the amount of the group III source species supplied to the growth region by lateral diffusion is larger, and the crystal layer thickness is larger.

On the other hand, the change in the crystal composition is caused by both the diffusion of the group III source species in the vapor phase and the migration on the substrate surface, and the In composition increases as the mask width becomes wider. That is, the diffusion length of the In raw material is Ga
Since it is shorter than the diffusion length of the raw material, the concentration gradient in the lateral direction In becomes large, and more In is grown in the growth region.

In the conventional selective growth, in order to positively utilize this effect, the width of the dielectric mask 5 used is largely changed from a length shorter than the diffusion length of the source species in the vapor phase to a length longer than the diffusion length. It was However, in such a conventional selective growth, as described above, the crystal strain amount greatly changes as the crystal composition changes and the crystal layer thickness changes.

FIG. 1 shows a pattern of a stripe-shaped dielectric mask (also simply referred to as “dielectric mask”) 5 used in the method for manufacturing a semiconductor optical device of the present invention.

In the conventional selective growth, as shown in FIG. 10 (A), a stripe-shaped dielectric mask 5 formed by only a pair of growth regions 2 having a width of 1.5 μm is used.

On the other hand, in the present invention, the width is 1.5 μm.
Centered on the growth region 2 of 100 .mu.m, a plurality of parallel lines (also referred to as "array form") are formed with a period .LAMBDA. The dielectric mask 5 is formed. At this time, the period Λ of the dielectric mask 5 is set to be shorter than the diffusion length of the group III raw material species in the vapor phase.

A change in the growth rate of the GaInAsP crystal with respect to the width of the dielectric mask 5 (the dielectric pattern) when the mask pattern according to the present invention shown in FIG. 1 is used and when the conventional pattern shown in FIG. FIG. 2A shows the experimental result of “the growth rate at the time of overall growth without using the body mask 5”, and FIG. 2B shows the experimental result of the change of the crystal composition with respect to the change of the growth rate.

As can be seen from FIG. 2 (B), when the selective growth of the present invention was used, the change in crystal composition wavelength could be greatly suppressed as compared with the conventional example, while the crystal growth rate was greatly changed. That is, the present inventor has newly found that a large change in layer thickness can be obtained while suppressing a change in crystal strain amount.

The effect of reducing the crystal strain is that the dielectric mask 5 having a width narrower than the diffusion length (tens of μm) of the raw material species such as In and Ga in the vapor phase is used. This is because the change in the crystal composition due to the difference in the diffusion length of the Ga raw material is suppressed.

The growth rate increase rate with respect to the width of the dielectric mask 5 is substantially proportional to the coverage rate of the dielectric mask 5. That is, all the raw material species that are not consumed (grown) in the coating region are consumed (grown) in the growth region.

With reference to FIG. 2A, for example, growth is performed when the growth region 2 has a width of 1.5 μm and the mask region of the dielectric mask 5 (also referred to as “mask region 5”) has a width of 1.5 μm. When the rate is “1”, the growth rate is “2” when the growth region 2 has a width of 1.5 μm and the mask region 5 has a width of 3.0 μm. As a result, when the growth pressure was 150 torr, the change in the growth rate was about 3 times at maximum in the conventional selective growth.
I found that it can be changed more than twice.

As described above, in the method for manufacturing a semiconductor optical device of the present invention, the change in the crystal layer thickness is large with respect to the change in the width of the dielectric mask 5, but the change in the crystal composition is suppressed, that is, the amount of crystal strain. Can be suppressed.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in the order of manufacturing steps with reference to the drawings.

[0030]

First Embodiment <Tunable Wavelength Staircase Waveguide Structure (TSG) DBR Laser>
3 to 5 are views for explaining a manufacturing process of a wavelength variable step waveguide structure (TSG) DBR laser according to an embodiment of the present invention in process order.

FIG. 3A is a plan view showing a first selective growth mask pattern.

Referring to FIG. 3A, first, on the n-InP substrate 1, the active region, the phase adjustment region, and the D region are formed in the <011> direction.
BR area is provided and pitch is about 240nm only in DBR area
The diffraction grating 20 is formed.

Next, as a dielectric mask, S having a width of 5 μm is used.
The iO ₂ growth blocking mask 5 is formed so as to face each other with a 1.5 μm opening (growth region 2) in between.

FIG. 3B schematically shows a cross section of the crystal layer structure after the first selective growth. SiO shown in FIG.
_{2 On} the substrate 1 on which the growth stop mask 5 is formed, the first n
-GaInAsP light confinement layer 3, n-InP spacer layer 4, GaInAsP / GaInAsP multiple quantum well (MQW) layer 6, second i-GaInAsP light confinement layer 7, and p-InP cladding layer 8 are selectively grown.

At this time, the composition of the first and second GaInAsP optical confinement layers 3 and 7 grown in the opening (growth region 2) is 1.25 μm, and the layer thickness of both layers is 0.1 μm. .

The multiple quantum well layer 6 (GaInAsP)
Quantum well composition wavelength 1.6 μm, layer thickness 7 nm / GaIn
The composition wavelength of the AsP barrier was 1.3 μm, and the gain peak wavelength of the layer thickness of 10 nm) could be set to 1.55 μm.

After the first selective growth, a second film of about 50 nm thickness is formed.
Of the SiO ₂ film 55 is formed on the entire surface of the substrate, removing a portion wet etching only the second SiO ₂ film 55, FIG. 4
A mask pattern as shown in (C) is formed.

Then, by using this mask pattern, the p-InP cladding layer 8 and the second i-GaInAs in the phase adjustment region and the DBR region are selectively etched.
P light confinement layer 7, and GaInAsP / GaInAs
The P-multiple quantum well layer 6 is removed to form a sectional structure as shown in FIG.

Next, using the mask pattern of FIG. 4C, as shown in FIG. 5E, the phase adjustment region and the DBR are formed.
The i-GaInAsP layer 9 and the p-InP cladding layer 8 are formed only in the region by the second selective growth.

At this time, the composition wavelengths of the i-GaInAsP layer 9 in the phase adjusting region and the DBR region are respectively 1.3.
3 μm and 1.32 μm, and the layer thickness is 0.6
It was possible to set the thickness to 0.1 μm or 0.15 μm.

Although the layer thickness ratio of the i-GaInAsP layer 9 in both the phase adjustment region and the DBR region was as large as 4 times, the difference in crystal lattice could be suppressed to 0.05% or less. . As a result, the wavelength tunable staircase waveguide structure (TSG) has a layer thickness difference of twice or more between the phase adjustment region and the current injection layer (i-GaInAsP layer 9) in the DBR region.
It was possible to satisfy the necessary conditions for obtaining continuous wavelength tunable characteristics in the DBR laser.

After each semiconductor layer is formed in this way, the mask opening width of the SiO ₂ growth blocking mask 5 is set to 6 μm in the entire region (active region, phase adjusting region, DBR region), and the SiO ₂ stripe grows. Re-formation is performed so that only one pair on both sides of the region 2 remains, and using this mask, p-
The InP burying layer 10 (layer thickness: 1.5 μm) is MOVPE
The crystal grows. After that, the SiO ₂ film 11 was formed, and the upper electrode 12 and the lower electrode 13 were formed by the usual sputtering method or the like to obtain a TSG-DBR laser.

Element length 800 μm (active region length 300 μm
m, phase adjustment region length 200 μm, DBR region length 300 μm
When an element of m) was produced, the oscillation threshold current was 6 mA.
Shows laser oscillation, maximum optical output 15 mW, single current injection into phase adjustment region and DBR region Continuous wavelength variable width 7 n
m was obtained.

[0044]

Second Embodiment <Multiwavelength DFB Laser Array> FIGS. 6 to 9 are views for explaining a manufacturing process of a multiwavelength DFB (distributed feedback type) laser array according to a second embodiment of the present invention.

FIG. 6 shows a dielectric mask pattern for the first selective growth. First, the diffraction grating 20 having a pitch of about 240 nm is formed on the entire surface of the p-InP substrate 31. Next, with a period of 300 μm, 8 sets (DFB1, DFB2, ..., DF
A mask pattern for selective growth up to B8) is formed. The mask pattern is the same from DFB1 to DFB8, and the mask pattern per set is Si with a width of 3 μm.
Only a pair of O ₂ growth blocking masks 5 are formed so as to face each other with a 1.5 μm opening (growth region 2) in between.

FIG. 7 is a perspective view schematically showing the crystal structure after the first selective growth using this mask.

Referring to FIG. 7, growth region 2 on substrate 31
In addition, the first i-GaInAsP optical confinement layer 9, GaI
nAsP / GaInAsP multiple quantum well layer 6, n-In
The P layer 4 is selectively grown. At this time, the first optical confinement layer 9
Has a composition wavelength of 1.25 μm and a layer thickness of 0.1 μm.
Further, the gain peak wavelength of the multiple quantum well layer 6 (GaInAsP quantum well composition wavelength 1.6 μm, layer thickness 7 nm / GaInAsP barrier composition wavelength 1.3 μm, layer thickness 10 nm) could be set to 1.55 μm.

After the first selective growth, the first SiO ₂ film 5 is formed.
The second SiO ₂ film 55 with a thickness of about 50 nm
Is formed on the entire surface of the substrate. Then, the second SiO ₂ film 55
Partly removed by wet etching, DFB1 ~ D
In FB8, as a mask pattern per set,
An array-shaped dielectric stripe pattern 55 as shown in FIG. 8 is formed.

At this time, the second SiO ₂ film 55 is formed on the first SiO ₂ film 5 in the portion where the first SiO ₂ film 5 is present.

Further, the pattern shown in FIG.
The width of the second SiO ₂ film 55 is different in each set up to DFB8. The width is 3 μm in DFB1 and the width is 4 in DFB2.
.., DFB8 has a width of 10 .mu.m, which is different by 1 .mu.m for each set.

Using this second SiO ₂ mask 55,
As shown in FIG. 9, n-GaInAsP is formed in the growth region 2.
The layer 3 and the n-InP layer 30 are formed by the second selective growth.

At this time, n-GaI of DFB1 to DFB8
The composition wavelength of the nAsP layer 3 is 1.25 μm to 1.26 μm.
m, and the layer thickness could be 0.25 μm to 0.05 μm. At this time, the change in the composition strain amount of the n-GaInAsP layer 3 could be set to 0.05% or less. That is, in the DFB1 to DFB8, the n-GaInAsP layer 3
It was possible to suppress the change in the composition strain amount while increasing the layer thickness difference.

After each semiconductor layer is formed in this manner, a pair of SiO ₂ masks 5 and 55 on both sides of the growth region 2 are formed.
The mask opening width is set to 6 μm, and the other SiO ₂ stripe masks 55 formed in an array are removed by etching so that only one pair on both sides of the growth region 2 remains.

Using this mask, an n-InP buried layer 40 (layer thickness: 1.5 μm) is crystal-grown in the growth region 2,
After that, the SiO ₂ film 11 was formed, and the p-side electrode 12 and the n-side electrode 13 were formed by an ordinary sputtering method or the like, whereby a DFB laser array as a multi-wavelength light source could be obtained.

This DFB laser array is composed of n-GaIn
Since each AsP layer 3 has a different layer thickness, each laser (D
The equivalent refractive index (FB1 to DFB8) is changed from 3.24 to 3.20, and the oscillation wavelength is 1.555 μm.
To 1.535 μm could be distributed in the range of about 20 nm.

When eight DFB laser arrays each having a device length of 500 μm were produced, the oscillation wavelengths from DFB1 to DFB8 were 1.535 μm to 1.555 μm, and the average oscillation threshold current of each DFB laser was 6 mA, and the average. Good characteristics of optical output of 15 mW were obtained.

The embodiment of the present invention has been described above.
The present invention is also effective in selective growth using a material other than GaInAsP / InP.

Further, in the present invention, the method of forming the optical waveguide by selective growth with the opening width of the SiO ₂ mask being 1.5 μm has been described. However, the selective growth in which the opening width of the SiO ₂ mask for selective growth is made wider is explained. It is also valid for the law.

[0059]

As described above, in the method for manufacturing a semiconductor optical device according to the present invention, in the selective growth, the crystal layer thickness is largely changed in the regions having different mask widths while the crystal strain amount is hardly changed. Because it can be
Multi-wavelength DFB laser, multi-wavelength DBR laser, TSG-D
It is very promising for producing BR lasers and the like. That is, according to the present invention, the equivalent refractive index of the optical waveguide can be greatly changed in the waveguide direction, and there is an advantage that a multi-wavelength DFB laser array and a DBR laser array covering a wide wavelength range can be collectively formed. is there. In the conventional selective growth, when the crystal layer thickness is changed, the crystal strain amount is also changed, so that there is a problem that the crystal layer thickness cannot be made too thick. However, according to the present invention, the crystal layer thickness can be freely set. There is an advantage that it can be set to.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the operation of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.

FIG. 3 is a diagram for explaining one embodiment of the present invention in the order of manufacturing steps.

FIG. 4 is a diagram for explaining one embodiment of the present invention in the order of manufacturing steps.

FIG. 5 is a diagram for explaining an embodiment of the present invention in the order of manufacturing steps.

FIG. 6 is a view for explaining the second embodiment of the present invention in the order of manufacturing steps.

FIG. 7 is a diagram for explaining the second embodiment of the present invention in the order of manufacturing steps.

FIG. 8 is a diagram for explaining the second embodiment of the present invention in the order of manufacturing steps.

FIG. 9 is a view for explaining the second embodiment of the present invention in the order of manufacturing steps.

FIG. 10 is a diagram for explaining a conventional technique.

[Explanation of symbols]

1 n-InP semiconductor substrate 2 growth region 3 n-GaInAsP layer 4 n-InP layer 5 dielectric (SiO ₂ ) thin film 6 GaInAsP / GaInAsP multiple quantum well layer 7 i-GaInAsP semiconductor layer 8 p-InP layer 9 i-GaInAsP Layer 10 p-InP clad layer 11 SiO ₂ thin film 12 p-side electrode 13 n-side electrode 20 diffraction grating 30 n-InP layer 31 p-InP substrate 40 n-InP buried layer 55 second SiO ₂ thin film

Claims (7)

[Claims] 1. A method of manufacturing a semiconductor optical device, comprising the step of selectively crystallizing a semiconductor multilayer structure composed of a quantum well layer or a bulk layer in an optical waveguide region sandwiched between striped dielectric thin films, A method for manufacturing a semiconductor optical device, characterized in that a plurality of striped dielectric thin films are formed in parallel. 2. A plurality of the striped dielectric thin films are formed in parallel at a period Λ, and the period Λ is shorter than a diffusion length of a raw material species in a reaction tube during crystal growth. The method for manufacturing a semiconductor optical device according to claim 1. 3. The method for producing a semiconductor optical device according to claim 1, wherein the group III source species used during crystal growth is G
A method for manufacturing a semiconductor optical device, which is an organic metal containing at least one selected from the group consisting of a, In, and Al. 4. The method for manufacturing a semiconductor optical device according to claim 1, wherein the reaction tube pressure during crystal growth is 150 torr or less. 5. The period Λ of the striped dielectric thin film.
3. The method for manufacturing a semiconductor optical device according to claim 2, wherein the length is varied in the longitudinal direction. 6. The semiconductor light according to claim 2, wherein a plurality of groups of the plurality of striped dielectric thin films are arranged in parallel, and the period Λ is varied between the plurality of groups. Device manufacturing method. 7. A semiconductor optical device comprising an optical waveguide layer formed by selective crystal growth in a growth region sandwiched between striped dielectric thin films formed on a substrate, wherein the striped dielectric thin films are predetermined. The optical semiconductor element is characterized in that a plurality of crystal layers are arranged in parallel at a period of, and the thickness of the selectively grown crystal layer is varied, and accordingly, the equivalent refractive index of the optical waveguide is varied in the optical waveguide direction.