JPH1126874A - Optical semiconductor device - Google Patents

Abstract

(57) Abstract: An optical semiconductor device has a spot size symmetrical without increasing the series resistance of the optical semiconductor device. SOLUTION: A tapered waveguide section 6 in which the size of a core layer 2 for guiding light which is made of one or more layers continuously decreases toward a light emitting end face is integrated on an n-type semiconductor substrate 1. At the same time, the core layer 2 and n are formed only in the tapered waveguide section 6 and at least at the tip end of the tapered waveguide section 6.
A refractive index control layer 5 having a higher refractive index than the n-type semiconductor substrate 1 is provided between the substrate 1 and the n-type semiconductor substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device, and more particularly, to an optical semiconductor device such as a semiconductor laser in which a spot size converter used for optical fiber communication is integrated.

[0002]

2. Description of the Related Art Optical fiber communication has been widely used for trunk line communication since a large amount of information can be transmitted by one optical fiber, but recently, multimedia information has been provided to ordinary households. FTTH (Fiber to
the Home: Pull the optical fiber to the general home,
Attempts to provide large-capacity information such as images) have been proposed and are becoming practical.

Since the semiconductor laser module used in this system is premised on sales to general subscribers, it is essential to reduce the price and mass production. For this reason, in particular, the optical semiconductor element and the optical semiconductor module in the optical module are required. Optical coupling with fiber has become a major problem.

[0004] In order to solve such a problem, the thickness or width of the waveguide is changed in a tapered shape toward the emission end face, and a spot in which a tapered waveguide enabling direct coupling with an optical fiber is integrated. A semiconductor laser with a size converter is being developed.

In this semiconductor laser with a spot size converter, the light spot size is enlarged at the tip end of the tapered waveguide, which is the emission end, and approaches the spot size of the optical fiber. High coupling efficiency with the fiber is obtained.

In addition, since the positioning accuracy is relaxed,
Elements can be mounted by passive alignment for aligning with an optical fiber without emitting a semiconductor laser, and mass production of modules becomes possible.

An example of a conventional semiconductor laser with a spot size converter (for example, see Japanese Patent Application No. 6-165145) will be described with reference to FIGS. FIG. 7 is a perspective view of a conventional semiconductor laser with a spot size converter. First, a selective growth mask (not shown) having a stripe-shaped opening is provided on the surface of an n-type InP substrate 41, and an SCH layer is formed. (Light guide layer) 42, quantum well layer 43,
The SCH layer 44 and the p-type InP cladding layer 45 are continuously grown.

At this time, the width of the stripe-shaped opening provided in the selective growth mask is a tapered opening whose width gradually increases toward the emission end face in the region where the tapered waveguide portion 54 is formed, while the gain is increased. In the region where the region 55 is formed, the opening is made uniform and narrow so that the SCH layer 42 constituting the core layer, the quantum well layer 43 of the MQW structure (multiple quantum well structure), and the SCH layer 44 are formed. The thickness is gradually reduced in the tapered waveguide portion 54 toward the emission end face in a tapered shape, and the gain region 55 has a flat structure.

Next, after removing the selective growth mask,
Newly provided striped SiO _TwoMask (shown
) Is used as a mask for dry etching.
The p-type InP cladding layer 45 to the n-type InP substrate 41
Is mesa-etched to form a mesa stripe 46
To achieve.

Next, the SiO_TwoSelect mask growth mask
And a p-type InP
The buried layer 47 and the n-type InP current blocking layer 48 are selectively formed.
After lengthening, SiO_TwoThe mask is removed and the entire surface is p-type.
InP cladding layer 49 and p ⁺Type InGaAs contactor
A growth layer 50 is grown.

Next, a resist (not shown) is provided on the entire surface, and is patterned so as to remain only on the gain region 55. Then, the exposed p ⁺ -type InGaAs contact layer 5 is exposed.
0 is selectively removed.

Next, an SiO ₂ film 51 is provided on the entire surface, an opening is provided in a portion corresponding to the mesa stripe 46, a p-side electrode 52 is provided, and an n-side electrode 53 is provided on the back surface of the n-type InP substrate 41. Thereby, the basic structure of the semiconductor laser with the spot size converter is completed.

FIG. 8A is a cross-sectional view along the optical axis of the semiconductor laser with a spot size converter shown in FIG.
5, the light confinement ratio is high, and the light confinement ratio gradually decreases toward the tip of the tapered waveguide portion 54.
The following narrow radiation angles can be achieved.

Further, since the thickness of the quantum well layer 43 in the tapered waveguide portion 54 is smaller than the thickness in the gain region 55, the energy between the quantum levels increases, and the quantum well layer 43 becomes transparent to the oscillation wavelength in the gain region 55. since, it is not necessary to have a gain current is injected into the tapered waveguide section 54, it can be realized 10mA below the low threshold current I _th at the same time.

FIG. 8B is a cross-sectional view of the semiconductor laser with the spot size converter shown in FIG. 7 in the vicinity of the light emitting end face on the side of the tapered waveguide portion 54 and perpendicular to the optical axis. As shown in the figure, the shape of the spot size of the laser beam, and therefore, the light intensity distribution 56 becomes an asymmetric distribution in the vertical direction, deviates from the circular spot size of the optical fiber, and a sufficient optical coupling efficiency cannot be obtained. Which is due to the low refractive index n
It is pointed out that this is due to the influence of the type InP substrate 41.

That is, in a general semiconductor, the refractive index decreases due to the concentration of the doped impurity due to the influence of free carrier absorption irrespective of the p-type or n-type. The mass is larger than that of electrons, and the decrease in refractive index due to light absorption is smaller than that of an n-type semiconductor. For example, in the case of InP, the decrease in refractive index due to doping of n-type InP is larger than that of p-type InP.
Since the InP substrate 41 is doped at a high concentration of about 10 ¹⁸ cm ⁻³ , the refractive index is lower than that of the p-type InP cladding layers 45 and 49.

On the other hand, at the tip of the tapered waveguide portion 54, the spot size is enlarged to about 3 μm, and the optical electric field is extended to the n-type InP substrate 41 also serving as the n-type cladding layer. Since the refractive index is low, the optical electric field is pushed up toward the p-type InP cladding layers 45 and 49, and the light intensity distribution 56 is asymmetric in the vertical direction.

In order to solve such a problem, the present inventors have developed an n-type InP substrate between the n-type InP substrate and the SCH layer.
Since it is proposed to interpose a buffer layer (see Japanese Patent Application No. 8-271996 if necessary), this improved semiconductor laser with a spot size converter is shown in FIGS.
0 will be described.

FIG. 9 is a perspective view of a semiconductor laser having a spot size converter. First, an electron concentration of ³ × 10 ¹⁸ cm ⁻³ is placed on an n-type InP substrate 61. 0.0 × 10 ¹⁷ c
In m ^-3, thickness 2.5μm of n-type InP buffer layer 62
Is provided, a selective growth mask (not shown) having a stripe-shaped opening on the entire surface is provided, and the SCH layer 63, the quantum well layer 64, the SCH layer 65, and the p-type InP cladding layer 66 are sequentially grown.

[0020] Then, the entire surface is deposited an SiO ₂ film (not shown), after patterning the striped SiO ₂ mask width 1.5 [mu] m (not shown), the SiO ₂
Mesa etching is performed using the mask as a mask, and n-type In
The mesa stripe 67 is formed by etching so as to reach the P substrate 61.

Next, using this SiO ₂ mask as a selective growth mask, the Fe-doped InP buried layer 68 and the n-type InP current blocking layer 69 are sequentially grown in the same steps as in the SI-PBH type laser.

Next, after removing the SiO ₂ mask, the p-type InP cladding layer 70 and the p ⁺ -type InGa
Sequentially grown As contact layer 71, then the entire surface is provided a resist (not shown), after patterned to remain only on the gain region 76, the exposed p ⁺ -type I
The nGaAs contact layer 71 is selectively removed.

Next, an SiO ₂ film 72 is provided on the entire surface, an opening is provided in a portion corresponding to the mesa stripe 67, a p-side electrode 73 is provided, and an n-type InP substrate 61 is provided.
By providing the n-side electrode 74 on the back surface of the semiconductor laser, the basic structure of the semiconductor laser with a spot size converter is completed.

FIGS. 10 (a) and 10 (b) FIGS. 10 (a) and 10 (b) are cross-sectional views along the optical axis of the semiconductor laser with the improved spot size converter shown in FIG. 9, respectively. And a sectional view perpendicular to the optical axis in the vicinity of the emission end face. As is apparent from the figure, in the semiconductor laser with an improved spot size converter, an n-type InP buffer layer 62 having a low electron concentration is provided. Therefore, the decrease in the refractive index due to light absorption by free carriers in the n-type InP buffer layer 62 is reduced, and n
Since the influence of the type InP substrate 11 is reduced, the light intensity distribution 77 can be more symmetrically and sufficiently expanded in the tapered waveguide portion 75, thereby greatly increasing the coupling efficiency with a waveguide such as an optical fiber. To be improved.

[0025]

However, in the case of a conventional semiconductor laser with an improved spot size converter, n
Since the n-type InP buffer layer 62 having a lower carrier concentration than the n-type InP substrate 61 also exists in the gain region 76, the n-type InP
If the P buffer layer 62 is too thick, the resistance increases due to the n-type InP buffer layer 62, preventing current injection into the quantum well layer 64 serving as an active layer, and increasing the series resistance of the laser element. There is a problem that laser characteristics are impaired.

Accordingly, an object of the present invention is to make the spot size symmetrical without increasing the series resistance of the optical semiconductor device.

[0027]

FIG. 1 is an explanatory view of the principle structure of the present invention. Referring to FIG. 1, means for solving the problem in the present invention will be described. 1) and FIG. 1B are a cross-sectional view taken along the optical axis of an optical semiconductor device with a spot size converter of the present invention and a cross-sectional view in the vicinity of the exit end face, which is perpendicular to the optical axis.

1 (a) and 1 (b) (1) In the present invention, the size of the core layer 2 composed of one or more layers for guiding light continuously decreases toward the light emitting end face. In the optical semiconductor device in which the tapered waveguide section 6 is integrated on the n-type semiconductor substrate 1, the core layer 2 and the n-type are formed only in the tapered waveguide section 6 and at least at the tip of the tapered waveguide section 6. A feature is that a refractive index control layer 5 having a higher refractive index than the n-type semiconductor substrate 1 is provided between the semiconductor substrate 1 and the semiconductor substrate 1.

As described above, since the refractive index control layer 5 having a higher refractive index than the n-type semiconductor substrate 1 is provided only in the tapered waveguide portion 6, the series resistance in the gain region 7 can be increased without increasing the series resistance. Since the light intensity distribution 9 can be made symmetric, the coupling efficiency with the optical fiber can be increased without impairing the laser characteristics.

(2) Further, according to the present invention, in the above (1), the refractive index control layer 5 has a lower carrier concentration than the n-type semiconductor substrate 1 and a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or less. It is an n-type semiconductor layer.

When such a refractive index control layer 5 is formed of an n-type semiconductor layer, the carrier concentration may be lower than that of the n-type semiconductor substrate 1, and in particular, the carrier concentration of the n-type semiconductor substrate 1 (−10) Considering ¹⁸ cm ⁻³ ), it is desirable to set the carrier concentration to 5 × 10 ¹⁷ cm ⁻³ or less in order to obtain the desired effect.

(3) The present invention is characterized in that, in the above (1), the refractive index control layer 5 is a high-resistance semiconductor layer of either an intrinsic type or an impurity compensation type.

As described above, the refractive index control layer 5 may be an intrinsic or impurity-compensated high-resistance semiconductor layer, that is, an i-type semiconductor layer, and may be an n-type semiconductor layer or a p-type semiconductor layer. The refractive index can be made higher than used.

(4) The present invention is characterized in that, in the above (1), the refractive index control layer 5 is a p-type semiconductor layer having the same carrier concentration as the p-type cladding layers 3 and 4. .

When the refractive index control layer 5 is formed of a p-type semiconductor layer, the carrier concentration (n _h ) of the p-type semiconductor layer is set to be substantially equal to that of the p-type cladding layers 3 and 4. , The refractive index distribution can be made extremely symmetrical, and therefore, the light intensity distribution 9 can be made more symmetrical. It should be noted that in this case, substantially the same level
It means a range of _h ± 0.5n _h.

(5) The present invention is characterized in that in any one of the above (2) to (4), the refractive index control layer 5 is either a diffusion layer or an ion implantation layer.

As described above, the refractive index control layer 5 may be formed by diffusion or ion implantation, and the n-type semiconductor layer, the i-type semiconductor layer,
Alternatively, a p-type semiconductor layer can be formed, and when protons, that is, hydrogen ions or oxygen ions are used, an n-type semiconductor layer or an i-type semiconductor layer can be formed depending on the dose.

(6) The present invention is characterized in that in any one of the above (2) to (4), the refractive index control layer 5 is a selective growth layer.

Such a refractive index control layer 5 may be provided by selectively growing a semiconductor layer having a predetermined refractive index in a groove selectively provided in the n-type semiconductor substrate 1.

(7) In the present invention, in any one of the above (1) to (6), the thickness of the refractive index control layer 5 is
It is characterized by being at least 2 μm.

As described above, the thickness of the refractive index control layer 5 is 2 μm
As described above, the n-type semiconductor substrate 1 having a low refractive index
Can be reduced as much as possible.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, a first embodiment of the present invention will be described with reference to FIGS. Note that FIG.
FIG. 2A is a perspective view of an n-type InP substrate, and FIG.
3C is a cross-sectional view along the optical axis. FIGS. 3C to 4F are cross-sectional views perpendicular to the optical axis in the gain region. FIG. 4 is a cross-sectional view perpendicular to the optical axis in the vicinity of an emission end face of a wave guide.

Referring to FIG. 2 (a), first, the n-type carrier concentration is 1.0 to 3.0 × 10¹⁸cm
^-3For example, 2.0 × 10¹⁸ cm^-3N-type InP substrate
11 on the surface, for example, a stripe
SiO with mouth 13_TwoA mask 12 is provided, and Cd_ThreeZ
n_TwoZn as a diffusion source at 500 ° C for 60 minutes
Selectively diffuse to offset the n-type carrier concentration.
The carrier concentration is 2 μm or more, for example, 3 μm.
1 × 10 ¹⁷cm^-3N^-A mold diffusion region 14 is formed.

Next, after the SiO ₂ mask 12 is removed, a new S
After providing an iO ₂ mask (not shown) and providing a stripe-shaped opening, the SCH layer 15, the quantum well layer 16, and the SCH layer 1 are formed by using a metal organic chemical vapor deposition (MOVPE) method.
7, and the p-type InP cladding layer 18 is continuously grown.

At this time, the width of the stripe-shaped opening provided in the SiO ₂ mask is set to the length 20 for forming the tapered waveguide.
In the region of 0 μm, a tapered opening gradually increases in width toward the emission end face, while in the region of the laser having a length of 300 μm, that is, in the region where the gain region is formed, a uniform and narrow opening is formed. Thus, the SCH layer 15, the quantum well layer 16, and the SCH layer 17 constituting the core layer
Is tapered to a thickness of 1/3 over 200 μm toward the emission end face in the tapered waveguide portion, and has a flat structure in the gain region.

In the first embodiment,
The SCH layers 15 and 17 are formed to have a thickness of 50 to 150 nm, for example, 80 nm as a thickness in a region where the laser portion is formed.
Of the InGaAsP layer having a wavelength composition of 1.1 μm.
An InGaAsP barrier layer having an m-wavelength composition and an InGaAsP well layer having a thickness of 6 nm and a 1.35 μm-wavelength composition are alternately deposited so as to have seven well layers.
The thickness of the p-type InP cladding layer 18 is set to 100 to 700 n.
m, for example, 500 nm (0.5 μm).

Next, after removing the SiO ₂ mask, a new surface of 0.2 to 0.5 μm, for example, 0.3 μm in thickness is newly formed on the entire surface after the SiO ₂ mask is removed, as shown in FIG.
O ₂ film (not shown) is deposited, width 1.0-3.0 μm
m, for example, a 2.0 μm stripe-shaped SiO ₂ mask 19, and then the SiO ₂ mask 1 is patterned.
By using 9 as a mask, mesa etching is performed to a depth of 1.5 μm by dry etching using a methane-based gas to form a mesa stripe 20 reaching the n ⁻ type diffusion region 14.

Referring to FIG. 3D, MOVPE is performed in the same process as that of the SI-PBH laser using the SiO ₂ mask 19 as a selective growth mask.
The Fe-doped InP current blocking layer 21 is selectively grown by the method to bury the side surfaces of the mesa stripe 20.

Next, after removing the SiO ₂ mask 19 with a hydrofluoric acid-based etchant, a thickness of 100 μm is formed by MOVPE.
A p-type InP cladding layer 22 of 0 to 6000 nm, for example, 3000 nm (3 μm), and 200 to 2000 n
m, for example, 1000 nm (1 μm) p ⁺ -type InGa
An As contact layer 23 is sequentially grown.

Next, a resist (not shown) is deposited.
Patterning so that the tapered waveguide side becomes an opening.
And exposed p⁺Type InGaAs contact layer 23
After selective removal, the entire surface is 0.2-1.0μ thick
m, for example, 0.5 μm SiO _TwoDepositing a film 24,
In the gain region, the opening corresponding to the stripe-shaped mesa
Provided, and then a p-side electrode 25 and an n-side electrode 26 were provided.
Then, the spot size changes by cleaving the wafer.
The semiconductor laser with the exchanger is completed.

5 (a) and 5 (b). FIGS. 5 (a) and 5 (b) are sectional views taken along the optical axis of a semiconductor laser with a spot size converter according to the present invention, respectively.
5 is a cross-sectional view perpendicular to the optical axis in the vicinity of the emission end face. As is clear from the drawing, in the present invention, the n ⁻ -type diffusion region 1 having a low electron concentration is located only on the tapered waveguide portion 28 side.
4, the decrease in the refractive index due to light absorption by free carriers in the n ⁻ -type diffusion region 14 is reduced, and the influence of the n-type InP substrate 11 is reduced.
In the tapered waveguide portion 28, the light intensity distribution 27 can be more symmetrically and sufficiently widened, thereby greatly improving the coupling efficiency with a waveguide such as an optical fiber.

In the gain region 29, since the n ⁻ -type diffusion region 14 having a low electron concentration, that is, a high resistance does not exist, the series resistance of the laser element does not increase. There is no.

When the voltage-current characteristics of this device were measured, the device resistance was 8 Ω in the above-mentioned conventional semiconductor laser with an improved spot size converter, but in the case of the present invention, it was 4 Ω, which was a conventional spot laser. It was confirmed that the same resistance value as the semiconductor laser with the size converter was obtained.

The efficiency of direct coupling with a single mode fiber is -2.5 dB, and it has been confirmed that high optical coupling efficiency equivalent to that of a conventional semiconductor laser with an improved spot size converter can be obtained. Passive alignment becomes possible.

In the first embodiment,
Although the region for controlling the refractive index is formed by diffusion of the p-type impurity, it may be formed by ion implantation of the p-type impurity, and the concentration of the n-type carrier is reduced by irradiation with protons. The n-type InP substrate 11 may have a width of 100 μm and a depth of 3 μm.
Alternatively, an n ^- type InP layer having a low impurity concentration may be selectively grown and buried in the groove having an m-shaped stripe.

Next, the second and third embodiments of the present invention will be described with reference to FIG. FIG. 6A is a sectional view taken along the optical axis of a semiconductor laser with a spot size converter according to a second embodiment of the present invention. This is completely the same as the first embodiment except that the i-type region 30 is used instead of the n ⁻ -type diffusion region 14 as a layer to be controlled.

The i-type region 30 may be formed by introducing a p-type impurity such as Zn by diffusion or ion implantation and compensating for the n-type impurity of the n-type InP substrate 11, It may be formed by semi-insulation by irradiation or implantation of oxygen ions. Further, a stripe-shaped groove having a width of 100 μm and a depth of 3 μm is provided in the n-type InP substrate 11, and undoped In
The P layer may be selectively grown and buried.

In this case, the refractive index of the i-type region 30 is n
^{Since the} refractive index can be made higher than that of the-type diffusion region 14, the optical electric field can be expanded to the i-type region 30 side,
The optical coupling rate with the optical fiber can be increased.

FIG. 6B is a sectional view taken along the optical axis of a semiconductor laser with a spot size converter according to a third embodiment of the present invention. This is exactly the same as the first embodiment except that a p-type diffusion region 31 is used instead of the n ⁻ -type diffusion region 14 as a layer for controlling the refractive index.

The p-type diffusion region 31 is formed by introducing a p-type impurity such as Zn by diffusion or ion implantation to form an n-type
It may be formed by inverting the conductivity type of the P substrate 11, or alternatively, a stripe-shaped groove having a width of 100 μm and a depth of 3 μm is provided in the n-type InP substrate 11, and a p-type InP layer is selected in this groove. It is also possible to grow and embed it.

In this case, by setting the impurity concentration of the p-type diffusion region 31 to be substantially the same as the impurity concentration of the p-type InP cladding layers 18 and 22, the refractive index distribution above and below the tapered waveguide portion 28 can be substantially reduced. Because it can be symmetric, the spot size can be almost symmetric in the vertical direction,
The optical coupling rate with the optical fiber can be further increased. It should be noted that making the impurity concentration of the p-type diffusion region 31 substantially equal to the impurity concentration of the p-type InP cladding layers 18 and 22 is as follows.
Not necessarily required.

Although the embodiments of the present invention have been described above, the length of the n ⁻ type diffusion region 14, the i type region 30, or the p type diffusion region 31 as the refractive index control layer is 50 μm.
The present invention is not limited to this, and may be appropriately determined according to the length of the tapered waveguide portion 28, and need not be provided over the entire length of the tapered waveguide portion 28.

The stripe structure according to the present invention has an SI-structure.
The present invention is not limited to the PBH structure, and various known buried stripe structures can be applied. For example, the periphery including the upper portion of the mesa stripe 20 of the tapered waveguide portion 28 is formed of an Fe-doped InP layer. It may be embedded.

In each embodiment of the present invention,
Although the tapered waveguide section 28 is of a vertical type in which a taper is formed in the thickness direction, a horizontal tapered waveguide section in which the width of the core layer is gradually reduced toward the emission end face (H.
Fukano, et al. , Electronics
Letters, vol. 31, No. 7,199
5, pp. 1434-1440), and is applicable not only to a semiconductor laser with a tapered waveguide but also to an optical semiconductor device having a spot size converter.

In each of the above embodiments, the quantum well layer has a thickness of 15 nm and a wavelength of 1.1 μm having a wavelength composition of 1.1 μm.
Although the nGaAsP barrier layer and the InGaAsP well layers each having a thickness of 1.35 μm and having a composition of 6 nm are alternately deposited so as to have seven well layers, the present invention is not limited to such a structure. Required wavelength, for example, 1.5μ
The composition, thickness, and number of layers of each layer may be arbitrarily selected according to the m band and the output.

In each of the above embodiments,
Although the present invention has been described as an nGaAsP / InP-based optical semiconductor device, the present invention is not limited to the InGaAsP / InP-based optical semiconductor device, but may be an InAlGaAs-based or InGaAs / Ga-based semiconductor device.
As / AlGaAs system or InGaP / AlIn
The present invention can also be applied to a GaP system or the like.

[0067]

According to the present invention, the refractive index control layer for expanding the light intensity distribution symmetrically is provided only in the tapered waveguide portion serving as the spot size converter.
The coupling efficiency with the optical waveguide can be greatly improved without deteriorating the optical device characteristics, thereby enabling passive alignment, enabling mass production of optical modules at low cost and optical fiber communication. It greatly contributes to the development of

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process partway through the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a manufacturing process of the first embodiment of the present invention up to the middle of FIG. 2;

FIG. 4 is an explanatory diagram of a manufacturing process of the first embodiment of the present invention after FIG. 3;

FIG. 5 is a cross-sectional view of the semiconductor laser with a spot size converter according to the first embodiment of the present invention.

FIG. 6 is a sectional view of a semiconductor laser with a spot size converter according to the second and third embodiments of the present invention.

FIG. 7 is a perspective view of a conventional semiconductor laser with a spot size converter.

FIG. 8 is a cross-sectional view of a conventional semiconductor laser with a spot size converter.

FIG. 9 is a perspective view of a conventional semiconductor laser with an improved spot size converter.

FIG. 10 is a cross-sectional view of a conventional semiconductor laser with an improved spot size converter.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 n-type semiconductor substrate 2 core layer 3 p-type cladding layer 4 p-type cladding layer 5 refractive index control layer 6 tapered waveguide section 7 gain region 8 mesa stripe 9 light intensity distribution 11 n-type InP substrate 12 SiO ₂ mask 13 opening 14 n ⁻ -type diffusion region 15 SCH layer 16 quantum well layer 17 SCH layer 18 p-type InP cladding layer 19 SiO ₂ mask 20 mesa stripe 21 Fe-doped InP current blocking layer 22 p-type InP cladding layer 23 p ⁺ -type InGaAs contact layer 24 SiO ₂ film 25 p-side electrode 26 n-side electrode 27 light intensity distribution 28 taper waveguide part 29 gain region 30 i-type region 31 p-type diffusion region 41 n-type InP substrate 42 SCH layer 43 quantum well layer 44 SCH layer 45 p-type InP cladding layer 46 Mesa stripe 47 P-type InP buried layer 48 n-type InP Current block layer 49 p-type InP cladding layer 50 p ⁺ -type InGaAs contact layer 51 SiO ₂ film 52 p-side electrode 53 n-side electrode 54 tapered waveguide section 55 gain region 56 light intensity distribution 61 n-type InP substrate 62 n-type InP buffer Layer 63 SCH layer 64 Quantum well layer 65 SCH layer 66 p-type InP cladding layer 67 mesa stripe 68 Fe-doped InP buried layer 69 n-type InP current blocking layer 70 p-type InP cladding layer 71 p ⁺ type InGaAs contact layer 72 SiO ₂ Film 73 p-side electrode 74 n-side electrode 75 tapered waveguide section 76 gain region 77 light intensity distribution

Claims (7)

[Claims] 1. A tapered waveguide in which the size of one or more core layers for guiding light is continuously reduced toward a light emitting end face is integrated on an n-type semiconductor substrate. In the optical semiconductor device, only in the tapered waveguide portion,
An optical semiconductor, wherein a refractive index control layer having a higher refractive index than the n-type semiconductor substrate is provided between the core layer and the n-type semiconductor substrate at least at a tip end of the tapered waveguide portion. element. 2. The method according to claim 1, wherein the refractive index control layer is an n-type semiconductor layer having a carrier concentration lower than that of the n-type semiconductor substrate and a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or less. 2. The optical semiconductor device according to 1. 3. The optical semiconductor device according to claim 1, wherein the refractive index control layer is an intrinsic type or impurity compensation type high resistance semiconductor layer. 4. The optical semiconductor device according to claim 1, wherein the p-type semiconductor layer has a carrier concentration substantially equal to that of the p-type cladding layer. 5. The optical semiconductor device according to claim 2, wherein the refractive index control layer is one of a diffusion layer and an ion implantation layer. 6. The optical semiconductor device according to claim 2, wherein the refractive index control layer is a selective growth layer. 7. The optical semiconductor device according to claim 1, wherein the thickness of the refractive index control layer is 2 μm or more.