JPH10275960A - Optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the high-speed modulation operation of an optical semiconductor element and at the same time, to enable the high-efficiency coupling of the element with an optical fiber by a method wherein a window region removed of an optical waveguide layer is etched into a narrow mesa shape and the width or thickness of a clad layer is changed according to the spread of a light distribution. SOLUTION: An optical semiconductor device comprises a structure, wherein a radio wave absorption semiconductor light modulator and a distributed feedback semiconductor laser are monolithically integrated. A modulator region 16, an electrode isolation region and a windodw region 15 are etched into a narrow mesa shape to contrive a reduction in the parasitic capacitance of the optical semiconductor device, the region 15 turns to the emitting end surface of the laser and the width of a narrow mesa 14 spreads into a tapered form. Light propagates while it spreads in the region 15 having not a waveguide structure, but reflection and scatteing of the light are hardly generated on the end surface of the narrow mesa 14 because the width of the mesa 14 spreads in a tapered form toward the emitting end surface. Accordingly, a unimodal outgoing light distribution is obtained without incurring a reduction in light output due to a scattering loss. As this result, the coupling efficiency of an optical fiber is as high as 50%.

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 capable of performing a high-speed modulation operation by an electric signal.

[0002]

2. Description of the Related Art In recent years, research and development for increasing the capacity of a trunk optical communication system have been actively pursued. In addition, in the current situation where the limitation of the loss of the optical fiber with respect to the transmission distance has been removed with the advent of the optical fiber amplifier, it is desired to increase the transmission distance by an external modulation method having a small wavelength chirp.
In particular, a semiconductor optical modulator which has a small wavelength chirp even at the time of high-speed modulation and can be monolithically integrated with a semiconductor laser as a light source is expected as a key device for a next-generation trunk optical communication system.

When a semiconductor optical modulator and a semiconductor laser are monolithically integrated, if there is reflection at the modulator-side end face, the reflected return light that reaches the laser region induces wavelength chirp. Therefore, in the semiconductor light modulator / semiconductor laser integrated light source, it is necessary to extremely reduce the end face reflectance on the modulator side, which is the emission end face. For example, an optical signal modulated at a rate of 2.5 Gbps
In order to transmit m, it is necessary to suppress the end face reflectance to about 0.01% or less. For this purpose, it is not enough to simply coat the exit end face with a low reflection film, and it is necessary to introduce a window structure.

FIG. 16 is a perspective view of an emission end face portion of a conventional electro-absorption type semiconductor optical modulator / distributed feedback type semiconductor laser integrated light source. In the figure, 1 is an n-type InP substrate, 2 is a light absorbing layer, 3 is an Fe-doped semi-insulating InP buried layer, 4
Is a p-type InP cladding layer, 5 is a p-type InGaAs contact layer, 6 is a p-type ohmic electrode made of Au / Zn / Au, 7 is a wiring / bonding pad made of Ti / Pt / Au, 8 is AuGe / Ni / Au An n-type ohmic electrode 9; a SiO ₂ film 9; and a low-reflection coating film 10 made of SiN _x . In order to reduce the end face reflectance, a window region 15 from which the light absorbing layer 2 has been removed is provided near the output end face. In order to enable a high-speed modulation operation, it is necessary to reduce the element parasitic capacitance, and the modulator region 16 and the window region 15 are subjected to narrow mesa processing.

[0005]

By the way, the light output from such an optical modulator / semiconductor laser integrated light source has a monomodal intensity distribution as much as possible in order to secure the coupling efficiency with the optical fiber. It is desirable to have.

FIG. 17 is a schematic explanatory view showing a state in which light is emitted from an emission end face of a conventional light modulator / semiconductor laser integrated light source. That is, in the modulator region 16, light propagates along the light absorption layer 2 which also serves as a waveguide. On the other hand, in the window region 15 having no waveguide structure, light is emitted while spreading, and is reflected and scattered on the side surface of the narrow mesa 14. At the same time as the light output is reduced due to the loss due to scattering, the emitted light distribution is greatly disturbed because the reflected light interferes. As a result, the coupling efficiency with the optical fiber was as low as about 25%, and it was difficult to increase the output.

As described above, in the conventional optical modulator / semiconductor laser integrated light source, when the narrow mesa structure and the window structure are provided at the same time, the loss in the window region increases and the coupling efficiency with the optical fiber decreases. Therefore, there is a problem that it is difficult to increase the output.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a window structure capable of performing a high-speed modulation operation and simultaneously coupling with an optical fiber with high efficiency. Is to make it happen.

[0009]

The essence of the present invention is to provide a high-speed modulation operation by changing the width or thickness of the cladding layer in accordance with the spread of the light distribution in the window region from which the optical waveguide layer has been removed. And high-output operation at the same time.

That is, the present invention provides an optical semiconductor device in which a stripe-shaped optical waveguide layer is embedded by a cladding layer, and the cladding layer has a narrow mesa shape including the optical waveguide layer. At the same time that the optical waveguide layer is removed, the width or thickness of the cladding layer changes in the vicinity of the output end face in accordance with the spread angle of light emitted from the end of the optical waveguide layer toward the output end face. It is characterized by being formed so that it does.

In a preferred embodiment of the present invention, the width or the thickness of the cladding layer is tapered in the vicinity of the exit end face, and the width or the thickness of the cladding layer is stepped in the vicinity of the exit end face. Change in the shape. Furthermore, this optical semiconductor element is characterized in that it is formed on the same semiconductor substrate as other optical semiconductor elements in an integrated manner.

[0012]

According to the present invention, the window structure in which the optical waveguide layer near the exit end face is removed is provided, and the end face reflectivity can be reduced. Further, since the cladding layer including the window region has a narrow mesa shape, the parasitic capacitance can be reduced, and a high-speed modulation operation can be realized. Further, in the window region, light is emitted while spreading from the end of the optical waveguide layer toward the emission end face, but the width or thickness of the cladding layer is formed so as to increase according to the spread angle of the light distribution. I have. Therefore, since light is not reflected or scattered on the side surface of the cladding layer, the light output is not reduced due to scattering loss, and the emitted light distribution is not disturbed. As a result, the coupling efficiency with the optical fiber is high, and high output can be achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (First Embodiment) FIG. 1 is a cross-sectional view of an optical semiconductor device according to a first embodiment of the present invention, taken along a waveguide direction, and shows an electroabsorption semiconductor optical modulator and a distributed feedback semiconductor laser. Are monolithically integrated. FIG. 2 is a perspective view of an emission end face portion of the optical semiconductor device of FIG. In the figure, 1 is an n-type InP substrate, 2 is a light absorbing layer, 12 is an active layer, 13 is a diffraction grating, 3 is Fe-doped semi-insulating In.
P buried layer, 4 is p-type InP clad layer, 5 is p-type I
nGaAs contact layer, 6 is a p-type ohmic electrode made of Au / Zn / Au, 7 is a wiring / bonding pad made of Ti / Pt / Au, 8 is AuGe / Ni / Au
N-type ohmic electrode composed of, 9 is a SiO ₂ film, 10 is a low reflection coating film composed of SiNx, 11 is Si /
It is a highly reflective coating film composed of a SiO ₂ multilayer film.
Modulator region 16, electrode separation region 17, and window region 15
Is etched into a narrow mesa shape to reduce the parasitic capacitance. The length of the window region 15 is 15 μm.
m, and the width of the narrow mesa 14 is 10 μm toward the emission end face.
The tapered shape extends from m to 25 μm.

FIG. 3 shows a horizontal view of the emission end face.
In the window region 15 having no waveguide structure, light propagates while spreading, but since the width of the narrow mesa 14 is tapered toward the emission end face, reflection at the side surface of the narrow mesa 14 Little scattering occurs. Therefore, a unimodal emission light distribution is obtained without causing a decrease in light output due to scattering loss. As a result, the coupling efficiency with the optical fiber was as high as 50%, and an optical output twice that of the conventional one was obtained.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a perspective view of an emission end face of an electro-absorption type optical modulator / distributed feedback type semiconductor laser integrated light source according to a second embodiment of the present invention. In FIG. 4, the same parts as in FIG.
The same reference numerals are given and the description is omitted. The cross-sectional structure along the waveguide of the optical semiconductor device of the present embodiment can be substantially the same as that shown in FIG.

In this embodiment, the p-type InP cladding layer 4 (and the p-type InGaAs contact layer 5) are formed in the modulator region 16, the electrode separation region 17, and the window region 15.
Is formed in advance in a narrow mesa shape by a selective growth method.

FIG. 5 is a plan view showing the wafer surface immediately before the selective growth of the p-type InP cladding layer 4. That is, the light absorption layer 2 and the active layer 12 are processed into a stripe shape, and the periphery thereof is buried with the burying layer 3, and then the growth inhibition masks 19, 19 are formed on the surfaces thereof. The growth prevention mask 19 has a role of preventing the epitaxial growth of the cladding layer 4 and is made of, for example, SiO 2
Can be used. The width of the mask 19 is 3 μm, and the interval between the masks 19 is 19 μm. However, in the window region 15, the interval between the masks 19, 19 is tapered from 10 μm to 25 μm toward the emission end face. The narrow mesa 14 can be formed by selectively growing the p-type InP cladding layer 4 on the wafer on which the growth inhibition masks 19 are formed. In the window region 15, since the width of the narrow mesa 14 is formed so as to expand in a tapered shape toward the emission end face, reflection and scattering do not occur on the side surface of the narrow mesa 14, and high output operation can be obtained.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a perspective view of an emission end face portion of an electro-absorption type optical modulator / distributed feedback type semiconductor laser integrated light source according to the third embodiment of the present invention. In FIG. 6, the same parts as in FIG.
The same reference numerals are given and the description is omitted. The cross-sectional structure along the waveguide of the optical semiconductor device of the present embodiment can be substantially the same as that shown in FIG.

The modulator region 16 and the window region 15 are etched into a narrow mesa shape to reduce parasitic capacitance. The width of the narrow mesa 14 is 10 μm in the modulator region 16 and 25 μm in the window region 15. The length of the window region 15 is 15 μm.

FIG. 7 shows a horizontal view of the emission end face portion.
Since the width of the narrow mesa 14 in the window region 15 is formed as wide as 25 μm, light propagating while spreading in the window region 15 is reflected and scattered on the side surface of the narrow mesa 14 before reaching the emission end face. There is no. Therefore, a single-peaked outgoing light distribution is obtained without lowering the optical output due to scattering loss, and the coupling efficiency with the optical fiber is high.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a horizontal view of an emission end face of an electro-absorption type optical modulator / distributed feedback type semiconductor laser integrated light source according to a fourth embodiment of the present invention. In FIG. 8, the same parts as in FIG.
The same reference numerals are given and the description is omitted. The cross-sectional structure along the waveguide of the optical semiconductor device of the present embodiment can be substantially the same as that shown in FIG.

The width of the narrow mesa 14 is 10 μm in the modulator region 16. The length of the window region 15 is 15 μm, and the width of the narrow mesa 14 is changed by 5 μm every 5 μm. That is, the width of the narrow mesa 14 gradually increases from 10 μm to 25 μm toward the emission end face. As a result, reflection and scattering do not occur on the side surface of the narrow mesa 14, and a high output operation can be obtained.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a horizontal view of an emission end face portion of an electro-absorption optical modulator / distributed feedback semiconductor laser integrated light source according to a fifth embodiment of the present invention. In FIG. 9, the same parts as in FIG.
The same reference numerals are given and the description is omitted. The cross-sectional structure along the waveguide of the optical semiconductor device of the present embodiment can be substantially the same as that shown in FIG.

The width of the narrow mesa 14 is 10 μm in the modulator region 16. The length of the window region 15 is 15 μm, and in the region from the emission end face to 10 μm, the narrow mesa 1
4 has a width of 25 μm. That is, in the region of the window region 15 from the end of the light absorption layer 2 to the length of 5 μm, the width of the narrow mesa 14 is the same as that of the modulator region 16.
μm. However, at a position 5 μm in length from the end of the light absorbing layer 2, the light distribution spreads to only several μm. As a result, there is no reflection or scattering on the side surface of the narrow mesa 14, and a high output operation can be obtained.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 10 is a horizontal view of an emission end face portion of an electro-absorption optical modulator / distributed feedback semiconductor laser integrated light source according to a sixth embodiment of the present invention. 10, the same parts as those in FIG. 3 are denoted by the same reference numerals as in FIG. 3, and the description thereof will be omitted. The cross-sectional structure along the waveguide of the optical semiconductor device of the present embodiment can be substantially the same as that shown in FIG.

In this embodiment, the length of the window region 15 is 15
μm, but the width of the narrow mesa 14 is 25 μm from the emission end face.
In the region of m, it changes from 10 μm to 25 μm in a tapered shape. That is, the width of the narrow mesa 14 changes not only in the window area 15 but also in the middle of the modulator area 16. The surface orientation of the side surface of the narrow mesa 14 differs between a region where the width of the narrow mesa 14 is constant and a region where the width of the narrow mesa 14 changes. Therefore, when the narrow mesa 14 is formed by etching, the side etching amount is different, and it may be difficult to control the width of the narrow mesa 14. In such a case, if the width of the narrow mesa 14 is gradually changed as in the present embodiment, there is an advantage that the control of the width of the mesa becomes easy.

In this embodiment, the length of the tapered region is 25.
μm, which is longer than the length of the window region 15 of 15 μm. As a result, the tapered region extends not only in the window region 15 but also in the modulator region 16. However, the increase in the width of the narrow mesa 14 in the modulator region 16 is slight, and the increase in the parasitic capacitance is negligible, so that the high-speed performance is not impaired.

(Seventh Embodiment) Next, a seventh embodiment of the present invention will be described with reference to FIG. FIG. 11 is a horizontal view of an emission end face of an electro-absorption type optical modulator / distributed feedback type semiconductor laser integrated light source according to a seventh embodiment of the present invention. 11, the same portions as those in FIG. 3 are denoted by the same reference numerals as those in FIG. 3, and the description thereof will be omitted. The cross-sectional structure along the waveguide of the optical semiconductor device of the present embodiment can be substantially the same as that shown in FIG.

In this embodiment, the length of the window region 15 is 15
The width of the narrow mesa 14 is tapered from 10 μm to 25 μm in a region from the position of 15 μm to the position of 5 μm from the emission end face. That is, in the region from the emission end face to 5 μm, the width of the narrow mesa 14 is 25 μm.
It is constant at μm.

By adopting such a shape, there is an advantage that "position shift" in the cleavage step can be dealt with. That is, the end face of the optical semiconductor element is usually formed by cleaving the semiconductor substrate. In this cleaving step, the position of the end face may be shifted by about several μm. FIG. 12 is a horizontal view of the emission end face portion of the optical semiconductor device of FIG. 11 before such a cleavage step. Before the cleavage step, two optical semiconductor elements are placed in the window region 1.
5 is connected. According to the present embodiment, the cleavage position 2
Since the width of the narrow mesa 14 is constant at 25 μm near 0, the width of the narrow mesa 14 at the emission end face does not become narrower than 25 μm even if the cleavage position 20 is slightly shifted. As a result, each of the cleaved and separated optical semiconductor elements has a narrow mesa 1 in a region several μm from the emission end face.
4 are formed so as to have a constant width of 25 μm. That is, the width of the narrow mesa 14 is reduced at the emission end face,
The problem of reflecting and scattering outgoing light can be solved.

(Eighth Embodiment) Next, an eighth embodiment of the present invention will be described.
Will be described with reference to FIG. FIG. 13 is a cross-sectional view of an electro-absorption optical modulator / distributed feedback semiconductor laser integrated light source according to an eighth embodiment of the present invention, taken along the waveguide direction. 13, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and description thereof will be omitted.
In this embodiment, the p-type InP cladding layer 4 (and the p-type InGaAs contact layer 5) is previously formed in a narrow mesa shape by a selective growth method. FIG. 14 shows p-type In
FIG. 5 is a plan view illustrating a wafer surface immediately before selective growth of a P cladding layer 4. That is, the light absorption layer 2 and the active layer 12 are processed into a stripe shape, and the periphery thereof is buried with the burying layer 3.
9 is formed. The width of the growth inhibition mask 19 made of SiO ₂ is 3 μm, and the interval between the masks 19 is 19 μm.
It is. However, in the window region 15, the width of the growth prevention mask 19 is tapered from 3 μm to 30 μm toward the emission end face.

In the case where the p-type InP cladding layer 4 is selectively grown on such a wafer, the wider the width of the growth-blocking mask 19, the higher the p of the region sandwiched by those masks.
The growth rate of the type InP cladding layer 4 increases. This is because the growth raw material supplied on the mask 19 is not deposited on the mask but is taken into the InP layer around the mask. Therefore, in window region 15, p-type In
The P cladding layer 4 is formed so that the thickness thereof increases in a tapered shape toward the emission end face. As a result, p-type InP
Reflection and scattering on the upper surface of the cladding layer 4 are small, and highly efficient coupling with the optical fiber can be obtained.

In the above example, the p-type InP cladding layer 4
Although only the thickness of the tapered shape was expanded, for example,
If the p-type InP cladding layer 4 is selectively grown using the growth inhibition masks 19 and 19 having the shape shown in FIG. 15, the width and the thickness of the p-type InP cladding layer 4 are simultaneously tapered in the window region 15. Can be spread. As a result, in both the width direction and the layer thickness direction, the reflected and scattered outgoing light is eliminated, the coupling efficiency with the optical fiber is improved, and a high light output can be obtained.

The present invention is not limited to the embodiment described above. In the embodiment, the structure in which the width or the thickness of the narrow mesa is changed to a tapered shape, a stepped shape, a rectangular shape, or the like is described. A structure combining shapes may be used. Further, in the embodiment, the InGaAsP-based optical semiconductor device has been described.
The present invention can be applied to various material systems such as a GalnP system. Further, in the embodiment, the structure in which the optical modulator and the semiconductor laser are monolithically integrated has been described. However, other than the above, a single semiconductor laser, an optical modulator, an optical amplifier, an optical switch, an optical coupler, an optical waveguide, The present invention can be applied in the same way to obtain the same various effects even in an element structure in which is integrated.

The light absorbing layer and the active layer may be made of a bulk material or a multiple quantum well structure. Further, the semiconductor buried layer is not limited to the InP layer, and for example, an InGaAsP layer or a semiconductor layer in which an InP layer and an InGaAsP layer are stacked may be used.

Various types of semiconductor layers can be used for the conductivity type of the semiconductor substrate and the semiconductor buried layer. In addition, various modifications can be made without departing from the spirit of the present invention.

[0037]

As described in detail above, according to the present invention,
Even if a narrow mesa structure is provided to reduce the parasitic capacitance and a window structure is provided to reduce the end face reflectance, there is no scattering loss and an emission light distribution suitable for coupling with an optical fiber is obtained. It is possible. Therefore, it is possible to provide a light source that can achieve a high-speed modulation operation and a high output operation, and that has a wide and small wavelength chirp, thereby realizing a large capacity and long distance trunk optical communication system.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an optical semiconductor device according to a first embodiment along a waveguide direction.

FIG. 2 is a perspective view of an emission end face portion of the optical semiconductor device according to the first embodiment.

FIG. 3 is a horizontal view of an emission end face portion of the optical semiconductor device according to the first embodiment.

FIG. 4 is a perspective view of an emission end face portion of an optical semiconductor device according to a second embodiment.

FIG. 5 is a horizontal view showing the wafer surface before the growth of the cladding layer of the optical semiconductor device according to the second embodiment.

FIG. 6 is a perspective view of an emission end face portion of an optical semiconductor device according to a third embodiment.

FIG. 7 is a horizontal view of an emission end face portion of an optical semiconductor device according to a third embodiment.

FIG. 8 is a horizontal view of an emission end face portion of an optical semiconductor device according to a fourth embodiment.

FIG. 9 is a horizontal view of an emission end face of an optical semiconductor device according to a fifth embodiment.

FIG. 10 is a horizontal view of an emission end face of an optical semiconductor device according to a sixth embodiment.

FIG. 11 is a horizontal view of an emission end face portion of an optical semiconductor device according to a seventh embodiment.

FIG. 12 is a horizontal view of a light emitting end face portion of an optical semiconductor device according to a seventh embodiment before a cleavage step.

FIG. 13 is a cross-sectional view of an optical semiconductor device according to an eighth embodiment along a waveguide direction.

FIG. 14 is a horizontal view showing a wafer surface of an optical semiconductor device according to an eighth embodiment before a cladding layer is grown.

FIG. 15 is a horizontal view illustrating a growth prevention mask for an optical semiconductor device according to another embodiment.

FIG. 16 is a perspective view of an emission end face portion of a conventional optical semiconductor element.

FIG. 17 is a horizontal view of an emission end face portion of a conventional optical semiconductor element.

[Explanation of symbols]

Reference Signs List 1 n-type InP substrate 2 light-absorbing layer 3 Fe-doped semi-insulating lnP buried layer 4 p-type InP cladding layer 5 p-type InGaAs contact layer 6 p-type ohmic electrode 7 wiring / bonding pad 8 n-type ohmic electrode 9 SiO ₂ film 10 Low reflection coating film 11 High reflection coating film 12 Active layer 13 Diffraction grating 14 Narrow mesa 15 Window region 16 Modulator region 17 Electrode separation region 18 Laser region 19 Growth inhibition mask 20 Cleavage position

Claims (4)

[Claims] 1. An optical semiconductor device in which a stripe-shaped optical waveguide layer is embedded by a cladding layer, and wherein the cladding layer has a narrow mesa shape including the optical waveguide layer.
The width of the cladding layer or the width of the cladding layer in the vicinity of the emission end face, depending on the spread angle of light radiated from the end of the optical waveguide layer toward the emission end face while the optical waveguide layer is being removed near the emission end face. An optical semiconductor device characterized in that it is formed so that its thickness changes. 2. The optical semiconductor device according to claim 1, wherein the width or the thickness of the cladding layer changes in a tapered shape in the vicinity of the emission end face. 3. The optical semiconductor device according to claim 1, wherein the width or thickness of the cladding layer changes stepwise in the vicinity of the emission end face. 4. The optical semiconductor device according to claim 1, wherein the optical semiconductor device is integrated with another optical semiconductor device on the same semiconductor substrate.