JP2004235182A - Semiconductor optical element and optical transmitter/receiver using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor optical element by which an optical guide can be formed in a length proper to a high-speed optical transmission and which can be integrated in a monolithic manner, and to provide an optical transmitter/receiver using it. <P>SOLUTION: The semiconductor optical element has a reflector 7 composed of at least two kinds of semiconductor layers having different refractive indices formed on a semiconductor substrate 1, the optical guide 2 held by a lower clad layer 3 and an upper clad layer 4 formed on the reflector 7, a reflecting mirror 5 arranged on at least one end face of the optical guide 2 at an angle of 45° to the surface of the substrate 1 and an antireflection film 6 formed on the rear of the substrate 1 at a position opposed to the reflecting mirror 5. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor optical device typified by a semiconductor laser and a photodiode, and more particularly to a semiconductor optical device suitable for high-speed optical transmission and an optical transceiver using the same.
[0002]
[Prior art]
Optical transmission technology plays a major role in increasing the speed and capacity of information transmission between the recent Internet, communication networks, and computers. Among them, the semiconductor optical elements at the center are a semiconductor laser as a light source and a photodiode as a light receiving element, that is, a semiconductor light receiving element, and have been greatly developed in terms of high reliability and high performance.
[0003]
A semiconductor laser is typically divided into an edge-emitting type and a surface-emitting type. In the edge-emitting type, a relatively long optical waveguide is formed in parallel with the substrate, so that a large output is easily obtained. On the other hand, the surface-emitting type has a feature that since an optical waveguide is formed perpendicular to the substrate, a laser is emitted from the back surface of the substrate and is easily integrated. In either case, the optical waveguide forms an active layer that generates light. A resonator necessary for laser light emission is formed by sandwiching both ends of the optical waveguide with reflecting mirrors.
[0004]
In general, an edge-emitting semiconductor chip is obtained by lapping (polishing) a substrate after epitaxial growth to an appropriate thickness and then simultaneously cutting out the chip and forming a resonator end face by double-side cleavage. Double-sided cleavage is performed using a scalpel, a razor, or a cleaver. However, since both sides are cleaved, it is difficult to use an edge-emitting semiconductor laser as a part of an optical (electronic) integrated circuit, or to provide an external reflecting mirror on the laser emission end face side. The mold is generally limited to use as a single part. In addition, it is extremely difficult to monolithically integrate the edge-emitting type because a semiconductor laser having a cleaved end face cannot perform a performance test without element isolation. In addition, in order to perform cleavage, a lower limit must be set for the resonator length, and only 200 μm or more is manufactured at present.
[0005]
On the other hand, in a surface emitting laser having a vertical resonator type configuration in which a resonator is formed in a direction perpendicular to the substrate surface and laser light is emitted in the vertical direction, the resonator is configured in the vertical direction. It is difficult to increase the length of the resonator serving as the gain region, and therefore, a sufficient gain cannot be obtained and a high light output cannot be obtained. Therefore, the surface emitting laser has not been put into practical use.
[0006]
For the semiconductor laser having the above structure, the end surface of the semiconductor stack 81 is formed by the inclined surface 80 made of a reflective film, as shown in FIG. 9, the light beam is guided to the back surface of the substrate 71, and the reflecting mirror 84 is provided on the back surface of the substrate 71. A semiconductor laser having the provided structure is disclosed in Patent Document 1.
[0007]
Next, a relatively long optical waveguide is also formed in the semiconductor light receiving element in parallel with the substrate, a waveguide type in which light is incident from the cleavage end surface, an optical waveguide is formed perpendicular to the substrate, and the light is directed to the substrate surface. There is a vertical incidence type. In the semiconductor light receiving element, a surface incidence type is common. The optical waveguide forms an absorption layer that absorbs light.
[0008]
As in the case of the semiconductor laser, the waveguide type has a lower limit for the length of the waveguide to perform cleavage, whereas the surface incident type has a difficulty in lengthening the waveguide.
[0009]
[Patent Document 1]
JP-A-8-97514
[0010]
[Problems to be solved by the invention]
In the edge emitting semiconductor laser, the electric capacity increases in proportion to the length of the resonator. Therefore, in order to cope with high-speed optical transmission, it is necessary to shorten the resonator length and reduce the electric capacity. For example, in a directly modulated semiconductor laser capable of supporting a transmission speed of 40 Gbps on the trunk line, the resonator length is estimated to be about several tens of μm in order to obtain a required high frequency characteristic. It is difficult to form such a short resonator length by cleavage.
[0011]
In a distributed feedback semiconductor laser (DFB laser), which is a kind of edge emitting type, a diffraction grating is formed along an active layer in order to operate at a single wavelength. The phase of the diffraction grating at the end face is determined by the position of the cleaved diffraction grating, and thereby the oscillation wavelength is determined. The period of the diffraction grating is usually 200 nm to 400 nm. Therefore, the period is controlled with an accuracy of 200 nm for a length of 200 μm, for example. As long as the cleaved end face is used, it is practically difficult to control the phase of the diffraction grating, that is, to control the wavelength.
[0012]
Further, as described above, since it is difficult to monolithically integrate a semiconductor laser using a cleavage end face as a resonator reflector, a semiconductor laser and a semiconductor light receiving element must be separately mounted in a transmission / reception module equipped with a light source and a receiver. I do not get. Therefore, it is difficult to reduce the size of the module, and stray capacitance due to wiring hinders high-speed transmission.
[0013]
On the other hand, in the surface emitting laser, as described above, since the resonator length is only about several μm at most, a sufficiently large gain cannot be obtained, and it is difficult to increase the light output. Further, since the resonator is formed perpendicular to the substrate surface, it is practically impossible to form a diffraction grating in the resonator portion, and a DFB laser as a surface emitting laser has not been realized. Furthermore, it is difficult to integrate an optical modulator on the resonator.
[0014]
Further, in a semiconductor laser having a 45 ° inclined reflecting film and having a reflecting mirror on the back surface of the substrate, a length twice as large as the thickness of the substrate is added to the optical path. Since the substrate thickness usually exceeds 100 μm, it is not only possible to obtain a short optical waveguide for high-speed transmission, but also the amount of light beam reflected and returned because the light beam becomes wider as it approaches the back surface of the substrate. May decrease, and resonance necessary for laser oscillation may not be obtained.
[0015]
Next, also in the light receiving element, in the surface incidence type currently widely used, as described above, since the light receiving layer is formed perpendicular to the substrate, the light absorbing region is thin, and the high speed optical transmission system. However, there is a tendency for sensitivity to be insufficient. The waveguide type is not employed for high-speed optical transmission because the electric capacity increases.
[0016]
Furthermore, in an optical transceiver that incorporates a transmitter and a receiver in one module, a semiconductor laser that is a transmitter emits light from an end surface, and a semiconductor light-receiving element that is a receiver enters light from a substrate surface. Therefore, it is difficult to manufacture the transmitter and the receiver monolithically.
[0017]
An object of the present invention is to provide a semiconductor optical device capable of making an optical waveguide a length suitable for high-speed optical transmission and monolithically integrated, and an optical transceiver using the same.
[0018]
[Means for Solving the Problems]
For example, as shown in FIG. 1, a semiconductor optical device of the present invention for achieving the above object includes a reflector 7 formed on a semiconductor substrate 1 and made of semiconductor layers having different refractive indexes, and a reflector. The optical waveguide 2 sandwiched between the lower clad layer 3 and the upper clad layer 4 formed on the optical disc 7, and the reflecting mirror 5 disposed on at least one end face of the optical waveguide 2 at an angle of 45 ° with respect to the surface of the substrate 1. And an antireflection film 6 formed on the back surface of the substrate 1 at a position facing the reflecting mirror 5.
[0019]
In such a semiconductor optical device of the present invention, the effective optical waveguide length is the optical waveguide length above the reflector 7 and is not affected by the thickness of the substrate 1. Furthermore, since the length due to the thickness of the reflector 7 and the lower cladding layer 3 is remarkably shorter than the length of the optical waveguide 2 horizontal to the surface of the substrate 1, the length of the optical waveguide above the reflector 7 is It can be represented by the length of the optical waveguide 2 that is substantially horizontal to the surface of the substrate 1. Since the length of the optical waveguide 2 is determined by photolithography, there is no lower limit of the length as in the case of cleavage. That is, it becomes possible to make the optical waveguide a length suitable for high-speed optical transmission.
[0020]
In the semiconductor optical device of the present invention, a semiconductor laser is formed by using the optical waveguide 2 as an active layer and forming a resonator using reflection of a light beam by the reflector 7. Since the Bragg reflector 7 becomes a resonator mirror, light can be confined in the active layer region. In FIG. 1, the 45 ° inclined reflecting mirror 5 is disposed only on one end face of the optical waveguide 2 and the reflecting film 67 formed after the etching is disposed on the other end face. It is possible to dispose 45 ° inclined reflecting mirrors 5 on both end faces.
[0021]
A part of the resonating light beam reaches the back surface of the substrate 1 via the reflector 7. At this time, since the antireflection film 6 is formed on the back surface of the substrate 1, the light beam that has reached the back surface of the substrate 1 is emitted outside without returning to the inside of the semiconductor.
[0022]
By using the photolithography technique as described above, the resonator can be accurately manufactured to a length of several tens of μm, and it is easy to cope with high speed. Further, compared with a conventional surface emitting laser having a short resonator length, the gain region can be greatly increased, so that it is possible to cope with higher output.
[0023]
By arranging a diffraction grating along the active layer, a distributed feedback laser can be formed. In the manufacture of such a laser, since the diffraction grating is formed by photolithography and is not accompanied by processing such as cleavage, the phase control of the diffraction grating is not changed and the wavelength controllability is improved.
[0024]
In the semiconductor optical device of the present invention, a semiconductor light-receiving device capable of wavelength selection is formed by using the optical waveguide 2 as an absorption layer and matching the wavelength exhibiting high reflectivity of the reflector 7 with the wavelength that prevents reception. Of the light beam incident from the antireflection film 6, the light beam having a reception blocking wavelength is reflected by the reflector 7 and does not reach the absorption layer. That is, the reflector 7 becomes an optical filter.
[0025]
The absorption layer can be accurately manufactured to a length of several tens of μm by using the photolithography technique as described above, and has a higher speed and higher sensitivity than a conventional semiconductor light receiving element having a short absorption layer length. It becomes easy to cope with the conversion. Although the reflector 7 will be described later in detail, it can be omitted.
[0026]
In any of the above elements, since the light is extracted from the back surface of the substrate, it is not always necessary to form a cleaved end face. If the elements are electrically insulated, the elements can be operated without being physically separated. As a result, a plurality of elements can be monolithically integrated. Similarly, by using a semi-insulating substrate, electronic devices such as a semiconductor laser, a light receiving element, and a transistor can be monolithically integrated, and a light source, a driver, a light receiving element, and an amplifier can be integrated.
[0027]
Further, since the semiconductor laser according to the present invention is a surface emitting type, it can be monolithically integrated with the surface incident type light receiving element. The surface incident type light receiving element may be a conventional type light receiving element in addition to the light receiving element according to the present invention, in which light is vertically incident on a substrate and then guided to a horizontal optical waveguide by a 45 ° inclined reflecting mirror.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a semiconductor optical device and an optical transmission / reception apparatus using the same according to the present invention will be described in more detail with reference to embodiments of the invention shown in some drawings.
[0029]
【Example】
<Example 1>
A first embodiment in which the semiconductor optical device is configured as a 1.3 μm band semiconductor laser is shown in FIGS. 2 shows a perspective structure of the semiconductor laser, and FIG. 3 shows a cross-sectional structure. The structure of this example will be described based on a method for manufacturing an element.
[0030]
On the n-InP substrate 8, an n-InP buffer layer 9 and a Bragg reflector 10 having a quarter-wavelength optical length lattice-matched to InP are formed by crystal growth. The Bragg reflector 10 is composed of a laminated film of n-InGaAs and n-InAlAs, and has a reflectance of 90%.
[0031]
After taking out the substrate 8 from the crystal growth furnace and masking it with an insulating film or the like, the Bragg reflector 10 at a desired portion is etched to form the Bragg reflector 11 having a reflectance of 50%.
[0032]
After removing the etching mask, the substrate 8 is again introduced into the crystal growth furnace, the n-InP buffer layer 12 is formed by crystal growth, and then the upper surface thereof is flattened, and then the n-InGaAlAs lattice-matched to InP is formed. Strained quantum well composed of side SCH (Separate Configuration Heterostructure) layer 13, InGaAlAs strained barrier layer (bandgap 1.32eV, barrier layer thickness 8nm) and InGaAlAs strained quantum well layer (bandgap 0.87eV, well layer thickness 6nm) The active layer 14, the p-InGaAlAs upper SCH layer 15 lattice-matched to InP, the p-InP cladding layer 16, the p-InGaAs cap layer 17, and the p-InGaAs contact layer 18 are formed by MOVPE (Metal Organic Che). Successively formed by crystal growth by ical Vapor Deposition) method. In addition, for the crystal growth, a gas source MBE (Molecular Beam Epitaxy) method or a CBE (Chemical Beam Epitaxy) method can be used.
[0033]
Next, using an insulating film or the like as a mask, a ridge as shown in FIG. 2 is formed by a photoetching process. Etching at this time does not matter, and in addition to photo-etching, wet method, RIE (Reactive Ion Etching), RIBE (Reactive Ion Beam Etching), ion milling, and the like are possible. Etching is stopped in the middle of the p-InP cladding layer 16 so as not to reach the strained quantum well active layer 14.
[0034]
Next, using the insulating film as a mask, the resonator is mesa-etched to the lower SCH layer 13 at an angle of 45 ° to form a reflective surface, and then a periodic film of an amorphous silicon film and a silicon dioxide film is formed on the reflective surface. A high reflectivity film 21 is formed, and the reflection surface is a 45 ° inclined reflecting mirror.
[0035]
Thereafter, a p-side ohmic electrode 19 is formed on the upper surface of the contact layer 18, and an n-side ohmic electrode 20 is formed on the back surface of the substrate 8. A mask is previously masked with an oxide on the back surface of the substrate 8 facing the reflecting mirror, and the n-side ohmic electrode 20 is removed by lift-off. An antireflection film 22 made of a silicon oxynitride film is formed at the site where the electrodes have been removed. If the light extraction surface is processed into a spherical surface, the coupling efficiency with the fiber can be improved.
[0036]
The elements are separated by dicing to obtain a semiconductor laser element having a resonator length of about 80 μm. Thereafter, bonding is performed on the heat sink with the element facing down.
[0037]
In the semiconductor laser of this example, when a voltage is applied between the electrodes 19 and 20, light emission occurs in the strained quantum well active layer 14. The emitted beam is reflected by a 45 ° reflector, resonates between the Bragg reflectors 10 and 11, and becomes laser light. Since the Bragg reflector 11 has a lower reflectance, a part of the laser light passes through the Bragg reflector 11 and reaches the back surface of the substrate 8 and is emitted to the outside through the antireflection film 22. The reflectance of the antireflection film 22 is set to 10% or less so that the light beam that reaches the back surface of the substrate 8 does not return to the inside of the semiconductor and become interference light.
[0038]
The prototype semiconductor laser oscillated continuously at room temperature with a threshold current of about 10 mA, the oscillation wavelength was about 1.3 μm, and stably oscillated in a transverse single mode up to a maximum optical output of 30 mW. Further, even when the light output was increased, the end face did not deteriorate, and the maximum light output of 30 mW was limited by thermal saturation. Further, when 30 semiconductor lasers were continuously driven with light output at a constant 15 mW under an ambient temperature of 80 ° C., all elements operated stably for 10,000 hours or more without deterioration of the end face.
[0039]
The produced 1.3 μm band semiconductor laser is suitable for application to a light source of a subscriber optical transmission system.
[0040]
Since the present invention does not depend on the structure of the optical waveguide, for example, a BH (Buried Heterostructure) structure may be used as the optical waveguide structure in addition to the above-described embodiments. Needless to say, the present invention is applicable to semiconductor lasers in the 0.98 μm band and 1.55 μm band in addition to the 1.3 μm band described above as the oscillation wavelength.
[0041]
Although a single layer film made of a silicon oxynitride film is used as the antireflection film 22, a laminated film of a high refractive index film and a low refractive index film may be used. It is desirable to use a material having a refractive index of 1.9 or higher, such as a silicon nitride film, an amorphous silicon film, an aluminum nitride film, a titanium dioxide film, a tantalum oxide film, or a hafnium oxide film, as the high refractive index film. As the low refractive index film, it is desirable to use a material having a refractive index of 1.7 or less, such as a silicon dioxide film, an aluminum oxide film, and a magnesium fluoride film. Similarly, a periodic film made of an amorphous silicon film and a silicon dioxide film is used as the high reflectance film, but it goes without saying that a combination of the above-described high refractive index film and low refractive index film may be used.
[0042]
Further, in this embodiment, the 45 ° reflectors are formed on both end faces of the resonator. However, when cleaving is possible by increasing the resonator length to some extent, one end face is formed by cleaving. A reflective film may be formed. Alternatively, the structure shown in FIG. 1 can be used in which one end face is etched and then a reflective film is formed.
[0043]
Furthermore, although the n-side ohmic electrode 20 is formed on the back surface of the substrate 8, the electrode 20 may be formed on the exposed surface of the buffer layer by etching a part of the element partway through the buffer layer. In this case, the antireflection film 22 may be formed on the entire back surface of the substrate 8. In this manner, the electrode 20 can be formed on the same surface as the p-side ohmic electrode 19, and a semiconductor laser can be formed using a semi-insulating substrate.
[0044]
According to this embodiment, the optical waveguide can be made 80 μm in length suitable for high-speed optical transmission, and the laser beam can be extracted in the direction perpendicular to the substrate. Further, since the Bragg reflectors 10 and 11 can be formed using the same crystal growth furnace as the other crystal layers, the manufacturing process is simple and a highly practical semiconductor laser can be realized.
<Example 2>
FIG. 4 shows a second embodiment in which the semiconductor optical element is configured as a wavelength tunable laser element. This element is formed by integrating a 1.3 μm band semiconductor laser and a wavelength conversion element, and FIG. 4 shows its cross-sectional structure.
[0045]
SiO ₂ The InP substrate 23 is masked by using an insulating film such as an InP buffer layer 24 and a Bragg reflector 25 having a reflectivity of 95% made of lattice-matched InGaAs and InAlAs only at a desired portion, and then the active layer 60 A semiconductor laser portion 61 having an oscillation wavelength of 1.3 μm and having a wavelength of 1 is formed.
[0046]
Next, an InP buffer layer 24 adjacent to the semiconductor laser unit 61, a Bragg reflector 26 having a reflectance of 60% and made of lattice-matched InGaAs and InAlAs is formed, and a variable wavelength conversion element 62 is formed thereon by selective growth. Make it. As the wavelength variable element 62, a multi-electrode distributed feedback laser may be used, or a multi-electrode distributed reflector laser may be used. The laser serving as the light source and the active layer 60 of the wavelength conversion element may be formed to directly contact each other, or a waveguide structure may be formed in the middle to introduce light into the conversion element 62.
[0047]
The end surfaces of the semiconductor laser 61 and the wavelength conversion element 62 are etched to 45 ° to form a reflection surface, and the high reflectivity film 27 is formed on the reflection surface to form a reflection mirror. An antireflection film 28 is formed on the back surface of the substrate. Thereafter, unnecessary portions are removed by etching or lift-off, and ohmic electrodes are formed except for the antireflection film 28.
[0048]
According to the present embodiment, a semiconductor laser 61 having a resonator length of 50 μm can be formed, and this can be integrated with the wavelength conversion element 62, and a semiconductor optical device that performs wavelength sweeping in a maximum wavelength range of 40 nm is realized. I was able to. The tunable laser element obtained by integrating the manufactured 1.3 μm band semiconductor laser 61 and the wavelength conversion element 62 is suitable for application to a light source of a subscriber optical transmission system.
<Example 3>
FIG. 5 shows a third embodiment in which the semiconductor optical device is configured as an optical modulator integrated laser device. This element is formed by integrating a 1.55 μm band semiconductor laser and an optical modulator, and FIG. 5 shows a sectional structure thereof.
[0049]
SiO ₂ The InP substrate 23 is masked by using an insulating film such as an InP buffer layer 24 and a Bragg reflector 29 having a reflectivity of 90% made of lattice-matched InGaAs and InAlAs only at a desired portion, and then the InP buffer layer 24 is laminated to form a diffraction grating 30. A resonator is manufactured by laminating a waveguide layer, an active layer 63, and the like on the diffraction grating 30 to form a distributed feedback semiconductor laser portion 65 having an oscillation wavelength of 1.55 μm.
[0050]
Next, the InP buffer layer 24, the absorption layer 31, and the like are stacked adjacent to the semiconductor laser portion 65, and the optical modulator 66 is fabricated by selective growth. As the optical modulator 66, an electroabsorption optical modulator or a Mach-Zehnder optical modulator may be used.
[0051]
After etching both end surfaces vertically, InP is buried in the etched portion to form an InP buried layer 64, and then the InP buried layer 64 is etched by 45 ° to form a reflective surface. After the electrodes are formed, a high reflectivity film 27 is formed on the reflecting surface to form a reflecting mirror, and an antireflection film 28 is formed on the back surface of the substrate facing the reflecting mirror.
[0052]
Since the reflecting mirror portion of the light modulator 66 has a window structure and the thickness of the substrate 23 is about 100 μm, even when the reflectance of the antireflection film 28 is 1%, the return light intensity of the light modulator 66 is not output. It became 0.01% or less of the light intensity. As a result, transmission at 100 km is possible in optical transmission at a bit rate of 40 Gbps. According to this embodiment, it is possible to realize an optical modulator integrated laser element in which a 1.55 μm band semiconductor laser 65 and an optical modulator 66 are integrated, which is suitable for use as a light source of a trunk optical transmission system.
<Example 4>
FIG. 6 shows a fourth embodiment in which the semiconductor optical device is configured as a photodiode made of an InGaAlAs compound semiconductor. FIG. 6 shows the cross-sectional structure.
[0053]
On the p-InP substrate 32, the p-InAlAs lower cladding layer 33 is 0.5 μm, the p-InGaAlAs lower second core layer 34 is 1.5 μm, the undoped InGaAlAs light absorbing layer 35 is 1.5 μm, and the n-InGaAlAs upper first layer. The 2-core layer 36 was laminated in order of 1.5 μm, the n-InAlAs upper cladding layer 37 was 1.0 μm, and the n-InGaAs contact layer 38 was 0.2 μm.
[0054]
Here, the band gap wavelength of the upper second core layer 36 and the lower second core layer 34 is 1.1 μm, and the band gap wavelength of the light absorption layer 35 is 1.4 μm. This semiconductor multilayer structure was formed into a mesa structure by chemical etching.
[0055]
Thereafter, a reflection surface of 45 ° was formed on the end face of the absorption layer 35, and a high reflectivity film 39 was formed thereon to form a reflecting mirror. The light receiving portion has a waveguide width of 30 μm and a length of 100 μm. Next, an n-side electrode 40 and a p-side electrode 41 were formed. By the lift-off, the electrode on the light receiving surface at the position facing the reflecting mirror was removed, and the antireflection film 42 was formed.
[0056]
When the fabricated photodiode is optically coupled with signal light having a wavelength of 1.3 μm from a flat-end dispersion-shifted fiber having a spot radius Wf of about 4 μm, a light receiving sensitivity of 0.98 A / W is obtained at a bias voltage of 2 V. It was. In addition, the above-mentioned signal light misalignment tolerance is ± 2.0 μm in the vertical direction and ± 12.0 μm in the horizontal direction when the degradation is 0.5 dB, sufficiently covering the amount of misalignment during surface mounting using the passive alignment method. It became possible value. The maximum cutoff frequency at a bias voltage of 2 V was 10 GHz. It should be noted that the same effect can be obtained even if the above structure is constituted by an InGaAsP-based semiconductor layer.
[0057]
In this embodiment, the light absorption layer 35 is a semiconductor layer having no light receiving sensitivity for signal light having a wavelength of 1.55 μm and having light receiving sensitivity for signal light having a wavelength of 1.3 μm. The same effect can be obtained even when a semiconductor layer having light receiving sensitivity is used for light.
[0058]
According to this example, it was possible to realize a semiconductor light receiving element in which the optical waveguide was lengthened to improve the reception sensitivity and the light beam was incident from a direction perpendicular to the substrate.
<Example 5>
FIG. 7 shows a fifth embodiment in which the semiconductor optical device is configured as a photodiode with a Bragg reflector made of an InGaAlAs compound semiconductor. FIG. 7 shows the cross-sectional structure.
[0059]
A Bragg reflector 43 made of InGaAs and InAlAs is formed on the p-InP substrate 32, and a p-InAlAs lower cladding layer 33, a p-InGaAlAs lower second core layer 44, an undoped InGaAs light absorption layer 45, and an n-InGaAlAs upper portion. A second core layer 46, an n-InAlAs upper cladding layer 37, and an n-InGaAs contact layer 38 were sequentially stacked.
[0060]
Here, the reflectance of the Bragg reflector 43 was set to 99.99% for 1.3 μm light. The band gap wavelength of the upper second core layer 46 and the lower second core layer 44 is 1.3 μm. After forming the mesa structure, a 45 ° reflective surface was formed by etching, and a high reflectivity film 47 was formed on the reflective surface to obtain a reflecting mirror. An antireflection film 48 is formed on the back surface of the substrate, and unnecessary portions are removed to form electrodes.
[0061]
When the semiconductor light receiving element according to this example was used in a transmission / reception module having a received signal wavelength of 1.55 μm and a transmitted signal wavelength of 1.3 μm, the sensitivity ratio of the semiconductor light receiving element to the received signal and the transmitted signal was 38 dB. . Thus, since the reflector 43 is a good optical filter, there is no need to install a prefilter for blocking transmission signals in front of the light receiving element.
<Example 6>
An optical transmitter / receiver (optical transmitter / receiver module) constituted by using a semiconductor laser and a semiconductor light receiving element according to the present invention is shown in FIG. 8 as a sixth embodiment.
[0062]
First, the above-described semiconductor laser 50 having an oscillation wavelength of 1.3 μm according to the present invention is formed on the semi-insulating substrate 49. The semiconductor laser 50 may be integrated with an optical modulator, or may be integrated with a wavelength variable element.
[0063]
Next, a laser driving circuit IC (Integrated Circuit) 51 is formed on the same semi-insulating substrate adjacent to the semiconductor laser 50. Further, a semiconductor light receiving element 52 having sensitivity to light having a wavelength of 1.55 μm is formed, and finally a preamplifier circuit IC 53 is manufactured adjacent to the semiconductor light receiving element 52.
[0064]
Formation of each layer starting from the semiconductor substrate of each element and each circuit described above is performed independently by crystal growth on the semi-insulating substrate 49 and photolithography. The antireflection films of the semiconductor laser 50 and the semiconductor light receiving element 52 are common to both, and are formed on the entire back surface of the semi-insulating substrate 49. In addition, in each of the semiconductor laser 50 and the semiconductor light receiving element 52, one electrode is formed on the surface exposed by etching to the middle of the semiconductor substrate or a layer formed thereon. The elements and circuits formed on the semi-insulating substrate 49 are electrically insulated from each other by the semi-insulating substrate 49.
[0065]
By performing desired wiring between each element and each circuit, the main part of the optical transceiver can be formed monolithically on a single substrate. The wiring distance is shortened, and the impedance due to the wiring can be reduced to 40Ω or less. In optical transmission at a bit rate of 40 Gbps, 10 ^-8 The minimum light receiving sensitivity that gives an error rate of −38 dB was good.
[0066]
In the optical transmitter / receiver of this embodiment, the laser beam is emitted and incident in the same vertical direction with respect to the back surface of the semi-insulating substrate 49. Therefore, monolithic integration is easy and highly integrated and compact device ( Module).
[0067]
【The invention's effect】
According to the present invention, in a semiconductor optical device, light can be extracted from the vertical direction of the substrate and the length of the optical waveguide can be adjusted according to the purpose. The semiconductor optical receiving element can be easily manufactured. In addition, since it is possible to configure without using the cleavage end face, monolithic integration is possible.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a basic configuration of a semiconductor optical device according to the present invention.
FIG. 2 is a perspective view for explaining a first embodiment of the present invention.
FIG. 3 is a sectional view for explaining a first embodiment of the present invention.
FIG. 4 is a sectional view for explaining a second embodiment of the present invention.
FIG. 5 is a sectional view for explaining a third embodiment of the present invention.
FIG. 6 is a cross-sectional view for explaining a fourth embodiment of the present invention.
FIG. 7 is a cross-sectional view for explaining a fifth embodiment of the present invention.
FIG. 8 is a sectional view for explaining a sixth embodiment of the present invention.
FIG. 9 is a cross-sectional view for explaining an example of a conventional semiconductor laser.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,8,23,32 ... Semiconductor substrate, 2 ... Optical waveguide, 3,33 ... Lower clad layer, 4, 37 ... Upper clad layer, 5 ... 45 degree reflector, 6, 22, 28, 42, 48 ... Reflection Prevention film, 7, 10, 11, 25, 26, 29, 43 ... Bragg reflector, 9, 12, 24 ... buffer layer, 13 ... lower SCH layer, 14 ... strained quantum well active layer, 15 ... upper SCH layer , 16 ... cladding layer, 17 ... cap layer, 18, 38 ... contact layer, 19, 41 ... p-side electrode, 20, 40 ... n-side electrode, 21, 27, 39, 47 ... high reflectivity film, 30 ... diffraction Lattice, 31, 35, 45 ... absorption layer, 34, 44 ... lower second core layer, 36, 46 ... upper second core layer, 49 ... semi-insulating substrate, 50 ... semiconductor laser, 51 ... laser drive circuit IC, 52 ... Semiconductor light receiving element, 53 ... Preamplifier circuit IC, 67 ... Reflection .

Claims (13)

A semiconductor substrate, a reflector made of at least two types of semiconductor layers having different refractive indexes formed on the substrate, a lower cladding layer formed on the reflector, and an optical light formed on the lower cladding layer A waveguide, an upper clad layer formed on the optical waveguide, a reflecting mirror disposed at an angle of 45 ° with respect to the surface of the substrate on at least one end surface of the optical waveguide, and a position facing the reflecting mirror And an antireflection film formed on the back surface of the substrate. 2. The semiconductor optical device according to claim 1, wherein the reflectance of the antireflection film is 10% or less. 2. The semiconductor optical device according to claim 1, wherein the optical waveguide is an active layer that emits light, and a resonator is formed including the active layer and the reflector. 4. The semiconductor laser according to claim 3, wherein the semiconductor laser is a distributed feedback semiconductor laser in which a diffraction grating is disposed along the active layer inside the resonator. 4. The semiconductor laser according to claim 3, wherein a wavelength conversion element is integrated adjacent to the resonator. 4. The semiconductor laser according to claim 3, wherein an optical modulator is integrated adjacent to the resonator. 2. The semiconductor optical device according to claim 1, wherein the optical waveguide is a light absorption layer, and the reflector is an optical filter for blocking light reception at a specific wavelength. An integrated semiconductor optical device, wherein a plurality of the semiconductor optical devices according to claim 1 are monolithically integrated on the same semiconductor substrate. A semi-insulating substrate;
2. The semiconductor light-receiving element according to claim 1, wherein the optical waveguide is an active layer that emits light, a resonator is formed including the active layer and the reflector, and the antireflection film is omitted. Laser,
2. The semiconductor optical device according to claim 1, wherein the optical waveguide is a light absorption layer, the reflector is an optical filter for blocking light reception at a specific wavelength, and the antireflection film is omitted. A semiconductor light-receiving element that is
An optical transmitter / receiver characterized in that the semiconductor laser and the semiconductor light receiving element are monolithically integrated on the semi-insulating substrate, and an antireflection film is formed on the back surface of the semi-insulating substrate. 10. The semiconductor optical device according to claim 9, wherein the reflectance of the antireflection film formed on the back surface of the semi-insulating substrate is 10% or less. At least one of a semiconductor substrate, a lower cladding layer formed on the substrate, an optical absorption layer formed on the lower cladding layer, an upper cladding layer formed on the absorption layer, and the absorption layer And a reflection mirror disposed at an angle of 45 ° with respect to the surface of the substrate, and an antireflection film formed on the back surface of the substrate at a position facing the reflection mirror. Semiconductor light receiving element. A semi-insulating substrate;
The semiconductor laser according to claim 3, wherein the antireflection film is omitted;
A second lower cladding layer formed on a semiconductor substrate different from the semiconductor laser substrate; an optical absorption layer formed on the second lower cladding layer; and an optical absorption layer formed on the absorption layer. A semiconductor light receiving element having a second upper cladding layer and a second reflecting mirror disposed at an angle of 45 ° with respect to the surface of the substrate on at least one end face of the absorption layer;
An optical transmitter / receiver characterized in that the semiconductor laser and the semiconductor light receiving element are monolithically integrated on the semi-insulating substrate, and an antireflection film is formed on the back surface of the semi-insulating substrate. 13. The semiconductor optical device according to claim 12, wherein the reflectance of the antireflection film formed on the back surface of the semi-insulating substrate is 10% or less.

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