JPH0832102A - Photodetector - Google Patents

Abstract

PURPOSE:To optically couple the main surface of a substrate with an optical fiber extended in the direction parallel to the main surface and, at the same time, to obtain a high optical coupling efficiency between the main surface and the optical fiber by making light from an optical waveguide incident to a photoelectric conversion layer after the light is reflected by an inclined mirror surface. CONSTITUTION:Since an optical waveguide 32 having a core layer which is formed in parallel with the main surface of a substrate 16 and an inclined mirror surface 38 which is inclined against the main surface of the substrate 15 are formed on the substrate 16 in a photodetector 14, light which is made incident to the photodetector 14 in parallel with the main surface of the substrate 16 can be made incident to a light receiving window section 24 constituting a photoelectric conversion section by changing the incident angle in the direction perpendicular to the main surface while the light is confined in the direction perpendicular to the advancing direction of the light. Therefore, the main surface of the substrate 16 can be optically coupled with an optical fiber 40 extended in the direction parallel to the main surface and, at the same time, a high optical coupling efficiency can be obtained between the main surface and fiber 40, since the diffusion of light can be suppressed before the light is made incident to the light receiving window section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector, and more particularly to the structure of a semiconductor photodetector used as a detector in optical communication, optical measurement, optical memory and the like.

[0002]

2. Description of the Related Art Semiconductor photodetectors (light receiving elements)
Is used as a photodetector in optical communication, optical measurement, optical memory and the like. Especially, the back-thinned photodetector is
Since the capacitance between the electrodes can be made small, it is suitable for high-speed operation and has been put to practical use as a light-receiving element for high-speed optical communication.

FIG. 5 is a cross-sectional view of a conventional photodetector in a direction orthogonal to the main surface of a substrate showing a back illuminated pin type photodiode as an example. N of the photodiode 60
A buffer layer 64, a non-doped active layer 66, and a light receiving window portion 68 are formed on the main surface of the type InP (n-InP) substrate 62. The signal light that has passed through the optical fiber 40 from the back surface of the substrate in a direction perpendicular to the main surface of the substrate 62 enters the light receiving window portion 68, is converted into an electrical signal, and is then converted into the electrodes 70 and 72.
Taken out via. As the photodetector, a front-illuminated type is used in addition to the back-illuminated type shown in the figure, and any of them detects light in a direction orthogonal to the substrate.

A semiconductor laser, for example, is used as a signal light source for the semiconductor photodetector, and the semiconductor laser generally emits laser light in a direction parallel to the main surface of the substrate. That is, in the relationship between the main surface of the substrate and the traveling direction of light, the semiconductor laser and the photodetector are different in direction by 90 degrees. Therefore, in order to incorporate the semiconductor laser and the photodetector in one optical module and optically connect the optical fibers arranged in parallel with each other and these elements, it is conventionally necessary to adopt the following structure. there were.

FIG. 6 shows an example thereof, in which FIG. 6 (a) shows a semiconductor laser and FIG. 6 (b) shows a photodetector. In FIG. 10A, the entire substrate on which the semiconductor laser is formed is mounted on the main surface 82 of the carrier 78 of the semiconductor laser 76, and the output light from the active layer 80 of the semiconductor laser 76 is the main surface of the carrier 78. It is incident on the optical fiber 40 extending in the direction parallel to the surface 82. Further, in FIG. 2B, the carrier 8 of the photodetector 60 is
The entire substrate having the back illuminated photodetector formed thereon is mounted on the first main surface 86 of No. 4, and the optical fiber 40 extending in the direction orthogonal to the first main surface 86 of the carrier 84 is attached to the back surface of the substrate. Signal light enters. The electrode 92 of the photodetector 60 is formed on the first major surface 86 of the carrier 84.
It is connected to a bonding pad (not shown) formed above and extends to a signal line 90 formed on the second main surface 88 of the carrier 84.

In the optical module combining the semiconductor laser and the photodetector shown in FIG. 6, by arranging the carriers on which these elements are mounted in parallel, a large number of semiconductor lasers and photodetectors and the elements corresponding to these elements are mutually connected. Allows direct connection with parallel optical fibers.

In another conventional optical module, each substrate (element substrate) on which a semiconductor laser and a back illuminated photodetector are formed can be mounted on one main surface of a common carrier (common substrate). . FIG. 7 shows a photodetector in this optical module. In the figure, the light emitting side end of the optical fiber 40 that enters light into the photodetector 60 is cut at 45 degrees, and the inclined end surface 94 obtained by this cutting is used as a mirror surface. This changes the direction of the light incident from the optical fiber 40 by 90 degrees. If such a configuration is adopted, it is possible to optically couple the back illuminated photodetector 60 and the optical fiber 40 extending parallel to the main surface of the carrier 78, and as described above, mount both the semiconductor laser and the photodetector on a common carrier. To enable.

[0008]

In the conventional example shown in FIG. 6, the structure of the carrier forming the mounting parts of the respective elements of the semiconductor laser and the photodetector is different for each type of element. The mounting components different for each element not only increase the cost of the mounting components, but also in an optical module in which both elements are incorporated, it is necessary to separately manufacture and assemble both elements. Therefore, the assembling cost is increased and the cost of the entire optical module is increased.

Further, in the optical module employing the photodetector shown in FIG. 7, by providing both elements on the common carrier, it is possible to reduce the component cost and the element assembling cost. Is difficult to cut, and there is a problem that a lot of man-hours are required for the cutting. Further, in this case, the optical coupling efficiency between the optical fiber and the photodetector decreases to, for example, about 50 to 80%, and the optical transmission efficiency decreases. Furthermore, since the end of the optical fiber on the light emission side cannot be supported, the optical fiber becomes a cantilever and is easily affected by mechanical vibration.
There is also a problem that its reliability is reduced.

In view of the above, the present invention provides a photodetector that enables optical coupling with an optical fiber extending in a direction parallel to the main surface of a substrate and that can obtain high optical coupling efficiency with the optical fiber. Therefore, it is possible to form a photodetector and a semiconductor laser on a common carrier, and to reduce the number of parts and the number of steps for assembling elements, thereby reducing the cost of an optical module used for optical communication or the like. .

[0011]

In order to achieve the above object, a photodetector of the present invention is formed on a substrate and a main surface of the substrate, and receives light in a direction orthogonal to the main surface to generate an electric signal. A photoelectric conversion layer for conversion, an optical waveguide having a core layer formed on the substrate substantially parallel to the main surface, and a light emitting side end portion of the optical waveguide having an angle of about 45 degrees with the main surface. And a tilted mirror surface that makes an angle, and the tilted mirror surface reflects light from the optical waveguide to enter the photoelectric conversion layer.

Here, as the photodetector of the present invention, either a semiconductor photodiode or an avalanche photodiode can be adopted. Further, as the materials of the substrate, the photoelectric conversion layer, and the optical waveguide in the present invention, any conventionally used materials can be used.

As the material of the optical waveguide, it is preferable to use, for example, fluorine-based polyimide, epoxy resin, deuterated polymethylmethacrylate, polycarbonate, polystyrene and the like.

It is preferable to employ a structure in which the end surface on the light incident side of the core layer has an angle of about 5 to 10 degrees with respect to the direction orthogonal to the main surface. In this case, the amount of reflected light returning from the photodetector to the light source side is It can be reduced.

The optical waveguide is preferably formed directly in a groove formed by etching on the substrate. In this case, photolithography technology and ion beam etching technology can be used, and the manufacturing process is particularly simplified.

As the core layer, it is preferable to adopt a slab type core layer. In this case, the light can be confined in the direction parallel to the main surface, and the spread of the light can be further suppressed,
Higher optical coupling efficiency with the optical fiber can be obtained.

[0017]

In the photodetector of the present invention, the optical waveguide having the core layer parallel to the main surface of the substrate and the inclined mirror surface inclined to the main surface are formed on the substrate, so that the light is incident in the direction parallel to the main surface of the substrate. The incident light can be incident on the photoelectric conversion layer while being confined in the direction orthogonal to the traveling direction thereof while changing the angle in the direction orthogonal to the main surface. For this reason, optical coupling is enabled between the main surface of the substrate and the optical fiber extending in the parallel direction, and diffusion of light before entering the photoelectric conversion layer is suppressed to a small level, so that it is high with the optical fiber. Optical coupling efficiency is obtained.

[0018]

The present invention will be described in more detail with reference to the drawings. FIG. 1 shows the structure of a photodetector according to an embodiment of the present invention, together with its carrier and optical fiber.
It is sectional drawing which follows the axis | shaft of the optical waveguide of a photodetector.
2 is an enlarged sectional view of the photodetector of FIG. 1 taken along the line II-II. The photodetector of this embodiment is configured as a back-illuminated photodetector, and can be formed on the same carrier as the semiconductor laser.

A wiring layer 12 forming a signal line is formed on the main surface of the carrier 10, and an n ⁺ -InP buffer layer 18 and an undoped InGa are formed on the main surface of the n-InP substrate 16.
An As active layer 20 and an n ^-- InP layer 22 are sequentially formed as epitaxial growth layers. The n ⁻ -InP layer 22 and the undoped InGaAs active layer 20 are selectively Zn-diffused to form a light receiving window portion 24. Light receiving window 2
P-electrode 26 made of AuZn on the n ⁻ -InP layer 22 including 4 and AuGe on the buffer layer 18 that surrounds the n ⁻ -InP layer 22 in a direction parallel to the main surface of the substrate with a groove interposed therebetween. The formed n-electrode 28 is formed. The photodetector 14 forms a so-called pin type photodiode, and has a mesa structure because it takes p and n electrodes from the epitaxial growth layer side. However, the active layer structure of the photodetector of the present invention may be avalanche type,
The structure may be mesa-planar or planar.

In FIG. 1, an optical waveguide 32 made of an organic material is formed in the groove 30 on the back surface of the substrate 16, and the end face 34 of the optical waveguide 32 on the light incident side is the end face 3 of the carrier 10.
Consistent with 6. The end surface 38 of the optical waveguide 32 on the light emitting side forms an inclined mirror surface that makes an angle of about 45 degrees with the main surface of the substrate 16. The light from the optical fiber 40 enters in parallel with the main surface of the substrate 16, is sent from the incident side end face 34 of the optical waveguide 32 to the outgoing side inclined mirror surface 38 via the core layer 42 of the optical waveguide, and further, The light receiving window portion 24 which is reflected by the inclined mirror surface 38 and becomes light in the direction orthogonal to the main surface to form a photoelectric conversion portion.
Incident on.

The photodetector of the above embodiment is manufactured as follows. This state will be further described with reference to FIG. FIG. 3 is an enlarged view of the photodetector in FIG. First, n ⁺ -InP is formed on the main surface of the n-InP substrate 16.
The buffer layer 18, the undoped InGaAs active layer 20, and the n ⁻ -InP layer 22 are sequentially grown to form the light receiving window portion 2.
Zn diffusion is selectively performed only on No. 4. Next, a groove surrounding the light receiving window portion 24 is formed under the active layer by etching to form a mesa structure.

After that, Au is used as the p electrode 26 in the light receiving window.
The Zn electrode is formed on the buffer layer 18 as an n-electrode 28 using AuG.
Form each e-electrode. Next, the back surface of the substrate 16 is polished until the substrate thickness becomes 100 μm, and then the light receiving window portion 24
A stripe groove 30 having a width of 50 μm and a depth of 20 μm is formed by etching at a position on the back surface of the substrate which overlaps with the plane. Next, a low reflection film 44 having a reflectance of 1% is formed on the surface of the groove 30.
For example, a SiN film is formed.

Next, the refractive index n ₁ = 1.52 in the groove 30.
Is applied and thermally cured to form the lower clad layer 46 of the optical waveguide 32. In the lower clad layer 46, the light receiving window portion 2 is formed by ion beam etching using oxygen ions using a SiO ₂ film (not shown) as a mask.
A second stripe groove having a width of 10 μm and a depth of 15 μm is formed across the plane 4 in a plane. Subsequently, the refractive index n ₂ = 1.
53 fluoride polyimide is applied and thermally cured, and then etched again by ion beam etching using oxygen ions to a thickness of 5 μm. By this etching, the thickness of the core layer of the optical waveguide 32 in the second stripe groove is determined, and the core layer 42 having a thickness of 10 μm is formed. The thickness of the core layer 42 of 10 μm is an example,
In this case, the diameter is set to the same value as the diameter of the general mode field of the single mode fiber 40.

Next, the SiO ₂ film is removed, and the refractive index n ₃ =
After applying 1.52 (= n ₁ ) fluoride polyimide and thermally curing it, ion beam etching using oxygen ions is performed. In this case, the upper cladding layer 48 is obtained by etching back the fluoride polyimide until the substrate surface is exposed. As a result, the slab type optical waveguide 32 having the core layer 44 with a thickness of 10 μm is formed.

Next, on the optical waveguide 32, about 10 μm each from the center of the light receiving window portion 24 toward the stripe groove.
A mask having an opening between distant positions is formed of a SiO ₂ film. The right side of the substrate is lowered in the drawing so that the back surface (main surface) of the substrate is inclined at about 45 degrees from the horizontal plane. Subsequently, ion beam etching using oxygen ions is performed using the SiO ₂ film as a mask to remove the end portion of the core layer 42 of the optical waveguide 32 by etching in the direction of 45 degrees. As a result, as shown in FIG. 3, an inclined surface 38 having an inclination of 45 degrees with the main surface of the substrate is formed on the emission side end surface of the optical waveguide 32.

Thereafter, the surface of the inclined surface 38 has a reflectance of 90.
% High reflection film 50 is formed, and the inclined surface 38 is formed as an inclined mirror surface. As the high reflection film 50, a multilayer dielectric film of a SiO ₂ film and an amorphous Si film, a laminated film in which a metal film is deposited on an insulating film, or the like is adopted. Then cut the entire wafer,
Each photodetector element is obtained by division. Optical waveguide 3
The incident-side end face 34 on the coupling side of the second optical fiber 40 is obtained when the wafer is cleaved. A SiN film is formed on the cleaved surface 34 as a low reflection film 52 for preventing reflection.

FIG. 4 is a sectional view showing the photodetector of the second embodiment of the present invention. The photodetector 14A of the present embodiment is provided with the optical waveguide 3 on the coupling side with the optical fiber 40.
2 end face 54 with respect to the direction perpendicular to the main surface of the substrate by about 5
It is formed so as to form an angle of 10 degrees. This shape is obtained by ion beam etching using oxygen ions. The end surface 54 is made of SiN as in the previous embodiment.
A low reflection film 56 for preventing reflection is formed of a film.
This structure is adopted to reduce the intensity of the reflected light returning from the optical waveguide 32 to the optical fiber 40 side. The other structure is the same as that of the previous embodiment, and other elements are the same as those shown in FIGS.
The same reference numerals are given and their explanations are omitted.

In each of the above-mentioned embodiments, an example in which an organic dielectric material is used as the material of the optical waveguide has been described. However, in addition to the organic dielectric material, the material of the optical waveguide is a semiconductor, an oxide crystal, or a silica-based material. Glass etc. can be used.

When an organic material is used as the material of the optical waveguide as in the above embodiment, the organic material can be easily formed by using the spin coating method. It has the advantage of being easy to form. Further, since the strain caused by the difference in the thermal expansion coefficient is hardly applied to the substrate, there is an advantage that the reliability of the photodetector is improved. As the organic material, in addition to fluoride polyimide, polyurethane, epoxy resin, KPR photoresist, siloxane polymer, etc. can be used.
Particularly, the fluoride polyimide and the siloxane-based polymer have advantages that moisture absorption and hydrolysis hardly occur, and that heat resistance is good.

When a semiconductor is adopted as the optical waveguide material, for example, InGaAsP (n =
InP (n = 3.3.4) as the material for the cladding layer.
The waveguide structure can be easily formed by using the method 2) and combining the growth by the CVD method and the pattern etching technique. When semiconductor materials are used in this way, they have a small difference in coefficient of thermal expansion from the substrate, and
Since the lattice mismatch rate can be suppressed to a small value, the reliability of the obtained photodetector is improved.

Silica glass (Si
When O ₂ ) is adopted, the high refractive index core layer is obtained by Ge doping. In this case, a combination of ordinary methods for forming an optical waveguide such as a CVD method and a flame hydrolysis method can be used. Silica glass has the advantages that patterning and thick film formation are easy, and the waveguide loss is low. When silica glass is used, the refractive index is about 1.45 in the clad layer and about 1.46 in the core layer.

When an oxide crystal is used as the optical waveguide material, Si ₃ N ₄ , Nb ₂ O ₅ , Ta ₂ O ₅ , ZnO or the like is used, and among these, a high refractive index material and a low refractive index material are used. Select materials and use in combination. In this case, the CVD method and the sputtering method can be used to form the optical waveguide.

In each of the above-mentioned embodiments, the optical waveguide and the inclined mirror surface are formed in the groove on the back surface of the substrate. Here, a configuration in which only the inclined mirror surface is solely formed in the groove or on the back surface of the substrate is also conceivable. Even with such a configuration, the signal light from the optical fiber extending in the direction parallel to the main surface of the substrate is supplied to the substrate. It can be converted into light in the direction orthogonal to the main surface. However, in this case, there is a drawback that the light emitted from the optical fiber spreads significantly before entering the photoelectric conversion part of the photodetector, and the optical coupling efficiency between the optical fiber and the photodetector decreases.

The present invention has been described above mainly on the basis of the preferred embodiments thereof, but the constitution of each embodiment is merely an example, and the photodetector of the present invention has various modifications and alterations from the constitutions of the above respective embodiments. It can be changed. For example, the photodetector in the present invention is not limited to the back-illuminated type,
It can be applied to the front-illuminated type.

[0035]

As described above, according to the photodetector of the present invention, the optical coupling with the optical fiber extending in the direction parallel to the main surface of the substrate becomes possible and the optical coupling efficiency with the optical fiber is improved. Therefore, it is possible to use a common mounting component for the photodetector and the semiconductor laser, which not only reduces the cost of the mounting component but also the number of steps for assembling the element, and the manufacturing cost of the optical module used for optical communication and the like. And the reliability and energy efficiency are improved.

[Brief description of drawings]

FIG. 1 is a sectional view taken along the axis of an optical waveguide showing a photodetector according to a first embodiment of the present invention together with an optical fiber.

FIG. 2 is an enlarged sectional view of the photodetector of FIG. 1 taken along the line II-II.

FIG. 3 is an enlarged view of the photodetector of FIG.

FIG. 4 is a sectional view taken along the axis of an optical waveguide showing a photodetector of a second embodiment of the present invention together with an optical fiber.

FIG. 5 is a cross-sectional view of a conventional back-illuminated photodetector.

6A and 6B are cross-sectional views showing a photodetector and a semiconductor laser in an optical module of a first conventional example.

FIG. 7 is a cross-sectional view showing a photodetector in an optical module of a second conventional example together with its carrier.

[Explanation of symbols]

Reference Signs List 10 carrier 12 wiring layer 14 photodetector 16 substrate 18 n ⁺ -InP buffer layer 20 undoped InGaAs active layer 22 n ^-- InP layer 24 light receiving window portion 26 p electrode 28 n electrode 30 groove 32 optical waveguide 34, 54 light incident on optical waveguide Side end face 36 Carrier end face 38 Inclined mirror face 40 Optical fiber 42 Core layer 44, 52, 56 Low reflection film 46 Lower clad layer 48 Upper clad layer 50 High reflection film

Claims (5)

[Claims] 1. A substrate, a photoelectric conversion layer formed on the main surface of the substrate, for receiving light in a direction orthogonal to the main surface, and converting the light into an electric signal, the substrate being substantially parallel to the main surface. An optical waveguide having a core layer formed on the optical waveguide, and an inclined mirror surface formed at an end of the optical waveguide on the light emitting side and forming an angle of about 45 degrees with the main surface, wherein the inclined mirror surface is separated from the optical waveguide. A photodetector, which reflects the light of (1) and enters the photoelectric conversion layer. 2. The photodetector according to claim 1, wherein an end surface of the core layer on the light incident side has an angle of about 5 to 10 degrees with respect to a direction perpendicular to the main surface. 3. The photodetector according to claim 1, wherein the material of the optical waveguide contains at least one of fluorine-based polyimide, epoxy resin, deuterated polymethylmethacrylate, polycarbonate and polystyrene. 4. The photodetector according to claim 1, wherein the optical waveguide is formed in a groove formed by etching on the substrate. 5. The photodetector according to claim 1, wherein the core layer is formed as a slab type core layer.