Abstract:
A semiconductor light-receiving device including (a) a semiconductor substrate, (b) a multi-layered including a first buffer layer having a first electrical conductivity and lying on the semiconductor substrate, a first clad layer having a first electrical conductivity and lying on the first buffer layer, a light-absorbing layer having a first electrical conductivity and lying on the first clad layer, a second clad layer having a second electrical conductivity and lying on the light-absorbing layer, and a second buffer layer having a second electrical conductivity and lying on the second clad layer, (c) a first electrode formed on the second buffer layer, and (d) a second electrode formed on a lower surface of the semiconductor substrate. The multi-layered structure has at least one portion which is inclined to a direction in which a light introduced into the device is directed. For instance, the multi-layered structure has opposite end portions inclined to the direction. A portion of the multi-layered structure making inclination with the direction provides the same advantageous effect as that a light-receiving area of a light-receiving layer of the multi-layered structure is effectively increased. Thus, the semiconductor light-receiving device could be readily coupled to other devices through optical fibers. In addition, there can be obtained a high coupling efficiency which is greater than 90%. Furthermore, the semiconductor light-receiving device provides a high quantum efficiency which is greater than 90%, and enables to accomplish high-speed response at a speed greater than 20 Gbps.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 08/886,164, filed Jun. 30, 1997, now U.S. Pat. No. 6,020, 620. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a semiconductor light-receiving device to be employed for optical communication and optical data processing, and a method of fabricating the same. 
     2. Description of the Related Art 
     A compound semiconductor light-receiving device has been put to practical use as a wide-range wavelength light receiver with high sensitivity for optical communication and optical data processing. Above all, a semiconductor light-receiving device for a wavelength of 1.3 μm or 1.55 μm, which is a wavelength for high capacity long-distance optical communication, is usually made of InGaAs. 
     It is necessary for a PIN photo diode made of InGaAs to minimize a junction capacity of individual devices in order to accomplish ultra-high speed response greater than 40 Gbps, and to form a light-absorbing layer thinner in order to reduce running time of carriers. 
     However, in a presently commercially available light-receiving device having a surface through which the device receives a light, if a light-receiving diameter is made smaller for reducing a junction capacity, optical coupling would be difficult to properly take place when the light-receiving device receives a light from an optical fiber, resulting in deterioration of coupling efficiency. On the other hand, if a light-receiving layer made of InGaAs were formed thinner, it would be possible to reduce running time of carriers, however, with the result of reduction in quantum efficiency. Thus, reduction in a junction capacity and enhancement in coupling efficiency, and reduction in carrier running time and enhancement in quantum efficiency are in a trade-off relationship. Hence, since a direction in which a light is directed is coaxial with a direction in which carriers run in either process, reduction in light-receiving sensitivity is unavoidable, even if high-speed response could be accomplished. 
     In order to avoid influence due to the above mentioned trade-off relationship, there has been suggested a waveguide type light-receiving device in which a direction in which a light runs is deflected by 90 degrees to a direction in which carriers run. 
     FIG. 1 illustrates one of conventional waveguide type light-receiving devices, which has been suggested by K. Kato et al. in “High efficiency, waveguide InGaAs pin photodiode with bandwidth of 40 GHz”, Electronic Data Communication Association Spring Conference, 1991, pp. 4-200, C-183. The illustrated waveguide type light-receiving device includes a semi-insulating InP substrate  20 , an insulating layer  21  formed on the substrate  20 , a waveguide type light-receiving region  22  formed on the insulating layer  21 , a pair of polyimide layers  23  sandwiching the light-receiving region  22  therebetween, a p-side electrode  24  formed over the light-receiving region  22  and the polyimide layers  23 , and an n-side electrode  25  formed on the insulating layer  21 . The waveguide type light-receiving region  22  acts as a waveguide, and is comprised of an n-InGaAsP clad layer  22   a,  an n-InGaAs light-absorbing layer  22   b,  a p-InGaAs light-receiving layer  22   c,  a p-InGaAsP clad layer  22   d,  and a p-InGaAsP contact layer  22   e.  The waveguide type light-receiving region  22  is formed by successive, epitaxial growth of these layers. The p-side electrode  24  makes electrical contact with the p-InGaAsP contact layer  22   e,  and the n-side electrode  25  makes electrical contact with the n-InGaAsP clad layer  22   a.  The polyimide layers  23  sandwiching the light-receiving region  22  therebetween to thereby reduce a capacity of a bonding region. 
     In the illustrated waveguide type light-receiving device, a light is introduced into the device through an end surface of the light-receiving region  22 , and is transferred and absorbed in the n-InGaAs light-absorbing layer  22   b  and the p-InGaAs light-absorbing layer  22   c  both vertically sandwiched between the clad layers  22   d  and  22   a.    
     Carriers generated due to absorption of a light are transferred to an external circuit (not illustrated) through the p-InGaAsP clad layer  22   d,  p-InGaAsP contact layer  22   e,  and p-side electrode  24 . Since absorption of a light is accomplished in a length-wise direction of the light-receiving region  22 , it is possible to obtain high quantum efficiency. In addition, since carriers run perpendicularly to the light-receiving region  22 , running time of carriers is dependent only on a thickness of the n-InGaAs light absorbing layer  22   b.    
     The above mentioned waveguide type light-receiving device has a problem as follows. If the n-InGaAs light absorbing layer  22   b  is formed thinner for reducing carriers running time, optical coupling efficiency would be deteriorated because a light introduced into the device through an optical fiber has a greater diameter than a thickness of the n-InGaAs light absorbing layer  22   b.  In contrast, if the n-InGaAs light absorbing layer  22   b  is formed thicker for enhancing optical coupling efficiency, it would be accompanied with an increase in running time of carriers. 
     FIGS. 2A to  2 C illustrate another semiconductor waveguide light-receiving device suggested in Japanese Unexamined Patent Publication No. 3-35555. FIG. 2A is a top plan view of the device, FIG. 2B is a cross-sectional view of the device taken along the line IIB—IIB in FIG. 2A, and FIG. 2C is a cross-sectional view of the device taken along the line IIC—IIC in FIG.  2 A. 
     The illustrated semiconductor waveguide light-receiving device includes a semiconductor substrate  30 , a buffer layer  31  formed on the substrate  30 , a waveguide  32  formed partially on the buffer layer  31 , a light-receiving layer  33 , and a junction forming layer  34 . The waveguide  32 , the light-receiving layer  33 , and the junction forming layer  34  are sandwiched by fillers  35 . The light-receiving layer  33  and the junction forming layer  34  cooperate with each other to form a light-receiving device, and are formed tapered in a direction indicated with an arrow X in which a light is directed. On the junction forming layer  34  are alternately formed p-type regions  36   a  and n-type regions  36   b  arranged in a direction indicated with the arrow X. 
     A light is introduced into the device through an end surface  37  thereof, and is transferred through the waveguide  33  in a direction indicated with the arrow X. 
     FIG. 3 illustrates still another semiconductor waveguide light-receiving device suggested in Japanese Unexamined Patent Publication No. 4-268770. 
     The illustrated device includes an InP substrate  40 , an InGaAsP clad layer  41  formed on the substrate  40 , an InGaAsP core layer  42  formed on the InGaAsP clad layer  41 , clad layers  43  and  44  both made of an InGaAsP multi-layered structure formed on the InGaAsP core layer  42 , an InGaAsP layer  45  formed on the InGaAsP core layer  42 , an n-side electrode  46  formed on a lower surface of the substrate  40 , and a p-side electrode  47  formed on an upper surface of the InGaAsP layer  45 . The multi-layered structure  43  and  44  are formed by alternately depositing layers for absorbing a light thereinto and layers transparent to a light. The multi-layered structure  44  is formed partially on the multi-layered structure  43  in the form of a ridge. 
     The multi-layered structures  43  and  44  act as a light-absorber. A light is introduced into the device through a side surface thereof in a direction indicated with an arrow X, and is converted into electricity in the multi-layered structures  43  and  44 . 
     In both of the above mentioned waveguide light-receiving devices, a light is introduced into the devices through end surfaces thereof. However, the devices have a problem that optical coupling efficiency is quite low. In the above mentioned conventional waveguide light-receiving devices, if an n-InGaAs light-receiving layer is formed thinner for reducing running time of carriers, optical coupling efficiency would be deteriorated because an incident light has a sufficiently greater diameter than a thickness of the n-InGaAs light-receiving layer. In contrast, if an n-InGaAs light-receiving layer were formed thicker for enhancing optical coupling efficiency, running time of carriers would be increased. Thus, the above mentioned waveguide light-receiving devices could not improve optical coupling efficiency. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor light-receiving device which is capable of efficiently receiving a light thereinto in high optical coupling efficiency, and a method of fabricating the same. 
     In one aspect, there is provided a semiconductor light-receiving device including (a) a semiconductor substrate, and (b) a multi-layered structure including: a first semiconductor layer having a first electrical conductivity and lying on the semiconductor substrate; a second semiconductor substrate having a first electrical conductivity and lying on the first semiconductor layer; and a third semiconductor layer having a second electrical conductivity and lying on the second semiconductor layer. The multi-layered structure has at least one portion which is inclined to a direction in which a light introduced into the device is directed. 
     In a preferred embodiment, the multi-layered structure has end portions which are inclined to the direction. It is preferred that the multi-layered structure is embedded in the semiconductor substrate so that the multi-layered structure is formed tapered at end portions thereof. 
     The multi-layered structure may have continuously formed three portions: a first portion inclined to the direction; a second portion extending in parallel with the direction; a third portion inclined to the direction. For instance, the first and third portions may have the same degree by which the first and third portions are inclined. 
     It is preferable that band gap energies El, E 2  and E 3  of the first, second and third semiconductor layers, respectively, have a relation defined as E 1 &gt;E 2 &gt;E 3 . 
     There is further provided a semiconductor light-receiving device including (a) a semiconductor substrate, (b) a multi-layered structure having a first buffer layer having a first electrical conductivity and lying on the semiconductor substrate, a first clad layer having a first electrical conductivity and lying on the first buffer layer, a light-absorbing layer having a first electrical conductivity and lying on the first clad layer; a second clad layer having a second electrical conductivity and lying on the light-absorbing layer, and a second buffer layer having a second electrical conductivity and lying on the second clad layer, (c) a first electrode formed on the second buffer layer, and (d) a second electrode formed on a lower surface of the semiconductor substrate. The multi-layered structure has at least one portion which is inclined to a direction in which a light introduced into the device is directed. 
     It is preferable that the semiconductor substrate is made of InP, the first and second buffer layers are made of InP, the first and second clad layers are made of InGaAsP, and the light-absorbing layer is made of InGaAs. 
     The light-absorbing layer has a thickness preferably in the range of 0.7 μm and 1.3 μm both inclusive, and more preferably of 1.0 μm. 
     It is preferable that the semiconductor light-receiving device further includes an insulating layer disposed adjacent to and in level with the multi-layered structure; and a bonding electrode formed on an upper surface of the insulating layer and in electrical connection with the first electrode, in which case, it is preferable that the semiconductor substrate has an exposed region at the opposite side of the insulating layer with respect to the multi-layered structure, a lowermost layer of the multi-layered structure having a portion extending over the exposed region. 
     There is still further provided a semiconductor light-receiving device including (a) a semiconductor substrate, and (b) a layered waveguide formed on the semiconductor substrate, the waveguide having a portion making inclination with a side plane of the semiconductor substrate through which a light is introduced into the semiconductor light-receiving device. 
     It is preferable that the portion is opposite end portions of the waveguide, and that the waveguide is embedded in the semiconductor substrate. 
     In another aspect, there is provided a method of fabricating a semiconductor light-receiving device, including the steps of (a) forming a recess in a semiconductor substrate by wet etching, and (b) forming a layered waveguide in the recess by epitaxial growth. 
     There is further provided a method of fabricating a semiconductor light-receiving device, including the steps of (a) forming a recess in a semiconductor substrate so that the recess has inclined surfaces, (b) forming a multi-layered structure in the recess so that the multi-layered structure fills the recess, the multi-layered structure including a plurality of semiconductor layers, (c) etching a portion of the multi-layered structure longitudinally thereof until the semiconductor substrate appears, (d) forming an insulating layer in a region etched in the step (c) so that the insulating layer is level with the multi-layered structure, (e) forming a contact electrode on the multi-layered structure, (f) forming a bonding electrode on the insulating layer so that the bonding electrode is in electrical connection with the contact electrode, and (g) forming an electrode on a lower surface of the semiconductor substrate. 
     A semi-insulating substrate may be employed in place of the semiconductor substrate in the step (a). It is preferable that the recess is formed by wet etching in the step (a). 
     The multi-layered structure may include a first buffer layer having a first electrical conductivity; a first clad layer having a first electrical conductivity and lying on the first buffer layer, a light-absorbing layer having a first electrical conductivity and lying on the first clad layer, a second clad layer having a second electrical conductivity and lying on the light-absorbing layer, and a second buffer layer having a second electrical conductivity and lying on the second clad layer. It is also preferable that the semiconductor substrate is made of InP, the first and second buffer layers are made of InP, the first and second clad layers are made of InGaAsP, and the light-absorbing layer is made of InGaAs. 
     The method may further include the step (h) of forming a film over a resultant for protecting a surface thereof, the contact electrode being formed in a hole of the film. The step (h) is to be carried out between the steps (d) and (e). 
     It is preferable that the multi-layered structure is etched in the step (c) so that a longitudinal portion thereof is removed at one side until the semiconductor substrate appears and a longitudinal portion thereof is removed at the opposite side until the first buffer layer appears. 
     The advantages obtained by the aforementioned present invention will be described hereinbelow. 
     The first advantage is that a semiconductor light-receiving device in accordance with the present invention can be readily coupled to an optical fiber with high coupling efficiency greater than 90%. 
     This is because that the waveguide or multi-layered structure is formed to have at least one portion which is inclined to a direction in which a light introduced into the device is directed, which provides the same effect as that a cross-sectional or light-receiving area of the n-InGaAs light-receiving layer is increased as viewed from a plane through which a light is introduced into the device. 
     The second advantage is that it is possible to obtain high quantum efficiency greater than 90%. 
     The reason is as follows. A semiconductor light-receiving device in accordance with the present invention may have continuously formed three portions by forming inclined portions in the device: a first portion inclined to a direction in which an incident light run in the device; a second portion extending in parallel with the direction; a third direction inclined to the direction. Thus, when viewed from a plane of the device through which a light is introduced into the device, it is possible to have the same effect as that a thickness of the n-InGaAs light-receiving layer is increased. 
     The third advantage is that it is possible to accomplish high-speed response beyond 20 Gbps. 
     This is because that it is possible to reduce running time of carriers by forming an n-InGaAs light-receiving layer to have a thickness of 1 μm. 
     The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating a conventional semiconductor light-receiving device. 
     FIG. 2A is a top plan view illustrating another conventional semiconductor light-receiving device. 
     FIG. 2B is a cross-sectional view taken along the line IIB—IIB in FIG.  2 A. 
     FIG. 2C is a cross-sectional view taken along the line IIC—IIC in FIG.  2 A. 
     FIG. 3 is a perspective view illustrating still another conventional semiconductor light-receiving device. 
     FIG. 4 is a cross-sectional view illustrating a semiconductor light-receiving device in accordance with the first embodiment of the present invention. 
     FIG. 5 is a perspective view of the device illustrating in FIG.  4 . 
     FIGS. 6A to  6 H are cross-sectional views of a semiconductor light-receiving device in accordance with the first embodiment, illustrating respective steps of a method of fabricating the same. 
     FIG. 7 is a cross-sectional view illustrating a semiconductor light-receiving device in accordance with the second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 4 and 5 illustrate a semiconductor light-receiving device in accordance with the first embodiment of the present invention. 
     As illustrated in FIG. 4, a semiconductor light-receiving device in accordance with the first embodiment includes an n-InP substrate  1  having a trapezoid-shaped, raised portion  1   a,  a multi-layered structure  14  embedded in the trapezoid-shaped, raised portion  1   a,  a SiNx film  7  covering an upper surface of the n-InP substrate  1  therewith, a p-side contact electrode  8  formed on an uppermost layer of the multi-layered structure  14 , and n-side electrode  10  formed on a lower surface of the n-InP substrate  1 . 
     As illustrated in FIG. 5, there is formed a polyimide layer  11  having the same reverse trapezoidal cross-section as the multi-layered structure  14 , adjacent to and making close contact with the trapezoid-shaped, raised portion  1   a.  The polyimide layer  11  is in level with the trapezoid-shaped, raise portion  1   a.  On an upper surface of the polyimide layer  11  is formed a p-side electrode  9 , which extends towards the trapezoid-shaped, raised portion  1   a  to cover and make electrical contact with the p-side contact electrode  8 . 
     The trapezoid-shaped, raised portion  1   a  has inclined end surfaces. A signal light Z is introduced into the semiconductor light-receiving device through one of the end surfaces, which is hereinafter referred to as a light-receiving plane  12 . 
     The multi-layered structure  14  acts as a waveguide, and is comprised of an n-InP layer  2  as a first buffer layer, an n-InGaAsP clad layer as a first clad layer  3 , an n-InGaAs light-absorbing layer  4 , a p-InGaAsP clad layer as a second clad layer  5 , and a p-InP layer  6  as a second buffer layer  6 , which layers are deposited in this order on the n-InP substrate  1 . 
     The n-InGaAs light-absorbing layer  4  is designed to have a thickness of 1 μm. 
     As illustrated in FIGS. 4 and 5, the multi-layered structure  14  is a reverse trapezoid in shape, and hence end surfaces  14   a  and  14   b  inclined to a direction in which the signal light Z runs in the device. The inclined end surfaces  14   a  and  14   b  have the same inclination angle of about 56 degrees. However, it should be noted that the end surfaces  14   a  and  14   b  may be designed to have different inclination angles. 
     Since the multi-layered structure  14  is reverse trapezoid-shaped, the multi-layered structure  14  may be considered to have continuously formed three portions: a first portion A including the inclined end surface; a second portion B extending in parallel with a direction in which the signal light Z runs in the multi-layered structure  14 ; a third portion C including the inclined end surface  14   b.    
     FIGS. 6A to  6 H illustrate respective steps of a method of fabricating the above mentioned semiconductor light-receiving device illustrated in FIGS. 4 and 5. First, as illustrated in FIG. 6A, on an n-InP semiconductor substrate or a semi-insulating substrate  1  having a trapezoid-shaped, raised portion  1   a  is formed an etching mask  13  having a width of 5 μm and a space of 30 μm, and made of, for instance, photoresist. Then, wet etching is carried out to thereby form a reverse trapezoid-shaped recess in the trapezoid-shaped, raised portion  1   a.  The recess has an upper width of 30 μm and a depth of 10 μm, and hence has inclined sidewalls  1   b.  In the wet etching, the substrate  1  is etched so that an etching angle is kept uniformly about 56 degrees due to crystal lattice. 
     Then, as illustrated in FIG. 6B, there are formed oxide films  16  both on an upper surface of the reverse trapezoid-shaped portion  1   a  which is not to be etched, and on outer surface of the substrate  1 . The oxide mask  16  will prevent crystal growth thereon. 
     Then, the multi-layered structure  14  is formed in the reverse trapezoid-shaped recess by chemical vapor deposition (CVD). There are successively deposited the n-InP buffer layer  2  having a carrier concentration of 1×15 cm −3  and a thickness of 0.5 μm (FIG.  6 B), the n-InGaAsP clad layer  3  having a carrier concentration of 1×15 cm −3  and a thickness of 0.5 μm (FIG.  6 C), the n-InGaAs light-absorbing layer  4  having a carrier concentration of 1×15 cm −3  and a thickness of 1 μm (FIG.  6 D), the p-InGaAsP clad layer  5  having a carrier concentration of 1×15 cm −3 , a thickness of 0.5 μm and a band gap energy of 1.08 eV (FIG.  6 E), and the p-InP layer  6  having a carrier concentration of 1×18 cm −3  (FIG.  6 F). The p-InP layer  6  is deposited in such a manner that it completely fills the recess and forms a flat upper surface of the multi-layered structure  14 , as illustrated in FIG.  6 F. 
     Herein, the layers  2 ,  3 ,  4 ,  5  and  6  are designed to have particular dimensions such as a carrier concentration and a thickness, however it should be noted that they may be designed to have other dimensions. Specifically, the layers  2  to  5  may be designed to have a carrier concentration equal to or smaller than 2×15 cm −3  and a thickness in the range of 1 to 2 μm both inclusive. 
     Then, a resultant is etched, for instance, by reactive ion beam etching (RIBE) until the n-InP substrate  1  appears, leaving a 10 μm-width stripe-shaped region not to be etched, as illustrated in FIG.  5 . Then, the polyimide layer  11  is formed on the thus etched region so that the polyimide layer  11  has the same height as that of the reverse trapezoid-shaped, raised portion  1   a  of the substrate  1 . 
     Then, as illustrated in FIG. 6G, the oxide film  16  are removed to expose the substrate and then there is formed a SiNx film  7  over a resultant, for instance, by plasma-enhanced chemical vapor deposition (PCVD). The SiNx film  7  protects a surface of the device. Then, a through hole is formed throughout a thickness of the SiNx film  7  on the p-InP layer  6 , and the p-side contact electrode  8  is formed in the through hole. Then, the bonding p-side electrode  9  is formed on an upper surface of the polyimide layer  11  so that the bonding electrode  9  extends to and makes electrical contact with the contact electrode  8 . 
     Then, the n-side electrode  10  is formed on a lower surface of the n-InP substrate  1 . Thus, there is completed the semiconductor light-receiving device in accordance with the first embodiment. 
     When a light is introduced into the above mentioned semiconductor light-receiving device through the light-receiving plane  12 , a light is absorbed by about 60% by the n-InGaAs light absorbing layer  4  in the first portion A of the multi-layered structure  14 . Then, a light having passed the first portion A without being absorbed thereinto is absorbed in the n-InGaAsP clad layer  3 , the n-InGaAs light absorbing layer  4  and the p-InGaAsP clad layer  5  in the second portion B of the multi-layered structure  14 . A light having passed the first and second portions A and B without being absorbed thereinto is introduced into and absorbed in the third portion C of the multi-layered structure  14 . A light having been absorbed into the first, second and/or third portions A, B and/or C is converted to electricity in the n-InGaAs layer  4  to thereby generate carriers. An electric field applied to the p-side and n-side electrodes  9  and  10  leads the thus generated carriers to an external circuit (not illustrated) through the p-InGaAsP clad layer  5 , the p-InP layer  6  and the p-side electrode  9 . 
     As a result, suppose that the n-InGaAsP clad layer  3 , n-InGaAs light; absorbing layer  4 , and p-InGaAsP clad layer  5  have band gap energies E 1 , E 2  and E 3 , respectively, the band gap energies have a relation defined as E 1 &gt;E 2 &gt;E 3 . 
     As mentioned so far, in accordance with the first embodiment, the multi-layered structure  14  or the waveguide is designed to have inclined end portions. Thus, it is possible to have the same advantageous effect as that a thickness of the n-InGaAs light absorbing layer  4  as viewed from the light-receiving plane  12  is made thicker. As a result, the light-receiving device could be readily coupled to an optical fiber through the end surface or light-receiving plane, and it would be possible to have high optical coupling efficiency greater than 90% and high quantum efficiency greater than 90%. In addition, it would be possible to make a response at a speed greater than 20 Gbps by designing the n-InGaAs light absorbing layer  4  to have a thickness in the range of 0.7 μm and 1.3 μm both inclusive, preferably a thickness of 1.0 μm. If the thickness is smaller than 0.7 μm, the coupling efficiency is too much reduced, and if the thickness is greater than 1.3 μm, running time of carriers is too much increased. 
     In the above mentioned first embodiment, the multi-layered structure  14  is fabricated by chemical vapor deposition. It should be noted that the multi-layered structure  14  might be fabricated by liquid deposition, MOCVD, MBE or ALE. 
     FIG. 7 illustrates a semiconductor light-receiving device in accordance with the second embodiment of the present invention, which is different from the semiconductor light-receiving device in accordance with the first embodiment illustrated in FIGS. 4 and 5 in that the n-InP substrate  1  in the second embodiment has an exposed region  1   c  at the opposite side of the insulating layer  11  with respect to the multi-layered structure  14 . Namely, the exposed region  1   c  of the substrate  1  is located adjacent to the multi-layered structure  14 . A part of the n-InP layer  2  extends over the exposed region  1   c.  The other structure of the semiconductor light-receiving device in accordance with the second embodiment is the same as that of the semiconductor light-receiving device in accordance with the first embodiment. 
     A method of fabricating a semiconductor light-receiving device in accordance with the second embodiment is explained hereinbelow with reference to FIGS. 6A to  6 H. Though the FIGS. 6A to  6 H are drawings for explaining the method of fabricating the semiconductor light-receiving device in accordance with the first embodiment, a method mentioned later has a lot of common steps as the method illustrated in FIGS. 6A to  6 H, and hence FIGS. 6A to  6 H are referred to again. 
     First, as illustrated in FIG. 6A, on a semi-insulating InP substrate  15  having a trapezoid-shaped, raised portion  1   a  is formed an etching mask  13  having a width of 5 μm and a space of 30 μm, and made of photoresist. Then, wet etching is carried out to thereby form a reverse trapezoid-shaped recess in the trapezoid-shaped, raised portion  1   a.  The recess has an upper width of 30 μm and a depth of 10 μm, and hence has inclined sidewalls  1   b.  In the wet etching, the substrate  15  is etched so that an etching angle is kept uniformly about 56 degrees due to crystal lattice. 
     Then, as illustrated in FIG. 6B, there are formed oxide films  16  both on an upper surface of the reverse trapezoid-shaped portion  1   a  which is not to be etched, and on outer surface of the substrate  15 . The oxide mask  16  will prevent crystal growth thereon. 
     Then, the multi-layered structure  14  is formed in the reverse trapezoid-shaped recess by CVD. There are successively deposited the n-InP buffer layer  2  having a carrier concentration of 1×15 cm −3  and a thickness of 0.5 μm (FIG.  6 B), the n-InGaAsP clad layer  3  having a carrier concentration of 1×15 cm −3  and a thickness of 0.5 μm (FIG.  6 C), the n-InGaAs light-absorbing layer  4  having a carrier concentration of 1×15 cm −3  and a thickness of 1 μm (FIG.  6 D), the p-InGaAsP clad layer  5  having a carrier concentration of 1×15 cm −3 , a thickness of 0.5 μm and a band gap energy of 1.08 eV (FIG.  6 E), and the p-InP layer  6  having a carrier concentration of 1×18 cm −3  (FIG.  6 F). The p-InP layer  6  is deposited in such a manner that it completely fills the recess and forms a flat upper surface of the multi-layered structure  14 , as illustrated in FIG.  6 F. 
     Then, a resultant is etched by RIBE at one side with respect to the multi-layered structure  14  until the semi-insulating InP substrate  15  appears, and at the other side until the n-InP layer  2  appears, leaving a 10 μm-width stripe-shaped region of the multi-layered structure  14  not to be etched, as illustrated in FIG.  7 . Then, the polyimide layer  11  is formed on the thus etched region in which the substrate  15  appears so that the polyimide layer  11  has the same height as that of the reverse trapezoid-shaped, raised portion  1   a  of the substrate  15 . 
     Then, as illustrated in FIG. 6G, there is formed a SiNx film  7  over a resultant by PCVD. The SiNx film  7  protects a surface of the device. Then, a through hole is formed throughout a thickness of the SiNx film  7  on the p-InP layer  6 , and the p-side contact electrode  8  is formed in the through hole. Then, the bonding p-side electrode  9  is formed on an upper surface of the polyimide layer  11  so that the bonding electrode  9  extends to and makes electrical contact with the contact electrode  8 . 
     Then, the n-side electrode  10  is formed on a lower surface of the substrate  15 . Thus, there is completed the semiconductor light-receiving device in accordance with the second embodiment. 
     When a light is introduced into the above mentioned semiconductor light-receiving device through the light-receiving plane  12 , a light is absorbed by about 60% by the n-InGaAs light absorbing layer  4  in the first portion A of the multi-layered structure  14 . Then, a light having passed the first portion A without being absorbed thereinto is absorbed in the n-InGaAsP clad layer  3 , the n-InGaAs light absorbing layer  4  and the p-InGaAsP clad layer  5  in the second portion B of the multi-layered structure  14 . A light having passed the first and second portions A and B without being absorbed thereinto is introduced into and absorbed in the third portion C of the multi-layered structure  14 . A light having been absorbed into the first, second and/or third portions A, B and/or C is converted to electricity in the n-InGaAs layer  4  to thereby generate carriers. An electric field applied to the p-side and n-side electrodes  9  and  10  leads the thus generated carriers to an external circuit (not illustrated) through the p-InGaAsP clad layer  5 , the p-InP layer  6  and the p-side electrode  9 . 
     As mentioned so far, in accordance with the second embodiment, the multi-layered structure  14  or the waveguide is designed to have inclined end portions, similarly to the first embodiment. Thus, it is possible to have the same advantageous effect as that a thickness of the n-InGaAs light absorbing layer  4  as viewed from the light-receiving plane  12  is made thicker. As a result, the light-receiving device could be readily coupled to an optical fiber through the end surface or light-receiving plane, and it would be possible to have high optical coupling efficiency greater than 90% and high quantum efficiency greater than 90%. In addition, it would be possible to make a response at a speed greater than 20 Gbps by designing the n-InGaAs light absorbing layer  4  to have a thickness of 1.0±0.3 μm. 
     Similarly to the first embodiment, the multi-layered structure  14  may be fabricated by liquid deposition, CVD, MOCVD, MBE or ALE. 
     While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims. 
     The entire disclosure of Japanese Patent Application No. 8-169736 filed on Jun. 28, 1996 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.