JP2005353661A - Semiconductor photodetector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor photodetector capable of efficiently entering a light signal to the same extent as in the case of entering it aslant or in parallel, from the semiconductor layer side, even when it is used by making a light signal incident aslant from the substrate side, while the damage generated by a cleavage is less likely to reach the photoelectric converter. <P>SOLUTION: On a semiconductor substrate 1, a photoelectric converter 5 consisting of an n-InP layer 2, an i-InGaAs (light absorption layer) 3, and a p-InP layer 4 is formed. In an end-face incident semiconductor photodetector 100, wherein a light signal 11 enters from the end face side of a photoelectric converter 5, the end face of photoelectric converter 5 is formed almost at right angles to the surface of the semiconductor substrate 1 by etching, and has a light-receiving surface 12 for receiving the light signal 11. The semiconductor substrate 1 or a semiconductor layer comprises a tilted terrace 13 located at the outside of the light-receiving surface 12 of the photoelectric converter 5, and a level terrace 14 located between the tilted terrace 13 and the surface 12 of the photoelectric converter 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor light receiving element, and more particularly to a semiconductor light receiving element for converting an optical signal into an electric signal in an optical communication network or the like.

  In recent years, research and development and practical application of waveguide-type semiconductor light-receiving elements (hereinafter referred to as waveguide-type semiconductor light-receiving elements) have been promoted as semiconductor light-receiving elements for optical communication. This is a semiconductor light-receiving element in which a waveguide-type semiconductor light-receiving element makes an optical signal incident from the end face, and the signal is faster than a surface-incident semiconductor light-receiving element that makes the optical signal incident from a direction perpendicular to the semiconductor layer. This is because it is easy to achieve both responsiveness and high photoelectric conversion efficiency.

In recent years, a waveguide type semiconductor light receiving element 800 having a cross-sectional structure shown in FIG. A waveguide type semiconductor light receiving element 800 includes an n ⁺ -InP buffer layer 82, an n ⁺ -InGaAsP intermediate refractive index layer 83, a light absorption layer 84, and a p ⁺ -InGaAsP band discontinuous relaxation layer on a semi-insulating InP substrate 81. 85, p ⁺ -InP cladding layer 86, and p ⁺ -InGaAs contact layer 87 are sequentially stacked.

Further, in the waveguide type semiconductor light receiving element 800, a V groove having a forward mesa structure is formed by wet etching, and one surface of the V groove is used as a light receiving surface, and scratching is performed using the bottom of the V groove. It has a structure in which elements are separated. The optical signal incident from the light receiving surface is absorbed while propagating through the light absorption layer 84, converted into an electrical signal, and output through the electrodes 88 and 89.
Japanese Patent Laid-Open No. 11-68127

  However, in such a conventional semiconductor light-receiving element that forms a V-groove, the light-receiving surface and the cleavage plane are formed using the V-groove formed by wet etching, and the light-receiving surface and the cleavage plane are separated from each other. Therefore, there is a problem in that damage caused by the separation of the element may reach the part (hereinafter referred to as a photoelectric conversion unit) that converts the optical signal of the semiconductor light receiving element into an electric signal. In addition, when an optical signal is incident obliquely from the semiconductor substrate side, the optical signal is incident on the light receiving surface at an acute angle. Therefore, when the optical signal is incident obliquely from the semiconductor layer side or incident parallel to the semiconductor layer. Compared with this, there is a problem that the optical signal is more easily reflected, the spot size of incident light on the light receiving surface is increased, the optical power per unit area is reduced, and the light is not efficiently incident.

  Further, in the conventional semiconductor light receiving element in which no V-groove is formed, the position accuracy of the device separation gap is low, and the crack may be scratched in the vicinity of the end face of the photoelectric conversion unit. There was a problem that it often occurred. And, in the case of a configuration in which the position of the scratch is sufficiently separated from the photoelectric conversion unit to avoid damage, the optical signal is blocked by the semiconductor substrate, so that it cannot be used for an application in which the optical signal is incident obliquely from the semiconductor substrate side. There was a problem.

  The present invention has been made to solve such a problem, and the damage caused by scratching is less likely to reach the photoelectric conversion portion than in the conventional waveguide type semiconductor light receiving element, and the optical signal is obliquely inclined from the substrate side. A semiconductor light-receiving element capable of causing an optical signal to be incident as efficiently as it is when used by being incident obliquely from the semiconductor layer side or when used by being incident parallel to the semiconductor layer. Is to provide.

  In view of the above points, the invention according to claim 1 is configured such that a photoelectric conversion unit including a plurality of semiconductor layers including a light absorption layer is formed on a semiconductor substrate, and an optical signal is incident from an end face side of the photoelectric conversion unit. In the edge-incident semiconductor light-receiving element, the end surface of the photoelectric conversion unit is formed substantially perpendicular to the surface of the semiconductor substrate by etching, has a light-receiving surface that receives the optical signal, and the end surface of the photoelectric conversion unit The semiconductor substrate located on the outer side or the semiconductor layer on the semiconductor substrate includes an inclined terrace portion located on the outer side of the light receiving surface of the photoelectric conversion unit, the light receiving surface of the photoelectric conversion unit, and the inclined terrace portion And a horizontal terrace portion located between the two.

  With this configuration, the end face of the photoelectric conversion part is formed almost perpendicularly to the surface of the semiconductor substrate by etching, and the scratching position is provided at a position separating the horizontal terrace part and the inclined terrace part from the light receiving surface. Damage caused by scratching is less likely to reach the photoelectric conversion part than a type semiconductor light receiving element, and even when an optical signal is incident obliquely from the substrate side and used obliquely from the semiconductor layer side or a semiconductor It is possible to realize a semiconductor light-receiving element capable of making an optical signal incident as efficiently as in the case where the light is incident parallel to the layer.

  The invention according to claim 2 is the invention according to claim 1, wherein the width of the horizontal terrace portion, which is the distance from the photoelectric conversion portion side edge of the inclined terrace portion to the light receiving surface of the photoelectric conversion portion, is C. The distance from the surface of the horizontal terrace portion to the interface on the substrate side of the light absorption layer is D, and the traveling direction of the optical signal and the light reception incident from an angle from the semiconductor substrate with respect to an axis perpendicular to the light receiving surface The angle formed by the axis perpendicular to the surface is the incident angle α, and the angle formed by the surface of the inclined terrace portion and the axis perpendicular to the light receiving surface is the tilt angle β, the incident angle α is the tilt angle β. The horizontal terrace has a configuration in which the width C of the horizontal terrace satisfies the relationship C ≦ D / tan α.

  With this configuration, in addition to the effect of the first aspect, the incident angle α is equal to or smaller than the inclination angle β, and the horizontal terrace width C satisfies the relationship C ≦ D / tan α. A semiconductor light receiving element that can be appropriately secured in the end face of the portion can be realized.

  According to a third aspect of the present invention, in the first or second aspect, the semiconductor light receiving element includes a protective film 8 that covers at least an end face of the photoelectric conversion unit, and the protective film is provided on the light receiving surface. The optical signal is configured to function as a low reflection film.

  With this configuration, in addition to the effects of the first or second aspect, a protective film is formed so as to also serve as a low reflection film, so that a semiconductor light receiving element that can omit a separate step of forming a low reflection film is realized. be able to.

  According to a fourth aspect of the present invention, in the third aspect, the average thickness of the protective film on the light receiving surface is d, the refractive index of the protective film on the light receiving surface is n, and the wavelength of the optical signal Is λ, and arcsin (sin α / n) is an angle θ between light propagating through the protective film and an axis perpendicular to the light receiving surface, the average thickness d of the protective film on the light receiving surface is λ / (4n cos θ) in the vicinity, wherein the protective film on the light receiving surface has a thickness that functions as the low reflection film.

  With this configuration, in addition to the effect of the third aspect, the average thickness d of the protective film on the light receiving surface is a thickness in the vicinity of λ / (4n cos θ), and the protective film on the light receiving surface functions as a low reflection film. As a result, a semiconductor light receiving element capable of achieving an appropriate reflectance can be realized.

  According to a fifth aspect of the present invention, in the third or fourth aspect, the protective film is formed so as to cover at least an end face of the photoelectric conversion unit and not cover a region on the inclined terrace portion. It has a configuration.

  With this configuration, in addition to the effect of claim 3 or claim 4, since the protective film is formed so as not to cover the region on the inclined terrace portion, this protective film is formed by chemical etching of the inclined terrace portion. It is possible to realize a semiconductor light-receiving element that can be used as a mask and can omit the mask formation step.

  The invention according to claim 6 is the structure according to any one of claims 1 to 5, wherein the photoelectric conversion unit has a pn junction, and the pn junction does not reach an end face of the photoelectric conversion unit. have.

  According to this configuration, in addition to the effect of any one of claims 1 to 5, the pn junction in the photoelectric conversion unit does not reach the end surface of the photoelectric conversion unit, and therefore, it is generated due to a defect near the end surface of the photoelectric conversion unit. A semiconductor light receiving element capable of reducing dark current can be realized.

  In the present invention, the end face of the photoelectric conversion portion is formed almost perpendicularly to the surface of the semiconductor substrate by etching, and the scratching position is provided at a position separating the horizontal terrace portion and the inclined terrace portion from the light receiving surface. Damage caused by scratching is less likely to reach the photoelectric conversion part than a type semiconductor light receiving element, and even when an optical signal is incident obliquely from the substrate side and used obliquely from the semiconductor layer side or a semiconductor It is possible to provide a semiconductor light receiving element having an effect that an optical signal can be made to enter as efficiently as the case where it is made incident on a layer in parallel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, taking as an example an edge-incident semiconductor light-receiving element having a PIN structure.

(First embodiment)
FIG. 1 is a cross-sectional view showing a schematic structure of a semiconductor light receiving element according to a first embodiment of the present invention. In FIG. 1, a semiconductor light receiving element 100 includes an n-InP layer 2, an i-InGaAs layer 3, and a p-InP layer 4 in this order on the (100) plane of a semiconductor substrate 1 made of n-InP. Have a layered structure. Here, the i-InGaAs layer 3 is a semiconductor layer that absorbs the incident optical signal 11 and is referred to as a light absorption layer.

A protective film 7 is formed on the surfaces of the semiconductor substrate 1 and the semiconductor layers 2 to 4. Note that a contact hole is formed in the protective film 7 on the semiconductor layer 4 in order to ensure electrical contact between the p-electrode 6 and the p-InP layer 4. A contact layer made of, for example, n ⁺ -InGaAs may be provided between the p-electrode 6 and the p-InP layer 4 to ensure good electrical contact. An n-electrode 8 is formed on the surface of the semiconductor substrate 1 opposite to the surface on which the semiconductor layers 2 to 4 are formed.

  Hereinafter, a semiconductor layer including the n-InP layer 2, the i-InGaAs layer (light absorption layer) 3, and the p-InP layer 4 is referred to as a photoelectric conversion unit 5. Here, the end surface of the photoelectric conversion unit 5 is formed substantially perpendicular to the surface of the semiconductor substrate 1 (hereinafter referred to as the substrate surface) and has a light receiving surface 12 that receives the optical signal 11. The light receiving surface 12 is a region of an end surface for appropriately allowing an optical signal to enter the photoelectric conversion unit 5 (see FIG. 1). In the semiconductor substrate 1, an inclined terrace portion 13 is formed outside the light receiving surface of the photoelectric conversion portion 5, and a horizontal terrace portion 14 is formed between the light receiving surface 12 and the inclined terrace portion 13 of the photoelectric conversion portion 5.

  Here, as shown in FIG. 1, the optical signal 11 is incident at an angle closer to the semiconductor substrate 1 than the axis perpendicular to the light receiving surface 12. Therefore, the axis perpendicular to the light receiving surface 12 is substantially horizontal to the substrate surface. In addition, an angle formed by the traveling direction of the optical signal 11 and an axis perpendicular to the light receiving surface 12 is α (hereinafter referred to as an incident angle), and an angle formed by the inclined terrace portion 13 and the substrate surface is β (hereinafter referred to as an inclination angle). (See FIG. 1).

  The width of the horizontal terrace portion 14 that is the distance from the side of the inclined terrace portion 13 on the photoelectric conversion portion 5 side to the light receiving surface 12 of the photoelectric conversion portion 5 is C, and the i-InGaAs layer (light absorption) from the surface of the horizontal terrace portion 14 The distance to the interface of the layer 3 on the semiconductor substrate 1 side is defined as D (see FIG. 1).

  In the following description, it is assumed that the distance D is equal to the layer thickness of the n-InP layer 2. Here, the incident angle α of the optical signal 11 is equal to or smaller than the inclined angle β of the inclined terrace portion 13, the width C of the horizontal terrace portion 14, the layer thickness D of the n-InP layer 2, and the incident angle α of the optical signal 11. It is assumed that a relationship of C ≦ D / tan α is established.

  A semiconductor film (hereinafter referred to as an epitaxial film) for each of the layers 2 to 4 is formed using a technique such as MOVPE (Metal Organic Vapor Phase Epitaxy) or MBE (Molecular Beam Epitaxy). Further, for example, Sn or S may be used as the n-type impurity, and Zn or the like may be used as the p-type impurity.

The thicknesses of the epitaxial films for the layers 2 to 4 are, for example, 0.5 to 1 μm, 0.5 to 4 μm, and 0.5 to 2 μm from the semiconductor substrate 1 side toward the p-InP layer 4, respectively. And Further, the impurity concentration of the epitaxial film for the n-InP layer 2 and the p-InP layer 4 is, for example, in the range of 5 × 10 ¹⁷ to 1 × 10 ¹⁸ (cm ⁻³ ). Note that these values of film thickness and impurity concentration are examples, and are not limited to these.

  Next, formation of the light receiving surface, element isolation, and the like will be described with reference to FIGS. 2 and 3 are process diagrams for explaining formation of a light receiving surface, element isolation, and the like. The cross-sectional views shown in FIGS. 2 and 3 are cross-sections taken along the (0-11) plane. In the following, it is assumed that the photoelectric conversion unit 5 is formed so that the (011) plane becomes the light receiving surface 12. Here, the p-electrode 6 is formed on the surface of the photoelectric conversion unit 5 excluding the region in the vicinity of the end face of the photoelectric conversion unit 5, and the (011) plane is formed to be the light receiving surface 12. To do.

First, a SiO ₂ or SiN _x film is deposited on the surface of the epitaxial film L4 for the p-InP layer 4 using a technique such as CVD (Chemical Vapor Deposition), and the photoelectric conversion portion 5 is formed using a photolithography technique. A mask 21 is formed (see FIG. 2A). Here, the shape of the mask 21 is a rectangle whose one side is substantially parallel to the [0-11] axis direction.

  However, the shape of the mask 21 is not limited to this rectangle, and may be a polygon, a sector, or other shapes. Next, dry etching is performed using the mask 21 to remove the epitaxial films L2, L3, and L4 for the n-InP layer 2, the i-InGaAs layer 3, and the p-InP layer 4, and the photoelectric conversion unit 5 is formed. (See FIG. 2 (b)).

When the photoelectric conversion unit 5 is formed, the mask 21 is removed (see FIG. 2C), and a film (hereinafter referred to as a passivation film) 22 such as SiN _x , SiO ₂ or the like is deposited as a protective film (FIG. 2). 2 (d)). The passivation film 22 is formed to be a so-called low reflection (hereinafter referred to as LR) film on the light receiving surface 12. In other words, during the deposition, the passivation film 22 is deposited so as to go around the light receiving surface 12.

Since the passivation film 22 functions as an LR film on the light receiving surface 12, the film thickness d on the light receiving surface 12 is about d = λ / (4n cos θ), and the reflectance is about 10% or less. Either film thickness is determined. Here, the symbol n is the refractive index of the material for the passivation film 22, the symbol λ is the wavelength of the optical signal, and the symbol θ is the angle formed between the light propagating through the passivation film 22 and the axis perpendicular to the light receiving surface 12. Arcsin (sin α / n). As the material for the passivation film 22, SiN _x , SiO ₂ or the like can be used as described above, but other materials may be used, or a multilayer film made of these materials may be used. Further, the passivation film 22 may be formed by vapor deposition such as electron beam vapor deposition or other film forming methods.

  Next, in order to ensure electrical contact between the p-electrode 6 and the p-InP layer 4 using photolithography technology, wet etching that separates the contact holes and the semiconductor light-receiving elements adjacent in the [011] direction is performed. A mask (hereinafter referred to as an element isolation mask) is formed (see FIG. 2E). Since the element isolation mask uses the protective film 7 as a mask, the element isolation mask is hereinafter referred to as an element isolation mask (protective film 7).

  Here, the shape of the inclined terrace portion 13 is obtained by wet etching using the opening of the element isolation mask (protective film 7), that is, the opening of the passivation film 22 deposited on the semiconductor substrate 1. Have However, the element isolation mask may have any shape as long as the inclined terrace portion 13 can be obtained by wet etching, and may have a stripe shape, an island shape, or other shapes.

  After the process shown in FIG. 2E is completed, a p-electrode 6 is formed so as to be in electrical contact with the p-InP layer 4 through the contact hole by using a photolithography technique (FIG. 2F). reference). After the p-electrode 6 is formed, a resist film is formed, and a resist film (hereinafter referred to as a protective resist film) 23 is left so as to cover the p-electrode 6 by using a photolithography technique (see FIG. 3G). ). This protective resist film 23 is for protecting the p-electrode 6 from etching erosion when forming the above-mentioned groove having the forward mesa structure.

  After the protective resist film 23 is formed, a solution of hydrochloric acid / phosphoric acid or Br / methanol is used as an etchant, and wet etching is performed using an element isolation mask to form a forward mesa structure (FIG. 3 (h) )reference). Here, the above-mentioned etchant is not necessarily limited to these solutions, and other solutions may be used as long as they can form a forward mesa. The portion of the forward mesa obtained by the above etching is the inclined terrace portion 13.

  When the forward mesa (inclined terrace portion 13) that separates the adjacent semiconductor light receiving elements is formed, the protective resist film is removed (see FIG. 3I). Next, the surface of the semiconductor substrate 1 where the photoelectric conversion portion 5 is not formed (hereinafter referred to as the back surface) is polished (see FIG. 3J), and the n-electrode 8 is formed on the polished back surface (see FIG. (See FIG. 3 (k)). The n electrode 8 may be made of, for example, an AuGeNi alloy. Note that the formation of the n-electrode 8 is not necessarily performed in this order, and may be performed prior to other processes or may be performed in another order. Further, if necessary, an alloy process may be included.

  Separation between adjacent semiconductor light receiving elements in the [011] direction can be performed by scratching at the cracking position shown in FIG. 3 (k), that is, at the position where the forward mesa groove is deepest. In the above description, the manufacturing process of the semiconductor light receiving element 100 in which the passivation film 22 is not deposited on the inclined terrace portion 13 has been described. Hereinafter, the passivation film on the inclined terrace portion 13 will be described with reference to FIGS. 4 and 5. A manufacturing process of the semiconductor light receiving element 100 on which 22 is deposited will be described.

  The steps shown in FIGS. 4A to 4D are the same as the steps shown in FIGS. 2A to 2D, and the description thereof is omitted. After the passivation film 22 is formed, a resist film is formed, and a resist pattern 24 for forming an element isolation mask is formed by using a photolithography technique (see FIG. 4E ′). Next, etching is performed using the resist pattern 24 as a mask to form an element isolation mask 25 (see FIG. 4F ′).

  After the element isolation mask 25 is formed, a solution of hydrochloric acid / phosphoric acid or Br / methanol is used as an etchant, and wet etching is performed using the element isolation mask 25 to form a forward mesa structure (FIG. 5 ( g ′)). Thereby, the inclined terrace portion 13 is formed. When the inclined terrace portion 13 is formed, the resist pattern 24 and the element isolation mask 25 are removed (see FIG. 5 (h ′)).

  Next, a passivation film 26 is deposited (see FIG. 5 (i ′)), and contact holes are formed using a photolithography technique (see FIG. 5 (j ′)). Thereby, the protective film 7 ′ is formed. After the contact hole is formed, a p-electrode 6 is formed so as to be in electrical contact with the p-InP layer 4 through the contact hole by using a photolithography technique (see FIG. 5 (k ′)).

  After the p-electrode 6 is formed, the back surface of the semiconductor substrate 1 is polished, and the n-electrode 8 is formed on the polished back surface (see FIG. 5 (l ′)). Note that the formation of the n-electrode 8 is not necessarily performed in this order, and may be performed prior to other processes or may be performed in another order. Further, if necessary, an alloy process may be included.

  Conventionally, the LR film is manufactured by making a semiconductor light receiving element array by cleaving the wafer on which the photoelectric conversion portion is formed, and forming the LR film on the light incident end face of the semiconductor light receiving element array by using an electron beam evaporation method. It was. After the formation of the LR film, the semiconductor light-receiving element array was separated by scratching the semiconductor light-receiving element array. Therefore, the possibility that the semiconductor light receiving element is damaged increases, the possibility that the end surface on which the optical signal is incident increases, the jig necessary for these steps is required, and it takes time to perform the steps. There was a serious problem. As described above, it is possible to avoid such a problem by forming the protective film that also serves as the LR film.

  In addition, since the light receiving surface 12 is formed perpendicular to the semiconductor substrate 1, even when the optical signal 11 is incident obliquely from the semiconductor substrate 1 side, the optical signal 11 is incident obliquely from the semiconductor layer side or incident parallel to the semiconductor layer. The optical signal 11 is incident as efficiently as it does. Furthermore, since the inclined terrace portion 13 is provided so that the optical signal 11 is not blocked by the semiconductor substrate 1, the optical signal 11 can also be used for an oblique incidence from the semiconductor substrate 1 side.

  Further, by adopting the structure of the semiconductor light receiving element disclosed in Japanese Patent Application Laid-Open No. 2004-55620, which is an invention related to the same applicant as the present applicant, the light is incident obliquely from the semiconductor layer side, and The optical signal can be incident with higher efficiency than in the case where it is incident in parallel with the semiconductor layer.

  The operation of the semiconductor light receiving element 100 according to the first embodiment of the present invention will be described below. First, the optical signal 11 incident on the photoelectric conversion unit 5 via the light receiving surface 12 is absorbed by the i-InGaAs layer (light absorption layer) 3 while propagating through the photoelectric conversion unit 5 forming the waveguide, and is thus electronic. Generate hole pairs. Of the electron-hole pairs generated in the i-InGaAs layer (light absorption layer) 3, holes move in the direction of the p electrode 6, electrons move in the direction of the n electrode 8, and are detected as electric signals. Is done.

  As described above, in the semiconductor light receiving element according to the first embodiment of the present invention, the end surface of the photoelectric conversion unit is formed substantially perpendicular to the surface of the semiconductor substrate by etching, and the scratch position is from the light receiving surface to the horizontal terrace portion. And the sloped terrace part are separated from each other, so that damage caused by scratches is less likely to reach the photoelectric conversion part than the conventional waveguide type semiconductor light receiving element, and an optical signal is incident obliquely from the substrate side. Even when it is used, an optical signal can be made to be incident as efficiently as when it is used obliquely incident from the semiconductor layer side or when it is used incident parallel to the semiconductor layer.

  In addition, since the incident angle α is equal to or smaller than the inclination angle β and the width C of the horizontal terrace satisfies the relationship of C ≦ D / tan α, the above-described region serving as the light receiving surface should be appropriately secured in the end surface of the photoelectric conversion unit. Can do.

  In addition, since a protective film is formed so as to also serve as a low-reflection film, it is possible to omit a separate process of forming a low-reflection film, which increases the possibility of damaging the semiconductor light receiving element, and an end face on which an optical signal is incident It is possible to avoid the problem that the possibility of fouling increases.

  In addition, the average thickness d of the protective film on the light receiving surface is a thickness in the vicinity of λ / (4n cos θ), and the protective film on the light receiving surface has a thickness that functions as a low reflection film, so that an appropriate reflectance is achieved. it can.

  Further, since the protective film is formed so as not to cover the region on the inclined terrace portion, this protective film can be used as a mask when the inclined terrace portion is formed by chemical etching, and the mask forming step is omitted. can do.

  In the above description, the semiconductor light receiving element having the PIN structure is described as an example of the semiconductor light receiving element. However, any semiconductor light receiving element having a pn junction, an avalanche photodiode, or the like can be used as long as it is an edge incident type semiconductor light receiving element. The semiconductor light receiving element may be used. In the above description, the example in which the present invention is applied to a single semiconductor light receiving element has been described. However, the present invention can also be applied to an array PD.

(Second Embodiment)
FIG. 6 is a cross-sectional view showing a schematic structure of a semiconductor light receiving element according to the second embodiment of the present invention. In FIG. 6, a semiconductor light receiving element 600 is provided with a semiconductor layer 42 made of an i-InP layer or an n ⁻ -InP layer instead of the p-InP layer 4, and p-type impurities are present in the central region of the semiconductor layer 42. A diffused region 43 is formed. Hereinafter, the semiconductor layer 42 is referred to as an i-InP layer, and the region 43 is referred to as a p-type impurity diffusion region 43.

  The impurity concentration of the p-type impurity diffusion region 43 is in the same order as the impurity concentration of the p-InP layer 4 described above. The p-type impurity diffusion region 43 is in contact with the i-InGaAs layer 3 or extends to the i-InGaAs layer 3 but does not reach the end face of the photoelectric conversion unit 52 (see FIG. 6). To do. A pn junction is formed in the boundary region between the p-type impurity diffusion region 43 and the i-InP layer 3 and the i-InP layer around the p-type impurity diffusion region 43. With this configuration, the pn junction is not exposed to the end face of the photoelectric conversion unit 52.

Hereinafter, a method of forming the p-type impurity diffusion region 43 will be described with reference to FIG. FIG. 7 is a process diagram for explaining a method of forming the p-type impurity diffusion region 43. The p-type impurity diffusion region 43 is formed by first depositing a SiN _x film on the epitaxial film L42 for the i-InP layer, and etching the SiN _x film using a photolithography technique, an etching technique, or the like. Then, a mask 71 having a window with a predetermined shape is formed (see FIG. 7A).

Next, using the SiN _x mask 71 described above, the impurity concentration immediately below the surface of the epitaxial film L42 for the i-InP layer is, for example, about 1 to 5 × 10 ¹⁸ (cm ⁻³ ). Is diffused (see FIG. 7B). Here, the diffusion is performed by thermal diffusion in the gas phase, and it is preferable to use it as an impurity for diffusing Zn. The thermal diffusion of Zn in the gas phase is known and will not be described. Finally, the p-type impurity diffusion region 43 is formed by removing the mask 71 made of SiN _x (see FIG. 7C).

  As described above, the semiconductor light receiving element according to the second embodiment of the present invention is provided with a p-type impurity diffusion region in addition to the effect of the semiconductor light receiving element according to the first embodiment of the present invention. Since the pn junction in the conversion part does not reach or be exposed to the end face of the photoelectric conversion part, dark current generated due to defects near the end face of the photoelectric conversion part can be reduced.

  In each of the above embodiments, the interface position between the n-InP layer 2 and the semiconductor substrate 1 is the horizontal terrace portion 14 position. However, the interface position is not limited to this, for example, the interface position May be formed in the middle of the inclined portion, or may be formed in a part of the photoelectric conversion portion 5.

  The semiconductor light-receiving element according to the present invention is less susceptible to damage caused by scratches than the conventional waveguide-type semiconductor light-receiving element, and even when used with an optical signal obliquely incident from the substrate side. For applications such as semiconductor light-receiving elements that have the effect of allowing an optical signal to be incident as efficiently as when entering obliquely from the layer side or when entering parallel to a semiconductor layer Is also applicable.

Sectional drawing which shows the general | schematic structure of the semiconductor light receiving element concerning the 1st Embodiment of this invention Process diagram for explaining formation of a light-receiving surface, element isolation, and the like of a semiconductor light-receiving element (structure having no protective film on an inclined terrace portion) according to the first embodiment of the present invention Process diagram for explaining formation of a light-receiving surface, element isolation, and the like of a semiconductor light-receiving element (structure having no protective film on an inclined terrace portion) according to the first embodiment of the present invention Process drawing for demonstrating formation, element isolation, etc. of the light-receiving surface of the semiconductor light-receiving element according to the first embodiment of the present invention (a structure in which the inclined terrace portion is covered with a protective film) Process drawing for demonstrating formation, element isolation, etc. of the light-receiving surface of the semiconductor light-receiving element according to the first embodiment of the present invention (a structure in which the inclined terrace portion is covered with a protective film) Sectional drawing which shows the general | schematic structure of the semiconductor photodetector which concerns on the 2nd Embodiment of this invention Process diagram for explaining a method of forming p-type impurity diffusion region 43 Sectional view showing the structure of a conventional semiconductor light receiving element

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 n-InP layer 3 i-InGaAs layer (light absorption layer)
4 p-InP layer 5, 52 photoelectric conversion part 6, 88 p electrode 7, 7 'protective film 8, 89 n electrode 11 optical signal 12 light receiving surface 13 inclined terrace part 14 horizontal terrace part 21, 25 mask 22, 26 passivation film 23 Protective resist film 42 Semiconductor layer 81 Semi-insulating InP substrate 82 n ⁺ -InP buffer layer 83 n ⁺ -InGaAsP intermediate refractive index layer 84 Light absorbing layer 85 p ⁺ -InGaAsP band discontinuous relaxation layer 86 p ⁺ -InP cladding Layer 87 p ⁺ -InGaAs contact layer 100, 600, 800 Semiconductor light receiving element L2 Epitaxial film for n-InP layer L3 Epitaxial film for i-InGaAs layer L4 Epitaxial film for p-InP layer

Claims (6)

An end face incident type in which a photoelectric conversion part (5) composed of a plurality of semiconductor layers including a light absorption layer (3) is formed on a semiconductor substrate (1), and an optical signal (11) is incident from the end face side of the photoelectric conversion part. In the semiconductor light receiving element (100) of
The end surface of the photoelectric conversion unit is formed substantially perpendicularly to the surface of the semiconductor substrate by etching, has a light receiving surface that receives the optical signal, and the semiconductor substrate positioned outside the end surface of the photoelectric conversion unit or The semiconductor layer on the semiconductor substrate includes an inclined terrace portion (13) positioned outside a light receiving surface of the photoelectric conversion portion, and a horizontal position positioned between the light receiving surface of the photoelectric conversion portion and the inclined terrace portion. A semiconductor light-receiving element comprising a terrace portion (14).   The width of the horizontal terrace portion, which is the distance from the side of the inclined terrace portion on the photoelectric conversion portion side to the light receiving surface of the photoelectric conversion portion, is C, and from the surface of the horizontal terrace portion to the substrate side of the light absorption layer The distance to the interface is D, and the angle between the traveling direction of the optical signal incident from the angle from the semiconductor substrate with respect to the axis perpendicular to the light receiving surface and the axis perpendicular to the light receiving surface is the incident angle α. When the angle formed by the surface of the inclined terrace portion and the axis perpendicular to the light receiving surface is an inclination angle β, the incident angle α is equal to or less than the inclination angle β, and the width C of the horizontal terrace is C ≦ D 2. The semiconductor light receiving element according to claim 1, wherein a relationship of / tan [alpha] is satisfied.   The semiconductor light receiving element has a protective film (7) covering at least an end face of the photoelectric conversion unit, and the protective film functions as a low reflection film for the optical signal on the light receiving surface. 3. The semiconductor light receiving element according to claim 1, wherein the semiconductor light receiving element is characterized in that   The average thickness of the protective film on the light receiving surface is d, the refractive index of the protective film on the light receiving surface is n, the wavelength of the optical signal is λ, and the light propagating through the protective film and the light receiving surface When the angle θ formed by the axis perpendicular to the axis is arcsin (sin α / n), the average thickness d of the protective film on the light receiving surface is a thickness in the vicinity of λ / (4n cos θ), and the light receiving surface The semiconductor light-receiving element according to claim 3, wherein the protective film has a thickness that functions as the low-reflection film.   5. The semiconductor light receiving element according to claim 3, wherein the protective film covers at least an end face of the photoelectric conversion unit and does not cover a region on the inclined terrace unit. 6.   6. The semiconductor light receiving device according to claim 1, wherein the photoelectric conversion unit has a pn junction, and the pn junction does not reach an end face of the photoelectric conversion unit. 7. element.

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