阅读说明：本技术 雪崩光电探测器(变型)及其制造方法(变型) (Avalanche photodetector (variants) and method for its manufacture (variants) ) 是由 尼古拉·阿法纳塞维奇·科洛博夫 康斯坦丁·尤列维奇·西塔斯基 维塔利·埃马努伊洛维奇·舒宾 德 于 2020-03-04 设计创作，主要内容包括：提出一种雪崩光电探测器(APD),其中光电转换器和至少一个雪崩放大器位于同一晶片上,雪崩放大器的倍增层覆盖导电晶片的整个表面,接触层形成在倍增层的某一区域中。在接触层外部,倍增层作为光电转换器起作用,从而促进光载流子进入雪崩放大器。围绕雪崩放大器的填充介质的圆形凹槽抑制了由相邻雪崩放大器产生的光电通信噪声,从而允许制造具有更高阈值灵敏度的多通道雪崩仪器。(An Avalanche Photodetector (APD) is proposed in which a photoelectric converter and at least one avalanche amplifier are located on the same wafer, the multiplication layer of the avalanche amplifier covering the entire surface of the conductive wafer, the contact layer being formed in a certain region of the multiplication layer. Outside the contact layer, the multiplication layer functions as a photoelectric converter, thereby promoting entry of photo-carriers into the avalanche amplifier. The circular recess of the fill medium surrounding the avalanche amplifier suppresses the optoelectronic communication noise generated by adjacent avalanche amplifiers, allowing the fabrication of a multi-channel avalanche instrument with higher threshold sensitivity.)

1. A method for fabricating an avalanche photodetector, the method comprising the steps of:

-forming a multiplication layer on the entire top surface of the semiconductor wafer,

-forming at least one avalanche amplifier in a region of the top surface of the multiplication layer by: etching a circular recess along the boundary of said region of said multiplication layer such that the depth of said circular recess is less than the thickness of said multiplication layer, then filling said recess with a dielectric material and positioning the contact layer of said at least one avalanche amplifier inside the region bounded by said recess, thereby forming a photoelectric converter layer outside the region bounded by said recess,

-placing a dielectric layer on a top surface of the photoelectric converter,

-placing a first electrode made of a transparent material on the surface of both the contact layer and the dielectric layer, and

-forming a second electrode on the bottom surface of the semiconductor wafer.

2. A method for fabricating an avalanche photodetector, the method comprising the steps of:

-forming a multiplication layer on the entire top surface of the semiconductor wafer,

-etching an additional closed recess on the top surface of the multiplication layer, such that the depth of the additional closed recess is greater than or equal to the thickness of the multiplication layer, but less than the total thickness of the combination of the wafer and the multiplication layer, and forming a photodetector inside the area delimited by the recess,

-filling the additional closed recess with highly doped polysilicon of the same conductivity type as the conductivity type of the multiplication layer,

-forming at least one avalanche amplifier in a certain area of the top surface of the multiplication layer delimited by the additional closed recess by: etching a circular recess along the boundary of said region of said multiplication layer such that the depth of said circular recess is less than the thickness of said multiplication layer, then filling said recess with a dielectric material and positioning the contact layer of said at least one avalanche amplifier inside the region bounded by said recess, thereby forming a photoelectric converter layer outside the region bounded by said recess,

-placing a dielectric layer on a top surface of the photoelectric converter,

-placing a first electrode made of a transparent material on the surface of both the contact layer and the dielectric layer, and

-forming a second electrode on the bottom surface of the semiconductor wafer.

3. The method of claims 1-2, wherein the semiconductor wafer is made of a low resistance material.

4. A method as claimed in claims 1 to 3 wherein the multiplication layer is formed on the wafer surface using an epitaxial process.

5. The method of claims 1-4, wherein both the wafer and the multiplication layer are made of the same semiconductor material.

6. The method of claims 1-5, wherein the contact layer is made by doping the multiplication layer with a dopant that forms a layer with opposite conductivity.

7. The method of claims 2-6, wherein the additional closed groove has a width of 1.5 μm to 2.0 μm.

8. The method according to claims 2-7, wherein a high resistive layer is placed on the contact layer of the avalanche amplifier before the first electrode is placed.

9. An avalanche photodetector fabricated according to the method of claim 1, the photodetector comprising:

-a semiconductor wafer having a semiconductor layer,

-a multiplication layer covering the entire top surface of the semiconductor wafer,

-a contact layer placed on a certain portion of the multiplication layer defined by circular recesses filled with a dielectric, the depth of the circular recesses being smaller than the thickness of the multiplication layer, wherein the contact layer forms at least one avalanche amplifier and a photoelectric converter outside the recesses,

a dielectric layer covering a top surface of the photoelectric converter,

-a first transparent electrode covering the surface of both the contact layer and the dielectric layer, and

-a second electrode formed on the bottom surface of the semiconductor wafer.

10. An avalanche photodetector fabricated according to the method of claim 2, the photodetector comprising:

-a semiconductor wafer having a semiconductor layer,

-a multiplication layer covering the entire surface of the semiconductor wafer,

-a contact layer placed on a certain portion of the multiplication layer defined by circular recesses filled with a dielectric, the depth of the circular recesses being smaller than the thickness of the multiplication layer, wherein the contact layer forms at least one avalanche amplifier and a photoelectric converter outside the recesses,

a dielectric layer covering a top surface of the photoelectric converter,

a first transparent electrode covering the surfaces of both the contact layer and the dielectric layer,

-an additional closed recess having a depth greater than or equal to the thickness of the multiplication layer but less than the total thickness of the combination of the wafer and the multiplication layer and filled with highly doped polysilicon of the same conductivity type as that of the multiplication layer, wherein an avalanche amplifier and a photoelectric converter are located inside the region delimited by the recess,

-a high resistance layer between the contact layer and the first electrode, and

-a second electrode formed on the bottom surface of the semiconductor wafer.

11. The avalanche photodetector of claim 10, wherein the width of the additional closed groove is 1.5 μ ι η to 2.0 μ ι η.

Technical Field

The claimed invention relates to Avalanche Photodetectors (APDs), which are fast and highly sensitive instruments widely used in LiDAR, communication systems, machine vision, robotics, medicine, biology, environmental monitoring, and the like.

Background

A conventional Avalanche Photodetector (APD) includes a plurality of semiconductor layers disposed on a semiconductor wafer.

A set of semiconductor layers forms a photoelectric converter in which signal photons are absorbed to generate free charge carriers, i.e. electrons or electron holes. These photo-generated charge carriers then enter another set of semiconductor layers, the avalanche amplifier, where a region of sufficient electric field strength to avalanche multiply the charge carriers is formed.

The threshold sensitivity is a fundamental parameter of APDs and depends on the characteristics of both the photoelectric converter and the avalanche amplifier.

The threshold sensitivity is largely limited by the dark current of the avalanche amplifier, which is mainly caused by the high intensity field required for avalanche multiplication of the photo-carriers.

In order to reduce the dark current of the avalanche amplifier and thereby improve the threshold sensitivity of the APD, the area occupied by the avalanche amplifier can be made smaller relative to the area occupied by the photoelectric converter.

An example of this can be seen, for example, in the avalanche photodetectors according to patents US 9,035,410 and RU 2,641,620, in which the avalanche amplifier and the photoelectric converter, comprising two layers (contact layer and multiplication layer), are both located on the same wafer, with the area of the photoelectric converter being larger than that of the amplifier.

In the APD according to patent RU 2,641,620, the multiplication layer is made of semiconductor material of the same conductivity type as that of the signal photoelectric converter, facing the wafer and directly adjoining the autonomous photoelectric converter, which allows to reduce the excessive dark noise caused by the photo-carriers transmitted from the photoelectric converter to the avalanche amplifier through the external circuit (see US 9,035,410).

The main drawback is that having the multiplication layer independent of the photoelectric converter blocks the photo-carriers generated in the photoelectric converter layer from reaching the multiplication layer, resulting in a multiplied optical signal loss. This results in a decrease in the threshold sensitivity, which is an essential parameter of the photodetector.

It is an object of the present invention to fabricate an Avalanche Photodetector (APD) with high threshold sensitivity that will not be limited by inefficient transport of photo-carriers from the photo-electric converter to the avalanche amplifier. Furthermore, in case multiple avalanche amplifiers are used for the same APD, the proposed APD has less dark current and less interference noise from neighboring avalanche amplifiers.

By solving all these problems, it would be possible to improve the threshold sensitivity, which is a fundamental parameter of APDs.

Disclosure of Invention

The claimed invention includes an Avalanche Photodetector (APD) and method for fabricating the APD that allows for more efficient transport of photo-carriers from the photoelectric converter to the avalanche amplifier by placing the multiplication layer entirely over the conductive wafer. The contact layer of at least one avalanche amplifier is formed in a certain region of the multiplication layer. Therefore, the multiplication layer outside the contact layer functions as a photoelectric converter. As a result, the photo carriers that have been induced in the photoelectric converter will enter the multiplication region of the avalanche amplifier without obstruction. A first electrode and a second electrode of the avalanche photodetector are disposed on the contact layer and the wafer, respectively.

In order to suppress interference noise from adjacent avalanche amplifiers (noise generated when parasitic photoelectrons from photons of a thermoelectric charge carrier in an adjacent avalanche amplifier enter the multiplication region), a circular groove filled with a dielectric material and surrounding the contact layer of the avalanche amplifier is used.

To reduce dark current of the APD from adjacent wafer areas, a closed groove is etched on the surface of the multiplication layer, the depth of the closed groove is greater than or equal to the thickness of the multiplication layer but less than the combined total thickness of the wafer and multiplication layer, and a photodetector is formed within the area bounded by the groove. The groove is filled with highly doped polysilicon with the same conductive type as that of the multiplication layer.

To improve efficiency, the semiconductor wafer should be made of a low resistance material.

It is feasible that both the wafer and the multiplication layer are made of the same semiconductor material.

The multiplication layer on the wafer surface can be made using an epitaxial method, and the contact layer can be made by doping the multiplication layer with a dopant that forms a layer with the opposite conductivity.

It is also feasible that the width of the additional groove along the perimeter of the photoelectric converter region does not exceed 2 μm.

It is also possible to place a high resistance layer between the contact layer of the avalanche amplifier and the first electrode.

Drawings

The objects, features and advantages of the present invention will be further pointed out in the detailed description and drawings.

In the drawings:

fig. 1 is a schematic cross-section of a claimed APD according to a first embodiment, the APD comprising: a semiconductor wafer 101; a multiplication layer 102 covering the entire surface of the semiconductor wafer having the same conductivity type as that of the multiplication layer; a circular groove 103 filled with a dielectric material; a dielectric layer 104 covering the surface of the multiplication layer 102; a contact layer 106 made by diffusion of highly doped polysilicon 105 of conductivity opposite to that of the multiplication layer, wherein at least one avalanche amplifier 107 and a photoelectric converter 108 outside the avalanche amplifier are formed; a first electrode 109 made of a transparent material and located on the surfaces of both the contact layer 106 and the dielectric layer 104; and a second electrode 110 formed on the bottom surface of the semiconductor wafer 101.

Fig. 1A shows a process of placing a multiplication layer 102 on a silicon wafer 101. Fig. 1B shows a process of forming a circular recess 103 filled with a dielectric.

Fig. 1C shows a process of placing a dielectric layer 104 on the surface of the multiplication layer 102, wherein a window is created in the dielectric layer, which is filled with highly doped polysilicon 105 having a conductivity opposite to that of the multiplication layer.

Fig. 1D shows a process of forming a region of avalanche amplifiers 107 by creating a contact layer 106 by diffusion from highly doped polysilicon 105 filling a window in the dielectric layer 104 on top of the multiplication layer, wherein at least one avalanche amplifier 107 and a photoelectric converter 108 located outside the avalanche amplifier are formed.

Fig. 1E shows a process of forming a first electrode 109 made of a transparent conductive material on the surfaces of the contact layer 107 and the dielectric layer 104.

Fig. 1F shows a process of forming the second electrode 110 on the semiconductor wafer 101.

Fig. 2 is a schematic cross-section of a claimed APD according to a second embodiment, the APD comprising: a semiconductor wafer 201; a multiplication layer 202 covering the entire surface of the semiconductor wafer having the same conductivity type as that of the multiplication layer; a circular groove 203 filled with a dielectric material; a dielectric layer 204 covering the surface of the multiplication layer 202; a contact layer 206 made by diffusion of highly doped polysilicon 205 of conductivity opposite to that of the multiplication layer, wherein at least one avalanche amplifier 207 and a photoelectric converter 208 outside the avalanche amplifier are formed; an additional closed groove 211, the width of which is 1.5 μm to 2.0 μm, the depth of which is greater than or equal to the multiplication layer thickness but less than the total thickness of the combination of the wafer and the multiplication layer, and the additional closed groove 211 is filled with highly doped polysilicon of the same conductivity type as that of the multiplication layer and surrounds the avalanche amplifier 207 and the photoelectric converter 208; a high resistance layer 212 formed on the contact layer 206 in the avalanche amplifier 207 region; a transparent electrode 209 formed on the surfaces of the high-resistance layer 212 and the dielectric layer 204; and a second electrode 210 formed on the bottom surface of the semiconductor wafer 201.

Fig. 2A shows a process of placing a multiplication layer 202 on a silicon wafer 201.

Fig. 2B shows a process of forming an additional closed recess 211, the additional closed recess 211 being filled with highly doped polysilicon of the same conductivity type as that of the multiplication layer, so that a photodetector can be formed inside the recess.

Fig. 2C shows the process of forming a circular recess 203 filled with dielectric material in the region of the proposed location of the avalanche amplifier 207.

Fig. 2D shows the process of placing a dielectric layer 204 on the surface of the multiplication layer 202, wherein a window is created in said dielectric layer, which is filled with highly doped polysilicon 205 with a conductivity opposite to that of the multiplication layer.

Fig. 2E shows the process of forming the avalanche amplifier 207 region by creating a contact layer 206 by diffusion of highly doped polysilicon 205 filling a window in the dielectric layer 204 on top of the multiplication layer, wherein at least one avalanche amplifier 207 and a photoelectric converter 208 located outside the avalanche amplifier are formed.

Fig. 2F shows a process of forming a high resistance layer 212 on the contact layer 206 in the region of the avalanche amplifier 207.

Fig. 2G shows a process of forming a first electrode 209 made of a transparent conductive material on the surfaces of the contact layer 206 and the dielectric layer 204.

Fig. 2H illustrates a process of forming the second electrode 210 on the semiconductor wafer 201.

Fig. 3A is a schematic top view of an APD including a single avalanche amplifier 207 and a groove 211 according to a second embodiment.

Fig. 3B is a schematic top view of an APD including three avalanche amplifiers 207 and grooves 211 according to a second embodiment.

Detailed Description

The reference numbers used in the present disclosure and figures (except for the number 100 (incident light)) consist of three digits, where the first digit is the figure number and the last two digits denote a particular element of the design.

For example, the marker 206 points to element number 06 in FIG. 2 (see list below).

The following labels are used to point to specific elements of the design:

01-a wafer, wherein the wafer is,

02-a multiplication layer, wherein the multiplication layer is a single layer,

03-a circular groove is formed in the inner wall of the groove,

04-a dielectric layer, wherein the dielectric layer is formed on the substrate,

05-a layer of highly doped polysilicon,

06-the contact layer(s) -the contact layer,

07-an avalanche amplifier, and a method for operating the same,

08-a photoelectric converter, which is a photoelectric converter,

09-the first electrode,

10-a second electrode, the second electrode,

11-the additional closed recess or recesses,

12-high resistance layer.

Fig. 1 shows a schematic cross-section of the claimed APD according to a first embodiment, comprising: a semiconductor wafer 101; a multiplication layer 102 covering the entire surface of the semiconductor wafer having the same conductivity type as that of the multiplication layer; a circular groove 103 filled with a dielectric material; a dielectric layer 104 covering the surface of the multiplication layer 102; a contact layer 106 made by diffusion of a highly doped polysilicon layer 105 of conductivity opposite to that of the multiplication layer, wherein at least one avalanche amplifier 107 and a photoelectric converter 108 outside the avalanche amplifier are formed; a first electrode 109 made of a transparent material and located on the surfaces of both the contact layer 106 and the dielectric layer 104; and a second electrode 110 formed on the bottom surface of the semiconductor wafer 101.

The method for fabricating the APD shown in fig. 1 is further illustrated by fig. 1A, 1B, 1C, 1D, 1E, 1F, including the following sequential steps:

placing a multiplication layer 102 having the same conductivity type as that of the wafer on a silicon wafer 101 (see fig. 1A);

forming at least one circular groove 103 on the surface of the multiplication layer 102, and then filling the circular groove with a dielectric material (see fig. 1B);

placing a dielectric layer 104 on the surface of the multiplication layer 102 (see fig. 1C);

creating a window in the region of the dielectric layer 104 bounded by the circular recess 103, and then filling the window with highly doped polysilicon 105 of opposite conductivity to that of the multiplication layer; then, creating a contact layer 106 by diffusion of highly doped polysilicon 105 filling the window of the dielectric layer 104, forming one or more avalanche multiplier 107 regions in the multiplication layer, thereby forming at least one avalanche multiplier 107 and a photoelectric converter 108 located outside the avalanche multiplier (see fig. 1D);

forming a first electrode 109 made of a transparent conductive material on top of the contact layer 106 and the dielectric layer 104 (see fig. 1E);

a second electrode 110 is formed on the semiconductor wafer 101 (see fig. 1F).

The exemplary APD according to fig. 1 can be fabricated using methods involving the formation of a multiplication layer 102 by epitaxy, the multiplication layer 102 having a width of 5 μm-7 μm and a doping concentration higher than 10¹⁸cm^-3P + type silicon wafer 101 with a doping concentration of 10¹⁵cm^-3-10¹⁷cm^-3Is made of p-type silicon. On top of the multiplication layer, a circular groove 103 is formed using photolithography and plasma etching, the circular groove 103 having a diameter of 1.0 μm to 2.0 μm, a depth of 1.5 μm to 2.0 μm, and a width of 0.4 μm to 0.5 μm, and then the circular groove 103 is filled with a dielectric material. A dielectric layer 104 having a thickness of about 1.0 μm to 1.5 μm is placed on the surface of the multiplication layer 102 using a thermal chemical deposition method, and in this layer 104 where the circular recess 103 is located, a window is created using photolithography and plasma etching, and then this window is filled with highly doped polysilicon 105 using a thermal chemical deposition method, the conductivity of this highly doped polysilicon 105 being opposite to that of the multiplication layer and the doping concentration being at least 10¹⁹cm^-3. In the multiplication layer, one or more avalanche amplifier 107 regions are formed by creating a contact layer 106 by diffusion of the dopant from the highly doped polysilicon 105, the depth of penetration of the dopant from the highly doped polysilicon 105 being less than the depth of the circular recess 103. Meanwhile, the photoelectric converter layer 108 is formed outside the avalanche amplifier. From GA first electrode 109 made of a transparent material of GO or AZO type is formed on top of both the contact layer 106 and the dielectric layer 104, while a second electrode 110 is formed on the bottom surface of the semiconductor wafer 101, which second electrode 110 is an aluminum foil with a thickness of about 0.5-1.0 μm.

The APD shown in fig. 1 operates as follows:

a positive voltage is applied to the electrode 109 relative to the electrode 110 sufficient to trigger impact ionization in the multiplication layer 102 of the avalanche amplifier 107, resulting in free charge carrier multiplication.

Incident light 100 falling on the surface of the photoelectric converter 108 is absorbed, generating free charge carriers, i.e., electrons and electron holes. Free electrons (photoelectrons) in the photoelectric converter 108 that have been caused by light drift toward the avalanche multiplication layer 102 driven by superposition of electric fields (one of which bleeds out from the avalanche amplifier 107 and the other of which is caused by the first electrode 109 in the photoelectric converter) and are multiplied there, producing an output signal of APDs, while holes enter the wafer 101. Photoelectrons that have been caused by light in the non-depletion region of the photoelectric converter 104 are collected in the depletion region of the photoelectric converter by diffusion caused by a free electron concentration gradient in the photoelectric converter.

Fig. 2 shows a schematic cross-section of the claimed APD according to a second embodiment, comprising: a semiconductor wafer 201; a multiplication layer 202 covering the entire surface of the semiconductor wafer having the same conductivity type as that of the multiplication layer; a circular groove 203 filled with a dielectric material; a dielectric layer 204 covering the surface of the multiplication layer 202; a contact layer 206 made by diffusion of highly doped polysilicon 205 of conductivity opposite to that of the multiplication layer, wherein at least one avalanche amplifier 207 and a photoelectric converter 208 outside the avalanche amplifier are formed; an additional closed recess 211, the width of which is 1.5 μm to 2.0 μm, the depth of which is greater than or equal to the multiplication layer thickness, but less than the total thickness of the combination of the wafer and the multiplication layer, and which additional closed recess 211 is filled with highly doped polysilicon of the same conductivity type as that of the multiplication layer, wherein inside the region delimited by said recess the avalanche amplifier 207 and the photoelectric converter 208 are positioned; a high resistance layer 212 formed on the contact layer 206 in the avalanche amplifier 207 region; a transparent electrode 209 formed on the surfaces of the highly doped polysilicon 205, the high resistance layer 212, and the dielectric layer 204; and a second electrode 210 formed on the bottom surface of the semiconductor wafer 201.

The method for fabricating the APD shown in fig. 2 is further illustrated by fig. 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H and comprises the following sequence of steps:

placing a multiplication layer 202 having the same conductivity type as that of the wafer on a silicon wafer 201 (see fig. 2A);

etching an additional closed recess 211 in the multiplication layer 202 and the wafer 201, and then filling this additional closed recess 211 with highly doped polysilicon of the same conductivity type as that of the multiplication layer, so as to form a photodetector inside the region delimited by said recess (see fig. 2B);

forming at least one circular groove 203 on the surface of the multiplication layer where the avalanche amplifier 207 is located, and then filling the circular groove 203 with a dielectric material (see fig. 2C);

placing a dielectric layer 204 on the surface of the multiplication layer 202 (see fig. 2D);

creating a window in the dielectric layer 204 above the multiplication layer and within the limits of the circular recess 203, then filling this window with highly doped polysilicon 205 of opposite conductivity to that of the multiplication layer, and creating a contact layer 206 by diffusion of dopants from the highly doped polysilicon 205, forming at least one avalanche amplifier 207 region in the multiplication layer 202, thus forming at least one avalanche amplifier 207 and a photoelectric converter 208 outside the avalanche amplifier (see fig. 2E);

placing a high resistance layer 212 on the highly doped polysilicon 205 (see fig. 2F);

forming a first electrode 209 made of a transparent conductive material on top of the high-resistance layer 212 and the dielectric layer 204 (see fig. 2G);

a second electrode 210 is formed on the bottom surface of the semiconductor wafer 201 (see fig. 2H).

Methods involving splicing the multiplication layer 202 to the doping by epitaxy may be usedConcentration higher than 10¹⁸cm^-3The exemplary APD according to fig. 2 is fabricated with a method on a p + -type silicon wafer 201 in which the multiplication layer 202 has a width of 5 μm to 7 μm and a doping concentration of 10¹⁵cm^-3-10¹⁷cm^-3Is made of p-type silicon. Then, an additional closed recess 211 is etched on the surface of the multiplication layer 202, the closed recess 211 having a width of 1.5 μm to 2.0 μm and a depth greater than or equal to the multiplication layer thickness but less than the total thickness of the combination of the wafer and the multiplication layer, and the additional closed recess 211 is filled with highly doped polysilicon of the same conductivity type as that of the multiplication layer 202, so that a photodetector can be formed inside the region delimited by said recess. On top of the multiplication layer, a circular groove 203 is formed using photolithography and plasma etching, the circular groove 203 having a diameter of 1.0 μm to 2.0 μm, a depth of 1.5 μm to 2.0 μm, and a width of 0.4 μm to 0.5 μm, and then the circular groove 203 is filled with a dielectric material. A dielectric layer 204 having a thickness of about 1.0 μm to 1.5 μm is deposited on the surface of the multiplication layer 202 using a thermal chemical deposition method, and in the layer 204 where the circular recess 203 is located, a window is created using photolithography and plasma etching, and then the window is filled with highly doped polysilicon 205 using a thermal chemical deposition method, the conductivity of the highly doped polysilicon 205 being opposite to that of the multiplication layer and the doping concentration being at least 10¹⁹cm^-3. In the multiplication layer, one or more avalanche amplifier 207 regions are formed by creating a contact layer 206 by diffusion of the dopant from the highly doped polysilicon 205, the depth of penetration of the dopant from the highly doped polysilicon 205 being less than the depth of the circular recess 203. Meanwhile, the photoelectric converter layer 208 is formed outside the avalanche amplifier. A high resistance layer 212 made of high resistance polysilicon is formed on the highly doped polysilicon 205. A first electrode 209 made of a transparent conductive material of ITO or AZO type is formed on top of both the high resistance layer 212 and the dielectric layer 204, while a second electrode 210 is formed on the bottom surface of the semiconductor wafer 201, the second electrode 210 being an aluminum foil with a thickness of about 0.5 μm to 1.0 μm.

The APD according to the second embodiment as shown in figure 2, i.e. having a groove extending along the edge of the multiplication layer, is characterized in that it allows to suppress the inflow of parasitic charge carriers (dark and light) from the adjacent regions into the avalanche amplifier. To effectively suppress such parasitic currents, the recess will be filled with highly doped polysilicon of the same conductivity type as that of the multiplication layer, the depth of the recess being greater than the multiplication layer thickness but less than the total thickness of the combination of the wafer and the multiplication layer. Otherwise, this APD embodiment functions in the same manner as shown in fig. 1.