CN111312836B

CN111312836B - Photoelectric detector

Info

Publication number: CN111312836B
Application number: CN202010112946.2A
Authority: CN
Inventors: 杜建华; 关峰; 高宇鹏; 袁广才; 王忠国; 徐国良; 王政焱; 陈明; 杨春雷
Original assignee: BOE Technology Group Co Ltd; Shenzhen Institute of Advanced Technology of CAS
Current assignee: BOE Technology Group Co Ltd; Shenzhen Institute of Advanced Technology of CAS
Priority date: 2020-02-24
Filing date: 2020-02-24
Publication date: 2021-12-24
Anticipated expiration: 2040-02-24
Also published as: CN111312836A

Abstract

The present application provides a photodetector. The photoelectric detector comprises a substrate, a first electrode layer formed on the substrate, a light absorption layer with a first conductivity type formed on the first electrode layer, a tunneling junction layer formed on the light absorption layer, a semiconductor layer with a second conductivity type formed on the tunneling junction layer, and a transparent second electrode layer formed on the semiconductor layer. The tunneling junction layer is made of a mixture of magnesium sulfide and zinc sulfide. The photoelectric detector provided by the application can improve the impedance of a film structure of the photoelectric detector, effectively reduces the dark current of the photoelectric detector, enables a tunneling junction to have an excellent photomultiplier effect under reverse bias, and improves the sensitivity of the photoelectric detector.

Description

Photoelectric detector

Technical Field

The application relates to the technical field of semiconductors, in particular to a photoelectric detector.

Background

The Copper Indium Gallium Selenide (CIGS) material has higher light absorption rate and higher quantum efficiency, and can be applied to photoelectric detection devices, so that the photoelectric detection devices achieve better photoelectric conversion effect.

However, the resistance of each film layer of the photodetector adopting copper indium gallium selenide is small, so that the dark current of the photodetector is large, and the performance of the photodetector is affected.

Disclosure of Invention

An embodiment of the present application provides a photodetector, the photodetector includes:

a substrate;

a first electrode layer formed on the substrate;

a light absorption layer having a first conductivity type formed on the first electrode layer;

the tunneling junction layer is formed on the light absorption layer and is made of a mixture of magnesium sulfide and zinc sulfide;

a semiconductor layer having a second conductivity type formed on the tunnel junction layer;

a transparent second electrode layer formed on the semiconductor layer.

In one embodiment of the present application, in the tunnel junction layer, the ratio of the amount of magnesium sulfide to zinc sulfide is in a range of 0.1 to 0.5:0.5 to 0.9.

In one embodiment of the present application, the ratio of the amount of magnesium sulfide to zinc sulfide species in the tunnel junction layer ranges from 0.25: 0.75.

in one embodiment of the present application, the tunnel junction layer 40 has a thickness of 100nm to 2000 nm.

In one embodiment of the present application, the first conductivity type is p-type and the second conductivity type is n-type;

the light absorption layer is made of copper indium gallium selenide.

In one embodiment of the present application, the light absorbing layer has a thickness of 0.5 μm to 3 μm.

In one embodiment of the present application, the photodetector further comprises a buffer layer formed between the light absorbing layer and the tunnel junction layer;

the thickness of the buffer layer is 30 nm-100 nm.

In one embodiment of the present application, the thickness of the semiconductor layer is 30nm to 100 nm.

In one embodiment of the present application, the first electrode layer has a thickness of 0.5 μm to 2 μm.

In one embodiment of the present application, the thickness of the second electrode layer is 200nm to 700 nm.

The embodiment of the application achieves the main technical effects that:

according to the photoelectric detector provided by the embodiment of the application, the tunneling junction layer is made of the mixture of magnesium sulfide and zinc sulfide, so that the resistance value of the tunneling junction layer is higher, the impedance of the film structure of the photoelectric detector is improved, and the dark current of the photoelectric detector is effectively reduced; in addition, the tunneling junction is made of a mixture of magnesium sulfide and zinc sulfide, so that the tunneling junction has an excellent photomultiplier effect under reverse bias, the sensitivity of the photoelectric detector can be improved, and the performance of the photoelectric detector can be improved.

Drawings

FIG. 1 is a schematic diagram of a photodetector structure provided in an exemplary embodiment of the present application;

fig. 2 is a flowchart of a method for manufacturing a photodetector according to an exemplary embodiment of the present application.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present application. The word "if" as used herein may be interpreted as "at … …" or "when … …" or "in response to a determination", depending on the context.

The following describes a photodetector provided in an embodiment of the present application in detail with reference to the drawings. The embodiments described below and the features of the embodiments can be combined with each other without conflict.

In the embodiments of the present application, for convenience of description, the up-down direction is defined by defining the direction from the substrate to the first electrode layer as up and the direction from the first electrode layer to the substrate as down. It is easy to understand that the different direction definitions do not affect the actual operation of the process and the actual shape of the product.

The embodiment of the application provides a photoelectric detector. Referring to fig. 1, a photodetector 100 provided in the present embodiment includes a substrate 10, a first electrode layer 20, a light absorption layer 30, a tunnel junction layer 40, a semiconductor layer 50, and a second electrode layer 60.

Wherein the first electrode layer 20 is formed on the substrate 10. The light absorbing layer 30 is formed on the first electrode layer 20, and the light absorbing layer 30 has a first conductive type. The tunnel junction layer 40 is formed on the light absorbing layer 30, and the material of the tunnel junction layer 40 is a mixture of magnesium sulfide and zinc sulfide. The semiconductor layer 50 is formed on the tunnel junction layer 40, and the semiconductor layer 50 has a second conductivity type. The second electrode layer 60 is formed on the semiconductor layer 50.

In the photodetector 100 provided in the embodiment of the present application, the tunneling junction layer 40 is made of a mixture of magnesium sulfide and zinc sulfide, so that the resistance of the tunneling junction layer 40 is relatively high, and the impedance of the film structure of the photodetector 100 is improved, thereby effectively reducing the dark current of the photodetector 100; in addition, the tunnel junction 40 is made of a mixture of magnesium sulfide and zinc sulfide, so that the tunnel junction 40 has an excellent photomultiplier effect under a reverse bias, the sensitivity of the photodetector can be improved, and the performance of the photodetector can be improved.

In the photodetector 100 provided in the embodiment of the present application, one of the first electrode layer 20 and the second electrode layer 60 is connected to a positive electrode of an applied voltage, and the other is connected to a negative electrode of the applied voltage, so as to generate an electric field. Light is incident from the second electrode layer 60 of the photodetector 100, absorbed through the light absorbing layer 30, and photo-generated carriers (electrons and holes) are generated, and the carriers are transported by the reverse electric field, so that the reverse current is increased. The greater the intensity of the light, the greater the reverse current.

In one embodiment, the substrate 10 may be a glass substrate, and the material of the substrate 10 may be soda-lime glass, for example. Of course, in other embodiments, other materials may be used for the substrate 10, such as sapphire, etc.

In one embodiment, the material of the first electrode layer 20 may be metallic molybdenum. The molybdenum metal has good conductivity, so that an electric field can be provided by an electrode externally connected with the electric field. In other embodiments, other materials with good conductivity can be used for the first electrode layer 20.

In one embodiment, the thickness of the first electrode layer 20 is 0.5 μm to 2 μm. When the thickness of the first electrode layer 20 is within the range, the phenomenon that the normal operation of the photodetector is affected due to the fact that the resistance of the first electrode layer 20 is too large because the thickness of the first electrode layer 20 is too small can be avoided; too large a thickness of the first electrode layer 20 to cause excessive stress of the first electrode layer 20 on the substrate 10, which may result in bending of the substrate 10, can also be avoided. The thickness of the first electrode layer 20 may be, for example, 0.5 μm, 0.7 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, or the like.

In one embodiment, the first conductivity type is p-type and the second conductivity type is n-type. That is, the light absorbing layer 30 is a p-type light absorbing layer, and the semiconductor layer is an n-type semiconductor layer. The light absorbing layer 30 forms a PN junction with the semiconductor layer 50.

In one embodiment, the material of the light absorbing layer 30 is CIGS. The copper indium gallium selenide material is a direct band gap semiconductor material, the forbidden band width of the copper indium gallium selenide material can be continuously adjusted within 1.04 eV-1.67 eV, and the copper indium gallium selenide material has higher light absorption rate and higher quantum efficiency. The copper indium gallium selenide material is applied to the photoelectric detector 100 as the light absorption layer 30, so that the photoelectric detector can achieve a better photoelectric conversion effect, and the sensitivity of the photoelectric detector 100 can be improved.

In one embodiment, when the material of the light absorption layer 30 is copper indium gallium selenide, the thickness of the light absorption layer 30 is 0.5 μm to 3 μm. When the thickness of the light absorbing layer 30 is within this range, it is possible to prevent the light absorbing effect from being poor due to the too small thickness of the light absorbing layer 30; it is also possible to avoid that the thickness of the light absorbing layer 30 is too large to cause carrier recombination, which in turn causes a decrease in the detection efficiency of the photodetector. The thickness of the light absorption layer 30 may be, for example, 0.5. mu.m, 0.8. mu.m, 1.0. mu.m, 1.5. mu.m, 1.6. mu.m, 1.7. mu.m, 1.8. mu.m, 1.9. mu.m, 2. mu.m, 2.5. mu.m, 3. mu.m, or the like.

In one embodiment, the photodetector 100 may also include a buffer layer 70 formed between the light absorbing layer 30 and the tunnel junction layer 40. The buffer layer 70 protects the light absorbing layer 30 from damaging the surface of the light absorbing layer 30 when the tunnel junction layer 40 is formed, thereby preventing defects from being generated on the surface of the light absorbing layer 30. The buffer layer 70 may be a highly dense film layer, and has a better protective effect on the light absorbing layer 30.

In one embodiment, the buffer layer 70 has a thickness of 30nm to 100 nm. The thickness of the buffer layer 70 is within this range, which can prevent the buffer layer 70 from being too small to effectively protect the light absorption layer 30 from the buffer layer 70; it is also avoided that the thickness of the buffer layer 70 is too large to affect the carrier transport efficiency and thus the sensitivity of the photodetector 100. The thickness of the buffer layer 70 may be, for example, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or the like.

In one embodiment, the material of buffer layer 70 is cadmium sulfide. In other embodiments, the buffer layer 70 may be made of zinc sulfide.

In one embodiment, in the tunnel junction layer 40, the ratio of the amount of magnesium sulfide to zinc sulfide is in a range of 0.1 to 0.5:0.5 to 0.9. The mass ratio of magnesium sulfide to zinc sulfide is in this range, which can make the resistance value of the tunnel junction layer 40 larger, thereby effectively reducing the dark current of the photodetector. The mass ratio of magnesium sulfide to zinc sulfide in the tunnel junction layer 40 may be, for example, 0.2:0.8, 0.3:0.7, 0.4:0.6, 0.5:0.5, etc.

In one embodiment, the ratio of the amount of magnesium sulfide to zinc sulfide species in the tunnel junction layer 40 is 0.25: 0.75. When the ratio of the amounts of the magnesium sulfide and the zinc sulfide is 0.25:0.75, the resistance of the tunnel junction layer 40 can be maximized, and the impedance of the photodetector 100 can be more effectively improved, thereby being more beneficial to reducing the dark current of the photodetector.

In one embodiment, the tunnel junction layer 40 has a thickness of 100nm to 2000 nm. When the thickness of the tunnel junction layer 40 is within the range, it is possible to avoid that the resistance of the tunnel junction layer 40 is too small to effectively reduce the dark current of the photodetector 100 due to too small thickness of the tunnel junction layer 40, and to avoid that the tunnel junction cannot tunnel due to too large thickness of the tunnel junction layer 40. The thickness of the tunnel junction layer 40 may be, for example, 100nm, 300nm, 500nm, 1000nm, 1300nm, 1500nm, 1800nm, 2000nm, or the like.

In one embodiment, the material of the semiconductor layer 50 may be zinc oxide, that is, the semiconductor layer 50 is an intrinsic zinc oxide film layer.

In one embodiment, the thickness of the semiconductor layer 50 is 30nm to 100 nm. When the thickness of the semiconductor layer 50 is within the range, the phenomenon that the film layer distribution of the semiconductor layer 50 is uneven due to too small thickness of the semiconductor layer 50, so that part of the surface of the tunneling junction layer 40 is exposed to influence the formation of a PN junction can be avoided; it is also avoided that the thickness of the semiconductor layer 50 is too large to affect the carrier transmission efficiency and thus the sensitivity of the photodetector 100. The thickness of the semiconductor layer 50 may be, for example, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, or 100 nm.

In one embodiment, the material of the second electrode layer 60 is a mixture of metallic aluminum and zinc oxide. Thus, the second electrode layer 60 has good conductivity, and the second electrode layer 60 has high light transmittance.

In the preparation of the second electrode layer 60, a zinc oxide target and an aluminum target may be simultaneously sputtered. When the material of the semiconductor layer 50 is zinc oxide, a zinc oxide target can be used for sputtering during preparation, and the zinc oxide target can be continuously used during preparation of the second electrode layer 60 after the preparation of the semiconductor layer 50 is completed, so that the target does not need to be replaced, and the process complexity is favorably reduced. In other embodiments, other transparent conductive materials, such as indium tin oxide, indium zinc oxide, etc., can be used for the second electrode layer 60.

In one embodiment, the thickness of the second electrode layer 60 is 200nm to 700 nm. The thickness of the second electrode layer 60 is within the range, so that the problem that the normal operation of the photoelectric detector is influenced due to the fact that the resistance of the second electrode layer 60 is large and a large enough electric field cannot be generated due to the fact that the thickness of the second electrode layer 60 is too small can be avoided; it can also be avoided that the thickness of the second electrode layer 60 is too large, which results in the light transmittance of the second electrode layer 60 being reduced, and further affects the light absorption effect of the photodetector. The thickness of the second electrode layer 60 may be, for example, 200nm, 250nm, 300nm, 350nm, 400nm, 500nm, 600nm, 700nm, or the like.

The embodiment of the present application further provides a method for manufacturing a photodetector, and referring to fig. 2, the method for manufacturing includes the following steps 210 to 260. As will be described in detail below.

In step 210, a substrate is provided.

In one embodiment, the surface of the substrate 10 may be cleaned to remove stains from the surface of the substrate 10, thereby improving adhesion between the subsequently formed first electrode layer 20 and the substrate 10. In one exemplary embodiment, the surface of the substrate 10 may be sequentially cleaned with an aqueous solution of a detergent, an aqueous solution of NaOH, and a deionized water solution, and then evaporated to dryness under a high temperature vacuum after the cleaning is completed.

In step 220, a first electrode layer is formed on the substrate.

In one embodiment, the material of the first electrode layer 20 may be metallic molybdenum. In other embodiments, other materials with good conductivity can be used for the first electrode layer 20.

In one embodiment, the thickness of the first electrode layer 20 is 0.5 μm to 2 μm. When the thickness of the first electrode layer 20 is within the range, the phenomenon that the normal operation of the photodetector is affected due to the fact that the resistance of the first electrode layer 20 is too large because the thickness of the first electrode layer 20 is too small can be avoided; too large a thickness of the first electrode layer 20 to cause excessive stress of the first electrode layer 20 on the substrate 10, which may result in bending of the substrate 10, can also be avoided.

In one embodiment, the first electrode layer 20 may be formed by evaporating a metal target onto the substrate 10 using a dc magnetron sputtering method. When the material of the first electrode layer 20 is molybdenum, the metal target material used is a molybdenum target material.

In step 230, a light absorbing layer having a first conductivity type is formed on the first electrode layer.

In one embodiment, the first conductivity type is p-type, and the material of the light absorbing layer 30 is copper indium gallium selenide. The copper indium gallium selenide material is applied to the photoelectric detector 100 as the light absorption layer 30, so that the photoelectric detector can achieve a better photoelectric conversion effect, and the sensitivity of the photoelectric detector 100 can be improved.

In one embodiment, magnetron sputtering followed by selenization or co-evaporation three-step methods may be used to prepare light absorbing layer 30.

In one embodiment, when the material of the light absorption layer 30 is copper indium gallium selenide, the thickness of the light absorption layer 30 is 0.5 μm to 3 μm. When the thickness of the light absorbing layer 30 is within this range, it is possible to prevent the light absorbing effect from being poor due to the too small thickness of the light absorbing layer 30; it is also possible to avoid that the thickness of the light absorbing layer 30 is too large to cause carrier recombination, which in turn causes a decrease in the detection efficiency of the photodetector.

In step 240, a tunnel junction layer is formed on the light absorption layer, wherein the tunnel junction layer is made of a mixture of magnesium sulfide and zinc sulfide.

In one embodiment, in preparing the tunnel junction layer 40, a target containing magnesium, zinc and sulfur may be used to perform magnetron sputtering simultaneously, so as to obtain a mixture material of magnesium sulfide and zinc sulfide.

In one embodiment, in the tunnel junction layer 40, the ratio of the amount of magnesium sulfide to zinc sulfide is in a range of 0.1 to 0.5:0.5 to 0.9. The mass ratio of magnesium sulfide to zinc sulfide is in this range, which can make the resistance value of the tunnel junction layer 40 larger, thereby effectively reducing the dark current of the photodetector.

In one embodiment, the ratio of the amount of magnesium sulfide to zinc sulfide species in the tunnel junction layer 40 is 0.25: 0.75.

In one embodiment, the tunnel junction layer 40 has a thickness of 100nm to 2000 nm. When the thickness of the tunnel junction layer 40 is within the range, it is possible to avoid that the resistance of the tunnel junction layer 40 is too small to effectively reduce the dark current of the photodetector 100 due to too small thickness of the tunnel junction layer 40, and to avoid that the tunnel junction cannot tunnel due to too large thickness of the tunnel junction layer 40.

In step 250, a semiconductor layer having a second conductivity type is formed on the tunnel junction layer.

In one embodiment, the second conductivity type is n-type, i.e., the semiconductor layer 50 is an n-type semiconductor layer. The light absorbing layer 30 forms a PN junction with the semiconductor layer 50.

In one embodiment, the semiconductor layer 50 may be formed using a magnetron sputtering method.

In one embodiment, the thickness of the semiconductor layer 50 is 30nm to 100 nm. When the thickness of the semiconductor layer 50 is within the range, the phenomenon that the film layer distribution of the semiconductor layer 50 is uneven due to too small thickness of the semiconductor layer 50, so that part of the surface of the tunneling junction layer 40 is exposed to influence the formation of a PN junction can be avoided; it is also avoided that the thickness of the semiconductor layer 50 is too large to affect the carrier transmission efficiency and thus the sensitivity of the photodetector 100.

In step 260, a transparent second electrode layer is formed on the semiconductor layer.

In one embodiment, magnetron sputtering may be used to form the transparent second electrode layer 60.

In one embodiment, the material of the second electrode layer 60 is a mixture of metallic aluminum and zinc oxide. In the preparation of the second electrode layer 60, a zinc oxide target and an aluminum target may be simultaneously sputtered.

In one embodiment, the thickness of the second electrode layer 60 is 200nm to 700 nm. The thickness of the second electrode layer 60 is within the range, so that the problem that the normal operation of the photoelectric detector is influenced due to the fact that the resistance of the second electrode layer 60 is large and a large enough electric field cannot be generated due to the fact that the thickness of the second electrode layer 60 is too small can be avoided; it can also be avoided that the thickness of the second electrode layer 60 is too large, which results in the light transmittance of the second electrode layer 60 being reduced, and further affects the light absorption effect of the photodetector.

In one embodiment, between step 230 and step 240, the preparation method further comprises: a buffer layer 70 is formed on the light absorbing layer.

The buffer layer 70 protects the light absorbing layer 30 from damaging the surface of the light absorbing layer 30 when the tunnel junction layer 40 is formed, thereby preventing defects from being generated on the surface of the light absorbing layer 30. The buffer layer 70 may be a highly dense film layer, and has a better protective effect on the light absorbing layer 30.

In one embodiment, the buffer layer 70 may be prepared using a chemical water bath method. Compared with the magnetron sputtering method for forming the buffer layer 70, the chemical water bath method is adopted for preparing the buffer layer, so that the environment is protected, and the environmental pollution can be avoided.

In one embodiment, the buffer layer 70 has a thickness of 30nm to 100 nm. The thickness of the buffer layer 70 is within this range, which can prevent the buffer layer 70 from being too small to effectively protect the light absorption layer 30 from the buffer layer 70; it is also avoided that the thickness of the buffer layer 70 is too large to affect the carrier transport efficiency and thus the sensitivity of the photodetector 100.

According to the preparation method of the photoelectric detector provided by the embodiment of the application, the material of the tunneling junction layer 40 in the prepared photoelectric detector is a mixture of magnesium sulfide and zinc sulfide, so that the resistance value of the tunneling junction layer 40 is higher, the impedance of the film structure of the photoelectric detector 100 is improved, and the dark current of the photoelectric detector 100 is effectively reduced; in addition, the tunnel junction 40 is made of a mixture of magnesium sulfide and zinc sulfide, so that the tunnel junction 40 has an excellent photomultiplier effect under a reverse bias, the sensitivity of the photodetector can be improved, and the performance of the photodetector can be improved.

For the method embodiment, since it basically corresponds to the embodiment of the product, the description of the relevant details and beneficial effects may refer to the partial description of the product embodiment, and will not be repeated.

It is noted that in the drawings, the sizes of layers and regions may be exaggerated for clarity of illustration. Also, it will be understood that when an element or layer is referred to as being "on" another element or layer, it can be directly on the other element or layer or intervening layers may also be present. In addition, it will be understood that when an element or layer is referred to as being "under" another element or layer, it can be directly under the other element or intervening layers or elements may also be present. In addition, it will also be understood that when a layer or element is referred to as being "between" two layers or elements, it can be the only layer between the two layers or elements, or more than one intermediate layer or element may also be present. Like reference numerals refer to like elements throughout.

Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.

It will be understood that the present application is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims

1. A photodetector, characterized in that the photodetector comprises:

the material of the substrate is glass;

a first electrode layer formed on the substrate, wherein the material of the first electrode layer is molybdenum metal, and the thickness of the first electrode layer is 0.5-2 μm;

the light absorption layer is formed on the first electrode layer and has a first conduction type, the first conduction type is p type, the material of the light absorption layer is copper indium gallium selenide, and the thickness of the light absorption layer is 0.5-3 mu m;

the tunneling junction layer is formed on the light absorption layer and is made of a mixture of magnesium sulfide and zinc sulfide; in the tunnel junction layer, the mass ratio of magnesium sulfide to zinc sulfide is in the range of 0.1-0.5: 0.5 to 0.9; the thickness of the tunneling junction layer is 100 nm-2000 nm;

a semiconductor layer with a second conductivity type formed on the tunneling junction layer, wherein the second conductivity type is n-type, the semiconductor layer is made of zinc oxide, and the thickness of the semiconductor layer is 30 nm-100 nm;

and the transparent second electrode layer is formed on the semiconductor layer, the material of the second electrode layer is a mixture of metal aluminum and zinc oxide, and the thickness of the second electrode layer is 200 nm-700 nm.

2. The photodetector of claim 1, wherein a ratio of the amount of magnesium sulfide to zinc sulfide species in the tunnel junction layer is in a range of 0.25: 0.75.

3. the photodetector of claim 1, further comprising a buffer layer formed between the light absorbing layer and the tunnel junction layer;

the thickness of the buffer layer is 30 nm-100 nm.