TWI856875B - Light sensor and manufacturing method threrof - Google Patents

Abstract

A light sensor includes a lower electrode layer, an absorption layer and an upper electrode layer. The absorption layer is located on the lower electrode layer, in which the absorption layer includes a material that has an electron mobility greater than 300 cm ²/Vs and greater than two times of a hole mobility. The upper electrode layer is located on the absorption layer, and is configured to absorb the scattered high-speed excess electrons and to leave low-speed excess holes near the edges of the upper electrode layer. A downward photocurrent is generated by the photovoltage in the absorption layer due to the formation of positively charged region near the upper surface.

Description

Optical detector and manufacturing method thereof

The present disclosure relates to a photodetector and a method for manufacturing the photodetector.

In the field of far infrared detection, infrared detectors can be divided into two types, one is a detector that can operate at room temperature, and the other is a cooled detector. Generally speaking, detectors operating at room temperature have lower signal detection rates and image resolutions and cannot provide more accurate measurements. Only cooled detectors can provide higher detection rates and resolutions.

However, the above-mentioned uncooled detectors usually need to be cooled to the temperature of liquid nitrogen to operate normally because of the excessive dark current. This makes the maintenance cost of this type of detector very high, and because the cooling system is generally much larger than the detector itself, it also makes this type of detector difficult to set up.

One technical aspect of the present disclosure is a light detector.

According to an embodiment of the present disclosure, a photodetector includes a lower electrode layer, an absorption layer and an upper electrode layer. The absorption layer is located on the lower electrode layer, wherein the absorption layer includes a material whose electron mobility is required to be greater than 300 cm ² /Vs and greater than twice its hole mobility, and the absorption layer is configured to generate a photocurrent by utilizing the large difference between the electron mobility and the hole mobility. The upper electrode layer is located on the absorption layer and configured to absorb electrons in the photocurrent.

In one embodiment of the present disclosure, the absorption layer includes a semiconductor-semiconductor junction, a semiconductor-semimetal junction, a semimetal-semimetal junction, or a combination thereof with a built-in electric field pointing downward.

In one embodiment of the present disclosure, the top view shape of the upper electrode layer is at least one of a comb shape, a tree shape, a mesh shape, or a spiral shape.

In one embodiment of the present disclosure, the upper electrode layer is located in the trench of the absorption layer.

In one embodiment of the present disclosure, the upper electrode layer forms an Ohmic contact or a Schottky contact with the absorption layer.

In one embodiment of the present disclosure, the photodetector further comprises a substrate, which is located between the absorption layer and the lower electrode layer.

In one embodiment of the present disclosure, the photodetector further includes a buffer layer. The buffer layer is located between the substrate and the absorption layer.

In one embodiment of the present disclosure, the top electrode layer is rectangular in top view.

In one embodiment of the present disclosure, the material of the upper electrode layer is a transparent conductive film including indium tin oxide (ITO) or aluminum zinc oxide (AZO).

In one embodiment of the present disclosure, the photodetector further comprises a covering layer, which is located on the absorption layer and surrounds the upper electrode layer.

Another technical aspect of the present disclosure is a method for manufacturing a light detector.

According to an embodiment of the present disclosure, a method for manufacturing a photodetector includes providing an absorption layer, wherein the absorption layer includes a material whose electron mobility is required to be greater than 300 ^cm2 /Vs and greater than twice its hole mobility, and the absorption layer is configured to utilize the large difference between the electron mobility and the hole mobility to generate a photovoltage and thus form a photocurrent; depositing an upper electrode layer on the absorption layer, wherein the upper electrode layer is configured to absorb scattered high-speed photoelectrons and destroy the electrical neutrality around the upper electrode layer, causing the positive charge of the holes to accumulate to generate a photovoltage; and forming a lower electrode layer so that the absorption layer is located between the upper electrode layer and the lower electrode layer.

In one embodiment of the present disclosure, providing an absorption layer includes forming the absorption layer on a substrate.

In one embodiment of the present disclosure, forming a lower electrode layer so that the absorption layer is located between the upper electrode layer and the lower electrode layer includes forming the lower electrode layer on a surface of the substrate opposite to the absorption layer.

In one embodiment of the present disclosure, forming an absorption layer on a substrate includes forming the absorption layer using diffusion or ion distribution.

In one embodiment of the present disclosure, forming an absorption layer on a substrate includes using at least one of molecular beam epitaxy, chemical vapor deposition, physical vapor deposition, atomic layer deposition or liquid phase epitaxy.

In one embodiment of the present disclosure, a lower electrode layer is formed on a surface of the substrate opposite to the absorption layer so that the lower electrode layer forms an ohmic contact or a Schottky contact with the substrate.

In one embodiment of the present disclosure, the method for manufacturing a photodetector further includes forming a groove on the absorption layer, wherein the top view shape of the groove is at least one of a comb shape, a tree shape, a mesh shape or a spiral shape; and plating an upper electrode layer in the groove so that the upper electrode layer forms an Ohmic contact or a Schottky contact with the absorption layer.

In one embodiment of the present disclosure, the method for manufacturing a photodetector further includes forming a buffer layer on a substrate; and forming an absorption layer on the buffer layer.

In one embodiment of the present disclosure, the method for manufacturing the photodetector further includes forming a capping layer on the absorption layer; patterning the capping layer to form an opening exposing the absorption layer; and depositing an upper electrode layer in the opening.

In one embodiment of the present disclosure, an upper electrode layer is deposited on the absorption layer so that the upper electrode layer and the absorption layer form an ohmic contact or a Schottky contact.

In the above-mentioned embodiments of the present disclosure, since the absorption layer of the photodetector includes a material whose electron mobility is greater than twice the hole mobility, the large difference in electron-hole mobility can be used to generate photocurrent. Therefore, it can operate independently at room temperature without the assistance of a cooling system, and can also operate under zero bias, thereby providing far-infrared detection with high detectivity.

The embodiments disclosed below provide many different embodiments, or examples, for implementing the different features of the subject matter provided. Specific examples of components and arrangements are described below to simplify the present invention. Of course, these examples are only examples and are not intended to be limiting. In addition, the present invention may repeat component symbols and/or letters in each example. This repetition is for the purpose of simplicity and clarity, and does not itself specify the relationship between the various embodiments and/or configurations discussed.

Spatially relative terms such as "below," "beneath," "lower," "above," "upper," and the like may be used herein for descriptive purposes to describe the relationship of one element or feature to another element or feature as illustrated in the accompanying figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the accompanying figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

FIG. 1 shows a cross-sectional view of a photodetector 100 according to an embodiment of the present disclosure. Referring to FIG. 1 , the photodetector 100 includes a lower electrode layer 110, an absorption layer 120, and an upper electrode layer 130. The absorption layer 120 is located on the lower electrode layer 110, wherein the absorption layer 120 includes a material having an electron mobility greater than 300 cm ² /Vs and greater than twice the hole mobility, and the absorption layer 120 is configured to generate a photocurrent by utilizing the large difference between the electron mobility and the hole mobility. The upper electrode layer 130 is located on the absorption layer 120 and configured to absorb electrons e in the photocurrent. When a semiconductor or semi-metal material (such as the absorption layer 120) is excited by light L, electron-hole pairs are formed. At this time, since the electron mobility of certain specific materials (described in detail below) is high enough and is very different from the hole mobility, the electrons will scatter and diffuse much faster than the holes. When electron holes are generated around the upper electrode layer 130 (for example, the boundary 131 of the upper electrode layer 130 and the interface 132 between the upper electrode layer 130 and the absorption layer 120) after being exposed to light, fast electrons (e in the upper part of Figure 1) will enter the upper electrode layer 130 and leave slow holes (h in Figure 1). These holes that have lost electrons will form positive charges around the upper electrode layer 130. Compared with the lower electrode layer 110 that is not exposed to light, a vertical downward electric field E can be generated inside the device, thereby promoting the flow of carriers inside the absorption layer 120 and generating photocurrent. Representative materials with high electron mobility and a large gap between electron mobility and hole mobility include indium arsenide (InAs), indium antimonide (InSb), indium phosphide (InP), gallium arsenide (GaAs), gallium antimonide (GaSb), gallium indium arsenide (In _0.53 Ga _0.47 As), mercury cadmium telluride (Hg _1-x Cd _x Te), cadmium arsenide (Cd ₃ As ₂ ), combinations of the above materials, alloys of the above materials or other suitable materials. Table 1 shows the electron mobility and hole mobility of the above materials at room temperature: Material Electron mobility ( ) Hole mobility ( ) Indium arsenide 30000 200 Indium Antimonide 80000 800 Indium phosphide 4000 100 Gallium arsenide 8500 400 Gallium Antimonide 5000 1000 Gallium Indium Arsenide 13800 500 Mercury Cadmium Telluride 10000 100 Cadmium arsenide 15000 500 Table 1

As can be seen from Table 1, the above materials have a large difference between electron mobility and hole mobility at room temperature, and their electron mobility is at least twice that of their hole mobility, and even a hundred times difference for indium antimonide. Therefore, they can be used as the absorption layer 120 of the photodetector 100. The lower electrode layer 110 is configured to provide electrons to form a complete current loop in the photodetector 100. In some embodiments, an ohmic contact is formed between the upper electrode layer 130 and the absorption layer 120. In some embodiments, an ohmic contact is formed between the absorption layer 120 and the lower electrode layer 110, and the lower electrode layer 110 is covered by the absorption layer 120. The formation of ohmic contacts between the upper electrode layer 130 and the absorption layer 120 and between the lower electrode layer 110 and the absorption layer 120 can improve the electron collection efficiency of the entire photodetector 100. By properly doping the absorption layer 120 with holes (P-type), the device resistance can be reduced and the photocurrent can be increased, thereby achieving a higher detection rate and sensitivity. Appropriate P-type doping can also prevent the loss of forward photocurrent (towards the lower electrode layer 110 ) caused by the reverse thermocurrent (towards the upper electrode layer 130 ) generated by illumination and the reverse photocurrent (towards the upper electrode layer 130 ) generated by Schottky contact when the absorption layer 120 is in an N-type semiconductor state.

In addition to the above-mentioned Ohmic contact manufacturing method, a Schottky contact can also be formed between the upper electrode layer 130 and the absorption layer 120. Since the absorption layer 120 generally uses a P-type semiconductor, when the P-type semiconductor forms a Schottky junction with the metal of the upper electrode layer 130, the direction of its built-in electric field will point to the semiconductor absorption layer 120. When the built-in electric field E generates electron holes under light, it will accelerate the photoelectrons into the metal end and block the photoholes from entering the upper electrode layer 130. When perfect Ohmic contact is difficult to manufacture, this design can reduce the effect of contact resistance on photoelectron blocking, increase the probability of photoelectrons entering the electrode, and further improve the efficiency of photovoltage and photocurrent generation. However, this design is not applicable to the junction between the lower electrode layer 110 and the absorption layer 120. The junction of the lower electrode layer 110 is still mainly ohmic contact. Unless the total resistance of the device is too small, the total resistance of the device can be increased and thermal noise can be reduced by increasing the contact resistance through Schottky contact, adding a blocking layer, etc.

Since the absorption layer 120 of the photodetector 100 includes a material whose electron mobility is greater than twice the hole mobility, the large difference in electron-hole mobility can be used to generate photocurrent. Therefore, it can operate independently at room temperature without the assistance of a cooling system or an external bias voltage, and can provide high detection rate and high resolution far-infrared detection.

FIG. 2 shows a three-dimensional diagram of a photodetector 100a according to another embodiment of the present disclosure, wherein the absorption layer 120a may be a single material, or may be a region near the surface inside containing a semiconductor-semiconductor, semiconductor-semimetal or semimetal-semimetal junction region 122 with a built-in electric field pointing downward, and the junction region 122 may be, for example, an NP junction, an NIP junction, an IP junction, a P ^- P junction or a PP ⁺ junction, but is not limited thereto. The purpose of the junction region 122 is to generate electron-hole pair separation after absorbing photons (this layer can also be called an electron-hole separation layer). Then, the fast electrons will enter the upper electrode layer 130 on the upper surface, leaving behind slow holes. The spatial position of these holes that have lost electrons is still closer to the upper surface of the absorption layer 120a. Therefore, in addition to the holes near the boundary 131 and the interface 132 of the upper electrode layer 130 as described in the implementation method of Figure 1 (such as h in Figure 1 or h at the top of Figure 2), these holes additionally generated by the junction region 122 (h at the bottom of Figure 2) can further increase the amount of positive charge, thereby enhancing the downward electric field E and photocurrent in the vertical direction of the absorption layer 120 after illumination.

FIG. 3 shows a three-dimensional diagram of a photodetector 100b according to another embodiment of the present disclosure. Referring to FIG. 3, the photodetector 100b further includes a substrate 140. The substrate 140 is located between the absorption layer 120 and the lower electrode layer 110. In this embodiment, the top view shape of the upper electrode layer 130 is a comb shape. The reason for making such a shape is that the efficiency of absorbing electrons is the best at the edge of the upper electrode layer 130 (see FIG. 1), and therefore the strongest electric field E can be retained (see FIG. 1). Therefore, by designing the top view shape of the upper electrode layer 130 to be comb-shaped, the overall edge length of the comb-shaped portion of the upper electrode layer 130 can be lengthened within a limited area, thereby improving the efficiency of the photocurrent generated by the large difference between the electron mobility and the hole mobility. In some embodiments, the top view shape of the upper electrode layer 130 can also be a tree shape, a mesh shape, a spiral shape, etc., but the present disclosure is not limited thereto. In some embodiments, the photodetector 100b further includes a buffer layer 150, and the buffer layer 150 is located between the substrate 140 and the absorption layer 120. If the lattice mismatch between the material of the absorption layer 120 and the material of the substrate 140 is not matched, a buffer layer 150 can be used to alleviate this phenomenon. The material of the buffer layer 150 can include cadmium zinc telluride (CdZnTe), but the present disclosure is not limited thereto.

FIG. 4 shows a three-dimensional diagram of a photodetector 100c according to another embodiment of the present disclosure. Referring to FIG. 4, the photodetector 100c includes a lower electrode layer 110, an absorption layer 120, an upper electrode layer 130a, a substrate 140, and a buffer layer 150. This embodiment is different from the embodiment of FIG. 2 in that, in this embodiment, the top view shape of the upper electrode layer 130a is a rectangle, and the material of the upper electrode layer 130a is a thin film including a transparent conductive material such as indium tin oxide (ITO) or aluminum zinc oxide (AZO). In this embodiment, the entire upper electrode layer 130a of the transparent conductive material can be used as a region for collecting photoelectrons. Because the upper electrode layer 130a contains a transparent conductive material, the absorption layer 120 below can be illuminated by light. After being excited by the light, the photoelectrons are absorbed by the electrode composed of the transparent conductive material, thereby generating a photocurrent.

FIG. 5 shows a perspective view of a photodetector 100d according to another embodiment of the present disclosure. Referring to FIG. 5, the photodetector 100d includes a lower electrode layer 110, an absorption layer 120, an upper electrode layer 130, a substrate 140, and a buffer layer 150. This embodiment is different from the embodiment of FIG. 3 in that, in this embodiment, the photodetector 100d further includes a covering layer 160, which is located on the absorption layer 120 and surrounds the upper electrode layer 130. The covering layer 160 is configured to prevent the surface of the absorption layer 120 material from directly contacting the air, and at the same time reduce the defect density on the surface of the absorption layer 120. The material of the cover layer 160 may include cadmium zinc telluride (CdZnTe) or other insulating materials, but the present disclosure is not limited thereto.

FIG. 6 shows a cross-sectional view of a photodetector 100e according to an embodiment of the present disclosure. Referring to FIG. 6, the photodetector 100e includes a lower electrode layer 110, an absorption layer 120b, and an upper electrode layer 130. The absorption layer 120b is located on the lower electrode layer 110, and the upper electrode layer 130 is located on the absorption layer 120b, and is configured to absorb electrons e in the photocurrent. The difference between this embodiment and the embodiment of FIG. 1 is that in this embodiment, the absorption layer 120b has a trench 124, and a portion of the upper electrode layer 130 is located in the trench 124. Since the photoelectrons enter the upper electrode layer 130 through the spontaneous thermal scattering mechanism, and the number of photoelectrons entering the electrode is determined by their average collision distance (mean collision length), the greater the electron mobility, the longer the average collision distance, which means that more scattered photoelectrons can enter the electrode. However, generally speaking, the average collision distance of electrons is much less than 1 micron, which results in a shallower depth of the positive charge generation zone (active zone) in the present disclosure. However, the light penetration depth in the absorption layer 120 (such as the implementation method of Figure 1) is usually greater than 1 micron, which will result in a low internal quantum efficiency of the photodetector. Therefore, the electrode pattern trench 124 can be dug out in the absorption layer 120b by etching, etc., and then the metal electrode is filled into the trench 124. In this way, the range of electrons that can be collected will no longer be limited to the area around the electrode near the surface (such as the boundary 131 of the upper electrode layer 130), but can increase with the increase of the electrode depth (such as the depth of the photogenerated positive charge region 126).

It should be understood that the connection relationship, materials and functions of the components that have been described will not be repeated, and it is better to explain them first. In the following description, the manufacturing method of the light detector will be explained.

FIG. 7 is a flow chart of a method for manufacturing a photodetector according to an embodiment of the present disclosure. Referring to FIG. 7 , a method for manufacturing a photodetector comprises the following steps: First, in step S1, an absorption layer is provided, wherein the absorption layer comprises an electron mobility greater than 300 cm ² /Vs is greater than twice the hole mobility at the same time, the absorption layer is configured to generate photovoltage and thus form photocurrent by utilizing the great difference between the electron mobility and the hole mobility; then in step S2, an upper electrode layer is deposited on the absorption layer, wherein the upper electrode layer is configured to absorb scattered high-speed photoelectrons and destroy the electrical neutrality around the upper electrode layer, causing the positive charge of the holes to accumulate to generate photovoltage; finally in step S3, a lower electrode layer is formed so that the absorption layer is located between the upper electrode layer and the lower electrode layer.

In some embodiments, the manufacturing method of the photodetector is not limited to the above steps S1 to S3. For example, each of steps S1 to S3 may include other more detailed steps. In some embodiments, steps S1 to S3 may further include other steps between the two preceding and following steps, or may further include other steps before step S1 and further include other steps after step S3. Alternatively, some steps between steps S1 to S3 may be repeated. In the following description, at least the above steps will be described in detail.

Referring to FIG. 3 , in the embodiment of FIG. 3 , before forming the absorption layer 120 on the substrate 140, a buffer layer 150 is first formed on the substrate 140. Then, the absorption layer 120 is formed. The absorption layer 120 is formed by using molecular beam epitaxy (MBE), chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), liquid phase epitaxy (LPE), a combination of the above methods, or other suitable methods. Alternatively, in other embodiments, the buffer layer 150 may not be formed, but the substrate 140 may be implanted or diffused to form the absorption layer 120 inside the substrate 140, but the present disclosure is not limited thereto. The absorption layer 120 may be formed by implanting or diffusing ions to form an absorption layer 120a including a junction region 122 as in the embodiment of FIG. 2, or the entire absorption layer 120 may be doped by implanting or diffusing ions.

In some embodiments (such as the embodiment of FIG. 5 ), a capping layer 160 is then formed on the absorption layer 120; then, the capping layer 160 is patterned to form an opening exposing the absorption layer 120; and an upper electrode layer 130 is deposited on the absorption layer 120 in the opening. When the opening of the capping layer 160 is in a comb shape in top view, depositing the upper electrode layer 130 on the absorption layer 120 in the opening allows the upper electrode layer 130 to be in a comb shape in top view, and the upper electrode layer 130 forms an ohmic contact or a Schottky contact with the absorption layer 120. In other embodiments, the cover layer 160 may not be formed and the upper electrode layer 130 (such as the embodiment of FIG. 2) or 130a (such as the embodiment of FIG. 4) may be directly formed.

Next, the lower electrode layer 110 is formed so that the absorption layer 120 is located between the upper electrode layer 130 and the lower electrode layer 110. In some embodiments (such as the embodiment of FIG. 1), the lower electrode layer 110 is located on the surface of the absorption layer 120 facing away from the upper electrode layer 130. In some embodiments (such as the embodiment of FIG. 3), the lower electrode layer 110 is located on the surface of the substrate 140 facing away from the absorption layer 120. This step allows the lower electrode layer 110 to form an ohmic contact with the absorption layer 120 or the substrate 140. Unlike the upper electrode layer 130, the lower electrode layer 110 is uniformly distributed throughout the entire layer.

The foregoing outlines the features of several implementations so that those skilled in the art can better understand the state of the present disclosure. Those skilled in the art should understand that they can easily use the present disclosure as a basis for designing or modifying other processes and structures to achieve the same purpose and/or achieve the same advantages as the implementations described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they can make various changes, substitutions and modifications here without departing from the spirit and scope of the present disclosure.

100,100a,100b,100c,100d,100e: Photodetector

110: Lower electrode layer

120,120a: Absorption layer

122: Meeting area

124: Groove

126: Photogenerated positive charge region

130,130a: Upper electrode layer

131:Border

132: Interface

140: Substrate

150: Buffer layer

160: Covering layer

E: Electric field

S1, S2, S3: Steps

The disclosure is best understood from the following embodiments when read in conjunction with the accompanying illustrations. Note that various features are not drawn to scale, in accordance with standard practice in the industry. In fact, the dimensions of various features may be arbitrarily increased or decreased for clarity of discussion. FIG. 1 illustrates a cross-sectional view of a photodetector according to one embodiment of the disclosure. FIG. 2 illustrates a cross-sectional view of a photodetector according to another embodiment of the disclosure. FIG. 3 illustrates a stereoscopic view of a photodetector according to yet another embodiment of the disclosure. FIG. 4 illustrates a stereoscopic view of a photodetector according to yet another embodiment of the disclosure. FIG. 5 illustrates a stereoscopic view of a photodetector according to yet another embodiment of the disclosure. FIG. 6 illustrates a cross-sectional view of a photodetector according to one embodiment of the disclosure. FIG. 7 is a flow chart showing a method for manufacturing a photodetector according to one embodiment of the present disclosure.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

100b: Photodetector

110: Lower electrode layer

120: Absorption layer

130: Upper electrode layer

140: Substrate

150: Buffer layer

Claims (10)

A photodetector comprises: a lower electrode layer; an absorption layer located on the lower electrode layer, wherein the absorption layer comprises a material having an electron mobility greater than 300 cm ² /Vs and greater than twice of a hole mobility, and the absorption layer is configured to generate a photocurrent by utilizing the difference between the electron mobility and the hole mobility; and an upper electrode layer located on the absorption layer and configured to absorb electrons in the photocurrent. The photodetector as described in claim 1, wherein the absorption layer comprises a semiconductor-semiconductor junction, a semiconductor-semimetal junction, a semimetal-semimetal junction or a combination thereof with a built-in electric field facing downward. The photodetector as described in claim 1, wherein the top view shape of the upper electrode layer is at least one of a comb shape, a tree shape, a mesh shape or a spiral shape, and the upper electrode layer forms an Ohmic contact or a Schottky contact with the absorption layer. A photodetector as described in claim 3, wherein a portion of the upper electrode layer is located in a trench of the absorption layer. The photodetector as described in claim 1 further comprises: a substrate located between the absorption layer and the lower electrode layer; and a buffer layer located between the substrate and the absorption layer. The photodetector as described in claim 1, wherein the top view shape of the upper electrode layer is rectangular, and the upper electrode layer is a transparent conductive film comprising indium tin oxide (ITO) or aluminum zinc oxide (AZO). The photodetector as described in claim 1 further comprises: a covering layer located on the absorption layer and surrounding the upper electrode layer. A method for manufacturing a photodetector includes: providing an absorption layer, wherein the absorption layer includes a material having an electron mobility greater than 300 ^cm2 /Vs and greater than twice of a hole mobility, and the absorption layer is configured to generate a photovoltage and thus a photocurrent by utilizing the difference between the electron mobility and the hole mobility; depositing an upper electrode layer on the absorption layer, wherein the upper electrode layer is configured to absorb scattered photoelectrons and destroy the electrical neutrality around the upper electrode layer, causing positive charges of holes to accumulate to generate photovoltage; and forming a lower electrode layer so that the absorption layer is located between the upper electrode layer and the lower electrode layer. The method for manufacturing a photodetector as described in claim 8, wherein providing the absorption layer comprises: forming the absorption layer on a substrate. A method for manufacturing a photodetector as described in claim 9, wherein forming the lower electrode layer includes: forming the lower electrode layer on a surface of the substrate opposite to the absorption layer.

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