Photodetector and method of manufacturing the same

Abstract

To provide a photodetector.SOLUTION: There is provided a photodetector that includes: a lower electrode layer; an absorption layer which is located on the lower electrode layer, and includes a material having an electron mobility larger than 300 cm2 / Vs, the electron mobility being more than twice as large as the hole mobility; and an upper electrode layer which is located on the absorption layer and also configured to absorb high-speed photoelectrons dispersed around an upper electrode and leave low-speed light holes, so that the upper electrode layer generates electric charges on a top surface, generates a photovoltage in the absorption layer, and further generates a downward photocurrent.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to photodetectors and methods for manufacturing photodetectors. [Background technology]

[0002] In the field of far-infrared detection, infrared detectors can be divided into two types: detectors that can operate at room temperature and cooled detectors. Generally, detectors that operate at room temperature have low signal detection rate and image resolution and cannot provide accurate measurements, while only cooled detectors can provide high detection rate and resolution.

[0003] However, the dark current of such uncooled detectors is generally so large that they must be cooled to the temperature of liquid nitrogen to function properly, which increases the manufacturing and maintenance costs of such detectors and makes their deployment difficult because the volume of the cooling system is generally much larger than the volume of the detector itself. Summary of the Invention [Problem to be solved by the invention]

[0004] One technical aspect of the present disclosure is a photodetector. [Means for solving the problem]

[0005] According to one embodiment of the present disclosure, a lower electrode layer and a semiconductor device are provided on the lower electrode layer, the semiconductor device having an electron mobility of 300 cm 2 / Vs and more than twice the hole mobility, and is configured to utilize the large difference between electron and hole mobility to generate a photocurrent; and an upper electrode layer located on the absorption layer and configured to absorb electrons in the photocurrent.

[0006] In one embodiment of the present disclosure, the absorbing layer comprises a semiconductor-semiconductor junction, a semiconductor-semimetal junction, a semimetal-semimetal junction, or a combination thereof, with a built-in electric field pointing downward.

[0007] In one embodiment of the present disclosure, the upper electrode layer has at least one of a comb-like, a dendritic, a net-like, and a spiral shape in plan view.

[0008] In one embodiment of the present disclosure, the top electrode layer is located within the trenches of the absorber layer.

[0009] In one embodiment of the present disclosure, the top electrode layer and the absorber layer form an ohmic or Schottky contact.

[0010] In one embodiment of the present disclosure, the photodetector further includes a substrate, the substrate being located between the absorption layer and the bottom electrode layer.

[0011] In one embodiment of the present disclosure, the photodetector further includes a buffer layer located between the substrate and the absorbing layer.

[0012] In one embodiment of the present disclosure, the upper electrode layer has a rectangular shape in plan view.

[0013] In one embodiment of the present disclosure, the material of the upper electrode layer is a transparent conductive thin film including indium tin oxide (ITO) or aluminum zinc oxide (AZO).

[0014] In one embodiment of the present disclosure, the photodetector further includes a cover layer overlying the absorption layer and surrounding the top electrode layer.

[0015] Another technical aspect of the present disclosure is a method for manufacturing a photodetector.

[0016] According to one embodiment of the present disclosure, an electron mobility of 300 cm 2 / Vs and more than twice the hole mobility, and configured to utilize the large difference between the electron and hole mobilities to generate a photovoltage and further form a photocurrent; plating a top electrode layer on the absorption layer, configured to absorb the scattered high-speed photoelectrons and break electrical neutrality around the top electrode layer, causing a positive charge of holes to accumulate and generate a photovoltage; and forming a bottom electrode layer, wherein the absorption layer is located between the top electrode layer and the bottom electrode layer.

[0017] In one embodiment of the present disclosure, providing an absorber layer includes forming an absorber layer over a substrate.

[0018] In one embodiment of the present disclosure, forming the lower electrode layer and placing the absorber layer between the upper and lower electrode layers includes forming the lower electrode layer on a surface of the substrate opposite the absorber layer.

[0019] In one embodiment of the present disclosure, forming an absorber layer over the substrate includes forming the absorber layer using diffusion or ion implantation.

[0020] In one embodiment of the present disclosure, forming the absorber layer over the substrate includes using at least one of molecular beam epitaxy, chemical vapor deposition, physical vapor deposition, atomic layer deposition, or liquid phase epitaxy.

[0021] In one embodiment of the present disclosure, a lower electrode layer is formed on the surface of the substrate opposite the absorption layer, and an ohmic or Schottky contact is formed between the lower electrode layer and the substrate.

[0022] In one embodiment of the present disclosure, the method for manufacturing a photodetector further includes forming at least one trench having a comb-like, dendritic, net-like, or spiral shape in a plan view on the absorption layer, and plating an upper electrode layer into the trench to form an ohmic contact or a Schottky contact between the upper electrode layer and the absorption layer.

[0023] In one embodiment of the present disclosure, the method for fabricating a photodetector further includes forming a buffer layer on the substrate and forming an absorption layer on the buffer layer.

[0024] In one embodiment of the present disclosure, the method for manufacturing a photodetector further includes forming a cover layer over the absorber layer, patterning the cover layer to form openings that expose the absorber layer, and plating a top electrode layer in the openings.

[0025] In one embodiment of the present disclosure, a top electrode layer is plated on top of the absorber layer to form an ohmic or Schottky contact between the top electrode layer and the absorber layer. [Effects of the Invention]

[0026] In the above embodiment of the present disclosure, the absorber layer of the photodetector contains a material with an electron mobility more than twice that of the hole mobility. This allows for photocurrent generation by utilizing the large difference between electron and hole mobility. Therefore, the device can operate independently at room temperature without the aid of a cooling system, even under zero bias, providing high detectivity for far-infrared detection. The present disclosure employs a completely new concept for generating photovoltage and photocurrent signals. The higher electron mobility than the hole mobility of the absorber layer material allows for spontaneous generation of positive charges and photovoltage after illumination of the edge of the upper electrode. Therefore, the photovoltage or photocurrent signal can be maximized by measures such as reducing the width of the electrode line (increasing the electrode edge). Because the present disclosure utilizes the difference in thermal velocity of photocarriers to drive photovoltage and photocurrent, it is particularly suitable for use in far-infrared detectors at room temperature, without the aid of a cooling system. For the same reason, the present disclosure does not require the application of an additional bias, and this characteristic significantly reduces the dark current of the photodetector. In summary, this disclosure solves two major problems that mid- and far-infrared detectors have long faced: the photoreaction signal is too small when operated at room temperature, and the background noise is too large. The present invention can significantly improve the signal-to-noise ratio and detection rate of mid- and far-infrared detectors under room temperature conditions. [Brief explanation of the drawings]

[0027] Aspects of the present disclosure may be best understood by the following embodiments when read in conjunction with the drawings. It should be noted that, in accordance with standard practice in the industry, various features have not been drawn to scale. In fact, the sizes of various features may be arbitrarily increased or decreased for clarity of discussion. [Figure 1] FIG. 1 is a cross-sectional view illustrating a photodetector according to an embodiment of the present disclosure. [Figure 2] FIG. 10 is a cross-sectional view illustrating a photodetector according to another embodiment of the present disclosure. [Figure 3] FIG. 10 is a perspective view illustrating a photodetector according to another embodiment of the present disclosure. [Figure 4] FIG. 10 is a perspective view illustrating a photodetector according to a further embodiment of the present disclosure. [Figure 5] FIG. 10 is a perspective view illustrating a photodetector according to a further embodiment of the present disclosure. [Figure 6] FIG. 1 is a cross-sectional view illustrating a photodetector according to an embodiment of the present disclosure. [Figure 7] 1 is a flowchart illustrating a method for manufacturing a photodetector according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0028] The contents of the embodiments disclosed below provide many different embodiments or examples for implementing different features of the provided targets. Specific examples of elements and configurations are described below to simplify the present application. Of course, these examples are merely examples and are not intended to be limiting. Note that the present application may repeat element symbols and / or alphabets in each example. This repetition is used for simplicity and clarity and does not itself specify a relationship between each of the described embodiments and / or configurations.

[0029] Spatially relative terms, such as "below," "below," "lower," "above," "top," and the like, may be used herein for convenience of description to describe the relationship of one element or feature to another element or feature as shown in the drawings. Spatially relative terms are intended to encompass different orientations of the device during use or operation other than the orientation shown in the drawings. The device may be otherwise positioned (rotated 90 degrees or placed at other orientations) and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0030] FIG. 1 is a cross-sectional view illustrating a photodetector 100 according to one embodiment of the present disclosure. Please refer 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 and has an electron mobility of 300 cm. 2The upper electrode layer 130 includes a material having a mobility greater than V / Vs and greater than twice the hole mobility, and is configured to generate a photocurrent by utilizing the large difference between the electron and hole mobilities. The upper electrode layer 130 is located on the absorption layer 120 and is configured to absorb electrons e in the photocurrent. When a semiconductor or semimetal material (e.g., the absorption layer 120) is excited by light L, electron-hole pairs are formed. At this time, the electron mobility of some specific materials (described in more detail below) is sufficiently high and the difference with the hole mobility is so large that the electrons scatter and diffuse much faster than the holes. When electron-hole pairs are generated around the upper electrode layer 130 after illumination (for example, at the edge 131 of the upper electrode layer 130 and at the interface 132 between the upper electrode layer 130 and the absorption layer 120), fast electrons (upper e in FIG. 1) enter the upper electrode layer 130, while slow holes (h in FIG. 1) are left behind. These holes that have lost electrons form positive charges around the upper electrode layer 130, which generates a vertical downward electric field E inside the device compared to the unilluminated lower electrode layer 110, and further pushes the flow of internal carriers in the absorption layer 120 to generate photocurrent. Representative materials with high electron mobility and a large difference between electron mobility and hole mobility include indium arsenide (InAs), indium antimonide (InSb), indium phosphide (InP), gallium arsenide (GaAs), gallium antimonide (GaSb), and gallium arsenide indium (InP). 0.53 Ga 0.47 As), mercury cadmium telluride (Hg 1-x CD x Examples of suitable materials include cadmium arsenide (Cd3As2), combinations of the above materials, alloys of the above materials, or other suitable materials. Table 1 shows the electron and hole mobilities of the above materials at room temperature. [Table 1]

[0031] As can be seen from Table 1, the above materials have a very large difference between electron and hole mobilities at room temperature, with the electron mobility being at least twice as large as the hole mobility, and indium antimonide, for example, has a difference of 100 times. Therefore, they can be used as the absorption layer 120 of the photodetector 100. The bottom electrode layer 110 is configured to provide electrons to complete a current circuit within the photodetector 100. In some embodiments, an ohmic contact is formed between the top electrode layer 130 and the absorption layer 120. In some embodiments, an ohmic contact is formed between the absorption layer 120 and the bottom electrode layer 110, and the bottom electrode layer 110 is covered by the absorption layer 120. Forming 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. Appropriate hole (P-type) doping of the absorption layer 120 can reduce the device resistance and increase the photocurrent, thereby achieving higher detection efficiency and sensitivity. Appropriate P-type doping can prevent losses in the reverse thermal current (toward the upper electrode layer 130) generated after illumination, the reverse photocurrent (toward the upper electrode layer 130) generated by contact with the Schottky diode, and the forward photocurrent (toward the lower electrode layer 110) when the absorption layer 120 remains an N-type semiconductor.

[0032] In addition to the above-described ohmic contact fabrication method, a Schottky contact may be formed between the upper electrode layer 130 and the absorption layer 120. Because the absorption layer 120 is typically a P-type semiconductor, when a Schottky junction is formed between the P-type semiconductor and the metal of the upper electrode layer 130, the direction of the built-in electric field is oriented toward the semiconductor absorption layer 120. When illuminated and generating electron-holes, this built-in electric field E accelerates photoelectrons toward the metal edge, while simultaneously blocking the ingress of photoholes into the upper electrode layer 130. This design reduces the blocking effect of photoelectrons due to contact resistance when perfect ohmic contact is difficult to fabricate, improves the probability of photoelectrons entering the electrode, and further enhances the generation efficiency of photovoltage and photocurrent. 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 primarily an ohmic contact. As long as the total resistance of the device is not too small, methods of adding contact resistance, such as adding a Schottky contact or a blocking layer, can improve the total resistance of the device and reduce thermal noise.

[0033] The absorption layer 120 of the photodetector 100 contains a material whose electron mobility is more than twice as large as its hole mobility, and therefore can generate photocurrent by utilizing the large difference between the electron and hole mobilities. Therefore, the photodetector 100 can operate independently at room temperature without the assistance of a cooling system and additional bias, and can provide far-infrared detection with a high detection rate and high resolution.

[0034] 2 is a perspective view showing a photodetector 100a according to another embodiment of the present disclosure. Please refer to FIG. 2. The absorption layer 120a may be a single material, or may include a semiconductor-semiconductor, semiconductor-semimetal, or semimetal-semimetal junction area 122 in an inner area near the surface, where the built-in electric field is downward. The junction area 122 may be, for example, an NP junction, a NIP junction, an IP junction, a P - P joint or PP +The junction area 122 may be, but is not limited to, a junction. The purpose of the junction area 122 is as follows: after absorbing a photon, electron-hole pair separation (this layer is also called an electron-hole separation layer) is generated, and the high-speed electrons enter the upper electrode layer 130 on the upper surface, while the low-speed holes are left behind. The spatial positions of these holes that have lost electrons are still close to the upper surface of the absorption layer 120a. Therefore, in addition to the holes near the edge 131 and interface 132 of the upper electrode layer 130 described in the embodiment of FIG. 1 (e.g., h in FIG. 1 or upper h in FIG. 2), these additional holes (lower h in FIG. 2) generated by the junction area 122 can further increase the number of positive charges, which can strengthen the downward electric field E in the vertical direction of the absorption layer 120 after illumination and the photocurrent.

[0035] FIG. 3 is a perspective view illustrating a photodetector 100b according to another embodiment of the present disclosure. See 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 upper electrode layer 130 has a comb-like shape in plan view. This shape is fabricated because the edge of the upper electrode layer 130 (see FIG. 1) has the highest electron absorption efficiency and therefore can generate the strongest electric field E (see FIG. 1). Therefore, by designing the upper electrode layer 130 to have a comb-like shape in plan view, the overall edge length of the comb-like portion of the upper electrode layer 130 can be increased within a limited area, thereby improving the efficiency of photocurrent generated by a large difference between electron and hole mobility. In some embodiments, the upper electrode layer 130 may have a dendritic, net-like, spiral, or other shape in plan view, but the present disclosure is not limited thereto. In some embodiments, photodetector 100b further includes a buffer layer 150, which is located between substrate 140 and absorber layer 120. If there is a lattice mismatch between the material of absorber layer 120 and the material of substrate 140, a buffer layer 150 can be utilized to mitigate this problem. The material of buffer layer 150 may include cadmium zinc telluride (CdZnTe), although the present disclosure is not limited thereto.

[0036] FIG. 4 is a perspective view illustrating a photodetector 100c according to another embodiment of the present disclosure. Please refer 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. The difference between this embodiment and the embodiment of FIG. 3 is that the upper electrode layer 130a has a rectangular shape in plan view and is made of a thin film containing a transparent conductive material such as indium tin oxide (ITO) or aluminum zinc oxide (AZO). In this embodiment, the entire upper electrode layer 130a made of a transparent conductive material can serve as a photoelectron collecting region. Because the electrode layer 130a contains a transparent conductive material, the underlying absorption layer 120 can be illuminated. After being excited by the illumination, photoelectrons are absorbed by the electrode made of the transparent conductive material, thereby generating a photocurrent.

[0037] FIG. 5 is a perspective view illustrating a photodetector 100d according to a further embodiment of the present disclosure. Please refer to FIG. 5. The photodetector 100d includes a lower electrode layer 110, an absorber layer 120, an upper electrode layer 130, a substrate 140, and a buffer layer 150. The difference between this embodiment and the embodiment of FIG. 3 is that in this embodiment, the photodetector 100d further includes a cover layer 160 located on the absorber layer 120 and surrounding the upper electrode layer 130. The cover layer 160 is configured to prevent direct contact between the material surface of the absorber layer 120 and air and to reduce the defect density on the surface of the absorber layer 120. The material of the cover layer 160 may include cadmium zinc telluride (CdZnTe) or other insulating materials, although the present disclosure is not limited thereto.

[0038] FIG. 6 is a cross-sectional view illustrating a photodetector 100e according to one embodiment of the present disclosure. Please refer 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 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 within the trench 124. Since photoelectrons are pushed into the upper electrode layer 130 by a spontaneous thermal scattering mechanism, the number of photoelectrons that enter the electrode is determined by their mean collision length. The higher the electron mobility, the longer the mean collision distance, which means that more scattered photoelectrons can enter the electrode. However, the average collision distance of electrons is generally much smaller than 1 micron, resulting in a shallow depth of the positive charge generation area (active area) in this disclosure. However, the light penetration depth is generally greater than 1 micron in the absorption layer 120 (e.g., the embodiment of FIG. 1 ), resulting in a low internal quantum efficiency of the photodetector 100. Therefore, trenches 124 corresponding to the pattern of the upper electrode layer 130 can be first excavated in the absorption layer 120b by etching or other methods, and then a metal electrode can be filled in the trenches 124. In this way, the range of electron collection is not limited to the peripheral region of the upper electrode layer 130 near the surface (e.g., the edge 131 of the upper electrode layer 130 in FIG. 1 ), but can increase as the depth of the upper electrode layer 130 (e.g., the depth of the photopositive charge area 126) increases.

[0039] It should be understood that the element connections, materials and functions already described will not be repeated. In the following description, a method for manufacturing a photodetector will be described.

[0040] 7 is a flowchart illustrating a method for manufacturing a photodetector according to one embodiment of the present disclosure. Please refer to FIG. 7. The method for manufacturing a photodetector includes the following steps: First, in step S1, a photodetector having an electron mobility of 300 cm 2 / Vs and more than twice the hole mobility, and is configured to utilize the large difference between the electron mobility and the hole mobility to generate a photovoltage and further form a photocurrent; and in step S2, an upper electrode layer configured to absorb the scattered high-speed photoelectrons is plated on the absorption layer and destroys electrical neutrality around the upper electrode layer, causing positive hole charges to accumulate and generate a photovoltage; and finally in step S3, a lower electrode layer is formed, and the absorption layer is located between the upper electrode layer and the lower electrode layer.

[0041] In some embodiments, the method for manufacturing a 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 two adjacent steps, may further include other steps before step S1, or may 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.

[0042] See FIG. 3 . In the embodiment of FIG. 3 , before forming the absorber layer 120 on the substrate 140, a buffer layer 150 is first formed on the substrate 140. Then, the absorber layer 120 is formed. Forming the absorber layer 120 may include using a combination of molecular beam epitaxy (MBE), chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), liquid phase epitaxy (LPE), or other suitable methods. Alternatively, in other embodiments, the absorber layer 120 may be formed within the substrate 140 using ion implantation or diffusion without forming the buffer layer 150, although the present disclosure is not limited thereto. The absorbing layer 120 may be formed by ion implantation or diffusion to form the absorbing layer 120a including the junction area 122 in the embodiment of FIG. 2, or the entire absorbing layer 120 may be doped by ion implantation or diffusion.

[0043] In some embodiments (e.g., the embodiment of FIG. 5 ), the cover layer 160 is formed on the absorber layer 120, and the cover layer 160 is patterned to form openings that expose the absorber layer 120. The upper electrode layer 130 is plated on the absorber layer 120 in the openings. When the openings in the cover layer 160 have a comb-like shape in plan view, plating the upper electrode layer 130 on the absorber layer 120 in the openings can make the upper electrode layer 130 have a comb-like shape in plan view and form ohmic or Schottky contact between the upper electrode layer 130 and the absorber layer 120. In other embodiments, the upper electrode layer 130 (e.g., the embodiment of FIG. 3 ) or 130a (e.g., the embodiment of FIG. 4 ) can be directly formed without forming the cover layer 160.

[0044] Then, the lower electrode layer 110 is formed to place the absorber layer 120 between the upper electrode layer 130 and the lower electrode layer 110. In some embodiments (e.g., the embodiment of FIG. 1), the lower electrode layer 110 is located on the surface of the absorber layer 120 opposite the upper electrode layer 130. In some embodiments (e.g., the embodiment of FIG. 3), the lower electrode layer 110 is located on the surface of the substrate 140 opposite the absorber layer 120. This step allows for the formation of ohmic contact between the lower electrode layer 110 and the absorber layer 120 or the substrate 140. Unlike the upper electrode layer 130, the lower electrode layer 110 is uniformly distributed throughout the layer.

[0045] The foregoing has described features of several embodiments so that those skilled in the art may better understand aspects of the present disclosure. Those skilled in the art should appreciate that this disclosure may readily be used as a basis for designing or modifying other processes and structures to carry out the same purposes and / or achieve the same advantages as the embodiments described herein. Those skilled in the art should recognize that such equivalent structures can be realized without departing from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations can be made therein. [Explanation of symbols]

[0046] 100, 100a, 100b, 100c, 100d, 100e: Photodetector 110: Lower electrode layer 120, 120a: Absorbing layer 122: Joint area 124: Trench 126: Photopositive charge area 130,130a: Upper electrode layer 131: Edge 132: Interface 140: Circuit board 150:Buffer layer 160: Cover layer E: Electric field S1, S2, S3: Step

Claims

1. a lower electrode layer; A layer is disposed on the lower electrode layer and has an electron mobility of 300 cm at room temperature. ２ / Vs and more than twice the hole mobility at room temperature, and configured to generate photocurrent by utilizing the difference between the electron mobility and the hole mobility; and an upper electrode layer in direct contact with the absorption layer and configured to absorb photoelectrons, which have a faster thermal velocity and a longer collision distance than photoholes, wherein excess holes accumulate positive charge in a region of the absorption layer near the periphery of the upper electrode layer, destroying electrical neutrality and generating a photovoltage; and a vertically downward electric field is self-generated between the periphery of the upper electrode layer and the lower electrode layer of the photodetector, causing carriers in the absorption layer to flow by the electric field without the application of an external voltage, thereby generating a photocurrent; an ohmic contact is formed between the upper electrode layer and an upper surface of the absorption layer, an ohmic contact is formed between the lower electrode layer and a lower surface of the absorption layer, an area of ​​the upper electrode layer is smaller than an area of ​​the absorption layer, and at least a portion of the upper surface of the absorption layer is exposed.

2. The photodetector according to claim 1 , wherein the upper electrode layer has at least one of a comb-like, a tree-like, a net-like, and a spiral shape in plan view.

3. The photodetector of claim 2 , wherein the top electrode layer is located within a trench in the absorption layer.

4. The photodetector of claim 1 , further comprising a cover layer overlying the absorption layer and surrounding the top electrode layer.

5. Electron mobility is 300 cm at room temperature ２ / Vs and more than twice the hole mobility at room temperature, and configured to generate a photocurrent by utilizing the difference between the electron mobility and the hole mobility; plating an upper electrode layer on the absorption layer, the upper electrode layer being configured to absorb photoelectrons, which have a higher thermal velocity and a longer collision distance than photoholes; forming an ohmic contact between the upper electrode layer and an upper surface of the absorption layer; the area of ​​the upper electrode layer being smaller than that of the absorption layer, and at least a portion of the upper surface of the absorption layer being exposed; excess holes accumulating positive charge in a region of the absorption layer near the periphery of the upper electrode layer destroying electrical neutrality and generating a photovoltage; and self-generating a vertically downward electric field between the periphery of the upper electrode layer and a lower electrode layer of the photodetector, which causes carriers in the absorption layer to flow by the electric field without the application of an external voltage, generating a photocurrent; forming a lower electrode layer such that the absorption layer is located between the upper electrode layer and the lower electrode layer, and an ohmic contact is formed between the lower electrode layer and a lower surface of the absorption layer.

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