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 measurement, while only cooled detectors can provide high detection rate and resolution.

[0003] However, the above non-cooled detectors generally have too large a dark current and must be cooled to liquid nitrogen temperature to operate properly, which makes the manufacturing and maintenance costs of such detectors very high, and also makes it difficult to deploy such detectors, since 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 greater than twice the hole mobility, and configured to utilize the large difference between electron and hole mobility to generate a photocurrent, and an upper electrode layer over 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 a 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 a 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 absorbing 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, the electron mobility is 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 to further form a photocurrent; plating a top electrode layer on the absorbing layer, configured to absorb the scattered high speed photoelectrons and break electrical neutrality around the top electrode layer to accumulate positive charge of the holes to generate a photovoltage; and forming a bottom electrode layer such that the absorbing layer is between the top electrode layer and the bottom electrode layer.

[0017] In one embodiment of the present disclosure, providing an absorbent layer includes forming an absorbent 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 absorbing layer over a substrate includes forming the absorbing layer using diffusion or ion implantation.

[0020] In one embodiment of the present disclosure, forming an absorber layer over a 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 bottom electrode layer is formed on the surface of the substrate opposite the absorbing layer, and an ohmic or Schottky contact is formed between the bottom electrode layer and the substrate.

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

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

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

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

[0026] In the above embodiment of the present disclosure, the absorption layer of the photodetector includes a material with an electron mobility greater than twice the hole mobility, and therefore the photocurrent can be generated by utilizing the large difference between the electron mobility and the hole mobility, and therefore the photodetector can operate independently at room temperature without the assistance of a cooling system, and can also operate under zero bias, providing far-infrared detection with high detectivity. The present disclosure employs a completely new concept to generate photovoltage and photocurrent signals, and uses the characteristic that the internal electron mobility of the absorption layer material is higher than the hole mobility to spontaneously generate positive charges and photovoltage after illuminating the edge of the upper electrode. Therefore, the photovoltage or photocurrent signal can be maximized by means such as reducing the width of the electrode line (increasing the edge of the electrode). The present disclosure uses the thermal velocity difference of the photocarriers to drive the photovoltage and photocurrent, and is therefore particularly suitable for application of far-infrared detectors at room temperature without the assistance of a cooling system. For the same reason, the present disclosure does not require the application of an additional bias, and this characteristic can significantly reduce the dark current of the photodetector. In summary, this disclosure can solve two major problems that mid-far infrared detectors have faced for a long time: the photoreaction signal is too small when operating at room temperature, and the background noise is too large. The present invention can greatly improve the signal-to-noise ratio and detection rate of mid-far infrared detectors under room temperature conditions. [Brief description of the drawings]

[0027] Aspects of the present disclosure can be best understood in 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, sizes of various features may be arbitrarily increased or decreased for clarity of discussion. [Figure 1] FIG. 2 is a cross-sectional view illustrating a photodetector according to one embodiment of the present disclosure. [Diagram 2] FIG. 13 is a cross-sectional view illustrating a photodetector according to another embodiment of the present disclosure. [Diagram 3] FIG. 2 is a perspective view illustrating a photodetector according to another embodiment of the present disclosure. [Figure 4] FIG. 13 is a perspective view illustrating a photodetector according to a further embodiment of the present disclosure. [Diagram 5] FIG. 13 is a perspective view illustrating a photodetector according to a further embodiment of the present disclosure. [Figure 6] FIG. 2 is a cross-sectional view illustrating a photodetector according to one embodiment of the present disclosure. [Figure 7] 1 is a flowchart illustrating a method for manufacturing a photodetector according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The contents of the embodiments disclosed below provide many different embodiments or examples for implementing different features of the provided targets. Below, specific examples of elements and configurations are described to simplify the present application. Of course, these examples are merely examples and are not intended to be limiting. It should be noted that the present application may repeat the symbols and / or alphabets of elements in each example. This repetition is used for the purpose of 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. The 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 in other orientations) and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0030] FIG 1 is a cross-sectional view of a photodetector 100 according to an 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 2 / Vs and more 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 absorbing layer 120 and configured to absorb the electrons e in the photocurrent. When a semiconductor or semimetallic material (e.g., the absorbing layer 120) is excited by light L, electron-hole pairs are formed. At this time, the electron mobility of some specific materials (described in detail below) is sufficiently high and the difference with the hole mobility is very large, so 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), the fast electrons (e in the upper part of FIG. 1) enter the upper electrode layer 130, while the 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 vertically downward electric field E inside the device compared to the unilluminated lower electrode layer 110, and further pushes the flow of carriers inside the absorption layer 120 to generate photocurrent. Representative materials with high electron mobility and large electron-hole mobility difference are indium arsenide (InAs), indium antimonide (InSb), indium phosphide (InP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium gallium arsenide (InP), and gallium arsenide (GaAs). 0.53 Ga 0.47 As), mercury cadmium telluride (Hg 1-x CD x Te), cadmium arsenide (Cd3As2), combinations of the above materials, alloys of the above, 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 the electron mobility and the hole mobility at room temperature, the electron mobility being at least twice as large as the hole mobility, and even 100 times larger for indium antimonide, for example. 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 complete a current circuit 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. By 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, the electron collection efficiency of the entire photodetector 100 can be improved, and by doping the absorption layer 120 with appropriate holes (P type), the element resistance can be reduced and the photocurrent can be increased, thereby achieving a higher detection rate and sensitivity. By appropriate P type doping, when the absorption layer 120 is in the state of an N type semiconductor, the loss of the reverse thermal current (towards the upper electrode layer 130) generated after illumination, the reverse photocurrent (towards the upper electrode layer 130) generated by contact with the Schottky, and the forward photocurrent (towards the lower electrode layer 110) can be avoided.

[0032] In addition to the above-mentioned ohmic contact fabrication method, a Schottky contact may be formed between the upper electrode layer 130 and the absorption layer 120. The absorption layer 120 generally uses a P-type semiconductor, so when the P-type semiconductor and the metal of the upper electrode layer 130 form a Schottky junction, the direction of the built-in electric field is directed toward the semiconductor absorption layer 120. When the built-in electric field E is irradiated to generate electrons and holes, it accelerates the photoelectrons toward the metal edge, and at the same time blocks the photoholes from entering the upper electrode layer 130. This design can reduce the blocking effect on photoelectrons caused by contact resistance when perfect ohmic contact is difficult to fabricate, improve the probability of photoelectrons entering the electrode, and further improve the generation efficiency of photovoltage and photocurrent. However, this design is not applied to the junction between the lower electrode layer 110 and the absorption layer 120, and the junction of the lower electrode layer 110 is still mainly 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 includes a material with an electron mobility greater than twice that of the hole mobility, and therefore can utilize the very large difference in electron-hole mobility to generate photocurrent, and therefore can operate independently at room temperature without the assistance of a cooling system and additional bias, providing high detection rate and high resolution far-infrared detection.

[0034] 2 is a perspective view of a photodetector 100a according to another embodiment of the present disclosure. Please refer to FIG. 2. The absorbing layer 120a may be a single material, or may include a semiconductor-semiconductor, semiconductor-semimetal, or semimetal-semimetal junction area 122 in an inner surface-close region with a built-in electric field directed downward, and the junction area 122 may be, for example, an NP junction, a NIP junction, an IP junction, a P - P joint or PP +It may be, but is not limited to, a junction. The purpose of the junction area 122 is as follows: generate electron-hole pair separation (this layer is also called electron-hole separation layer) after absorbing photons, and the fast electrons enter the upper electrode layer 130 on the upper surface, but the slow holes are left behind, and the spatial position of these holes with lost electrons is still close to the upper surface of the absorption layer 120a, so 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 (for example, h in FIG. 1 or h in the upper part of FIG. 2), these additional holes (h in the lower part of FIG. 2) generated by the junction area 122 can further increase the number of positive charges, and enhance the downward electric field E in the vertical direction of the absorption layer 120 and the photocurrent after illumination.

[0035] FIG. 3 is a perspective view showing a photodetector 100b according to another embodiment of the present disclosure. Please refer 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 upper electrode layer 130 has a comb-like shape in plan view. The reason for fabricating the upper electrode layer 130 in such a shape is that the electron absorption efficiency is highest at the edge of the upper electrode layer 130 (see FIG. 1), and therefore the strongest electric field E (see FIG. 1) can be generated. Therefore, by designing the upper electrode layer 130 to have a comb-like shape in plan view, the length of the entire edge of the comb-like portion of the upper electrode layer 130 can be increased within a limited area, and the efficiency of the photocurrent generated due to the large difference between the electron mobility and the hole mobility can be improved. 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, the photodetector 100b further includes a buffer layer 150, which is located between the substrate 140 and the absorbing layer 120. If there is a lattice mismatch between the material of the absorbing layer 120 and the material of the substrate 140, a buffer layer 150 can be utilized to mitigate this problem. The material of the buffer layer 150 may include cadmium zinc telluride (CdZnTe), although the present disclosure is not limited thereto.

[0036] FIG. 4 is a perspective view showing 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 in this embodiment, the upper electrode layer 130a has a rectangular shape in plan view, 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 the photoelectron collecting region. Since the electrode layer 130a includes a transparent conductive material, the lower absorption layer 120 can be illuminated, and the photoelectrons after being illuminated and excited are absorbed by the electrode made of the transparent conductive material, thereby resulting in a photocurrent.

[0037] FIG. 5 is a perspective view showing 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 absorbing 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 absorbing layer 120 and surrounding the upper electrode layer 130. The cover layer 160 is configured to avoid direct contact between the material surface of the absorbing layer 120 and air, and to reduce the defect density on the surface of the absorbing 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.

[0038] FIG. 6 is a cross-sectional view showing a photodetector 100e according to an embodiment of the present disclosure. Please refer to FIG. 6. The photodetector 100e includes a lower electrode layer 110, an absorbing layer 120b, and an upper electrode layer 130. The absorbing layer 120b is located on the lower electrode layer 110, and the upper electrode layer 130 is located on the absorbing 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 absorbing layer 120b has a trench 124, and a part of the upper electrode layer 130 is located in the trench 124. Since the entry of photoelectrons into the upper electrode layer 130 is pushed by a spontaneous thermal scattering mechanism, the number of photoelectrons entering the electrode is determined by their mean collision length, and the higher the electron mobility, the longer the mean collision distance, which indicates that more scattered photoelectrons can enter the electrode. However, the average collision distance of electrons is generally all much smaller than 1 micron, so the depth of the positive charge generation area (active area) in the present disclosure is shallow. However, the light penetration depth is generally greater than 1 micron in the absorption layer 120 (e.g., the embodiment of FIG. 1), which results in a low internal quantum efficiency of the photodetector 100. Therefore, the trenches 124 of the pattern of the upper electrode layer 130 can be first excavated in the absorption layer 120b by a method such as etching, and then the metal electrode can be filled in the trenches 124. In this way, the range of electrons that can be collected is not limited to the surrounding area of ​​the upper electrode layer 130 close to the surface (e.g., the edge 131 of the upper electrode layer 130 in FIG. 1), but can be increased 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 already described element connections, materials and functions will not be repeated any further. In the following description, a method for manufacturing a photodetector will be described.

[0040] 7 is a flowchart showing a method for manufacturing a photodetector according to an 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 semiconductor device having 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 to further form a photocurrent; and in step S2, plating an upper electrode layer configured to absorb the scattered high-speed photoelectrons on the absorption layer and destroy electrical neutrality around the upper electrode layer to accumulate positive charges of holes to generate a photovoltage; and finally in step S3, forming a lower electrode layer and positioning the absorption layer 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, and 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. Or, 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] Please refer to Fig. 3. In the embodiment of Fig. 3, before forming the absorbing layer 120 on the substrate 140, a buffer layer 150 is first formed on the substrate 140. Then, the absorbing layer 120 is formed. Forming the absorbing layer 120 includes 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 absorbing layer 120 may be formed inside the substrate 140 using ion implantation or diffusion without forming the buffer layer 150, but 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 absorbing layer 120, and the cover layer 160 is patterned to form an opening exposing the absorbing layer 120, and the upper electrode layer 130 is plated on the absorbing layer 120 at the opening. When the opening of the cover layer 160 has a comb-like shape in plan view, the upper electrode layer 130 is plated on the absorbing layer 120 at the opening, so that the upper electrode layer 130 has a comb-like shape in plan view and the upper electrode layer 130 and the absorbing layer 120 form an ohmic contact or a Schottky contact. In other embodiments, the upper electrode layer 130 (e.g., the embodiment of FIG. 3) or 130a (e.g., the embodiment of FIG. 4) may be directly formed without forming the cover layer 160.

[0044] Then, the lower electrode layer 110 is formed so that the absorbing layer 120 is 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 a surface of the absorbing 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 a surface of the substrate 140 opposite the absorbing layer 120. This step allows an ohmic contact to be formed between the lower electrode layer 110 and the absorbing 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 above describes features of some embodiments so that those skilled in the art can better understand aspects of the present disclosure. It should be appreciated that those skilled in the art can readily use this disclosure as a basis for designing or modifying other processes and structures to achieve the same purposes and / or advantages of 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: Absorption layer 122: Joint area 124: Trench 126: Photopositive charge area 130,130a: Upper electrode layer 131: Edge 132: Interface 140: Substrate 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 ２ / Vs and greater than twice the hole mobility, and configured to utilize the difference between the electron mobility and the hole mobility to generate a photocurrent; a top electrode layer overlying the absorption layer and configured to absorb electrons in the photocurrent.

2. The photodetector of claim 1 , wherein 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.

3. 2. The photodetector of claim 1, wherein a planar shape of the upper electrode layer is at least one of a comb shape, a tree shape, a mesh shape, and a spiral shape, and the upper electrode layer and the absorption layer form an ohmic contact or a Schottky contact.

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

5. a substrate located between the absorption layer and the lower electrode layer; The photodetector of claim 1 further comprising a buffer layer located between the substrate and the absorbing layer.

6. 2. The photodetector according to claim 1, wherein the upper electrode layer has a rectangular shape in a plan view, and the upper electrode layer is a transparent conductive thin film containing indium tin oxide (ITO) or aluminum zinc oxide (AZO).

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

8. Electron mobility is 300 cm ２ / Vs and greater than twice the hole mobility, and configured to utilize the difference between the electron mobility and the hole mobility to generate a photovoltage to further form a photocurrent; plating an upper electrode layer on the absorbing layer, the upper electrode layer being configured to absorb scattered photoelectrons, and breaking electrical neutrality around the upper electrode layer to accumulate positive hole charges to generate a photovoltage; forming a bottom electrode layer such that the absorption layer is located between the top electrode layer and the bottom electrode layer.

9. Providing the absorbent layer comprises: The method of claim 8 comprising forming the absorbing layer over a substrate.

10. forming the lower electrode layer The method of claim 9 , further comprising forming the bottom electrode layer on a surface of the substrate opposite the absorption layer.

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