Light sensor

Abstract

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 and is made of a single material without homogeneous or heterogeneous interfaces. The upper electrode layer is located on the upper surface of the absorption layer, wherein the ratio of the perimeter of the upper electrode layer to the area of ​​the upper surface of the absorption layer is greater than 100 mm⁻¹. The absorption layer is configured to generate photocurrent and voltage around the upper electrode layer and near the interface with the upper surface of the absorption layer by utilizing the large difference between electron mobility and hole mobility.

Description

Technical Field

[0001] This disclosure relates to a photodetector, and more particularly to a photodetector having a junctionless self-powered absorption layer. Prior Technology

[0002] High-efficiency photodetector technology is a crucial component of today's high-tech industries. Traditionally, high-efficiency photodetectors employ semiconductor PN junction diodes or metal-semiconductor Schottky junction diodes. These two methods generate a built-in electric field to separate electron-hole pairs, thereby producing photocurrent. This approach is highly efficient in the visible and ultraviolet light bands, but in the mid- and far-infrared light bands, it is limited by the inherent carrier concentration and excessive dark current of narrow-bandgap semiconductor materials under uncooled conditions, thus hindering further improvements in sensor efficiency. Summary of the Invention

[0003] One of the technical features disclosed herein is a photodetector.

[0004] According to one embodiment of this 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 is a single material and does not contain homogeneous or heterogeneous junctions. The absorption layer contains a material with an electron mobility greater than 300 cm² / Vs and greater than twice the hole mobility. The absorption layer is unbiased and self-powered. The upper electrode layer is located on the upper surface of the absorption layer, wherein the ratio of the perimeter of the upper electrode layer to the area of ​​the upper surface of the absorption layer is greater than 100 mm⁻¹. The absorption layer is configured to generate a photocurrent near the interface between the perimeter of the upper electrode layer and the upper surface of the absorption layer, utilizing the significant difference between electron and hole mobility.

[0005] In one embodiment of this disclosure, the top view shape of the upper electrode layer is at least one of comb-like, tree-like, mesh-like, or spiral-like.

[0006] In one embodiment of this disclosure, the upper electrode layer is located in the trench of the absorption layer.

[0007] In one embodiment of this disclosure, the photodetector further includes a substrate and a buffer layer. The substrate is located between the absorption layer and the lower electrode layer. The buffer layer is located between the substrate and the absorption layer.

[0008] In one embodiment of this disclosure, the photodetector further includes a substrate and a buffer layer. The substrate is located below the absorption layer and the lower electrode layer. The buffer layer is located between the substrate and the absorption layer.

[0009] In one embodiment of this disclosure, the photodetector further includes a high electron concentration region. The high electron concentration region is located between the lower electrode layer and the absorption layer.

[0010] In one embodiment of this disclosure, the absorbent layer is L-shaped and stepped.

[0011] In one embodiment of this disclosure, the photodetector further includes a doped region. The doped region is located below the lower electrode layer and the absorption layer.

[0012] Another technical aspect disclosed herein is a photodetector.

[0013] According to one embodiment of this disclosure, a photodetector includes an absorption layer, a lower electrode layer, a transparent upper electrode layer, and a metal upper electrode layer. The absorption layer has a first surface and a second surface, and comprises a material with an electron mobility greater than 300 cm² / Vs and more than twice the hole mobility. The absorption layer is unbiased and self-powered. The lower electrode layer is located on the first surface of the absorption layer. The transparent upper electrode layer is located on and covers the second surface of the absorption layer. The absorption layer is configured to generate a photocurrent near the interface between the transparent upper electrode layer and the absorption layer by utilizing the significant difference between electron and hole mobility. The metal upper electrode layer is located on the transparent upper electrode layer, wherein the area of ​​the metal upper electrode layer is smaller than the area of ​​the transparent upper electrode layer.

[0014] In one embodiment of this disclosure, the band gap of the light-transmitting upper electrode layer is greater than or equal to 1.5 times the band gap of the absorption layer.

[0015] In one embodiment of this disclosure, the first surface faces away from the second surface.

[0016] In one embodiment of this disclosure, the photodetector further includes a high electron concentration region. The high electron concentration region is located between the lower electrode layer and the absorption layer.

[0017] In one embodiment of this disclosure, the first surface and the second surface are disposed adjacent to each other and form a stepped surface.

[0018] In one embodiment of this disclosure, the photodetector further includes a doped region. The doped region is located below the lower electrode layer and the absorption layer.

[0019] In one embodiment of this disclosure, the electron concentration of the light-transmitting upper electrode layer is denoted as nn, and the electron concentration of the absorption layer is denoted as np. The light-transmitting upper electrode layer and the absorption layer must satisfy the following relationship: nn≧10¹⁷cm⁻³, np≦10¹⁴cm⁻³ The unit for electron concentration is (cm⁻³).

[0020] In one embodiment of this disclosure, the electron affinity of the light-transmitting upper electrode layer is denoted as χn, the work function of the light-transmitting upper electrode layer is denoted as Φn, the electron affinity of the absorption layer is denoted as χp, and the work function of the absorption layer is denoted as Φp. Then, the light-transmitting upper electrode layer and the absorption layer must satisfy one of the following relationships: .

[0021] In the embodiments disclosed above, since the photodetector generates photocurrent by utilizing the significant difference in electron-hole mobility, it can operate independently at room temperature without the need for a cooling system or external bias voltage, thus providing high-detection-rate optical detection and high-resolution image detection. Furthermore, because the ratio of the perimeter of the upper electrode layer to the area of ​​the upper surface of the absorption layer is greater than 100 mm⁻¹, the detection efficiency is high, making it particularly suitable for applications in the infrared wavelength range. Simple Explanation of the Diagram

[0022] The nature of this disclosure can be best understood by reading it in conjunction with the accompanying illustrations and by the embodiments described below. Note that, according to standard practice in the industry, the various features are not drawn to scale. In fact, the dimensions of the various features may be increased or decreased arbitrarily for clarity of explanation. Figure 1 shows a perspective view of a photodetector according to an embodiment of the present disclosure. Figure 2A shows a cross-sectional view of the optical detector in Figure 1. Figure 2B illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 3A shows a top view of the light detector in Figure 1. Figure 3B illustrates a cross-sectional view of a photodetector according to yet another embodiment of this disclosure. Figure 3C illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 3D illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 4A shows a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 4B illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 5A illustrates a cross-sectional view of a photodetector according to yet another embodiment of this disclosure. Figure 5B illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 6 illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figures 7A, 7B, and 7C illustrate the band structure of the photodetector in Figure 6 under different conditions. Figure 8 shows a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 9A shows a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 9B illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Figure 9C illustrates a cross-sectional view of a photodetector according to another embodiment of this disclosure. Implementation

[0023] The following disclosure of embodiments provides many different implementations, or examples, for carrying out different features of the provided object. Specific examples of elements and arrangements are described below to simplify the subject matter. Of course, these examples are merely illustrative and are not intended to be limiting. Furthermore, element symbols and / or letters may be repeated in various examples. This repetition is for simplicity and clarity and does not in itself specify the relationship between the various embodiments and / or configurations discussed.

[0024] Spatial relative terms such as “below,” “under,” “lower,” “above,” and “upper” are used herein for descriptive purposes to describe the relationship between one element or feature and another, as shown in the accompanying drawings. Spatial relative terms are intended to cover different orientations of the device in use or operation other than those shown in the accompanying drawings. The device may be oriented in other ways (rotated 90 degrees or otherwise), and the spatial relative descriptors used herein shall be interpreted accordingly.

[0025] Figure 1 shows a perspective view of a photodetector 100 according to an embodiment of the present disclosure. Figure 2A shows a cross-sectional view of the photodetector 100 in Figure 1. Referring to Figures 1 and 2A, 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 is a single material and does not contain homogeneous or heterogeneous junctions (i.e., no internal junctions). The absorption layer 120 contains a material with an electron mobility greater than 300 cm² / Vs and greater than twice the hole mobility, so that the absorption layer 120 has no bias voltage and can be self-powered. In other words, the photodetector 100 has a junctionless, self-powered absorption layer 120, and when the absorption layer 120 receives light, it can generate voltage and current without an external power supply. An upper electrode layer 130 is located on the upper surface 122 of the absorption layer 120, wherein the absorption layer 120 is configured to generate a photocurrent around the upper electrode layer 130 and near the interface with the upper surface 122 of the absorption layer 120 by utilizing the large difference between electron mobility and hole mobility. When a semiconductor or half-metallic material (such as the absorption layer 120) is excited by light L, electron-hole pairs are formed. At this time, because the electron mobility of certain materials (described in detail below) is high enough and differs greatly from that of holes, the electron's thermal velocity is much faster than that of the hole. When electron holes are generated around the upper electrode layer 130 after being exposed to light (e.g., the boundary 131 of the upper electrode layer 130 and the interface 132 between the upper electrode layer 130 and the absorption layer 120), fast photoelectrons (e at the top of Figure 2A) will spontaneously enter the upper electrode layer 130, leaving slow photoholes (h in Figure 2A). These photoholes that have lost photoelectrons will form positive charges around the upper electrode layer 130. Compared with the lower electrode layer 110, which does not generate positive charges (the light does not reach it), a vertically downward electric field E and photovoltage can be generated inside the device, thereby driving the flow of carriers inside the absorption layer 120 and generating a photocurrent. Representative materials exhibiting high electron mobility and a large gap between electron and hole mobility include indium arsenide (InAs), indium antimonide (InSb), indium phosphide (InP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium gallium arsenide (In0.53Ga0.47As), mercury cadmium tellurium (Hg1-xCdxTe), cadmium arsenide (Cd3As2), combinations of the above materials, alloys thereof, or other suitable materials. Table 1 shows the electron 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, Tellurium 10000 100 Cadmium arsenide 15000 500 Table 1

[0026] As shown in Table 1, the aforementioned materials exhibit a significant difference between electron mobility and hole mobility at room temperature. Their electron mobility is at least twice that of their hole mobility, and in some cases, the difference is as much as one hundred times, as seen in 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 within the photodetector 100.

[0027] Figure 2B illustrates a cross-sectional view of a photodetector 100a according to yet another embodiment of this disclosure. Referring to Figure 2B, the embodiment in Figure 2B differs from that in Figure 2A in that, in this embodiment, the photodetector 100a further includes a high electron concentration region 180, the electron concentration of which must be higher than 10¹⁴ cm⁻³. The high electron concentration region 180 is located between the lower electrode layer 110 and the absorption layer 120. The high electron concentration region 180 provides a region where positive charge accumulation cannot occur, preventing light L from potentially passing through the entire absorption layer 120 to the lower electrode layer 110 when the absorption layer 120 is thinned. This prevents the generation of photocurrent (or voltage) pointing towards the upper electrode layer 130 at the interface between the lower electrode layer 110 and the absorption layer 120, thus offsetting or reducing the photocurrent (pointing towards the lower electrode layer 110) originally generated at the boundary 131 and interface 132 between the upper electrode layer 130 and the absorption layer 120. In some embodiments, the high electron concentration region 180 contains an intrinsic or N-type semiconductor that is homogeneous or heterogeneous with the absorption layer 120, but this disclosure is not limited thereto.

[0028] Figure 3A shows a top view of the photodetector 100 in Figure 1. Referring to Figure 3A, when calculating the perimeter of the upper electrode layer 130, taking the comb-shaped electrode embodiment in Figure 3A as an example, the total perimeter of the upper electrode layer 130 can be expressed by the following formula 1: …Formula 1

[0029] Where L is the perimeter of the upper electrode layer 130, W is the width of a finger electrode, D is the distance between two finger electrodes, L1 is the length of a finger electrode, and L2 is the width of the branch connecting the finger electrodes. N is the number of finger electrodes (taking Figure 3A as an example, N=8). It can be seen from the above formula that when the number of finger electrodes N increases, the perimeter L will also increase. In practical applications, the width W of the finger electrodes is usually on the order of micrometers, for example, in the range of 1 micrometer to 10 micrometers, but this disclosure is not limited to this. The area of ​​the upper surface 122 of the absorption layer 120 is defined as the area of ​​the upper electrode layer 130 occupying the upper surface 122 of the absorption layer 120. Taking the comb electrode embodiment in Figure 3A as an example, the area of ​​the upper surface 122 of the absorption layer 120 can be expressed by the following formula 2: Equation 2 Where A is the area of ​​the upper surface 122 of the absorption layer 120.

[0030] In practical applications, the area of ​​the upper surface 122 of the absorption layer 120 is in the range of 1 square millimeter to 9 square millimeters, for example, 4 square millimeters, but is not limited to this. Therefore, the ratio of the perimeter L of the upper electrode layer 130 of the photodetector 100 to the area A of the upper surface 122 of the absorption layer 120 is greater than 100 mm⁻¹, for example, 2500 mm⁻¹, but this disclosure is not limited to this. Since most of the photogenerated charge used to generate photovoltage in this embodiment is generated around the upper electrode layer 130 (e.g., the boundary 131 of the upper electrode layer 130 and the interface 132 between the upper electrode layer 130 and the absorption layer 120), maximizing the perimeter L of the upper electrode layer 130 of the photodetector 100 within a limited area can improve the photogenerated charge generation efficiency of the photodetector 100. Furthermore, the top view shape of the upper electrode layer 130 is not limited to a comb shape, but can also be a tree-like, mesh-like, or spiral shape, at least one of these.

[0031] Because the photodetector 100 generates photocurrent by utilizing the significant difference in electron-hole mobility, it can operate independently at room temperature without the need for a cooling system or external bias voltage, thus providing high detection rate and high resolution. Furthermore, since the ratio of the perimeter of the upper electrode layer 130 to the area of ​​the upper surface 122 of the absorption layer 120 is greater than 100 mm⁻¹, the photoresponse signal is large and the background dark current is small, resulting in a high signal-to-noise ratio even under uncooled conditions, making it particularly suitable for applications in the infrared band.

[0032] Figure 3B illustrates a cross-sectional view of a photodetector 100b according to yet another embodiment of this disclosure. Referring to Figure 3B, the photodetector 100b includes a lower electrode layer 110, an absorption layer 120, and an upper electrode layer 130. When the absorption layer 120 in Figure 2A is thinner, light L may pass through the entire absorption layer 120 in Figure 2A to reach the lower electrode layer 110, thereby generating a photocurrent (or voltage) pointing towards the upper electrode layer 130 at the interface between the lower electrode layer 110 and the absorption layer 120 in Figure 2A. This cancels out or reduces the photocurrent (pointing towards the lower electrode layer 110) originally generated between the upper electrode layer 130 and the absorption layer 120 in Figure 2A. The embodiment in Figure 3B differs from the embodiment in Figure 2A in that the absorption layer 120 in Figure 3B is made in an L-shape (stepped shape), and the lower electrode layer 110 is formed on the upper surface of the thinner portion of the absorption layer 120 to overcome the aforementioned problem of photocurrent cancellation.

[0033] Figure 3C illustrates a cross-sectional view of a photodetector 100c according to another embodiment of the present disclosure. Referring to Figure 3C, the photodetector 100c includes a lower electrode layer 110, an absorption layer 120, and an upper electrode layer 130. This embodiment differs from the embodiment in Figure 3B in that, in this embodiment, the photodetector 100c further includes a doped region 190. The doped region 190 is located below the lower electrode layer 110 and the absorption layer 120. The doped region 190 can increase the conductivity at the bottom of the photodetector 100c. In some embodiments, the doped region 190 comprises a heavily doped P-type semiconductor material that is homogeneous or heterogeneous with the absorption layer 120, but this does not limit the present disclosure.

[0034] For ease of fabrication, the design of the doped region 190 in Figure 3C can also be combined with the L-shaped absorption layer 120 in Figure 3B, with the doped region 190 fabricated below the L-shaped absorption layer 120 in Figure 3B, as shown in the photodetector 100d in Figure 3D.

[0035] Figure 4A illustrates a cross-sectional view of a photodetector 100e according to another embodiment of this disclosure. Referring to Figure 4A, the photodetector 100e includes a lower electrode layer 110, an absorption layer 120a, and an upper electrode layer 130a. The absorption layer 120a is located on the lower electrode layer 110, and the upper electrode layer 130a is located on the absorption layer 120a, configured to absorb electrons e in the photocurrent. This embodiment differs from the embodiment in Figure 2A in that, in this embodiment, the absorption layer 120a has a trench 124, and a portion of the upper electrode layer 130a is located within the trench 124. Since photoelectrons enter the upper electrode layer 130a through spontaneous thermal velocity and thermal scattering mechanisms, the number of photoelectrons entering the electrode is determined by their mean collision length. A higher electron mobility results in a longer mean collision length, representing more photoelectrons that can enter the electrode. However, generally, the mean collision length of electrons is much less than 1 micrometer, which results in a shallower depth of the positive charge generation region (active region) in this disclosure. However, the light penetration depth in the absorption layer 120 (as shown in the embodiment in Figure 2A) is typically greater than 1 micrometer, which results in a low internal quantum efficiency of the photodetector. Therefore, trenches 124 with an electrode pattern as shown in Figure 4A can be first drilled in the absorption layer 120a by means of etching or other methods, and then metal electrodes can be filled into the trenches 124. In this way, the range of electrons that can be collected will no longer be limited to the area around the electrodes near the surface (such as the boundary 131 of the upper electrode layer 130), but can increase with the increase of electrode depth (such as the depth of the photogenerated positive charge region 126).

[0036] Figure 4B illustrates a cross-sectional view of a photodetector 100f according to another embodiment of this disclosure. Referring to Figure 4B, the difference between this embodiment and the embodiment in Figure 4A is that, in this embodiment, the photodetector 100f further includes a high electron concentration region 180, and the high electron concentration region 180 is located between the lower electrode layer 110 and the absorption layer 120a. The high electron concentration region 180 is configured to provide a region where positive charge accumulation cannot occur.

[0037] Figure 5A illustrates a cross-sectional view of a photodetector 100g according to another embodiment of this disclosure. Referring to Figure 5A, the photodetector 100g 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 is a single material and does not contain homogeneous or heterogeneous junctions. This embodiment differs from the embodiment in Figure 1 in that, in this embodiment, the photodetector 100g further includes a substrate 140, which is located between the absorption layer 120 and the lower electrode layer 110. In some embodiments, the absorption layer 120 can be grown on any conductive substrate by epitaxy, chemical vapor deposition, a combination of the above, or other suitable methods. In some embodiments, if the difference between the lattice constant of the substrate 140 and the absorption layer 120 is too large, an additional epitaxial buffer layer 150 can be grown between the substrate 140 and the absorption layer 120, but this disclosure is not limited thereto.

[0038] Figure 5B illustrates a cross-sectional view of a photodetector 100h according to another embodiment of this disclosure. The photodetector 100h includes a lower electrode layer 110, an absorption layer 120, an upper electrode layer 130, a substrate 140, and a buffer layer 150. The difference between this embodiment and the embodiment in Figure 5A is that, in this embodiment, the lower electrode layer 110 is located in the recess 128 on the upper surface of the absorption layer 120. When the conductivity of the substrate 140 or the buffer layer 150 is insufficient or the resistance is too high, the photocurrent may not be able to pass through the substrate or the buffer layer. In this case, the lower electrode layer 110 is not suitable to be fabricated directly below the absorption layer 120. Instead, the absorption layer must be fabricated into an L-shape by means of etching or other methods. In this case, the lower electrode layer 110 is fabricated on the upper surface of the lower right recess 128 of the absorption layer.

[0039] The design of the upper electrode layer 130a in the trench 124 in Figure 4A can also be fabricated in the embodiments shown in Figures 3B, 3C, 3D, 5A, and 5B.

[0040] Figure 6 illustrates a cross-sectional view of a photodetector 100i according to another embodiment of this disclosure. Referring to Figure 6, the photodetector 100i includes an absorption layer 120, a lower electrode layer 110, a light-transmitting upper electrode layer 160, and a metallic upper electrode layer 170. The absorption layer 120 has a first surface 121 and a second surface 123, and the absorption layer 120 contains a material with an electron mobility greater than 300 cm² / Vs and greater than twice the hole mobility. The lower electrode layer 110 is located on the first surface 121 of the absorption layer 120. The light-transmitting upper electrode layer 160 is located on and completely covers the second surface 123 of the absorption layer 120, and the absorption layer 120 is configured to generate a photocurrent near the interface 162 between the light-transmitting upper electrode layer 160 and the absorption layer 120 by utilizing the large difference between the electron mobility and the hole mobility. When electron-hole pairs are generated in the absorption layer 120, photoelectrons e near the light-transmitting upper electrode layer 160 spontaneously enter the light-transmitting upper electrode layer 160 due to their higher thermal velocity, while photoholes h remain in the absorption layer 120 due to their lower thermal velocity. These remaining photoholes h generate positive charges near the interface 162 and produce a vertically downward electric field E and photovoltage in the absorption layer 120, thereby generating a photocurrent. In this embodiment, the first surface 121 and the second surface 123 are located on opposite sides of the absorption layer 120. The metal upper electrode layer 170 is located on the light-transmitting upper electrode layer 160, wherein the area of ​​the metal upper electrode layer 170 is smaller than the area of ​​the light-transmitting upper electrode layer 160. In this embodiment, the light-transmitting upper electrode layer 160 completely covers the absorption layer 120, therefore the ratio of the perimeter of the light-transmitting upper electrode layer 160 to the area of ​​the upper surface (i.e., the second surface 123) of the absorption layer 120 is very small. However, since the transparent top electrode layer 160 allows light L to pass through in this embodiment, the area capable of generating photogenerated charge e is almost the entire interface 162 between the transparent top electrode layer 160 and the absorption layer 120 (only a small area blocked by the metal top electrode layer 170 cannot generate photogenerated charge e). Because the transparent top electrode layer 160 must allow light L to pass through and for light L to be absorbed by the absorption layer 120 to generate photogenerated charge e, the band gap of the material of the transparent top electrode layer 160 must be larger than the band gap of the material of the absorption layer 120 to prevent light L from being absorbed at the transparent top electrode layer 160. Specifically, the band gap of the transparent top electrode layer 160 is greater than or equal to 1.5 times the band gap of the absorption layer 120. For example, in mid- and far-infrared detector applications, InSb with a band gap of 0.18 eV can be used as the absorption layer, paired with Ge with a band gap of 0.66 eV as the transparent top electrode layer. In some embodiments, the transparent top electrode layer 160 comprises an N-type semiconductor. In some embodiments, the absorption layer 120 comprises a P-type semiconductor. Furthermore, the transparent top electrode layer 160 requires appropriate doping to achieve sufficient carrier concentration and conductivity, but the internal carrier concentration cannot be so high as to cause free electron absorption, which would result in infrared light being absorbed by the transparent top electrode layer 160.Specifically, the electron concentration of the light-transmitting upper electrode layer 160 must be greater than 10¹⁷ cm⁻³. Meanwhile, to prolong the activity period of the holes, the electron concentration of the absorption layer 120 must also be minimized; the electron concentration of the absorption layer 120 must be less than 10¹⁴ cm⁻³.

[0041] Figures 7A, 7B, and 7C illustrate the band structure of the photodetector 100i in Figure 6 under different conditions. Referring to Figures 7A, 7B, and 7C, if the electron affinity of the transparent upper electrode layer 160 (generally n-type) is represented by χn, the work function of the transparent upper electrode layer 160 is represented by Φn, and the electron concentration of the transparent upper electrode layer 160 is represented by nn, the electron affinity of the absorption layer 120 (generally p-type) is represented by χp, the work function of the absorption layer 120 is represented by Φp, and the electron concentration of the absorption layer 120 is represented by np, then the transparent upper electrode layer 160 and the absorption layer 120 must satisfy the following relationship: nn≧1017 cm-3,np≦1014 cm-3; Furthermore, the light-transmitting upper electrode layer 160 and the absorption layer 120 must satisfy one of the following relationships:

[0042] If the case is Equation 2-1, the energy band structure between the transparent upper electrode layer 160 and the absorption layer 120 is shown in Figure 7A. If the case is Equation 2-2, the energy band structure between the transparent upper electrode layer 160 and the absorption layer 120 is shown in Figure 7B. If the case is Equation 2-3, the energy band structure between the transparent upper electrode layer 160 and the absorption layer 120 is shown in Figure 7C. This limitation is to prevent the photoelectrons e from being unable to enter the transparent upper electrode layer 160 from the absorption layer 120 due to a potential energy barrier formed at the interface 162 between the transparent upper electrode layer 160 and the absorption layer 120 during the thermal velocity or thermal scattering transmission process, which would result in the photoelectrons e failing to generate photovoltage and a decrease in the efficiency of the photodetector 100i.

[0043] Figure 8 illustrates a cross-sectional view of a photosensor 100j according to another embodiment of this disclosure. Referring to Figure 8, the photosensor 100j includes an absorption layer 120, a lower electrode layer 110, a light-transmitting upper electrode layer 160, and a metal upper electrode layer 170. This embodiment differs from the embodiment in Figure 6 in that, in this embodiment, the photosensor 100j may further include a high electron concentration region 180, whose electron concentration must be higher than 10¹⁴ cm⁻³. The high electron concentration region (layer) 180 is located between the lower electrode layer 110 and the absorption layer 120. When the absorption layer 120 is thinned during device fabrication, light L may pass through the entire absorption layer 120 to reach the lower electrode layer 110, thereby generating a photocurrent (or voltage) pointing towards the light-transmitting upper electrode layer 160 at the interface between the lower electrode layer 110 and the absorption layer 120. This cancels out the photocurrent (pointing towards the lower electrode layer 110) originally generated at the interface 162 between the light-transmitting upper electrode layer 160 and the absorption layer 120. The high electron concentration region 180 can then provide a region where positive charge accumulation cannot occur. In some embodiments, the high electron concentration region 180 contains a semiconductor of the same or different nature as the absorption layer 120, but this disclosure is not limited to this.

[0044] Figure 9A illustrates a cross-sectional view of a photodetector 100k according to another embodiment of this disclosure. Referring to Figure 9A, the photodetector 100k includes an absorption layer 120b, a lower electrode layer 110, a light-transmitting upper electrode layer 160, and a metal upper electrode layer 170. This embodiment differs from the embodiment in Figure 6 in that, in this embodiment, both the first surface 121 and the second surface 123 face the light source L, and the first surface 121 and the second surface 123 are disposed adjacent to each other and form a stepped surface. By changing the position of the lower electrode layer 110 to be offset horizontally from the light-transmitting upper electrode layer 160, the problem of light source L reaching the interface between the lower electrode layer 110 and the absorption layer 120b due to element thinning, thereby preventing the generation of photocurrent (or voltage) pointing towards the light-transmitting upper electrode layer 160, is avoided.

[0045] Figure 9B illustrates a cross-sectional view of a photodetector 100l according to another embodiment of this disclosure. Referring to Figure 9B, the photodetector 100l includes an absorption layer 120c, a lower electrode layer 110, a light-transmitting upper electrode layer 160, and a metal upper electrode layer 170. This embodiment differs from the embodiment in Figure 9A in that, in this embodiment, the photodetector 100l may further include a doped region 190. The doped region 190 is located below the lower electrode layer 110 and the absorption layer 120c. The doped region 190 can increase the conductivity at the bottom of the photodetector 100l. In some embodiments, the doped region 190 comprises a heavily doped P-type semiconductor material that is homogeneous or heterogeneous with the absorption layer 120c, but this does not limit the scope of this disclosure.

[0046] For ease of fabrication, the design of the doped region 190 in Figure 9B can also be combined with the L-shaped absorption layer 120b in Figure 9A, with the doped region 190 fabricated below the L-shaped absorption layer 120b in Figure 9A, as shown in the photodetector 100m in Figure 9C.

[0047] Although this disclosure is primarily designed for infrared light detection under uncooled conditions, in certain special cases, the inherent electron concentration at room temperature is too high due to the low bandgap of the absorber layer 120 material, such as InAs, InSb, InAsSb, and HgCdTe with bandgap below 0.4 eV. If the electron concentration cannot be reduced to the target concentration (e.g., 10¹⁴ cm⁻³) through p-type doping, it is still possible to reduce the electron concentration, extend the hole activity, and increase the photovoltage by operating at an appropriate low temperature.

[0048] The foregoing outlines the features of several embodiments, enabling those skilled in the art to better understand the nature of this disclosure. Those skilled in the art should understand that they can readily use this disclosure as the basis for designing or modifying other processes and structures to achieve the same objectives and / or advantages as the embodiments described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of this disclosure, and that various changes, substitutions, and alterations can be made to them without departing from the spirit and scope of this disclosure.

[0049] 100, 100a~100m: Light detector 110: Lower electrode layer 120, 120a, 120b, 120c: Absorption layers 121: First Surface 122: Upper surface 123: Second Surface 124: Trench 126: Photogenerated positive charge region 128: Depression 130, 130a: Upper electrode layer 131: Boundary 132: Interface 140:Substrate 150: Buffer layer 160: Transparent upper electrode layer 162: Interface 170: Metallic top electrode layer 180: High electron concentration region 190: Doped region D: Spacing E: Electric field e: electron, photogenerated charge h: Electric Hole L: Light L1: Length N: Quantity W: Width

[0050] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A photodetector comprising: a lower electrode layer; an absorption layer located on the lower electrode layer, wherein the absorption layer is a single material and does not contain homogeneous or heterogeneous junctions, the absorption layer comprising a material having an electron mobility greater than 300 cm² / Vs and greater than twice the hole mobility, the absorption layer being unbiased and self-powered; and an upper electrode layer located on an upper surface of the absorption layer, wherein a ratio of the perimeter of the upper electrode layer to an area of ​​the upper surface of the absorption layer is greater than 100 mm⁻¹, the absorption layer being configured to generate photocurrent and voltage by utilizing the large difference between the electron mobility and the hole mobility near an interface between the upper electrode layer and the upper surface of the absorption layer.

2. The photodetector as claimed in claim 1, wherein the top-view shape of the upper electrode layer is at least one of a comb-like, tree-like, mesh-like, or spiral shape.

3. The photodetector as claimed in claim 2, wherein the upper electrode layer is located in a trench of the absorption layer.

4. The photodetector as claimed 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.

5. The photodetector as claimed in claim 1 further comprises: a substrate located below the absorption layer and the lower electrode layer; and a buffer layer located between the substrate and the absorption layer.

6. The photodetector as claimed in claim 1 further comprises: a high electron concentration region located between the lower electrode layer and the absorption layer.

7. The photodetector as claimed in claim 1, wherein the absorption layer is L-shaped and stepped.

8. The photodetector as claimed in claim 7 further comprises: a doped region located below the lower electrode layer and the absorption layer.

9. A photodetector comprising: an absorption layer having a first surface and a second surface, wherein the absorption layer comprises a material having an electron mobility greater than 300 cm² / Vs and greater than twice the hole mobility, the absorption layer being unbiased and self-powered; and: a lower electrode layer located on the first surface of the absorption layer; a light-transmitting upper electrode layer located on and covering the second surface of the absorption layer, the absorption layer being configured to generate a photocurrent near an interface between the light-transmitting upper electrode layer and the absorption layer by utilizing the large difference between the electron mobility and the hole mobility, wherein an electron concentration of the light-transmitting upper electrode layer is denoted as nn, and an electron concentration of the absorption layer is denoted as np, and the light-transmitting upper electrode layer and the absorption layer must satisfy the following relationships: nn ≥ 10¹⁷ cm⁻³, np ≤ 10¹⁴ cm⁻³ The unit of the electron concentration is (cm-3); and a metal upper electrode layer is located on the light-transmitting upper electrode layer, wherein an area of ​​the metal upper electrode layer is smaller than an area of ​​the light-transmitting upper electrode layer.

10. The photodetector as claimed in claim 9, wherein a bandgap of the light-transmitting upper electrode layer is greater than or equal to 1.5 times the bandgap of the absorption layer.

11. The photodetector as claimed in claim 9, wherein the first surface faces away from the second surface.

12. The photodetector as claimed in claim 11 further comprises: a high electron concentration region located between the lower electrode layer and the absorption layer.

13. The photodetector as claimed in claim 9, wherein the first surface and the second surface are disposed adjacent to each other and form a stepped surface.

14. The photodetector as claimed in claim 13 further comprises: a doped region located below the lower electrode layer and the absorption layer.

15. The photodetector as described in claim 9, wherein an electron affinity of the transparent upper electrode layer is denoted as χn, a work function of the transparent upper electrode layer is denoted as Φn, an electron affinity of the absorption layer is denoted as χp, and a work function of the absorption layer is denoted as Φp, then the transparent upper electrode layer and the absorption layer must satisfy one of the following relationships: .

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