A room-temperature uncooled infrared photodetector based on an InGaAs triangular barrier structure

Abstract

This invention relates to the field of infrared photodetector research, specifically to a room-temperature uncooled infrared photodetector based on an InGaAs triangular barrier structure; from bottom to top, it comprises a substrate, an n-type doped III-V compound semiconductor layer, an i-type semiconductor layer, a δ-p-type doped III-V compound semiconductor layer, an i-type semiconductor layer, and an n-type doped III-V compound semiconductor layer, each of which is provided with electrodes; it can improve the problems of high background noise and low sensitivity caused by room temperature in traditional semiconductor photodetectors, and realize room-temperature infrared detection.

Description

Technical Field

[0001] This invention relates to the field of infrared photodetector research, specifically to a room-temperature uncooled infrared photodetector based on an InGaAs triangular barrier structure. Background Technology

[0002] Infrared photodetectors are widely used in astronomy (imaging stars in the infrared band), communications (fiber optic communications), and military applications (night vision imaging). Current infrared photodetectors can be divided into two categories based on their detection principles: semiconductor infrared detectors based on the photoelectric effect and thermal infrared detectors based on the infrared photothermal effect.

[0003] Semiconductor detectors based on the photoelectric effect have advantages such as high sensitivity, fast response speed, easy miniaturization, wavelength sensitivity, and easy pixelation. They are widely used in aerospace, missile guidance, infrared night vision, and other fields with high requirements for dynamic response speed, sensitivity, anti-interference, and imaging quality. However, because their signal-to-noise ratio is easily affected by temperature, they need to operate at low temperatures and therefore require cooling equipment. Thermosensitive detectors based on the infrared photothermal effect utilize the characteristic that the temperature rises after the sensitive element absorbs infrared light. Therefore, they have slow response speed, wide temperature spectrum characteristics, and low sensitivity, but do not require a cooling system, so the cost is lower.

[0004] The working principle of a semiconductor photodetector is that when incident light irradiates a semiconductor material, if the photon energy is greater than the bandgap, the photon energy is absorbed by the semiconductor, causing valence band electrons to jump to the conduction band, forming photogenerated electrons and holes. Since the absorption of photons by a semiconductor requires the photon energy to be greater than the semiconductor's bandgap, semiconductor materials used for infrared detection must have a small bandgap, such as narrow-bandgap semiconductor materials like PbS, HgCdTe, PbSnTe, InGaAs, InSb, and GaSb. To enable photogenerated electrons to generate an open-circuit voltage or form an external circuit current for detection, semiconductor infrared sensors are constructed with a PN or PIN structure, such as... Figure 1 and Figure 2 As shown.

[0005] For the PIN structure, an intrinsic I layer is added between the P-type layer and the N-type layer, which widens the width of the depletion layer under bias, increases the photon absorption efficiency, and suppresses the recombination of photogenerated electrons and holes.

[0006] To further improve the external quantum efficiency of infrared photodetectors, infrared detectors with semiconductor heterojunction structures were also designed, such as... Figure 3As shown in the diagram, in this band structure, the band steps of the P and I layers are located on the conduction band side, while the band steps of the N and I layers are located on the valence band side. Therefore, neither photogenerated electrons nor holes are hindered by the potential barrier, thus avoiding losses of photogenerated carriers at the interface and effectively suppressing recombination of photogenerated carriers, improving separation efficiency. Another advantage of this structure is that it can reduce the interference of forward diffusion current on the output signal. Because the P layer introduces a potential barrier in the conduction band, it hinders the injection of electrons from the I layer to the P layer caused by diffusion motion. Similarly, the injection of holes into the N layer is also suppressed, thus effectively reducing the impact of forward diffusion current on the device output. For devices with this structure, when selecting P and N layer materials, the band gap and electron affinity of the materials should be considered comprehensively to ensure that the conditions of this "stepped" band structure are met as much as possible. For the P layer material, the electron affinity should be as small as possible, and the band gap should not be too large to avoid the P layer material introducing a large band step in the valence band. For N-layer materials, the electron affinity should be similar to that of I-layer materials to avoid introducing large band steps in the conduction band. Therefore, material systems that satisfy this band structure are very limited, restricting their ability to detect different infrared wavelengths.

[0007] To avoid the limitation of material bandgap-dependent infrared photon wavelength selectivity, infrared photodetectors with quantum wells and superlattice structures have also been developed. For example... Figure 4 (a) and Figure 4 As shown in (b), superlattices can suppress Auger recombination through band structure design. Their effective electronic mass, especially in long-wave infrared superlattice materials, is relatively large, which is beneficial for suppressing tunneling current. Furthermore, this technology is based on relatively mature III-V compound semiconductor materials, achieving good material and device consistency. In addition, the detection wavelength is easily adjustable; different wavelength ranges can be obtained by changing the quantum well width and barrier height. Moreover, the spectral response bandwidth is narrow, and optical crosstalk between different bands is low, enabling dual-color and multi-color infrared detection.

[0008] However, semiconductor infrared photodetectors with the aforementioned structures are highly susceptible to thermal noise, requiring cooling equipment and operation at low temperatures to achieve a good signal-to-noise ratio. This is because electrons in the valence band can transition to the conduction band not only through photoexcitation but also through thermal excitation, resulting in a large dark current at room temperature, low gain of the photoelectric signal, and a poor signal-to-noise ratio. To suppress dark current, infrared detectors need to operate at low temperatures. Summary of the Invention

[0009] In order to overcome the shortcomings of the prior art, the present invention aims to provide a room temperature uncooled infrared photodetector with a triangular barrier structure, which can improve the problems of large background noise and low sensitivity caused by the influence of room temperature on traditional semiconductor photodetectors, and realize room temperature infrared detection.

[0010] To achieve the above objectives, the present invention employs the following technical solution:

[0011] The present invention provides a room temperature uncooled infrared photodetector with a triangular barrier structure, comprising, from bottom to top, a substrate, an n-type doped III-V compound semiconductor layer, an i-type semiconductor layer, a δ-p-type doped III-V compound semiconductor layer, an i-type semiconductor layer, and an n-type doped III-V compound semiconductor layer; each of the n-type doped III-V compound semiconductor layers is provided with electrodes.

[0012] Preferably, the substrate is a III-V semiconductor substrate.

[0013] Preferably, the III-V semiconductor substrate is an InP substrate.

[0014] Preferably, the δ-p-type doped III-V compound semiconductor layer is an InGaAs layer, and the p-type doping element is Mg.

[0015] Preferably, the n-type doped III-V compound semiconductor layer is an InGaAs layer.

[0016] Preferably, the i-type semiconductor layer is an InGaAs layer.

[0017] Preferably, the bandgap of the InGaAs layer is 0.8 eV.

[0018] Preferably, the height of the triangular barrier structure of the detector is 0.7 eV.

[0019] Preferably, the thickness of the δ-p-type doped III-V compound semiconductor layer is [missing information].

[0020] Preferably, the thickness of the n-type doped III-V compound semiconductor layer is on the micrometer scale.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention establishes a triangular barrier band structure using n-type doped III-V compound semiconductor layers, i-type semiconductor layers, δ-p-type doped III-V compound semiconductor layers, and n-type doped III-V compound semiconductor layers. This invention transforms the traditional photocurrent response based on photogenerated carriers into an indirect photocurrent response achieved by adjusting the barrier height through photon injection. This improves the problems of high background noise and low sensitivity in traditional semiconductor photodetectors caused by room temperature variations. Furthermore, this invention converts the illumination response into a change in the triangular barrier height, and since the current has an exponential relationship with the barrier height, the accumulation of thermally excited carriers at the barrier in dark environments does not affect the subsequent reduction in barrier height caused by photogenerated carriers. This effectively improves the on / off ratio and sensitivity of the photodetector, enabling room-temperature infrared detection. Attached Figure Description

[0023] Figure 1 A schematic diagram illustrating the process by which a PN junction absorbs infrared light and converts it into an electrical signal.

[0024] Figure 2 A schematic diagram illustrating the process by which a PIN junction absorbs infrared light and converts it into an electrical signal.

[0025] Figure 3 An infrared photodetector with a heterojunction structure having electron and hole barriers.

[0026] Figure 4 (a) is a schematic diagram of a superlattice;

[0027] Figure 4 (b) is a schematic diagram of a quantum well;

[0028] Figure 5 This is a schematic diagram of the epitaxial structure of the triangular barrier infrared photodetector of the present invention;

[0029] Figure 6 This is a schematic diagram of the band structure of the triangular barrier infrared photodetector of the present invention;

[0030] Figure 7 This is a schematic diagram showing the change in barrier height of the triangular barrier infrared photodetector before and after illumination according to the present invention.

[0031] Figure 8 This is a schematic diagram showing the changes in photocurrent and dark current with respect to bias voltage of the triangular barrier infrared photodetector of the present invention.

[0032] Figure 9 This is a schematic diagram of the triangular barrier epitaxial wafer structure of the present invention;

[0033] Figure 10 This is a schematic diagram of the triangular barrier band structure of the present invention;

[0034] Figure 11 This is a top view of the triangular barrier infrared photodetector of the present invention;

[0035] Figure 12 This is a graph showing the infrared detection performance of the triangular barrier infrared photodetector of the present invention. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0038] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0040] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0041] The present invention will now be described in further detail with reference to the accompanying drawings:

[0042] This invention provides a room-temperature uncooled infrared photodetector with a triangular barrier structure based on III-V compound semiconductors. From bottom to top, it comprises a substrate, an n-type doped III-V compound semiconductor layer, an i-type semiconductor layer, a δ-p-type doped III-V compound semiconductor layer, another i-type semiconductor layer, and an n-type doped III-V compound semiconductor layer. Each n-type doped III-V compound semiconductor layer has electrodes. The nipin semiconductor growth structure forms a triangular barrier band structure, enabling infrared photodetection. The substrate serves as the support structure for the detector, providing a stable mechanical foundation for the entire device. The n-type doped III-V compound semiconductor layer serves as the initial conductive layer of the detector, providing free electrons through n-type doping to participate in the conduction process. Simultaneously, this layer also serves as the incident layer for infrared radiation, receiving and absorbing infrared radiation. The i-type semiconductor layer, as the intrinsic layer, has conductivity between that of the n-type and δ-p-type doped III-V compound semiconductor layers. The i-type semiconductor layer mainly acts as a transition and buffer, helping to reduce lattice mismatch and stress at the interface, thus improving the stability and performance of the device. The δ-p-type doped III-V compound semiconductor layer provides holes through p-type doping, forming a pn junction with the n-type layer. Under infrared radiation, the holes in this layer recombine with the free electrons in the n-type layer, generating a photocurrent.

[0043] This invention epitaxially grows an n-type doped III-V compound semiconductor layer, an i-type semiconductor layer, a p-type doped compound semiconductor layer, an i-type semiconductor layer, and an n-type doped III-V compound semiconductor layer on a III-V semiconductor substrate, forming a structure having... Figure 5 The epitaxial structure shown and Figure 6 The device shown has a band structure.

[0044] When infrared light with photon energy greater than the bandgap is incident, holes migrate into the p-type doped compound semiconductor layer within the valence band and accumulate in the p-type doped compound semiconductor layer, causing the barrier height to decrease. When a bias voltage is applied to the device, the current density has an exponential inverse relationship with the barrier height, as shown in equation (1):

[0045]

[0046] Therefore, the device will generate a significant photocurrent gain. Here, A is the proportionality coefficient, T is the temperature, q is the carrier charge, φ0 is the barrier height, and V... B is the bias voltage, and k is the Boltzmann constant.

[0047] like Figure 7As shown, under dark conditions, when a bias voltage VB is applied, the dark current is very small because electrons must pass through a potential barrier of height φ0 to form a current. Under illumination, when the incident photon energy is greater than the band gap, photogenerated electrons and photogenerated holes are generated in the conduction band EC and valence band EV, respectively. The photogenerated holes move towards the p-layer, i.e., the barrier layer, under the built-in electric field formed by doping, and gradually accumulate. The accumulation of holes leads to a decrease in the potential barrier, thus resulting in a significant current gain under illumination. The ratio of photocurrent to dark current is:

[0048]

[0049] Among them, I light For photocurrent, I dark For dark current, φ0 * φ0 is the barrier height under illumination, q is the charge of the charge carriers, k is the Boltzmann constant, and T is the temperature.

[0050] like Figure 8 As shown, the current gain caused by illumination is exponentially proportional to the change in barrier height. The change in barrier height, in turn, depends on the concentration of photogenerated holes, i.e., it is proportional to the external quantum efficiency and the illumination intensity. When the illumination intensity increases, the concentration of photogenerated holes increases, the change in barrier height becomes larger, and therefore the photocurrent increases exponentially.

[0051] The substrate is a III-V semiconductor substrate, specifically an InP substrate. The InP substrate and the n-type doped III-V compound semiconductor layer exhibit excellent lattice matching. The n-type doped III-V compound semiconductor layer grown on the InP substrate can have a lower defect density and higher crystal quality, thus contributing to improved detector performance and stability. InP material has high thermal conductivity, which helps the detector effectively dissipate heat during operation, preventing performance degradation or failure due to overheating and ensuring the detector's reliability under long-term, high-power-density operating conditions.

[0052] The δ-p-type doped III-V compound semiconductor layer, n-type doped III-V compound semiconductor layer, and i-type semiconductor layer are all InGaAs layers. This ensures material consistency between the layers within the detector, helps reduce lattice mismatch and stress at the interfaces, lowers defect density, and thus improves the crystal quality and overall performance of the detector. Secondly, InGaAs material has a tunable band structure; by adjusting the In and Ga composition ratio, the spectral response range of the detector can be optimized. Particularly in the infrared band, InGaAs exhibits excellent absorption characteristics, enabling the detector to efficiently receive and convert infrared radiation into electrical signals. Furthermore, InGaAs material has a low dark current density, which helps reduce the detector's noise level and improve the signal-to-noise ratio. Especially under low-light conditions, low dark current is crucial for ensuring the detector's sensitivity and accuracy.

[0053] The p-type dopant is Mg, which can effectively introduce holes into the InGaAs layer, forming a stable p-type conductive channel. The combination of the Mg-doped p-type InGaAs layer and the n-type InGaAs layer can form a high-quality pn junction, which helps to improve the photoelectric conversion efficiency and response speed of the detector.

[0054] The bandgap of the InGaAs layer is 0.8 eV, corresponding to a wavelength of approximately 1.55 μm (according to the photon energy formula E = hν = hc / λ, where E is the photon energy, h is Planck's constant, ν is the photon frequency, λ is the wavelength, and c is the speed of light). The detector exhibits excellent spectral response characteristics in the infrared band, particularly in the near-infrared and mid-infrared regions. By adjusting the composition ratio of In and Ga, the bandgap of the InGaAs layer can be further fine-tuned to optimize the spectral response range of the detector and better match the wavelength of the target infrared radiation.

[0055] The detector's triangular barrier structure has a height of 0.7 eV, creating an effective electric field within the detector. This field facilitates the separation and migration of photogenerated carriers (electrons and holes) to their respective electrodes. A higher barrier height more effectively prevents carrier recombination, thereby improving the detector's photoelectric conversion efficiency. Simultaneously, this electric field helps reduce the detector's dark current, improving the signal-to-noise ratio. Due to the optimal match between the InGaAs layer's bandgap and the triangular barrier structure height, the detector can more effectively absorb and convert infrared radiation into electrical signals, contributing to improved quantum efficiency—the probability of each incident photon generating a photoelectron. This allows the detector to capture more infrared radiation energy, thereby enhancing its sensitivity and response speed.

[0056] Furthermore, the thickness of the δ-p type doped III-V compound semiconductor layer is The thickness of the n-type doped III-V compound semiconductor layer is on the micrometer scale.

[0057] Figure 9 This is a schematic diagram of the triangular barrier epitaxial wafer structure of the present invention; Figure 10 This is a schematic diagram of the triangular barrier band structure of the present invention; the present invention can control the sensitive wavelength of the sensor by adjusting the In / Ga ratio. The present invention uses In... 0.5 Ga 0.5 Taking As as an example, its sensitive wavelength is <1500nm (the test used 1300nm infrared). Increasing the In content shifts the wavelength towards longer wavelengths; increasing the Ga content shifts the wavelength towards shorter wavelengths. 0.5 Ga 0.5 The band gap of As is approximately 0.8 eV, and the height of the triangular barrier of the homojunction constructed through doping is approximately 0.7 eV. Insulation and isolation of the device are achieved through etching, such as... Figure 11 As shown, the individual device has a size of 50 μm and a photosensitive area size of 30 μm. Its detection performance for infrared light with a wavelength of 1300 nm is as follows: Figure 12 As shown.

[0058] In summary, this invention provides a novel infrared photosensor with a band structure (triangular barrier), enabling room-temperature, uncooled infrared detection and exhibiting higher photocurrent gain and photoresponsivity compared to existing infrared sensors. This invention transforms the traditional photocurrent response based on photogenerated carriers into an indirect response achieved by adjusting the barrier height through photon injection. This new structure and photocurrent response mechanism improves upon the problems of high background noise and low sensitivity in traditional semiconductor photodetectors caused by room temperature variations. In traditional diode-structured infrared photodetectors, the photocurrent intensity is directly proportional to the concentration of photogenerated carriers, i.e., proportional to the light intensity. However, under dark conditions, due to the small bandgap of the semiconductor material used in infrared photodetectors, thermally excited carriers become the main factor in dark current. Therefore, in low light intensity, the concentrations of photogenerated and thermally excited carriers are similar, resulting in a small switching ratio for the detector, hindering infrared detection applications. This invention converts the light response into a change in the height of a triangular potential barrier. The current has an exponential relationship with the barrier height, and the accumulation of thermally excited charge carriers at the barrier in a dark environment does not affect the subsequent reduction in barrier height caused by photogenerated charge carriers. This can effectively improve the on / off ratio and sensitivity of the photodetector and achieve room temperature infrared detection.

[0059] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A room-temperature uncooled infrared photodetector with a triangular barrier structure, characterized in that, From bottom to top, the structure includes a substrate, an n-type doped III-V compound semiconductor layer, an i-type semiconductor layer, a δ-p-type doped III-V compound semiconductor layer, an i-type semiconductor layer, and an n-type doped III-V compound semiconductor layer; each of the n-type doped III-V compound semiconductor layers is provided with an electrode.

2. The room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 1, characterized in that, The substrate is a III-V semiconductor substrate.

3. The room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 2, characterized in that, The III-V semiconductor substrate is an InP substrate.

4. The room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 1, characterized in that, The δ-p-type doped III-V compound semiconductor layer is an InGaAs layer, and the p-type doping element is Mg.

5. A room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 1, characterized in that, The n-type doped III-V compound semiconductor layer is an InGaAs layer.

6. A room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 5, characterized in that, The i-type semiconductor layer is an InGaAs layer.

7. A room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 4 or 6, characterized in that, The bandgap of the InGaAs layer is 0.8 eV.

8. A room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 1, characterized in that, The height of the triangular barrier structure of the detector is 0.7 eV.

9. A room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 1, characterized in that, The thickness of the δ-p-type doped III-V compound semiconductor layer is 10. A room-temperature uncooled infrared photodetector with a triangular barrier structure according to claim 1, characterized in that, The thickness of the n-type doped III-V compound semiconductor layer is on the micrometer scale.

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