Self-driven photoelectric detector based on C8-BTBTT / 4H-SiC heterojunction and preparation method thereof

Abstract

The invention discloses a self-driven photoelectric detector based on a C8-BTBT / 4H-SiC heterojunction and a preparation method thereof.The self-driven photoelectric detector sequentially comprises a back electrode, an inorganic functional layer, an organic functional layer and a top electrode from bottom to top, the inorganic functional layer is a 4H-SiC substrate and an n-type doped 4H-SiC epitaxial wafer located on the 4H-SiC substrate, and the organic functional layer is an n-type doped 4H-SiC epitaxial wafer. The 4H-SiC substrate is located on the back electrode; and the organic functional layer is made of C8-BTBT. The ultraviolet photoelectric detector has plasticity controllable high-performance self-driving.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, specifically relating to a self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction and its fabrication method. Background Technology

[0002] Ultraviolet (UV) photodetectors, as key optoelectronic components in modern sensing, communication, and imaging systems, are increasingly valued for their wide application in military and civilian fields, including missile tracking, missile plume detection, short-range communication security, ozone hole monitoring, and chemical / biological analysis. As a wide bandgap material, silicon carbide possesses excellent material properties such as a bandgap value (~3.2 eV) highly suitable for UV detection, high thermal stability, and chemical stability, making it a promising candidate material for UV photodetectors. Silicon carbide-based photodetectors are attracting increasing attention. Simultaneously, facing the growing threat of the global energy crisis, there is an urgent need to develop self-powered photodetectors.

[0003] In recent years, researchers have continuously explored new strategies to improve the performance of self-driven ultraviolet photodetectors. Organic-inorganic heterojunctions have become one of the solutions for self-driven photodetectors, allowing for low-cost solution processing and large-area deposition. Benefiting from this advanced design concept, a series of fruitful studies have been conducted on self-driven photodetectors using organic-inorganic hybrid heterojunctions. The paper *Physica Scripta*, 2022, 075804, discloses the fabrication of an organic-inorganic hybrid P3HT / β-Ga2O3 deep ultraviolet detector by growing β-Ga2O3 thin films using metal-organic chemical vapor deposition and spin-coating with P3HT solution. A pn ​​heterojunction was formed at the interface between P3HT and β-Ga2O3, improving the light response and constructing a self-driven device. This device exhibits excellent photoelectric performance, with an ultra-low dark current of 0.18 pA and a W / W output of 57.2 mA. −1 High response rate and 1.47×10 17 Jones at 1 μW cm −2 0 V detectivity.

[0004] In 2023, Qi et al. prepared high doping concentration (10⁻⁶) 19 cm -3A hybrid PEDOT:PSS / SiC pn heterojunction was formed by bonding a special PEDOT:PSS hole transport layer to a 4H-SiC substrate via a simple solution spin-coating method. Utilizing the abundant carrier concentration in 4H-SiC and the large built-in field at the hetero interface, the designed ultraviolet photodetector achieved a record-breaking self-powered responsivity of 2.15 A / W and an external quantum efficiency of 1053% (Appl. Phys. Lett 2023, 12, 191102). The photocurrent and response speed were improved thanks to the formation of the built-in electric field. Despite significant efforts, effective strategies and related physical mechanisms for controlling the self-powered behavior of silicon carbide heterojunctions to further enhance power and performance advantages are still under development.

[0005] Therefore, it is particularly important to develop high-performance self-driven ultraviolet photodetector material systems, architectures, and fabrication processes based on SiC. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing an ultraviolet photodetector that combines advantages in both power consumption and performance.

[0007] This invention provides a self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction, comprising, from bottom to top, a back electrode, an inorganic functional layer, an organic functional layer, and a top electrode, wherein: The inorganic functional layer is a 4H-SiC substrate and an n-type doped 4H-SiC epitaxial wafer located on the 4H-SiC substrate, wherein the 4H-SiC substrate is located on the back electrode; The organic functional layer is C8-BTBT.

[0008] Preferably, the material of the back electrode is Ni. The back electrode provided in this embodiment of the invention is used for outputting power supply signals.

[0009] Preferably, the resistivity of the silicon carbide substrate is 30 mΩ·cm.

[0010] Preferably, the doping concentration of the n-type doped 4H-SiC epitaxial wafer is 10. 14-16 cm 3 .

[0011] Preferably, the thickness of the inorganic functional layer is 3-30µm.

[0012] Preferably, the thickness of the organic functional layer is 50-150 nm.

[0013] Preferably, the top electrode is made of Ag and is used for inputting external power supply electrical signals.

[0014] Furthermore, the present invention also provides a method for fabricating a self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction, comprising: Step S1: Clean and dry the inorganic functional layer; Step S2: Form a back electrode on the dried inorganic functional layer 4H-SiC substrate, and form a C8-BTBT organic functional layer on the n-type doped 4H-SiC epitaxial wafer. Step S3: Form a top electrode on the C8-BTBT organic functional layer.

[0015] Preferably, step S1 involves sequentially cleaning the inorganic functional layer in an ultrasonic cleaner using sulfuric acid, hydrofluoric acid, hydrochloric acid, and ethanol. After blowing away the moisture with nitrogen, it is then dried.

[0016] Preferably, forming a back electrode on a dried 4H-SiC substrate includes: forming a back electrode on one side of the inorganic functional layer using magnetron sputtering, and then annealing it to make an ohmic contact between the back electrode and the inorganic functional layer.

[0017] More preferably, the annealing temperature is 950℃-1050℃, and the annealing time is 10-30 min. At high temperatures, the nickel atoms provided in this embodiment of the invention can diffuse on the semiconductor surface, filling surface defects and reducing interface states, thereby lowering the interface resistance. This diffusion effect helps to form a low-resistance ohmic contact.

[0018] Preferably, a C8-BTBT organic functional layer is formed on an n-type doped 4H-SiC epitaxial wafer with an inorganic functional layer, comprising: C8-BTBT material was added to chlorobenzene, and impurities were removed by magnetic stirring and filtration to obtain a C8-BTBT solution. A C8-BTBT solution was coated onto an n-type doped 4H-SiC epitaxial wafer using a solution spin-coating method, followed by annealing to obtain a C8-BTBT organic functional layer.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention is the first to combine a C8-BTBT organic functional layer with a silicon carbide inorganic functional layer to form a heterostructure that builds an internal electric field, thereby improving the efficiency of the ultraviolet photodetector, effectively increasing the open-circuit current and enhancing the stability of the device.

[0020] This invention utilizes a silicon carbide micron-sized thin film as a "window" layer to effectively absorb short-wave ultraviolet radiation, thereby exciting abundant electron-hole pairs. Correspondingly, the C8-BTBT thin film exhibits light absorption concentrated in the ultraviolet band, while displaying low absorbance in the visible light region. This unique material combination significantly enhances the optical effect for ultraviolet photodetectors, substantially increasing the photocurrent output.

[0021] The SiC / C8-BTBT organic-inorganic heterojunction self-driven ultraviolet photodetector provided by this invention can achieve a self-powered photodetection mode, meaning it can convert optical signals to electrical signals even at zero bias voltage, generating electrical signals without an external power supply. This self-driven characteristic greatly simplifies the application circuit design of the detector, reduces system complexity and cost, and is suitable for commercial applications and scientific research. The PN heterojunction of C8-BTBT and SiC can effectively detect ultraviolet light, which is particularly important for short-wavelength ultraviolet light imaging, which is difficult to capture with traditional imaging techniques. This heterojunction can be used to develop novel high-sensitivity imaging devices, such as ultraviolet imagers, for medical diagnostics, bioimaging, and environmental monitoring. It lays the foundation for the application of organic-inorganic heterojunctions in ultraviolet detection and logic function implementation. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for fabricating a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction, provided in a specific embodiment of the present invention. Figure 2 This is a self-driven ultraviolet photodetector device structure based on a C8-BTBT / 4H-SiC heterojunction provided in a specific embodiment of the present invention; Figure 3 This is the morphology of a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction provided in a specific embodiment of the present invention under an atomic force microscope; Figure 4 This is a schematic diagram of the working mechanism of a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction under illumination, provided in a specific embodiment of the present invention. Figure 5 This is the optical absorption spectrum of a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction provided in a specific embodiment of the present invention; Figure 6 This is a specific embodiment of the invention providing the dark-state current-voltage curve of a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction, obtained by applying a voltage from 3V to -20V. Figure 7The specific embodiment of the present invention provides a photoexcited state current-voltage curve of a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction, with an applied voltage of 3V to -20V and an illumination of 315nm. Figure 8 This is a continuous current-time curve of a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction provided in a specific embodiment of the present invention, obtained by applying a voltage of 0V and illumination of 315nm ultraviolet light. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0024] This invention utilizes the technological accumulation of typical third-generation semiconductor silicon carbide materials to combine them with low-cost and biocompatible organic materials. This invention proposes a design concept of organic-inorganic hybrid interface, taking advantage of the easy stacking of two-port devices, to stack organic materials with inorganic silicon carbide materials, and finally prepare a high-performance self-driven ultraviolet photodetector with controllable plasticity. The organic semiconductor material C8-BTBT is selected mainly based on the following aspects: (1) The light absorption range of C8-BTBT film is concentrated in the ultraviolet band, while the light absorption in the entire visible region is weak, which produces a stronger light effect and a larger photocurrent for ultraviolet photodetectors; (2) The HUMO and LUMO energy levels of C8-BTBT and 4H-SiC form a type II heterojunction, which is conducive to realizing a larger built-in electric field to achieve self-driven characteristics; (3) C8-BTBT has a relatively high hole mobility (the hole mobility is as high as 43 cm). 2 V −1 s −1 (4) Benzothiophene [3,2-b] benzothiophene (BTBT) is a promising gas-stable semiconductor core structure; (5) The sulfur atoms in the π-chain of BTBT provide the possibility of defect passivation effect, which is beneficial to reduce surface defects and form high-quality interface contact.

[0025] like Figure 2As shown, a specific embodiment of the present invention provides a self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction, which includes, from bottom to top, a back electrode, an inorganic functional layer, an organic functional layer, and a top electrode. The inorganic functional layer is a 4H-SiC substrate and an n-type doped 4H-SiC epitaxial wafer located on the 4H-SiC substrate, with the 4H-SiC substrate situated on the back electrode. The organic functional layer is C8-BTBT. The top electrode in this specific embodiment is made of Ag, and the back electrode is made of Ni.

[0026] In the fabrication method of the self-driven ultraviolet photodetector based on C8-BTBT / 4H-SiC heterojunction of the present invention, a specific photodetector device is designed and fabricated by means of layer stacking. The fabrication steps include: fabricating a back electrode on the back side of the substrate; fabricating an organic functional layer on the inorganic functional layer; and finally fabricating a top electrode on the organic functional layer.

[0027] In the fabrication method of the self-driven ultraviolet photodetector based on C8-BTBT / 4H-SiC heterojunction of the present invention, the environmental conditions are: room temperature and air environment. In air, C8-BTBT exhibits good stability, is not easily oxidized or decomposed, and has good repeatability.

[0028] In specific embodiments of this application, the fabrication method of a self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction is as follows: Figure 1 As shown, the specific implementation steps are as follows: I. Substrate Preprocessing: (1) First, the silicon carbide substrate and the epitaxial silicon carbide (n-4H-SiC) were cleaned by using sulfuric acid, hydrofluoric acid, hydrochloric acid and ethanol in an ultrasonic cleaner at 100 kHz and 70% power for 10 minutes respectively.

[0029] (2) Use nitrogen to blow away the moisture on the surface of the substrate after operation (1) and put it into an electric heating drying oven for drying at 120°C for 30 minutes.

[0030] II. Fabrication of back electrode by magnetron sputtering: (1) The thin film formed in step one is placed in a magnetron sputtering coating equipment and pre-sputtered on one side of the silicon carbide substrate for 30s. The vacuum degree is controlled at 10-6 Pa and the sputtering rate is 3 Å / S to obtain a nickel electrode with a thickness of about 200 nm.

[0031] (2) Take the substrate out of the magnetron sputtering coating equipment and put it into the rapid annealing furnace (RTP) for high-temperature annealing. The annealing conditions are: high temperature annealing at 990℃ for one minute, followed by cooling to room temperature and taking it out to obtain the ohmic contact back electrode.

[0032] The annealing temperature for Ni electrodes is 950℃-1050℃, and the annealing time is 1 minute. At high temperatures, nickel atoms can diffuse on the semiconductor surface, filling surface defects and reducing interface states, thereby lowering the interface resistance. This diffusion effect helps to form low-resistance ohmic contacts.

[0033] III. Preparation of Organic Functional Layers by Solution Spin Coating (1) Pretreatment of C8-BTBT solution: Dissolve C8-BTBT material in chlorobenzene to form a 5 mg / ml solution, place it in a magnetic stirrer and stir magnetically for 12 h, and filter it once using a 0.45 μm organic filter head to remove impurities contained in the solution.

[0034] (2) The C8-BTBT functional layer is prepared by solution spin coating on an n-type doped 4H-SiC epitaxial wafer. The spin coating is performed at a speed of 3000 rpm for 40 seconds. The preferred speed range is 3000-5000 rpm, and the spin coating time can be 40-60 seconds.

[0035] (3) The organic functional layer film was annealed in air using a hot platform at a temperature of 60°C for 20 minutes to obtain a film with a thickness of 50-150 nm.

[0036] IV. Fabrication of Top Electrode using Magnetron Sputtering (1) The thin film formed in step 3 is placed in a magnetron sputtering coating equipment and pre-sputtered on C8-BTBT for 30s. The vacuum degree is controlled at 10-6pa and the sputtering rate is 3.5Å / S. A silver electrode with a thickness of about 80nm is obtained by sputtering metal and using a ring pattern mask (inner diameter 100μm, outer diameter 150μm).

[0037] (2) Remove the substrate from the magnetron sputtering coating equipment to obtain the self-driven ultraviolet photodetector based on the 4H-SiC heterojunction of the present invention.

[0038] Figure 1 This is a flowchart of the fabrication method of the self-driven ultraviolet photodetector based on the C8-BTBT / 4H-SiC heterojunction of the present invention. Figure 2 This invention relates to a self-driven ultraviolet photodetector device structure based on a C8-BTBT / 4H-SiC heterojunction.

[0039] Figure 3 This is the morphology of the self-driven ultraviolet photodetector based on the C8-BTBT / 4H-SiC heterojunction described in this invention under an atomic force microscope. Figure 4This is a schematic diagram illustrating the working mechanism of the self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction described in this invention under illumination. We believe that the device's excellent light response originates from the large number of upright crystals on the surface of the C8-BTBT thin film. These upright crystals grow randomly, and although the roughness (Ra=24.5 nm) is relatively large, we believe this morphological feature is beneficial for ultraviolet absorption, which in turn translates into a stronger ultraviolet light response. When the C8-BTBT thin film is exposed to ultraviolet light stimulation, the optical absorption process of the C8-BTBT thin film with upright-grown crystals differs from that of organic thin films with flat surfaces and low roughness. Due to the expanded photosensitive area and the back-and-forth reflection of light between the crystals, a portion of the light is absorbed, and another portion is reflected and then absorbed again by another crystal. In this process of multiple absorptions, the absorption and utilization of external photons are greatly improved, and the number of photogenerated charge carriers is significantly increased, effectively enhancing the device's current response under illumination.

[0040] Figure 5 The optical absorption spectrum of the self-driven ultraviolet photodetector based on the C8-BTBT / 4H-SiC heterojunction described in this invention is shown in the figure. It can be seen from the figure that the absorption of the C8-BTBT / SiC film is enhanced in the ultraviolet band compared with the single-layer SiC film. The analysis shows that there are two main reasons: (1) The intrinsic absorption range of the C8-BTBT film is concentrated in the ultraviolet band, and it has significant ultraviolet light absorption characteristics; (2) The interface coupling induced by the C8-BTBT / SiC heterojunction interface significantly enhances the ultraviolet light absorption.

[0041] Figure 6 The self-driven ultraviolet photodetector based on the C8-BTBT / 4H-SiC heterojunction described in this invention, through the current-voltage curve of the applied voltage from 3V to -20V, shows that the leakage current of the detector is at the pA level. As the voltage level increases, it exhibits the characteristic of maintaining a constant current level, which confirms its good ohmic contact and the good interface state formed at the SiC / C8-BTBT heterojunction.

[0042] Figure 7 The self-driven ultraviolet photodetector based on the C8-BTBT / 4H-SiC heterojunction described in this invention, through the application of voltages from 3V to -20V and illumination at 315nm, shows that under ultraviolet light irradiation with an intensity of 600uw / cm2, the detector exhibits a negative photocurrent at the nA level, while simultaneously increasing the dark-state current by 105, demonstrating its preliminary ultraviolet photodetection capability.

[0043] Figure 8The self-driven ultraviolet photodetector based on a C8-BTBT / 4H-SiC heterojunction described in this invention, through continuous current-time curves under a 0V applied voltage and 315nm ultraviolet illumination, exhibits a short-circuit current as high as 80nA at a zero bias voltage of 0V. This characteristic demonstrates that even without an external voltage, it can achieve the conversion of optical signals to electrical signals. Therefore, it can autonomously generate electrical signals without relying on an external power supply, thus endowing the photodetector with self-driving capability.

[0044] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction, characterized in that, From bottom to top, it includes a back electrode, an inorganic functional layer, an organic functional layer, and a top electrode, wherein: The inorganic functional layer is a 4H-SiC substrate and an n-type doped 4H-SiC epitaxial wafer located on the 4H-SiC substrate, wherein the 4H-SiC substrate is located on the back electrode; The organic functional layer is C8-BTBT.

2. The self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 1, characterized in that, The material of the back electrode is Ni.

3. The self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 1, characterized in that, The resistivity of the silicon carbide substrate is 30 mΩ·cm.

4. The self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 1, characterized in that, The doping concentration of the n-type doped 4H-SiC epitaxial wafer is 10. 14-16 cm 3 .

5. The self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 1, characterized in that, The thickness of the inorganic functional layer is 3-30µm.

6. The self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 1, characterized in that, The thickness of the organic functional layer is 50-150 nm.

7. The self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 1, characterized in that, The material of the top electrode is Ag.

8. A method for fabricating a self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction, characterized in that, include: Step S1: Clean and dry the inorganic functional layer; Step S2: Form a back electrode on the dried inorganic functional layer 4H-SiC substrate, and form a C8-BTBT organic functional layer on the n-type doped 4H-SiC epitaxial wafer. Step S3: Form a top electrode on the C8-BTBT organic functional layer.

9. The method for fabricating a self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 8, characterized in that, Forming a back electrode on a dried 4H-SiC substrate includes: forming a back electrode on one side of the inorganic functional layer using magnetron sputtering, followed by annealing to make the back electrode and the inorganic functional layer form an ohmic contact.

10. The method for fabricating a self-driven photodetector based on a C8-BTBT / 4H-SiC heterojunction according to claim 8, characterized in that, A C8-BTBT organic functional layer is formed on an n-type doped 4H-SiC epitaxial wafer with an inorganic functional layer, including: C8-BTBT material was added to chlorobenzene, and impurities were removed by magnetic stirring and filtration to obtain a C8-BTBT solution. A C8-BTBT solution was coated onto an n-type doped 4H-SiC epitaxial wafer using a solution spin-coating method, followed by annealing to obtain a C8-BTBT organic functional layer.

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