Preparation method of novel bifunctional ultraviolet detector based on NiO / SiC heterojunction

Abstract

The invention belongs to the technical field of semiconductor photoelectric devices and sensors, and discloses a preparation method of a novel bifunctional ultraviolet detector based on NiO / SiC heterojunction. A SiC single crystal substrate is used as a device base structure and an electron donor, an ohmic contact metal electrode is prepared on a carbon cut-off surface of the SiC single crystal substrate, and a NiO thin film is deposited on a Si cut-off surface; when the device is used for photovoltaic mode detection, metal or metal oxide is partially deposited on the surface of the NiO thin film to serve as a top electrode so as to form ohmic contact for photoelectric signal acquisition; when the device is used in a PEC mode, the NiO surface is directly exposed to the electrolyte for a photoelectrochemical reaction. The obtained device has both photovoltaic type and photoelectrochemical PEC type ultraviolet response capabilities, can realize stable and efficient ultraviolet detection under the condition of no external bias voltage, is suitable for low-power-consumption and multi-scene ultraviolet light detection application requirements, and has outstanding technical innovation and wide application prospects.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic devices and sensors, specifically relating to a method for fabricating a dual-function ultraviolet detector based on a NiO / SiC heterostructure, and in particular an ultraviolet detector that combines photovoltaic and photoelectrochemical responses. Background Technology

[0002] Light with wavelengths ranging from 100 to 400 nm is called ultraviolet (UV) light, which is generally divided into three bands: UV-A (320-400 nm), UV-B (280-320 nm), and UV-C (100-280 nm). Due to its high photon energy and unique interactions with matter, UV light has wide applications in environmental monitoring, sterilization, biomedical diagnostics, and advanced optical communication. However, UV light poses potential hazards to both humans and materials. Prolonged exposure can cause DNA damage, skin aging, and even cancer; it can also lead to photodegradation of polymer materials, affecting their performance and lifespan. Therefore, detecting and identifying UV light is crucial. Currently, commercially available UV photodetectors are mainly silicon photodiodes and photomultiplier tubes (PMTs), both of which have significant limitations: due to the narrow bandgap of silicon, silicon photodiodes rely on external filters to improve selectivity; PMTs are bulky, fragile, and require high operating voltages, making them unsuitable for many applications. Therefore, there is an urgent need to develop higher-performance, more stable, and self-powered UV photodetectors to meet diverse application requirements.

[0003] Silicon carbide (SiC) is a key representative of third-generation semiconductor materials, maintaining excellent electronic properties even under extreme operating environments such as high temperature, high frequency, high voltage, and strong radiation. Among the many crystal forms of SiC, 4H-SiC exhibits superior performance, including a wide band gap (3.26 eV) and high thermal conductivity (4.9 W·cm⁻¹). -1 ·K-1), high electron saturation drift rate (2×10 7 cm s -1The excellent radiation resistance and outstanding chemical stability of SiC make it an ideal material for ultraviolet photodetectors used in harsh environments. Furthermore, 6H-SiC substrates, due to their relatively wide bandgap (3.0 eV), also have application potential in ultraviolet detectors. However, the fabrication of intrinsic SiC homojunction (pn or pin junction) devices typically requires extremely high temperatures (>1600℃). This high-temperature process is not only costly but also prone to introducing lattice defects, thus affecting the photoelectric performance of the device. Therefore, there are few reports on self-powered photodetectors based on SiC homojunctions, and their performance has not reached ideal levels. To address these issues, constructing heterojunction pn junctions of SiC is a highly feasible and flexible alternative. By combining commercially available n-type SiC substrates with other materials that are easily realized as p-type, the technical bottlenecks of homojunction structures can be effectively avoided, and device performance can be optimized through band engineering and interface modulation, providing greater material and process freedom for device structure design.

[0004] Oxide materials, due to their unique ferroelectric, ferromagnetic, piezoelectric, dielectric, photoelectric, and superconducting properties, exhibit broad application potential in heterostructure devices. Combining functional oxides with traditional wide-bandgap semiconductors can endow devices with more degrees of controllability, potentially breaking through the performance limitations of conventional semiconductor structures. NiO, a typical p-type oxide semiconductor, possesses a wide bandgap (3.7–4.0 eV), stable physicochemical properties, and good doping controllability [Suzuki, A., Jpn. J. Appl. Phys., 2016, 55: 121001], and is widely used in transparent electronic devices and optoelectronic devices. Constructing a heterostructure pn junction with NiO and n-type SiC can create a built-in electric field, effectively separating photogenerated carriers, thereby realizing a self-powered photodetector with ultraviolet response. This heterostructure not only avoids the high-temperature doping and complex annealing processes required for SiC homostructures, but also utilizes the high bandgap advantage of NiO to help improve the spectral selectivity and response efficiency of the device in the short-wave ultraviolet (especially UVC) region. Furthermore, NiO has a relatively low deposition temperature, making it suitable for large-area fabrication and offering good compatibility. On the other hand, NiO also exhibits excellent photoresponse behavior in photoelectrochemical (PEC) systems. When a NiO / SiC heterostructure forms a solid-liquid interface with an electrolyte, holes generated on the NiO surface can participate in the oxidation reaction under ultraviolet light irradiation, while electrons are transferred to the counter electrode through an external circuit, resulting in a significant photocurrent response. This type of PEC device has advantages such as simple structure, no need for external bias voltage, and low dark current, making it particularly suitable for underwater ultraviolet light detection.

[0005] In summary, based on the NiO / SiC heterostructure, both pn-type self-powered ultraviolet photodetectors and PEC-type photoelectrochemical ultraviolet detectors can be constructed simultaneously, possessing advantages such as high stability, fast response, and low power consumption, and showing broad application prospects in various practical application scenarios. Although NiO / SiC heteropn junctions have been reported in the literature, related research mainly focuses on material properties or basic electrical properties, and there are no reports of the application of this structure in practical ultraviolet photodetector devices. In particular, realizing photovoltaic (self-powered) ultraviolet detection functions in solid-state devices, and constructing photoelectrochemical (PEC) ultraviolet detectors based on this structure, are currently still in the research gaps. Therefore, developing a dual-function ultraviolet detector based on the NiO / SiC heterostructure has outstanding technological innovation and broad application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a dual-functional ultraviolet photodetector based on a NiO / SiC heterostructure. This device possesses both photovoltaic and photoelectrochemical (PEC) ultraviolet response capabilities, enabling stable and efficient ultraviolet detection without an external bias voltage. It is suitable for low-power, multi-scenario ultraviolet light detection applications. Specifically, the technical solution adopted by this invention is as follows:

[0007] A novel method for fabricating a bifunctional ultraviolet detector based on a NiO / SiC heterojunction includes the following steps:

[0008] (1) SiC single crystal substrate is selected as the basic structure of the device and electron donor;

[0009] (2) Fabrication of ohmic contact metal electrodes with carbon cut-off surfaces on SiC single crystal substrates:

[0010] First, metal is deposited on the carbon cutoff surface of the SiC single crystal substrate described in step (1) and then annealed to form a channel for connecting to external circuits and providing a stable electron output channel.

[0011] (3) Deposition of p-type NiO thin film:

[0012] The Si cutoff surface of the SiC single crystal substrate is surface treated, and then p-type NiO is grown on the Si cutoff surface of the SiC single crystal substrate by pulsed laser deposition (PLD), magnetron sputtering or molecular beam epitaxy to form a p-type NiO thin film layer, which forms a heterojunction with SiC.

[0013] (4) When the device is used for photovoltaic mode detection, metal or metal oxide is partially deposited on the surface of the p-type NiO thin film layer as the top electrode to form an ohmic contact for photoelectric signal acquisition, which is called a photovoltaic ultraviolet detector.

[0014] When the device is used in photoelectrochemical PEC mode, the surface of the p-type NiO thin film layer is directly exposed to the electrolyte for photoelectrochemical reactions, and it is called a photoelectrochemical ultraviolet detector.

[0015] In step (1), the SiC single crystal substrate includes an n-type 4H-SiC or an n-type 6H-SiC single crystal substrate, and the doping concentration is controlled at 10. 16 -10 20 cm -3 Within the range.

[0016] In step (2), the deposited metal includes Ni, Ti, Al or Au, or a multilayer structure or alloy formed by a combination of them.

[0017] In step (2), an ohmic contact is formed on the carbon cutoff surface of the SiC substrate: a conductive layer is first deposited on the carbon cutoff surface, followed by conventional annealing, so that the conductive layer and SiC are transformed into a stable, low-resistance ohmic interface, thereby achieving efficient collection of charge carriers and external circuit output. Apart from the functional requirement of "forming an ohmic contact", this step does not impose specific limitations on the metal composition of the conductive layer, the deposition method and the annealing conditions, which can be selected and optimized by those skilled in the art according to conventional processes.

[0018] In step (3), the surface treatment methods include: immersion in one or more of a 10% hydrofluoric acid aqueous solution or oxide buffered etchant (BOE) to remove the oxide layer, ultraviolet ozone treatment to remove organic residues, plasma bombardment to activate the surface state, or thermal annealing in an inert atmosphere to improve interface cleanliness and crystal quality.

[0019] In step (3), the p-type NiO includes undoped p-type NiO, or p-type NiO whose p-type characteristics are further enhanced by Li or Ag doping. Low-temperature deposition is used to prevent damage to the SiC surface and to protect the interface between p-type NiO and SiC. Pulsed laser deposition (PLD), molecular beam epitaxy (MBE), magnetron sputtering (PVD), atomic layer deposition (ALD), or sol-gel method can be used. The deposition thickness is 50 to 200 nm.

[0020] The typical conditions for pulsed laser deposition (PLD) are 193-1064 nm laser and 0.5-3 J cm⁻¹. -2 Energy density, 1-20 Hz, substrate temperature from room temperature to 300°C, oxygen partial pressure 10 -5 -10Pa;

[0021] Among them, molecular beam epitaxy (MBE) at 10 -8 -10 -5 Under ultra-high vacuum of Pa, high-purity Ni was used as the Ni beam source, and O2 / O3 jet plasma source was used to assist Ni beam growth, with the substrate temperature ranging from room temperature to 300℃.

[0022] Among them, the working pressure of magnetron sputtering PVD is 0.2-1Pa, the target power is 20-150W, the O2 / Ar volume ratio is 0.1-1.5, and the substrate is room temperature to 300℃;

[0023] The atomic layer deposition (ALD) temperature is 150-350℃, with alternating pulses of Ni organic precursor and O3 (or O2 plasma);

[0024] Among them, the sol-gel method uses 0.05-0.5 mol L. -1 Spin-coating the Ni(NO3)2 solution at 1000-4000 rpm and then annealing at below 400℃ for 10-60 min.

[0025] In step (4), in the photovoltaic ultraviolet detector, the top electrode on the surface of the p-type NiO thin film layer is made of conductive metal materials Au, Pt, Ni, or Ag to form a ring or grid, or a transparent ITO electrode, to meet the requirements of ultraviolet transmission and signal output. When the top electrode is made of conductive metal material, it can be deposited by magnetron sputtering or electron beam deposition, with a deposition thickness of 50 to 200 nm; when the top electrode is a transparent ITO electrode, it can be deposited by magnetron sputtering or PLD deposition, with a deposition thickness of 100 to 200 nm.

[0026] The top electrode described in step (4) can be deposited under conventional process conditions on conventional magnetron sputtering, electron beam evaporation or pulsed laser deposition equipment in the art; unless otherwise stated, the other deposition parameters are not specifically limited.

[0027] In step (4), when the device is operating in photoelectrochemical (PEC) mode, the surface of the p-type NiO thin film layer can be directly exposed to the liquid, forming a PEC system with the external reference electrode and the counter electrode, so that photogenerated carriers under ultraviolet light can participate in the redox reaction, thereby outputting a photoelectrochemical current signal.

[0028] The beneficial effects of this invention are:

[0029] This invention marks the first application of a NiO / SiC heterostructure in a photovoltaic ultraviolet (UV) detection device. The device generates a stable photoelectric response without an applied bias voltage, exhibiting typical self-powered pn junction characteristics. Furthermore, this invention is the first to use this heterostructure for photoelectrochemical (PEC) UV detection. The device demonstrates excellent photoresponse capability at the solid-liquid interface and can operate stably in a real seawater environment, exhibiting superior response performance and chemical stability. These functionalities have not been publicly reported in existing technologies, filling a technological gap in the application of NiO / SiC heterostructures in photovoltaic and PEC-type UV detection, demonstrating outstanding innovation and broad application prospects. Attached Figure Description

[0030] Figure 1 The graph shows the time response curves of light intensity and photocurrent of a NiO / SiC photovoltaic ultraviolet detector under ultraviolet irradiation.

[0031] Figure 2 The graph shows the time response curves of light intensity and photocurrent of the NiO / SiC PEC ultraviolet detector under ultraviolet irradiation.

[0032] Figure 3 This is a graph showing the cyclic stability test of the NiO / SiC PEC ultraviolet detector in a real seawater environment. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The accompanying drawings and the following embodiments are only for illustrating the invention and are not intended to limit the invention.

[0034] The present invention will be further illustrated by the following embodiments.

[0035] Example 1:

[0036] A novel bifunctional ultraviolet detector based on NiO / SiC heterojunction:

[0037] (1) An n-type 4H-SiC(0001) single crystal substrate with a doping concentration of 1×10⁻⁶ was selected. 19 cm -3 ;

[0038] (2) Fabrication of SiC ohmic contact metal electrode:

[0039] Ni / Au (Ni: 20nm, Au: 80nm) was deposited on the carbon cutoff surface of a SiC substrate using electron beam evaporation, followed by annealing at 900°C for 5 minutes in nitrogen to form a stable ohmic contact.

[0040] (3) Deposition of p-type NiO thin film:

[0041] The SiC substrate was cleaned using BOE, and PLD deposition was performed on its Si cutoff surface. The target material used was intrinsic p-type NiO, and the deposition oxygen pressure was 3.0 × 10⁻⁶. -3 The deposition temperature was room temperature, and the film thickness was controlled at approximately 50 nm.

[0042] (4) When the device is used for photovoltaic mode detection, a Ni metal grid is formed on the surface of the p-type NiO thin film layer to form an ohmic contact for photoelectric signal acquisition;

[0043] When the device is used in PEC mode, the p-type NiO surface can be exposed to the electrolyte for photoelectrochemical reactions.

[0044] Figure 1 The graph shows the time response curves of light intensity and photocurrent for the NiO / SiC photovoltaic ultraviolet detector fabricated in this example. The NiO / SiC photovoltaic ultraviolet detector exhibits a significant photoelectric response under 254nm ultraviolet light irradiation, with the light response intensity changing significantly with light intensity. It achieves stable photocurrent output without an external bias voltage and possesses good switching response characteristics.

[0045] Figure 2 The image shows the time response curves of light intensity and photocurrent for the NiO / SiC PEC-type ultraviolet detector fabricated in this example. The NiO / SiC heterostructure exhibits a stable photoelectrochemical (PEC) ultraviolet response even in actual seawater. Without external functionalities, the device generates a significant photocurrent under ultraviolet light irradiation, demonstrating good switching characteristics and environmental adaptability, indicating its capability for ultraviolet detection applications in real marine environments.

[0046] Example 2:

[0047] A novel bifunctional ultraviolet detector based on NiO / SiC heterojunction:

[0048] (1) An n-type 4H-SiC(0001) single crystal substrate with a doping concentration of 1×10⁻⁶ was selected. 19 cm -3

[0049] (2) Fabrication of SiC carbon-blocked ohmic contact metal electrode:

[0050] Ni / Au (Ni: 20nm, Au: 80nm) was deposited on the carbon cutoff surface of a SiC substrate using magnetron sputtering, followed by annealing at 900°C for 5 minutes in nitrogen to form a stable ohmic contact.

[0051] (3) Deposition of p-type NiO thin film:

[0052] The substrate was first cleaned with a 10% hydrofluoric acid aqueous solution. Magnetron sputtering was then performed on the Si cutoff surface of the 4H-SiC substrate using a 10wt% Li-doped p-type NiO target. The working atmosphere was an oxygen / argon mixture with an oxygen partial pressure of 0.1 Pa, a total working pressure of 0.2 Pa, an oxygen-argon ratio of 1, a target power of 100 W, and a deposition temperature of room temperature. The film thickness was 100 nm.

[0053] (4) When the device is used for photovoltaic mode detection, a Ni metal grid is formed on the surface of the p-type NiO thin film layer to form an ohmic contact for photoelectric signal acquisition;

[0054] When the device is used in PEC mode, the p-type NiO surface is directly exposed to the electrolyte for photoelectrochemical reactions.

[0055] Figure 3 The graph shows the cycling stability test results of the PEC ultraviolet detector prepared in this example in a real seawater environment. After 600 ultraviolet light switching cycles in a real seawater environment, the photocurrent intensity of the NiO / SiC PEC ultraviolet detector remained stable without significant attenuation, indicating that the device has good cycling stability and corrosion resistance, and is suitable for ultraviolet detection in long-term marine environments.

[0056] Example 3:

[0057] A high-quality room-temperature epitaxial growth method for p-type transparent functional oxide thin films on SiC substrates:

[0058] A novel bifunctional ultraviolet detector based on NiO / SiC heterojunction:

[0059] (1) An n-type 6H-SiC(0001) single crystal substrate was selected, with a doping concentration of 1×10⁻⁶. 19 cm -3

[0060] (2) Fabrication of SiC ohmic contact metal electrode:

[0061] Ni / Au (Ni: 20nm, Au: 80nm) was deposited on the carbon cutoff surface of a SiC substrate using magnetron sputtering, followed by annealing at 900°C for 5 minutes in nitrogen to form a stable ohmic contact.

[0062] (3) Deposition of p-type NiO thin film:

[0063] First, the substrate was cleaned with BOE solution. On the Si cutoff surface of the SiC substrate, a NiO thin film was deposited using molecular beam epitaxy. High-purity metallic Ni was evaporated using an electron beam source, and growth was assisted by an O2 / O3 jet plasma source. The growth temperature was set to approximately 300℃, and the growth pressure was controlled at 1.0 × 10⁻⁶. -5 The NiO film thickness is approximately 50 nm, with a pressure of around 100 Pa.

[0064] (4) When the device is used for photovoltaic mode detection, a transparent ITO electrode is deposited on the surface of a p-type NiO thin film layer by magnetron sputtering for photoelectric signal acquisition.

[0065] When the device is used in PEC mode, the p-type NiO surface is directly exposed to the electrolyte for photoelectrochemical reactions.

[0066] The common-sense operations and characteristics involved in the above embodiments are not described in detail here. However, the implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for fabricating a novel bifunctional ultraviolet detector based on a NiO / SiC heterojunction, characterized in that, Includes the following steps: (1) SiC single crystal substrate is selected as the basic structure of the device and electron donor; (2) Fabrication of ohmic contact metal electrodes with carbon cut-off surfaces on SiC single crystal substrates: First, metal is deposited on the carbon cutoff surface of the SiC single crystal substrate described in step (1) and then annealed to form a channel for connecting to external circuits and providing a stable electron output channel. (3) Deposition of p-type NiO thin film: The Si cutoff surface of the SiC single crystal substrate is surface treated, and then p-type NiO is grown on the Si cutoff surface of the SiC single crystal substrate by pulsed laser deposition (PLD), magnetron sputtering or molecular beam epitaxy to form a p-type NiO thin film layer, which forms a heterojunction with SiC. (4) When the device is used for photovoltaic mode detection, metal or metal oxide is partially deposited on the surface of the p-type NiO thin film layer as the top electrode to form an ohmic contact for photoelectric signal acquisition, which is called a photovoltaic ultraviolet detector. When the device is used in photoelectrochemical PEC mode, the surface of the p-type NiO thin film layer is directly exposed to the electrolyte for photoelectrochemical reactions, and it is called a photoelectrochemical ultraviolet detector.

2. The preparation method according to claim 1, characterized in that, In step (1), the SiC single crystal substrate includes an n-type 4H-SiC or an n-type 6H-SiC single crystal substrate, and the doping concentration is controlled at 10. 16 -10 20 cm -3 Within the range.

3. The preparation method according to claim 1, characterized in that, In step (2), the deposited metal includes Ni, Ti, Al or Au, or a multilayer structure or alloy formed by a combination of them.

4. The preparation method according to claim 1, characterized in that, In step (3), the surface treatment method includes immersion in one or more of a 10% hydrofluoric acid aqueous solution or an oxide buffer etchant BOE.

5. The preparation method according to claim 1, characterized in that, In step (3), the p-type NiO includes undoped p-type NiO, or p-type NiO whose p-type characteristics are further enhanced by Li or Ag doping; the deposition thickness is 50 to 200 nm.

6. The preparation method according to claim 1, characterized in that, In step (3), when p-type NiO is grown on the Si cutoff surface of a SiC single crystal substrate, pulsed laser deposition (PLD), molecular beam epitaxy (MBE), magnetron sputtering (PVD), atomic layer deposition (ALD), or sol-gel method are used; specifically: When using pulsed laser deposition of PLDs, typical conditions are 193-1064 nm laser and 0.5-3 J cm⁻¹. -2 Energy density, 1-20 Hz, substrate temperature from room temperature to 300°C, oxygen partial pressure 10 -5 -10Pa; When molecular beam epitaxy (MBE) is used, at 10 -8 -10 -5 Under ultra-high vacuum of Pa, high-purity Ni was used as the Ni beam source, and O2 / O3 jet plasma source was used to assist Ni beam growth, with the substrate temperature ranging from room temperature to 300℃. When using magnetron sputtering PVD, the working pressure is 0.2-1 Pa, the target power is 20-150 W, the O2 / Ar volume ratio is 0.1-1.5, and the substrate is room temperature to 300℃. When using atomic layer deposition (ALD), the temperature is 150-350℃, with alternating pulses of Ni organic precursor and O3 (or O2 plasma); When using the sol-gel method, use 0.05-0.5 mol L. -1 Spin-coating the Ni(NO3)2 solution at 1000-4000 rpm and then annealing at below 400℃ for 10-60 min.

7. The preparation method according to claim 1, characterized in that, In step (4), in the photovoltaic ultraviolet detector, the top electrode on the surface of the p-type NiO thin film layer is made of conductive metal materials Au, Pt, Ni or Ag to form a ring or grid, or a transparent ITO electrode.

8. The preparation method according to claim 7, characterized in that, In step (4), when the top electrode is made of a conductive metal material, magnetron sputtering or electron beam deposition is used, and the deposition thickness is 50 to 200 nm.

9. The preparation method according to claim 7, characterized in that, In step (4), when the top electrode is a transparent ITO electrode, magnetron sputtering or PLD deposition is used, and the deposition thickness is 100 to 200 nm.

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