Gallium nitride heterojunction ultraviolet detector and its fabrication method

Abstract

This invention provides a gallium nitride heterojunction ultraviolet detector and its fabrication method. The gallium nitride heterojunction ultraviolet detector includes a first electrode, a substrate, a two-dimensional h-BN layer, an undoped GaN nucleation layer, a p-type GaN layer, and a second electrode, stacked sequentially. This invention inserts a two-dimensional h-BN layer as an epitaxial template, simplifying the fabrication process and reducing costs, achieving high-quality GaN thin film growth. This invention uses a two-dimensional h-BN layer as a tunneling layer to optimize the structure of the gallium nitride heterojunction photodetector. Utilizing its atomic-level thickness and wide bandgap structure, charge carriers between heterojunctions can efficiently pass through the insulating layer via quantum tunneling, providing an efficient vertical transport path for photogenerated electron-hole pairs. Simultaneously, its interface passivation effect effectively suppresses interface scattering and recombination, achieving extremely low dark current.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a gallium nitride heterojunction ultraviolet detector and its fabrication method. Background Technology

[0002] Ultraviolet (UV) detectors have crucial applications in missile early warning, biochemical detection, non-line-of-sight communication, and flame sensing. Gallium nitride (GaN), as a representative of third-generation wide-bandgap semiconductor materials, is considered an ideal material for fabricating high-performance UV detectors due to its inherent advantages such as direct bandgap, high breakdown field strength, excellent physicochemical stability, and its band edge located precisely in the UV band.

[0003] However, the performance of traditional GaN-based ultraviolet detectors, especially those based on heteroepitaxial substrates (such as silicon substrates), is still limited by many factors. First, the significant lattice mismatch and difference in thermal expansion coefficients between GaN and common substrates lead to a high density of dislocations and other crystal defects in the epitaxial layer. These defects, acting as non-radiative recombination centers, significantly reduce carrier lifetime and mobility, and generate severe dark current, degrading the detector's signal-to-noise ratio and responsivity. Second, traditional heterojunctions suffer from current transport bottlenecks; interface states and defects at the interface hinder carrier transport, resulting in low photogenerated carrier separation efficiency and difficulty in simultaneously achieving photocurrent enhancement and dark current suppression, leading to poor photodetector sensitivity. Summary of the Invention

[0004] In view of this, the present invention provides a gallium nitride heterojunction ultraviolet detector and its fabrication method, which effectively suppresses the high leakage current phenomenon at the heterojunction interface, obtains excellent rectification characteristics and low dark current, and improves the photoelectric response performance of the device.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides a gallium nitride heterojunction ultraviolet detector, comprising a first electrode, a substrate, a two-dimensional h-BN layer, an undoped GaN nucleation layer, a p-type GaN layer and a second electrode stacked sequentially.

[0007] Preferably, the thickness of the two-dimensional h-BN layer is 1-3 nm; and / or,

[0008] AlN is bonded in the two-dimensional h-BN layer.

[0009] Preferably, the substrate is an n-type semiconductor material.

[0010] Preferably, the n-type semiconductor material includes silicon, gallium oxide, zinc oxide, or aluminum nitride.

[0011] Preferably, the thickness of the undoped GaN nucleation layer is 10-50 nm.

[0012] Preferably, the p-type GaN layer is doped with Mg, and the magnesium doping concentration is 5 × 10⁻⁶. 19 -2×10 20 cm -3 .

[0013] Preferably, the thickness of the p-type GaN layer is 0.1-2 μm.

[0014] On the other hand, the present invention provides a method for fabricating the gallium nitride heterojunction ultraviolet detector, comprising the following steps:

[0015] S1. Grow the two-dimensional h-BN layer on the substrate;

[0016] S2. Grow an undoped GaN nucleation layer on the two-dimensional h-BN layer;

[0017] S3. Grow the p-type GaN layer on the undoped GaN nucleation layer;

[0018] S4. A first electrode is grown on the side of the substrate away from the two-dimensional h-BN layer, and a second electrode is grown on the side of the p-type GaN layer away from the undoped GaN nucleation layer.

[0019] Preferably, in step S1, the specific steps for growing the two-dimensional h-BN layer on the substrate are as follows: a single-crystal h-BN thin film is grown on a copper foil by chemical vapor deposition, and the h-BN thin film is transferred to the substrate surface by polymethyl methacrylate-assisted wet transfer technology to form the two-dimensional h-BN layer.

[0020] Preferably, in step S4, the specific steps for forming the first electrode and the second electrode are as follows: the second electrode is prepared on p-type GaN by electron beam evaporation to form an ohmic contact, and the first electrode is prepared on the substrate surface to form an ohmic contact.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention inserts a two-dimensional h-BN layer. The two-dimensional h-BN layer utilizes its atomically flat surface and the absence of dangling bonds as an epitaxial template to effectively block the transmission of lattice mismatch from the lower substrate to the GaN active layer, thereby significantly reducing the dislocation density in the GaN epitaxial layer. It eliminates the need for the traditional complex and inefficient multilayer buffer layer structure, simplifies the fabrication process and reduces costs, and achieves high-quality GaN thin film growth, laying the foundation for high-performance devices.

[0023] (2) The present invention uses a two-dimensional h-BN layer as a tunneling layer. By utilizing its atomic-level thickness and wide bandgap structure, the charge carriers between heterojunctions can pass through the insulating layer through the quantum tunneling effect, providing an efficient vertical transport path for photogenerated electron-hole pairs. At the same time, its intrinsic insulation can effectively suppress dark current under reverse bias, thereby improving the signal-to-noise ratio and detectivity of the detector. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a gallium nitride heterojunction ultraviolet detector structure provided in an embodiment of the present invention;

[0025] Figure 2 This is a flowchart illustrating the fabrication process of a gallium nitride heterojunction ultraviolet detector according to an embodiment of the present invention.

[0026] Reference numerals: Gallium nitride heterojunction ultraviolet detector 100, first electrode 101, substrate 201, two-dimensional h-BN layer 202, undoped GaN nucleation layer 203, p-type GaN layer 204, second electrode 102. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0028] Ultraviolet (UV) detectors have crucial applications in missile early warning, biochemical detection, non-line-of-sight communication, and flame sensing. Gallium nitride (GaN), as a representative of third-generation wide-bandgap semiconductor materials, is considered an ideal material for fabricating high-performance UV detectors due to its inherent advantages such as direct bandgap, high breakdown field strength, excellent physicochemical stability, and its band edge located precisely in the UV band.

[0029] However, the performance of traditional GaN-based ultraviolet detectors, especially those based on heteroepitaxial substrates (such as silicon substrates), is still limited by many factors. First, the significant lattice mismatch and difference in thermal expansion coefficients between GaN and common substrates lead to a high density of crystal defects such as dislocations in the epitaxial layer. These defects, acting as non-radiative recombination centers, significantly reduce carrier lifetime and mobility, and generate severe dark currents, degrading the detector's signal-to-noise ratio and responsivity.

[0030] To solve the above technical problems, combined with Figure 1 The present invention provides a gallium nitride heterojunction ultraviolet detector 100, comprising a first electrode 101, a substrate 201, a two-dimensional h-BN layer 202, an undoped GaN nucleation layer 203, a p-type GaN layer 204 and a second electrode 102 stacked sequentially.

[0031] In the above technical solution, the first electrode 101 serves as the bottom electrode of the device, connected to the external circuit, and is used to collect or inject charge carriers. The substrate 201 provides mechanical support and a process-compatible platform. The two-dimensional h-BN layer 202 serves as a two-dimensional van der Waals buffer layer, breaking the rigid requirement of GaN for lattice matching with the substrate 201, providing an atomically flat and chemically inert epitaxial substrate, suppressing dislocations from penetrating upwards from the substrate 201, and also serving as an ultrathin high-bandgap insulating layer, introducing a MIS / MISM barrier, suppressing dark current injection and defect-assisted leakage current, and reducing 1 / f noise. The undoped GaN nucleation layer 203 first forms a GaN nucleation interface with low defect density and high crystal integrity on the h-BN, serving as a template layer for subsequent high-quality p-GaN epitaxy. Undoping can reduce impurity and ionization scattering, reduce interface trap states, and improve the minority carrier lifetime and mobility of the subsequent p-layer. The p-type GaN layer 204 serves as the main ultraviolet absorption layer and carrier collection channel. It exhibits strong absorption around 365 nm (GaN band edge); a Schottky barrier or quasi-ohmic contact can be formed at the metal contact. The second electrode 102 forms an electrical contact with p-GaN and extracts the signal.

[0032] This invention inserts a two-dimensional h-BN layer 202. The two-dimensional h-BN layer 202, with its atomically flat surface and absence of dangling bonds, serves as an epitaxial template, effectively blocking the propagation of lattice mismatch from the underlying substrate 201 to the GaN active layer. This significantly reduces the dislocation density in the GaN epitaxial layer, eliminating the need for traditional, complex, and inefficient multilayer buffer layer structures. This simplifies the fabrication process, reduces costs, and enables the growth of high-quality GaN thin films, laying the foundation for high-performance devices.

[0033] The two-dimensional h-BN layer 202, acting as a tunneling layer, utilizes its atomic-level thickness and wide bandgap structure to allow charge carriers between heterojunctions to traverse the insulating layer via quantum tunneling, providing an efficient vertical transport path for photogenerated electron-hole pairs. Simultaneously, its intrinsic insulation effectively suppresses dark current under reverse bias, improving the detector's signal-to-noise ratio and detectivity. The dangling-bond-free surface of h-BN effectively passivates interface states, reducing surface recombination rates, improving carrier collection efficiency, suppressing persistent photoconductivity, and significantly accelerating response speed, with rise / fall times reaching several microseconds. The wide bandgap of h-BN forms an extremely high barrier between n-Si and p-GaN, effectively suppressing recombination currents caused by various defects. The tunneling effect enhances carrier separation efficiency, generating higher open-circuit voltage and short-circuit current even at zero bias, achieving highly efficient self-powered detection.

[0034] Furthermore, the thickness of the two-dimensional h-BN layer 202 is 1-3 nm. If the two-dimensional h-BN layer 202 is too thick as an insertion layer, it will hinder carrier tunneling; if it is too thin, it will lead to insufficient interface passivation. The optimal thickness is 1-3 nm (3-9 atomic layers).

[0035] Furthermore, AlN is incorporated into the two-dimensional h-BN layer 202, and the ultrathin AlN and h-BN are combined to form a superlattice structure, which combines the lattice matching characteristics of AlN and the interface passivation characteristics of h-BN.

[0036] In some embodiments, the substrate 201 is an n-type semiconductor material, which in some embodiments includes silicon, gallium oxide, zinc oxide, or aluminum nitride. The combination of the n-type semiconductor substrate 201 and the h-BN insulating buffer enhances the built-in electric field, reduces dark current, and enables self-powered or low-biased high-sensitivity detection through bandgap engineering and back-gate modulation. Furthermore, it provides comprehensive advantages in terms of process, electrothermal, and system integration, resulting in low resistance, low noise, and high reliability, thereby significantly improving the overall performance and manufacturability of GaN-based ultraviolet detectors.

[0037] In some embodiments, the thickness of the undoped GaN nucleation layer 203 is 10-50 nm.

[0038] In some embodiments, the p-type GaN layer 204 is doped with Mg, and the magnesium doping concentration is 5 × 10⁻⁶. 19 -2×10 20 cm -3 .

[0039] In some embodiments, the thickness of the p-type GaN layer 204 is 0.1-2 μm.

[0040] Combination Figure 2 The present invention also provides a method for fabricating the gallium nitride heterojunction ultraviolet detector 100, comprising the following steps:

[0041] S1. The two-dimensional h-BN layer 202 is grown on the substrate 201;

[0042] S2. An undoped GaN nucleation layer 203 is grown on the two-dimensional h-BN layer 202;

[0043] S3. Grow the p-type GaN layer 204 on the undoped GaN nucleation layer 203;

[0044] S4. A first electrode 101 is grown on the side of the substrate 201 away from the two-dimensional h-BN layer 202, and a second electrode 102 is grown on the side of the p-type GaN layer 204 away from the undoped GaN nucleation layer 203.

[0045] This invention first grows an undoped GaN nucleation layer 203 at low temperature to prevent three-dimensional island growth and suppress the diffusion of Mg dopant, and then grows a Mg-doped p-type GaN host layer, which is responsible for absorbing ultraviolet light and generating photogenerated carriers.

[0046] In some embodiments, the specific steps of growing the two-dimensional h-BN layer 202 on the substrate 201 in step S1 are as follows: a single-crystal h-BN thin film is grown on a copper foil by chemical vapor deposition, and the h-BN thin film is transferred to the surface of the substrate 201 by polymethyl methacrylate-assisted wet transfer technology to form the two-dimensional h-BN layer 202.

[0047] In some embodiments, the specific steps for forming the first electrode 101 and the second electrode 102 in step S4 are as follows: the second electrode 102 is prepared on p-type GaN by electron beam evaporation to form an ohmic contact, and the first electrode 101 is prepared on the surface of the substrate 201 to form an ohmic contact.

[0048] In some embodiments, the steps for fabricating the gallium nitride heterojunction ultraviolet detector 100 are as follows:

[0049] 1) The n-type Si substrate 201 undergoes rigorous RCA cleaning and HF acid treatment to form a hydrogen-terminated inert surface, eliminating the native oxide layer and providing a van der Waals interface with h-BN, thus reducing interface states. Surface pretreatment processes are a type of surface pretreatment technology for semiconductor materials such as silicon, gallium oxide, zinc oxide, and aluminum nitride, including surface cleaning technology, surface planarization technology, and surface functional group treatment technology.

[0050] 2) A single-crystal h-BN thin film is grown on a copper foil using chemical vapor deposition (CVD), and the h-BN thin film is transferred to the surface of an n-type Si substrate 201 using a polymethyl methacrylate (PMMA)-assisted wet transfer technique. The h-BN preparation method is one of the following: chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), or molecular beam epitaxy (MBE).

[0051] 3) An undoped GaN nucleation layer 203 is epitaxially grown on an n-type Si substrate 201 covered with h-BN at a relatively low substrate temperature (500-650℃). The undoped GaN nucleation layer 203 is prepared by one of molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), or halide vapor phase epitaxy (HVPE), with a growth temperature of 500-650℃.

[0052] 4) Appropriately increase the temperature of substrate 201 (700-1000℃) to epitaxially grow a high-quality Mg-doped p-type GaN layer 204, which serves as the core ultraviolet light absorption region of the device. The p-type GaN layer 204 is prepared by one of molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), or halide vapor phase epitaxy (HVPE). The magnesium source is one of metallic magnesium, magnesia (Cp2Mg), or magnesium chloride (MgCl2), and the growth temperature is 700-1000℃.

[0053] 5) Electrode mesa are formed by photolithography and inductively coupled plasma (ICP) etching. A second electrode 102 is then fabricated on the p-type GaN layer 204 via electron beam evaporation to form an ohmic contact. A first electrode 101 is fabricated on the back side of the n-Si substrate 201 to form an ohmic contact. A vertical structure design is adopted, and the electrode deposition method is either electron beam evaporation or magnetron sputtering.

[0054] 6) Rapid thermal annealing (RTA) to optimize electrode ohmic contact.

[0055] Unless otherwise specified, all raw materials used in this invention are existing substances that can be purchased directly from the market.

[0056] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A gallium nitride heterojunction ultraviolet detector, characterized in that, It includes a first electrode, a substrate, a two-dimensional h-BN layer, an undoped GaN nucleation layer, a p-type GaN layer, and a second electrode stacked sequentially. The thickness of the two-dimensional h-BN layer is 1-3 nm; The two-dimensional h-BN layer contains AlN, and the ultrathin AlN is combined with h-BN to form a superlattice structure.

2. The gallium nitride heterojunction ultraviolet detector according to claim 1, characterized in that, The substrate is an n-type semiconductor material.

3. The gallium nitride heterojunction ultraviolet detector according to claim 2, characterized in that, n-type semiconductor materials include silicon, gallium oxide, zinc oxide, or aluminum nitride.

4. The gallium nitride heterojunction ultraviolet detector according to claim 1, characterized in that, The thickness of the undoped GaN nucleation layer is 10-50 nm.

5. The gallium nitride heterojunction ultraviolet detector according to claim 1, characterized in that, The p-type GaN layer is doped with Mg, and the magnesium doping concentration is 5 × 10⁻⁶. 19 -2×10 20 cm -3 .

6. The gallium nitride heterojunction ultraviolet detector according to claim 1, characterized in that, The thickness of the p-type GaN layer is 0.1-2 μm.

7. The method for fabricating a gallium nitride heterojunction ultraviolet detector according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Grow the two-dimensional h-BN layer on the substrate; S2. Grow an undoped GaN nucleation layer on the two-dimensional h-BN layer; S3. Grow the p-type GaN layer on the undoped GaN nucleation layer; S4. A first electrode is grown on the side of the substrate away from the two-dimensional h-BN layer, and a second electrode is grown on the side of the p-type GaN layer away from the undoped GaN nucleation layer.

8. The preparation method according to claim 7, characterized in that, In step S1, the specific steps for growing the two-dimensional h-BN layer on the substrate are as follows: a single-crystal h-BN thin film is grown on a copper foil by chemical vapor deposition, and the h-BN thin film is transferred to the substrate surface by polymethyl methacrylate-assisted wet transfer technology to form the two-dimensional h-BN layer.

9. The preparation method according to claim 7, characterized in that, In step S4, the specific steps for forming the first electrode and the second electrode are as follows: the second electrode is prepared on p-type GaN by electron beam evaporation to form an ohmic contact, and the first electrode is prepared on the substrate surface to form an ohmic contact.

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