Heterojunction self-powered ultraviolet photodetector and preparation method thereof

Abstract

The application discloses a heterojunction self-powered ultraviolet light detector and a preparation method thereof. The ultraviolet light detector comprises, from bottom to top, a substrate, an AlN nucleation layer, an AlN / AlGaN superlattice layer, an AlGaN transition layer, an AlN / GaN superlattice layer, a high-resistance GaN buffer layer and a u-GaN channel layer. The upper surface of the u-GaN channel layer is provided with a first interdigital region and a second interdigital region. The thickness of the u-GaN channel layer in the first interdigital region is higher than that of the u-GaN channel layer in the second interdigital region. The ultraviolet light detector further comprises an AlN insertion layer, an AlGaN barrier layer, a GaN cap layer, a source metal layer superimposed on the GaN cap layer and a drain metal layer superimposed on the u-GaN channel layer in the second interdigital region. The application solves the problem of high dark current caused by the introduction of a high-conductivity 2DEG channel in the prior art, and can obtain high responsivity in a low-power-consumption or self-powered mode.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, specifically relating to a heterojunction self-powered ultraviolet photodetector and its fabrication method. Background Technology

[0002] Ultraviolet photodetector technology has broad application prospects in environmental monitoring, flame detection, biomedical analysis, and industrial process control. Wide bandgap semiconductor materials, represented by GaN and AlGaN, have become ideal materials for fabricating high-performance ultraviolet photodetectors due to their excellent properties such as large bandgap, high electron saturation drift velocity, high thermal conductivity, good chemical stability, and strong radiation resistance.

[0003] The AlGaN / GaN heterojunction high electron mobility transistor (HEMT) structure, due to its unique polarization effect, can form a high-concentration, high-mobility two-dimensional electron gas (2DEG) at the AlGaN / GaN heterojunction interface. This 2DEG, combined with the high light absorption coefficient of the GaN layer, enables efficient lateral transport of photogenerated carriers, resulting in high responsivity. Furthermore, by adjusting the Al composition in the AlGaN layer, its bandgap can be continuously tuned within the range of 3.4–6.2 eV, corresponding to a peak response wavelength range of 200–365 nm.

[0004] In recent years, self-powered ultraviolet detectors have attracted widespread attention in low-power applications such as portable devices, Internet of Things (IoT) edge nodes, wireless sensor networks, and space exploration because they can operate without an external power source. Existing self-powered ultraviolet detectors mainly achieve spontaneous separation and collection of photogenerated carriers by constructing asymmetric electrode structures or utilizing the built-in electric field of heterojunctions, but there is still considerable room for improvement in key performance indicators such as responsivity and dark current.

[0005] In traditional symmetrical interdigitated electrode AlGaN / GaN HEMT structures, the highly conductive 2DEG channels are the main source of dark current, which limits the signal-to-noise ratio and detection sensitivity in low-light detection scenarios. Some self-powered detectors utilize the AlScN absorption layer to modulate the two-dimensional electron gas concentration, metal work function difference, or asymmetric structure of the AlGaN / GaN heterojunction to construct a built-in electric field, significantly reducing dark current and improving the signal-to-noise ratio and detection sensitivity in low-light detection scenarios. However, they have weak self-powering capability, high cost, and low responsivity.

[0006] In summary, existing technical solutions suffer from high dark current due to the high conduction 2DEG channel, and are highly dependent on external bias voltage, making it difficult to achieve high responsiveness in low power or self-powered modes. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, this invention provides a heterojunction self-powered ultraviolet photodetector and its fabrication method. The technical problem to be solved by this invention is achieved through the following technical solution: A heterojunction self-powered ultraviolet photodetector includes, from bottom to top, a substrate, an AlN nucleation layer, an AlN / AlGaN superlattice layer, an AlGaN transition layer, an AlN / GaN superlattice layer, a high-resistivity GaN buffer layer, and a u-GaN channel layer.

[0008] The upper surface of the u-GaN channel layer is provided with a first interdigitated region and a second interdigitated region; the thickness of the u-GaN channel layer in the first interdigitated region is higher than the thickness of the u-GaN channel layer in the second interdigitated region; in the layer projection of the first interdigitated region and the second interdigitated region onto the u-GaN channel layer, the fingers of the first interdigitated region and the fingers of the second interdigitated region are arranged intersectingly and do not contact each other.

[0009] The ultraviolet detector further includes an AlN insertion layer, an AlGaN barrier layer, a GaN cap layer, a source metal layer superimposed on the GaN cap layer, and a drain metal layer superimposed on the u-GaN channel layer in the second interdigitated region; wherein, the u-GaN channel layer in the first interdigitated region and the AlN insertion layer and the AlGaN barrier layer above it constitute an AlGaN / GaN heterojunction, and the AlGaN / GaN heterojunction and the GaN cap layer form an interdigitated transparent heterojunction electrode; the drain metal layer forms a metal interdigitated electrode.

[0010] The AlN / AlGaN superlattice layer is composed of alternating stacks of AlN and AlGaN, with an alternation period of 30 to 35. The Al composition of the AlN / AlGaN superlattice layer is 65 to 75%, and the thickness is 0.4 to 0.5 μm.

[0011] The Al composition of the AlGaN transition layer is 30%~40%, and the thickness is 1.0~1.5μm.

[0012] The AlN / GaN superlattice layer is composed of alternating stacked AlN and GaN layers with an alternation period of 35 to 40. The Al composition of the AlN / GaN superlattice layer is 10% to 20%, and the thickness is 1.5 to 2.0 μm.

[0013] In the transparent heterojunction electrode, the thickness of the u-GaN channel layer is 280~320nm; the thickness of the AlN insertion layer is 1~2nm; the AlGaN barrier layer is an undoped AlGaN layer with an Al composition of 20%~30% and a thickness of 15~25nm; and the thickness of the GaN cap layer is 2~5nm.

[0014] The transparent heterojunction electrode includes 20 to 30 transparent fingers, each of which has a width of 7 to 8 μm and a length of 200 to 300 μm.

[0015] The interdigitated metal electrode is a Ti / Al / Ni / Au composite metal layer with thicknesses of 20nm / 120nm / 50nm / 45nm respectively. The interdigitated metal electrode includes 20 to 30 metal fingers, each of which has a width of 2 to 3μm and a length of 200 to 300μm. The distance between the transparent finger strip and the adjacent metal finger strip projected onto the surface of the u-GaN channel layer is 1~3μm.

[0016] A method for fabricating a heterojunction self-powered ultraviolet photodetector includes the following steps: S1. An AlN nucleation layer, an AlN / AlGaN superlattice layer, an AlGaN transition layer, an AlN / GaN superlattice layer, a high-resistivity GaN buffer layer, a u-GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN cap layer are sequentially grown on the substrate.

[0017] S2. Define the target interdigitated region on the GaN cap layer.

[0018] S3. Etch the GaN cap layer and the AlGaN barrier layer, the AlN insertion layer and part of the u-GaN channel layer below it within the target interdigitated region, with the etching endpoint located inside the u-GaN channel layer; wherein, the area outside the target interdigitated region forms a first interdigitated region.

[0019] S4. Define a source electrode pattern on the upper surface of the GaN cap layer of the first interdigitated region, and define a second interdigitated region as a drain electrode pattern on the upper surface of the etched u-GaN channel layer; wherein, in the layer projection of the first interdigitated region and the second interdigitated region onto the u-GaN channel layer, the fingers of the first interdigitated region and the fingers of the second interdigitated region are arranged intersectingly and do not contact each other.

[0020] S5. A drain electrode metal layer is formed on the drain electrode pattern, and a source electrode metal layer is formed on the source electrode pattern.

[0021] S6. Anneal the current sample to form ohmic contacts between the drain metal layer and the underlying u-GaN channel layer, and between the source metal layer and the underlying GaN cap layer, to obtain a ready-to-be-completed heterojunction self-powered ultraviolet photodetector; wherein, the u-GaN channel layer in the first interdigitated region and the AlN insertion layer and the AlGaN barrier layer above it constitute an AlGaN / GaN heterojunction, and the AlGaN / GaN heterojunction and the GaN cap layer form an interdigitated transparent heterojunction electrode; the drain metal layer forms a metal interdigitated electrode.

[0022] The rapid annealing of the current sample includes: rapid annealing of the current sample at 750℃~850℃ for 30~60s.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: In the heterojunction self-powered ultraviolet detector provided by this invention, the drain electrode is disposed on the u-GaN channel layer, and the source electrode is disposed on a layer structure consisting of an AlN insertion layer, an AlGaN barrier layer, and a GaN cap layer stacked sequentially on the u-GaN channel layer. This deep mesa isolation structure eliminates leakage paths by cutting off the two-dimensional electron gas conductive channel. Furthermore, the device is provided with an AlN / AlGaN superlattice layer and an AlN / GaN superlattice layer. In this way, the alternately grown superlattice layers can effectively filter and annihilate penetrating dislocations, and the AlGaN transition layer maintains low defect density growth conditions. This low defect density epitaxial structure suppresses leakage generation. The two work together to give the device low dark current and high sensitivity characteristics. Building upon this foundation, this invention designs one electrode as a transparent AlGaN / GaN heterojunction structure retaining the 2DEG structure, serving as the light absorption and carrier collection window for the ultraviolet detector. This achieves efficient ultraviolet light absorption while maintaining the transparency of the electrode region. Compared to traditional opaque metal electrodes, this increases the photosensitive area and improves light absorption efficiency, effectively reducing the signal-to-noise ratio in weak light detection scenarios and enhancing the detector's sensitivity. The other electrode is designed as a Ti / Al / Ni / Au metal electrode, forming an asymmetric interdigitated electrode with the heterojunction transparent electrode. Utilizing the difference in work function and band structure between the two electrodes, an asymmetric built-in electric field is created, reducing the electrode spacing and increasing the light-receiving area. This enables efficient collection of photogenerated carriers under zero bias, improving the device's responsivity. Compared to traditional self-powered ultraviolet detectors, this significantly enhances the detector's response capability.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a heterojunction self-powered ultraviolet photodetector provided in an embodiment of the present invention; Figure 2 This invention provides a method for fabricating a heterojunction self-powered ultraviolet photodetector. Figure 3 This is a top view under a microscope of a heterojunction self-powered ultraviolet light detector provided in an embodiment of the present invention; Figure 4 This is a spectral responsivity and spectral power density spectrum of a heterojunction self-powered ultraviolet photodetector under 0 V bias voltage, provided in an embodiment of the present invention.

[0026] Figure label: 1. Substrate; 2. AlN nucleation layer; 3. AlN / AlGaN superlattice layer; 4. AlGaN transition layer; 5. AlN / GaN superlattice layer; 6. High-resistivity GaN buffer layer; 7. u-GaN channel layer; 8. AlN insertion layer; 9. AlGaN barrier layer; 10. GaN cap layer; 11A. Source electrode metal layer; 11B. Drain electrode metal layer; 101. Transparent finger strip; 111. Metal finger strip. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0028] The technical challenge addressed by this invention is that the high conduction 2DEG channel results in a large dark current in the device, and the device's photoelectric response is highly dependent on the external bias voltage, which limits the device's use in low-power and self-powered scenarios.

[0029] In a first aspect, embodiments of the present invention provide a heterojunction self-powered ultraviolet photodetector.

[0030] Please see Figure 1 , Figure 1 This is a schematic diagram of a heterojunction self-powered ultraviolet photodetector structure provided in an embodiment of the present invention. The heterojunction self-powered ultraviolet photodetector includes, from bottom to top, a substrate 1, an AlN nucleation layer 2, an AlN / AlGaN superlattice layer 3, an AlGaN transition layer 4, an AlN / GaN superlattice layer 5, a high-resistivity GaN buffer layer 6, and a u-GaN channel layer 7.

[0031] The upper surface of the u-GaN channel layer 7 is provided with a first interdigitated region and a second interdigitated region; the thickness of the u-GaN channel layer 7 in the first interdigitated region is higher than the thickness of the u-GaN channel layer 7 in the second interdigitated region; in the layer projection of the first interdigitated region and the second interdigitated region onto the u-GaN channel layer 7, the fingers of the first interdigitated region and the fingers of the second interdigitated region are arranged intersectingly and do not contact each other.

[0032] Specifically, see Figure 3As shown, in the layer projection of the first and second interdigitated regions onto the u-GaN channel layer 7, there is a gap between adjacent fingers (not shown in the figure), and there is a gap between the front end of the first interdigitated region and the root of the interdigitated fingers of the second interdigitated region, and there is also a gap between the front end of the second interdigitated region and the root of the interdigitated fingers of the first interdigitated region.

[0033] The heterojunction self-powered ultraviolet detector provided in this embodiment of the invention further includes an AlN insertion layer 8, an AlGaN barrier layer 9, a GaN cap layer 10, a source metal layer 11A superimposed on the GaN cap layer 10, and a drain metal layer 11B superimposed on the u-GaN channel layer 7 in the second interdigitated region; wherein, the u-GaN channel layer 7 in the first interdigitated region and the AlN insertion layer 8 and AlGaN barrier layer 9 above it constitute an AlGaN / GaN heterojunction, which is used to significantly improve the concentration and mobility of the two-dimensional electron gas (2DEG) when the invention is used, and the AlGaN / GaN heterojunction and the GaN cap layer 10 form an interdigitated transparent heterojunction electrode; the drain metal layer 11B forms a metal interdigitated electrode.

[0034] In this embodiment of the invention, the drain electrode metal layer 11B of the device is disposed on the u-GaN channel layer 7, and its source electrode metal layer 11A is disposed on a layer structure consisting of an AlN insertion layer 8, an AlGaN barrier layer 9, and a GaN cap layer 10 sequentially stacked on the u-GaN channel layer 7. This deep mesa isolation structure eliminates leakage paths by cutting off the two-dimensional electron gas conductive channel. Furthermore, the device is provided with an AlN / AlGaN superlattice layer 3 and an AlN / GaN superlattice layer 5. In this way, through-hole dislocations can be effectively filtered and annihilated by the alternately grown superlattice layers, and low defect density growth conditions are maintained by the AlGaN transition layer 4. This low defect density epitaxial structure suppresses leakage. The two work together to enable the device to have low dark current and high sensitivity characteristics. Building upon this, this invention designs one electrode as a transparent AlGaN / GaN heterojunction structure retaining the 2DEG, serving as the light absorption and carrier collection window for the ultraviolet detector. This achieves efficient ultraviolet light absorption while maintaining the transparency of the electrode region. Compared to traditional opaque metal electrodes, this increases the photosensitive area and improves light absorption efficiency, effectively reducing the signal-to-noise ratio in weak light detection scenarios and increasing the detector's sensitivity. The other electrode is designed as a Ti / Al / Ni / Au metal electrode, forming an asymmetric interdigitated electrode with the heterojunction transparent electrode. Utilizing the difference in work function and band structure between the two electrodes, an asymmetric built-in electric field is created, reducing the electrode spacing and increasing the light-receiving area. This achieves efficient collection of photogenerated carriers under zero bias, improving the device's responsivity. Compared to traditional self-powered ultraviolet detectors, this significantly improves the detector's response capability.

[0035] Preferably, substrate 1 is a silicon substrate with a thickness of 0.8~1.2mm, but it is not limited to this.

[0036] Preferably, the thickness of the AlN nucleation layer 2 is 0.1~0.3μm.

[0037] The AlN / AlGaN superlattice layer 3 is composed of alternating stacks of AlN and AlGaN, with the number of alternating periods preferably being 30 to 35. Preferably, the Al composition of the AlN / AlGaN superlattice layer is 65 to 75%, and its thickness is 0.4 to 0.5 μm.

[0038] Preferably, the Al composition of the AlGaN transition layer 4 is 30%~40%, and its thickness is 1.0~1.5 μm.

[0039] The AlN / GaN superlattice layer 5 is composed of alternating stacked AlN and GaN layers, with the number of alternating periods preferably being 35 to 40. Preferably, the Al composition of the AlN / GaN superlattice layer 5 is 10% to 20%, and the thickness of the AlN / GaN superlattice layer 5 is 1.5 to 2.0 μm.

[0040] Preferably, the thickness of the high-resistivity GaN buffer layer 6 is 0.8~1.2μm.

[0041] In one embodiment, the AlN / AlGaN superlattice layer 3 has 32 alternating periods of AlN and AlGaN, an Al composition of 70%, and a thickness of 0.5 μm. The AlGaN transition layer 4 has an Al composition of 35% and a thickness of 1.1 μm. The AlN / GaN superlattice layer 5 has 38 alternating periods of AlN and GaN layers, an Al composition of 15%, and a thickness of 1.75 μm. Thus, this embodiment of the invention effectively filters and annihilates penetrating dislocations through the alternating superlattice layers, and maintains low defect density growth conditions through the AlGaN transition layer. This low defect density epitaxial structure suppresses leakage current generation.

[0042] Preferably, in the transparent heterojunction electrode, the thickness of the u-GaN channel layer 7 in the second interdigitated region is 280~320nm; the thickness of the AlN insertion layer 8 is 1~2nm; the AlGaN barrier layer 9 is an undoped AlGaN layer with an Al composition of 20%~30% and a thickness of 15~25nm; and the thickness of the GaN cap layer 10 is 2~5nm.

[0043] In one embodiment, the thickness of the u-GaN channel layer 7 in the second interdigitated region is 300 nm. The AlN insertion layer 8 has a thickness of 1 nm and is used to reduce disordered scattering of the alloy. The AlGaN barrier layer 9 is an undoped AlGaN layer with an Al composition of 21% and a thickness of 20 nm. The GaN cap layer 10 has a thickness of 5 nm and is used to prevent the AlGaN barrier layer 9 from being oxidized and contaminated.

[0044] Preferably, the transparent heterojunction electrode includes 20 to 30 transparent fingers 101, each transparent finger 101 having a width of 7 to 8 μm and a length of 200 to 300 μm.

[0045] For example, a transparent heterojunction electrode may include 25 transparent fingers 101, each transparent finger 101 having a width of 7 μm and a length of 300 μm.

[0046] In one embodiment, the source metal layer 11A on the GaN cap layer 10 is a Ti / Al / Ni / Au composite metal layer, and the thicknesses of Ti / Al / Ni / Au are 20nm / 120nm / 50nm / 45nm respectively.

[0047] Thus, in this embodiment of the invention, the source electrode is designed as a transparent electrode with a 2DEG AlGaN / GaN heterojunction structure, serving as the light absorption and carrier collection window for the ultraviolet detector. While achieving efficient ultraviolet light absorption, the transparency of the electrode region is maintained. Compared with traditional opaque metal electrodes, this increases the photosensitive area and improves the light absorption efficiency, effectively reducing the signal-to-noise ratio in weak light detection scenarios and improving the sensitivity of the detector.

[0048] In one embodiment, the interdigitated metal electrode is a Ti / Al / Ni / Au composite metal layer, with the thicknesses of Ti / Al / Ni / Au being 20 / 120 / 50 / 45 nm, respectively.

[0049] Preferably, in the interdigitated metal electrode, there are 20 to 30 metal fingers 111, each of which has a width of 2 to 3 μm and a length of 200 to 300 μm. Preferably, the distance between the transparent fingers 101 and the adjacent metal fingers 111 projected onto the surface of the u-GaN channel layer 7 is 1 to 3 μm.

[0050] In one embodiment, the metal interdigitated electrode may include 26 metal fingers 111, each metal finger 111 having a width of 3 μm and a length of 300 μm; the spacing between the transparent fingers and adjacent metal fingers projected onto the surface of the u-GaN channel layer is 1.5 μm.

[0051] Thus, in this embodiment of the invention, the other electrode is designed as a Ti / Al / Ni / Au metal electrode, which together with the heterojunction transparent electrode forms an asymmetric interdigitated electrode. The difference in work function and band structure between the two electrodes is used to form an asymmetric built-in electric field, reducing the electrode spacing and increasing the light-receiving area. This enables efficient collection of photogenerated carriers under zero bias voltage, improving the responsivity of the device. Compared with traditional self-powered ultraviolet detectors, this significantly improves the detector's response capability.

[0052] It is understood that the depletion-mode AlGaN / GaN epitaxial wafer covered by the GaN cap layer selected in this invention is formed by a stacked structure from the substrate to the GaN cap layer. The GaN cap layer 10 is used to prevent the heterojunction from being oxidized and contaminated, and the depletion-mode channel is used to achieve zero-bias conduction. The combination of these two provides an ideal material basis for low dark current self-powered ultraviolet detection. In this invention, the drain is located on the etched u-GaN channel layer 7 (i.e., the u-GaN channel layer 7 of the second interdigitated region), and the source is located on top of the unetched GaN cap layer 10. The physical height difference between the two (e.g., 100~200 nm) can precisely cut off the 2DEG conductive channel, eliminating parasitic leakage paths. This invention drives efficient separation of photogenerated carriers through the polarization electric field of the AlGaN / GaN heterojunction and promotes directional collection of photogenerated carriers through the asymmetric electrode potential gradient. The synergy of these two factors enables the device to achieve high responsivity at zero bias.

[0053] Secondly, embodiments of the present invention provide a method for fabricating a heterojunction self-powered ultraviolet photodetector, such as... Figure 2 As shown, it includes the following steps: S1. On substrate 1, an AlN nucleation layer 2, an AlN / AlGaN superlattice layer 3, an AlGaN transition layer 4, an AlN / GaN superlattice layer 5, a high-resistivity GaN buffer layer 6, a u-GaN channel layer 7, an AlN insertion layer 8, an AlGaN barrier layer 9, and a GaN cap layer 10 are grown sequentially.

[0054] Specifically, an AlN nucleation layer 2, an AlN / AlGaN superlattice layer 3, an AlGaN transition layer 4, an AlN / GaN superlattice layer 5, a high-resistivity GaN buffer layer 6, a u-GaN channel layer 7, an AlN insertion layer 8, an AlGaN barrier layer 9, and a GaN cap layer 10 are sequentially grown on substrate 1 using MOCVD technology.

[0055] For example, an AlN nucleation layer 2 of 0.2 μm, a 32-period AlN / AlGaN superlattice layer of 0.5 μm, and an AlN / AlGaN superlattice layer of 1.1 μm are sequentially grown on a silicon substrate 1 using MOCVD. 0.35 Ga 0.65An N-transition layer 4, a 1.75 μm 38-period AlN / GaN superlattice 5, a 1 μm high-resistivity GaN buffer layer 6, a 300 nm u-GaN channel layer 7, a 1 nm AlN insertion layer 8, a 20 nm AlGaN barrier layer 9, and a 5 nm GaN cap layer 10 are formed to form a high-crystal-quality depletion-type AlGaN / GaN HEMT epitaxial wafer, namely the aforementioned depletion-type AlGaN / GaN epitaxial wafer.

[0056] S2. Define a second interdigitated region on the GaN cap layer.

[0057] Specifically, the surface of the epitaxial wafer prepared in step S1 is first cleaned, and then a second interdigitated region is formed by photolithography of interdigitated patterns on the surface of the GaN cap layer 10.

[0058] For example, the epitaxial wafer surface is first cleaned with 10% dilute hydrochloric acid for 1 minute to remove surface oxidation. After rinsing with deionized water and spin-drying, it is then dried in a 130°C dryer for 30 minutes to remove surface moisture. Next, photoresist AZ703 is spin-coated onto the GaN cap layer 10, pre-baked at 110°C for 1 minute, and then photolithographically lithographically performed using a MA6 contact UV lithography machine. Exposure is performed for 4.2 seconds, followed by development for 70 seconds, ultimately forming an interdigitated pattern on the epitaxial wafer. The interdigitated pattern has a width of 7 μm and a length of 300 μm.

[0059] S3. Etch the GaN cap layer 10 and the AlGaN barrier layer 9, the AlN insertion layer 8, and part of the u-GaN channel layer 7 within the target interdigitated region, with the etching endpoint located inside the u-GaN channel layer. The area outside the target interdigitated region forms a first interdigitated region.

[0060] Specifically, the etching in step S3 is performed using inductively coupled plasma etching (ICP) or reactive ion etching (RIE) techniques.

[0061] For example, using ICP technology, BCl3 gas is used for etching to a depth of approximately 170 nm to isolate the HEMT mesa; then, the photoresist is removed: the photoresist is removed by immersing in NMP solution heated to 80°C for 30 min, rinsing and drying, and then using a plasma photoresist remover with an Ar flow rate of 30 SCCM and an O2 flow rate of 200 SCCM at a power of 500 W for 10 min to completely remove the photoresist and form AlGaN / GaN transparent interdigitated fingers.

[0062] S4. Define a source electrode pattern on the upper surface of the GaN cap layer 10 in the first interdigitated region, and define a second interdigitated region as a drain electrode pattern on the upper surface of the etched u-GaN channel layer 7; wherein, in the layer projection of the first interdigitated region and the second interdigitated region onto the u-GaN channel layer, the fingers of the first interdigitated region and the fingers of the second interdigitated region are arranged intersectingly and do not contact each other.

[0063] Specifically, the sample surface after etching in step S3 is first cleaned, and then a drain electrode pattern is formed on the surface of the etched u-GaN channel layer 7 by photolithography, and a source electrode pattern is formed on the surface of the GaN cap layer 10 by photolithography.

[0064] For example, the current sample is first cleaned by acid washing with 10% dilute hydrochloric acid for 1 minute to remove surface impurities after photoresist removal, rinsing with deionized water and then spin-drying, followed by drying in a 130°C dryer for 30 minutes to remove surface moisture. Photoresist AZ703 is spin-coated onto the surface of the GaN cap layer 10, pre-baked at 110°C for 1 minute, and then photolithographically lithographically performed using a MA6 contact UV lithography machine for 4.5 seconds, followed by 60 seconds of development. The areas without photoresist form interdigitated patterns on the etched u-GaN channel layer 7, with interdigitations 3 μm wide and 300 μm long, forming a source electrode pattern on the surface of the GaN cap layer 10.

[0065] S5. A drain electrode metal layer 11B is formed on the drain electrode pattern, and a source electrode metal layer 11A is formed on the source electrode pattern.

[0066] Specifically, using electron beam evaporation (EBE) technology, Ti / Al / Ni / Au metal stacks are deposited on the u-GaN channel layer 7 and a portion of the GaN cap layer 10, respectively, with thicknesses of 20 / 120 / 50 / 45 nm. The Ti / Al / Ni / Au metal stack on the u-GaN channel layer 7 serves as the drain electrode metal layer 11B, and the Ti / Al / Ni / Au metal stack on the portion of the GaN cap layer 10 serves as the source electrode metal layer 11A.

[0067] S6. Anneal the current sample to form an ohmic contact between the drain electrode metal layer 11B and the u-GaN channel layer 7 below, and between the source electrode metal layer 11A and the GaN cap layer 10 below, to obtain a ready-to-be-completed heterojunction self-powered ultraviolet photodetector; wherein, the u-GaN channel layer 7, AlN insertion layer 8 and AlGaN barrier layer 9 on the first interdigitated region constitute an AlGaN / GaN heterojunction, and the AlGaN / GaN heterojunction and GaN cap layer 10 form an interdigitated transparent heterojunction electrode; the drain electrode metal layer 11B forms a metal interdigitated electrode.

[0068] Specifically, the sample obtained in step S5 is first degummed, and then the sample is rapidly annealed at 750℃~850℃ for 30~60s.

[0069] For example, most of the metal and photoresist are removed using a blue film. Then, the image is immersed in NMP solution heated to 80°C for 30 minutes to remove residual photoresist and metal. After rinsing and drying, a plasma photoresist remover is used at 500W power for 10 minutes with an Ar flow rate of 30 SCCM and an O2 flow rate of 200 SCCM to completely remove the photoresist, forming an alternating AlGaN / GaN transparent interdigitated and Ti / Al / Ni / Au metal interdigitated structure with an interdigitation spacing of 1.5 μm. Then, rapid annealing at 830°C for 30 seconds in an N2 environment forms the drain electrode metal layer 11B and the source electrode metal layer 11A, resulting in the fabricated heterojunction self-powered ultraviolet photodetector.

[0070] The preparation method of this invention is simple and compatible with standard semiconductor processes. By epitaxially producing depletion-mode AlGaN / GaNHEMT epitaxial wafers with high crystallinity, the etching depth can be precisely controlled and the electrode preparation process can be simplified to obtain an ultraviolet photodetector with low dark current and high responsivity under zero bias voltage. It is suitable for mass production and has good prospects for industrial application.

[0071] Please see Figure 3 , Figure 3This is a top view under a microscope of a heterojunction self-powered ultraviolet photodetector provided in an embodiment of the present invention. In this heterojunction self-powered ultraviolet photodetector, substrate 1 is a silicon substrate with a thickness of 1 mm; AlN nucleation layer 2 has a thickness of 0.2 μm; AlN / AlGaN superlattice layer 3 has 32 alternating AlN and AlGaN periods and a thickness of 0.5 μm; AlGaN transition layer 4 has an Al composition of 35% and a thickness of 1.1 μm; AlN / GaN superlattice layer 5 has 38 alternating AlN and GaN layers, an Al composition of 15%, and a thickness of 1.75 μm; high-resistivity GaN buffer layer 6 has a thickness of 1 μm; u-GaN channel layer 7 in the second interdigitated region has a thickness of 300 nm; AlN insertion layer 8 has a thickness of 1 nm; AlGaN barrier layer 9 has an Al composition of 21% and a thickness of 20 nm; and GaN cap layer 10 has a thickness of 5 nm. nm; the transparent heterojunction electrode includes 25 transparent fingers 101, each transparent finger 101 having a width of 7 μm and a length of 300 μm; the source metal layer 11A and the drain metal layer 11B are Ti / Al / Ni / Au composite metal layers, with the thicknesses of Ti / Al / Ni / Au being 20 nm / 120 nm / 50 nm / 45 nm respectively; the metal interdigitated electrode includes 26 metal fingers 111, each metal finger 111 having a width of 3 μm and a length of 300 μm; the spacing between the transparent fingers 101 and the adjacent metal fingers 111 projected onto the surface of the u-GaN channel layer 7 is 1.5 μm.

[0072] Tested using the MStarter200 detector system Figure 3 The performance of the device shown is as follows: Figure 4 As shown. Figure 4 This is the spectral responsivity and spectral power density spectrum of the heterojunction self-powered ultraviolet photodetector at 0 V bias. The horizontal axis represents wavelength (nm), ranging from 200 nm to 600 nm; the left vertical axis represents responsivity (A / W); and the right vertical axis represents power density (mW / cm²). A significant peak in responsivity occurs near 200 nm, indicating high photoelectric conversion efficiency in the deep ultraviolet band, thanks to the efficient separation and collection of photogenerated carriers by the strong polarization-induced electric field in the AlGaN / GaN heterojunction. Within the 200–280 nm range, the responsivity decreases sharply with increasing wavelength, exhibiting a steep slope. Above 280 nm, the responsivity remains zero, indicating that the detector has no response in the visible light band and possesses excellent solar-blind characteristics.

[0073] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A heterojunction self-powered ultraviolet photodetector, characterized in that, It includes a substrate stacked from bottom to top, an AlN nucleation layer, an AlN / AlGaN superlattice layer, an AlGaN transition layer, an AlN / GaN superlattice layer, a high-resistivity GaN buffer layer, and a u-GaN channel layer; The upper surface of the u-GaN channel layer is provided with a first interdigitated region and a second interdigitated region; the thickness of the u-GaN channel layer in the first interdigitated region is higher than the thickness of the u-GaN channel layer in the second interdigitated region; in the layer projection of the first interdigitated region and the second interdigitated region onto the u-GaN channel layer, the fingers of the first interdigitated region and the fingers of the second interdigitated region are arranged intersectingly and do not contact each other; The ultraviolet detector further includes an AlN insertion layer, an AlGaN barrier layer, a GaN cap layer, a source metal layer superimposed on the GaN cap layer, and a drain metal layer superimposed on the u-GaN channel layer in the second interdigitated region; wherein, the u-GaN channel layer in the first interdigitated region and the AlN insertion layer and the AlGaN barrier layer above it constitute an AlGaN / GaN heterojunction, and the AlGaN / GaN heterojunction and the GaN cap layer form an interdigitated transparent heterojunction electrode; the drain metal layer forms a metal interdigitated electrode.

2. The heterojunction self-powered ultraviolet photodetector according to claim 1, characterized in that, The AlN / AlGaN superlattice layer is composed of alternating stacks of AlN and AlGaN, with an alternation period of 30 to 35. The Al composition of the AlN / AlGaN superlattice layer is 65 to 75%, and the thickness is 0.4 to 0.5 μm.

3. The heterojunction self-powered ultraviolet photodetector according to claim 1, characterized in that, The Al composition of the AlGaN transition layer is 30%~40%, and the thickness is 1.0~1.5μm.

4. The heterojunction self-powered ultraviolet photodetector according to claim 1, characterized in that, The AlN / GaN superlattice layer is composed of alternating stacked AlN and GaN layers with an alternation period of 35 to 40. The Al composition of the AlN / GaN superlattice layer is 10% to 20%, and the thickness is 1.5 to 2.0 μm.

5. The heterojunction self-powered ultraviolet photodetector according to claim 1, characterized in that, In the transparent heterojunction electrode, the thickness of the u-GaN channel layer is 280~320nm; the thickness of the AlN insertion layer is 1~2nm; the AlGaN barrier layer is an undoped AlGaN layer with an Al composition of 20%~30% and a thickness of 15~25nm; and the thickness of the GaN cap layer is 2~5nm.

6. The heterojunction self-powered ultraviolet photodetector according to claim 1, characterized in that, The transparent heterojunction electrode includes 20 to 30 transparent fingers, each of which has a width of 7 to 8 μm and a length of 200 to 300 μm.

7. The heterojunction self-powered ultraviolet photodetector according to claim 1, characterized in that, The interdigitated metal electrode is a Ti / Al / Ni / Au composite metal layer with thicknesses of 20nm / 120nm / 50nm / 45nm respectively. The interdigitated metal electrode includes 20 to 30 metal fingers, each of which has a width of 2 to 3μm and a length of 200 to 300μm.

8. The heterojunction self-powered ultraviolet photodetector according to claim 1, characterized in that, The distance between the fingers of the transparent heterojunction electrode and the fingers of the metal interdigitated electrode projected onto the plane of the u-GaN channel layer is 1~3μm.

9. A method for fabricating a heterojunction self-powered ultraviolet photodetector, characterized in that, Includes the following steps: S1. An AlN nucleation layer, an AlN / AlGaN superlattice layer, an AlGaN transition layer, an AlN / GaN superlattice layer, a high-resistivity GaN buffer layer, a u-GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN cap layer are sequentially grown on the substrate. S2. Define the target interdigitated region on the GaN cap layer; S3. Etch the GaN cap layer and the AlGaN barrier layer, the AlN insertion layer and part of the u-GaN channel layer below it within the target interdigitated region, with the etching endpoint located inside the u-GaN channel layer; wherein, the area outside the target interdigitated region forms a first interdigitated region; S4. Define a source electrode pattern on the upper surface of the GaN cap layer of the first interdigitated region, and define a second interdigitated region as a drain electrode pattern on the upper surface of the etched u-GaN channel layer; wherein, in the layer projection of the first interdigitated region and the second interdigitated region onto the u-GaN channel layer, the fingers of the first interdigitated region and the fingers of the second interdigitated region are arranged intersectingly and do not contact each other. S5. A drain electrode metal layer is formed on the drain electrode pattern, and a source electrode metal layer is formed on the source electrode pattern; S6. Anneal the current sample to form ohmic contacts between the drain metal layer and the underlying u-GaN channel layer, and between the source metal layer and the underlying GaN cap layer, to obtain a ready-to-be-completed heterojunction self-powered ultraviolet photodetector; wherein, the u-GaN channel layer in the first interdigitated region and the AlN insertion layer and the AlGaN barrier layer above it constitute an AlGaN / GaN heterojunction, and the AlGaN / GaN heterojunction and the GaN cap layer form an interdigitated transparent heterojunction electrode; the drain metal layer forms a metal interdigitated electrode.

10. The method for fabricating a heterojunction self-powered ultraviolet photodetector according to claim 9, characterized in that, Perform rapid annealing on the current sample, including: rapid annealing of the current sample at 750℃~850℃ for 30~60s.

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