An ultraviolet detector and its preparation method

Abstract

This invention discloses an ultraviolet detector and its fabrication method, applicable to the semiconductor field. The detector includes: a substrate; a p-GaN layer located on one side of the substrate, the p-GaN layer including a p-GaN gate layer in a first region; a barrier layer located on the surface of the p-GaN layer facing away from the substrate; a channel layer located on the surface of the barrier layer facing away from the substrate, the channel layer including a nano-bump array in the first region and a remaining channel layer in the first region; the remaining channel layer is disposed between the nano-bump array and the barrier layer; and a passivation layer located on the surface of the channel layer facing away from the substrate. The barrier layer and the channel layer form a two-dimensional electron gas, and the p-GaN gate layer, barrier layer, and channel layer form a built-in electric field; the nano-bump array and the passivation layer form a polarized electric field; the built-in electric field at least covers a portion of the sidewalls of the nano-bump array. The ultraviolet detector achieves low dark current, high responsivity, and high response speed under the action of the built-in electric field and the polarized electric field.

Description

Technical Field

[0001] This invention relates to the field of semiconductor devices, and in particular to an ultraviolet detector and its fabrication method. Background Technology

[0002] Ultraviolet (UV) detectors have significant applications in military reconnaissance, space communication, environmental monitoring, biological detection, and flame detection. Traditional UV detectors mostly use silicon-based photodiodes and photomultiplier tubes; however, these devices suffer from problems such as slow response speed, low sensitivity, high dark current, and poor radiation resistance.

[0003] In recent years, ultraviolet detectors based on wide-bandgap semiconductor materials (such as GaN, AlGaN, and Ga2O3) have become a research hotspot due to their high breakdown voltage, high saturated electron drift velocity, high chemical stability, and good radiation resistance. In particular, the GaN material system, with its direct bandgap, high electron mobility, and good thermal conductivity, is suitable for fabricating high-performance ultraviolet detectors.

[0004] High electron mobility transistors (HEMTs), as a type of field-effect transistor based on a heterojunction structure, utilize two-dimensional electron gas (2DEG) to achieve high-speed, high-gain electron transport and are widely used in radio frequency, power electronics, and other fields. In recent years, some studies have begun to explore the use of HEMT structures for ultraviolet detection, achieving photoresponse by inducing changes in channel conductivity through ultraviolet light irradiation.

[0005] However, traditional GaN HEMTs are typically normally-on devices, meaning that a high concentration of two-dimensional electron gas already exists in the channel even without a gate voltage. This results in a large dark current under no-light conditions, which is detrimental to low-noise applications such as ultraviolet detection. Furthermore, conventional HEMT structures have limited absorption efficiency for ultraviolet light, low photogenerated carrier separation efficiency, and a difficulty in simultaneously achieving high response speed and responsivity. Current research on gate structures for normally-off ultraviolet detection GaN HEMTs mainly includes recessed gates, thin barrier layer gates, p-GaN gates, and fluoride gates. Specifically, the recessed gate achieves high-performance ultraviolet detectors by depositing an extremely thin gate metal layer on the gate oxide layer of the gate recess and applying a negative gate voltage to deplete the two-dimensional electron gas channel, providing a built-in electric field to assist the transport of photogenerated carriers. However, it requires a continuous application of a negative gate voltage, increasing the complexity of the driving circuit, and the gate metal also has a certain blocking effect on ultraviolet light. Thin barrier layer technology reduces the AlGaN barrier layer in the gate region until the two-dimensional electron gas is depleted. This method avoids blocking the illumination window and can effectively improve the device's responsivity. However, this gate structure cannot effectively suppress the continuous photoconductivity effect, resulting in a long turn-off time. Fluoride gates implant a certain dose of fluoride ions into the AlGaN barrier layer through an ion implantation process. Fluorine ions, with their strong electronegativity, raise the conduction band of the AlGaN barrier layer, thereby depleting the two-dimensional electron gas channel. However, fluorine ion implantation causes lattice damage to the AlGaN barrier layer, affecting the carrier density and mobility of the two-dimensional electron gas. Although fluorine ion treatment can suppress the persistent photoconductivity effect to some extent by reducing the defect density of the barrier layer, the response time of the device is still relatively long. The p-GaN gate depletes the two-dimensional electron gas channel through the high concentration of holes in the p-GaN cap layer. At the same time, the built-in electric field of the p-GaN layer is used to capture photogenerated holes, which can effectively separate electron-hole pairs and is beneficial for realizing high-response ultraviolet detectors. However, the p-GaN cap layer has strong absorption of 365nm ultraviolet light, making it difficult to realize high-response ultraviolet detectors.

[0006] Therefore, there is a need for an ultraviolet detector that can solve the technical problems of high dark current, low efficiency of ultraviolet light absorption and carrier separation, and consequently low responsivity and response speed of current ultraviolet detectors. Summary of the Invention

[0007] The purpose of this invention is to provide an ultraviolet detector and its fabrication method, which can solve the technical problems of high dark current, low ultraviolet light absorption and carrier separation efficiency, and consequently low responsivity and response speed of current ultraviolet detectors.

[0008] To address the aforementioned technical problems, this invention provides an ultraviolet detector, comprising, along its thickness direction, the following components: Substrate; A p-GaN layer located on one side of the substrate, the p-GaN layer including a p-GaN gate layer located in a first region; A barrier layer located on the surface of the p-GaN layer facing away from the substrate; A channel layer is located on the surface of the barrier layer facing away from the substrate. The channel layer includes a nano-bump array in a first region and a remaining channel layer in the first region. The remaining channel layer in the first region is disposed between the nano-bump array and the barrier layer. A passivation layer located on the surface of the channel layer facing away from the substrate; The barrier layer and the channel layer form a two-dimensional electron gas, and the p-GaN gate layer, the barrier layer and the channel layer form a built-in electric field; the nano-bump array and the passivation layer form a polarized electric field; the built-in electric field at least covers part of the sidewalls of the nano-bump array.

[0009] Optionally, the nano-bump array includes multiple spaced nanostructure units; The nanostructure unit is a nanoprotrusion structure with inclined sidewalls, and the sidewalls of the nanoprotrusion structure are inclined at an angle to the thickness direction.

[0010] Optionally, the trench layer may further include a trench layer located in the second region; The sum of the thickness of the remaining channel layer in the first region and the height of the nano-bump array is less than the thickness of the channel layer in the second region.

[0011] Optionally, it includes a source electrode and a drain electrode; the source electrode and the drain electrode are respectively located on the surface of the channel layer in the second region facing away from the substrate.

[0012] Optionally, the passivation layer includes a passivation layer on the surface of the nano-rough array located in the first region and a passivation layer on the surface of the channel layer located in the second region other than the source electrode and the drain electrode.

[0013] Optionally, the p-GaN gate layer is a Mg-doped GaN layer with a Mg atom concentration of 1×10⁻⁶. 19 cm -3 -1×10 20 cm -3 The thickness of the Mg-doped GaN layer is 50nm-500nm.

[0014] Optionally, it may also include a dielectric layer, which is located between the substrate and the p-GaN layer and is stacked with the substrate.

[0015] The present invention also provides a method for fabricating an ultraviolet detector, which is used to fabricate the ultraviolet detector described above, comprising: A buffer layer, a channel layer, a barrier layer, and a p-GaN layer are sequentially grown on the surface of the second substrate to form the first epitaxial structure. A dielectric layer is deposited on the surface of the first epitaxial structure, and the substrate and the dielectric layer are wafer-bonded. After wafer bonding, the second substrate is peeled off, the buffer layer is removed, and the second epitaxial structure is formed. The channel layer is etched on the surface of the second epitaxial structure to form a nano-rough array in the first region and a passivation layer is deposited to complete the fabrication of the ultraviolet detector.

[0016] Optionally, the p-GaN layer further includes a GaN layer located in the second region, the fabrication of which includes: The p-GaN layer in the second region is subjected to hydrogen plasma treatment using inductively coupled plasma to passivate the p-type doping of the p-GaN layer and form a GaN layer.

[0017] Optionally, the etching portion of the trench layer forming a nano-roughness array located in the first region includes: The pattern of the nano-bump array is defined in the channel layer of the first region using electron beam lithography; the nano-bump array is formed by plasma etching; and the etching damage is repaired by tetramethylammonium hydroxide solution after etching.

[0018] The ultraviolet detector provided by the present invention comprises, along its thickness direction, the following: a substrate; a p-GaN layer located on one side of the substrate, the p-GaN layer including a p-GaN gate layer located in a first region; a barrier layer located on the surface of the p-GaN layer facing away from the substrate; a channel layer located on the surface of the barrier layer facing away from the substrate, the channel layer including a nano-bump array located in the first region and a remaining channel layer located in the first region; the remaining channel layer located in the first region is disposed between the nano-bump array and the barrier layer; and a passivation layer located on the surface of the channel layer facing away from the substrate; wherein the barrier layer and the channel layer form a two-dimensional electron gas, the p-GaN gate layer, the barrier layer, and the channel layer form a built-in electric field; the nano-bump array and the passivation layer form a polarized electric field; and the built-in electric field at least covers a portion of the sidewalls of the nano-bump array.

[0019] As can be seen, in this ultraviolet detector, the p-GaN gate layer, barrier layer, and channel layer form a built-in electric field, while the nano-bump array and passivation layer form a polarized electric field. The built-in electric field at least covers part of the sidewalls of the nano-bump array. The built-in electric field formed by the p-GaN gate layer depletes the two-dimensional electron gas at the interface between the barrier layer and the channel layer. At this point, the normally-off characteristic of the ultraviolet detector can be achieved without applying a gate voltage, which can significantly reduce the dark current (down to the μA level). The nano-bump array located in the channel layer enhances the absorption efficiency of the ultraviolet detector for ultraviolet light. Through the synergistic effect of the built-in electric field introduced by the p-GaN gate layer and the polarized electric field introduced by the AlN passivation layer, the channel can be rapidly depleted in the dark state, suppressing the persistent photoconductivity effect. It can also effectively trap photogenerated holes, improve the separation efficiency of electron-hole pairs, which is beneficial to improving the responsivity and response speed of the device, and realizing rapid response and turn-off of ultraviolet light signals.

[0020] The present invention also provides a method for preparing an ultraviolet detector, which has the same beneficial effects as the ultraviolet detector described above, and will not be described in detail here. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of an ultraviolet detector provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the energy band structure of the heterojunction formed by the passivation layer and the channel layer in the ultraviolet detector provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of another ultraviolet detector provided in an embodiment of the present invention; Figure 4 A schematic diagram of electron concentration distribution near a two-dimensional electron gas channel of an ultraviolet detector provided in an embodiment of the present invention; Figure 5 A schematic diagram of electron concentration distribution near a two-dimensional electron gas channel of another ultraviolet detector provided in an embodiment of the present invention; Figure 6 A flowchart illustrating a method for fabricating an ultraviolet detector according to an embodiment of the present invention; Figures 7a-7h A process flow diagram of a method for fabricating an ultraviolet detector provided in an embodiment of the present invention; In the figure: 1. Substrate, 2. Dielectric layer, 3. p-GaN layer, 31. p-GaN gate layer, 32. GaN layer, 4. Barrier layer, 5. Channel layer, 51. Nano-bump array, 52. Remaining channel layer in the first region, 53. Channel layer in the second region, 6. Source electrode, 7. Drain electrode, 8. Passivation layer, 9. Second substrate, 10. Buffer layer. Detailed Implementation

[0023] The core of this invention is to provide an ultraviolet detector. Current GaN HEMT devices suffer from excessive dark current, low efficiency in ultraviolet light absorption and carrier separation, resulting in low responsivity and response speed. Furthermore, the p-GaN gate has a certain blocking effect on ultraviolet light, affecting the absorption of ultraviolet light by the GaN HEMT device and thus impacting the device's responsivity.

[0024] The ultraviolet detector provided by the present invention comprises, along its thickness direction, the following: a substrate 1; a GaN layer 3 located on one side of the substrate 1, the GaN layer 3 including a p-GaN gate layer 31 located in a first region; a barrier layer 4 located on the surface of the GaN layer 3 facing away from the substrate 1; a channel layer 5 located on the surface of the barrier layer 4 facing away from the substrate 1, the channel layer 5 including a nano-bump array 51 located in the first region and a remaining channel layer 52 located in the first region; the remaining channel layer 52 located in the first region is disposed between the nano-bump array 51 and the barrier layer 4; and a passivation layer 8 located on the surface of the channel layer 5 facing away from the substrate 1; wherein, the barrier layer 4 and the channel layer 5 form a two-dimensional electron gas, the p-GaN gate layer 31, the barrier layer 4, and the channel layer 5 form a built-in electric field; the nano-bump array 51 and the passivation layer 8 form a polarized electric field; and the built-in electric field at least covers a portion of the sidewalls of the nano-bump array 51.

[0025] In this ultraviolet detector, the p-GaN gate layer 31, barrier layer 4, and channel layer 5 form a built-in electric field, while the nano-bump array 51 and passivation layer 8 form a polarized electric field. The built-in electric field at least covers part of the sidewalls of the nano-bump array 51. Through the synergistic effect of the built-in electric field introduced by the p-GaN gate layer 31 and the polarized electric field introduced by the passivation layer 8, the separation of photogenerated carriers in the region where the nano-bump array 51 is located is promoted, achieving ultraviolet detection functions such as low dark current, high responsivity, and high response speed. It is suitable for ultraviolet detection systems with high sensitivity, low power consumption, and high integration. In addition, the passivation layer 8 can passivate the surface traps of the channel layer 5, suppress the degradation of the on-resistance of the ultraviolet detector, and improve the stability and reliability of the device.

[0026] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of an ultraviolet detector provided in an embodiment of the present invention.

[0029] See Figure 1 In this embodiment, the ultraviolet detector sequentially includes, along its thickness direction: a substrate 1; a GaN layer 3 located on one side of the substrate 1, the GaN layer 3 including a p-GaN gate layer 31 located in a first region; a barrier layer 4 located on the surface of the GaN layer 3 facing away from the substrate 1; a channel layer 5 located on the surface of the barrier layer 4 facing away from the substrate 1, the channel layer 5 including a nano-bump array 51 located in the first region and a remaining channel layer 52 located in the first region; the remaining channel layer 52 located in the first region is disposed between the nano-bump array 51 and the barrier layer 4; and a passivation layer 8 located on the surface of the channel layer 5 facing away from the substrate 1; wherein, the barrier layer 4 and the channel layer 5 form a two-dimensional electron gas, the p-GaN gate layer 31, the barrier layer 4, and the channel layer 5 form a built-in electric field; the nano-bump array 51 and the passivation layer 8 form a polarized electric field; and the built-in electric field at least covers part of the sidewalls of the nano-bump array 51 (i.e., part of the outer surface and part of the internal space of the nano-bump array 51).

[0030] The aforementioned substrate 1 serves as the base for the entire ultraviolet detector, and subsequent structures of the ultraviolet detector need to be built upon this substrate 1. Substrate 1 primarily functions as a support and heat dissipation element for the ultraviolet detector. The material of substrate 1 can be SiC (silicon carbide), Si (silicon), sapphire, etc. The specific material and dimensions of substrate 1 can be determined according to actual conditions and are not specifically limited here.

[0031] This embodiment does not impose specific limitations on the materials and thicknesses used for the GaN layer 3, barrier layer 4, channel layer 5, and passivation layer 8, as long as the barrier layer 4 and channel layer 5 form a two-dimensional electron gas, the p-GaN gate layer 31, barrier layer 4, and channel layer 5 form a built-in electric field, the nano-bump array 51 and passivation layer 8 form a polarized electric field, and the built-in electric field at least covers part of the sidewalls of the nano-bump array 51. These can be selected according to actual needs and will not be elaborated further here. For example, in this embodiment, GaN layer 3 is a Mg-doped GaN layer, barrier layer 4 is an AlGaN barrier layer, channel layer 5 is a GaN channel layer, and passivation layer 8 is an AlN passivation layer. The GaN channel layer can generate a strong photoelectric response to 365nm ultraviolet light.

[0032] In this embodiment, the coverage of the built-in electric field over the nano-protrusion array 51 can be controlled by adjusting the atomic concentration and thickness of the p-GaN layer 3. Specific control methods are detailed below and will not be elaborated upon here. In this embodiment, the built-in electric field covers at least a portion of the sidewalls of the nano-protrusion array 51 (i.e., a portion of the outer surface and a portion of the internal space of the nano-protrusion array 51). This can be achieved by the built-in electric field covering only a portion of the sidewalls (i.e., a portion of the outer surface and a portion of the internal space of the nano-protrusion array 51), or by the built-in electric field completely covering the nano-protrusion array 51. No specific limitation is made here. Ideally, the synergy between the built-in electric field and the nano-protrusion array 51, as well as the synergy between the built-in electric field and the polarization electric field, achieves the best results when the built-in electric field completely covers the nano-protrusion array 51. Specifically, in this embodiment, the built-in electric field completely covers the nano-protrusion array 51.

[0033] In this embodiment, the barrier layer 4 and the channel layer 5 form a two-dimensional electron gas. The p-GaN gate layer 31, the barrier layer 4, and the channel layer 5 form a PN junction, generating a built-in electric field. The built-in electric field introduced by the p-GaN gate layer 31 depletes the two-dimensional electron gas at the interface between the barrier layer 4 and the channel layer 5. At this time, the normally-off characteristic of the ultraviolet detector can be achieved without applying a gate voltage, which can significantly reduce the dark current (the dark current can be reduced to the μA level). Moreover, the p-GaN gate layer 31 is disposed below the two-dimensional electron gas channel, avoiding the p-GaN layer 3 from blocking ultraviolet light. At the same time, the built-in electric field can effectively trap photogenerated holes, improve the separation efficiency of electron-hole pairs, suppress the continuous photoconductivity effect, realize the rapid response and shutdown of ultraviolet light signals, and improve the responsivity of the ultraviolet detector.

[0034] In this embodiment, the channel layer 5 includes a nano-protrusion array 51 located in the first region and a remaining channel layer 52 located in the first region. The remaining channel layer 52 located in the first region is disposed between the nano-protrusion array 51 and the barrier layer 4. The nano-protrusion array 51 can regulate the absorption of ultraviolet light by the ultraviolet detector, and can significantly enhance the absorption efficiency of ultraviolet light by the channel layer 5. At this time, the nano-protrusion array 51 has an absorption enhancement region, which is the nano-protrusion array 51 itself.

[0035] In this embodiment, the nanoarray comprises multiple nanostructural units, which include any one of the following structures or any combination thereof: nanoprotrusions or nanodepressions. Adjacent nanostructural units may or may not be spaced apart; this embodiment does not impose specific limitations. The structure of the nanoprotrusion / depression array 51 can be adjusted according to actual needs to control the absorption of ultraviolet light by the ultraviolet detector. Similarly, this embodiment does not limit the spacing between adjacent nanostructural units; the spacing between adjacent units can be equal or unequal.

[0036] In this embodiment, the built-in electric field formed by the p-GaN gate layer 31 at least covers a portion of the sidewalls of the nano-bump array 51. At this time, the nano-bump array 51 is within the control range of the built-in electric field introduced by the p-GaN gate layer 31, achieving at least partial overlap between the absorption enhancement region of the nano-bump array 51 and the control region of the built-in electric field introduced by the p-GaN gate layer 31. Simultaneously, the built-in electric field introduced by the p-GaN gate layer 31 and the nano-bump array 51 work together, enhancing the absorption efficiency of the ultraviolet detector. Furthermore, the built-in electric field effectively traps photogenerated holes in the region of the nano-bump array 51, improving the electron-hole pair separation efficiency, enhancing the device's responsivity, and rapidly depleting channel electrons in the dark state, suppressing persistent photoconductivity, and achieving rapid response and shutdown of ultraviolet light signals.

[0037] In the ultraviolet detector of this application, a passivation layer 8 is disposed on the surface of the channel layer 5 facing away from the substrate 1. At this time, the nano-rough array 51 and the passivation layer 8 form a heterojunction, thereby forming a polarized electric field. Due to the lattice mismatch, a strong polarized electric field is generated from the channel layer 5 to the passivation layer 8, which drives electrons to migrate to the channel layer 5 and holes to accumulate at the heterojunction interface, further improving the separation efficiency of photogenerated electron-hole pairs and significantly improving the responsivity of the ultraviolet detector.

[0038] For details, please refer to Figure 2 , Figure 2 This is a schematic diagram of the energy band structure of the heterojunction formed by the passivation layer 8 and the channel layer 5 in the ultraviolet detector provided in an embodiment of the present invention. In the diagram, E... c Represents the bottom of the conduction band, E v The price range is represented by a top, E fRepresenting the Fermi level; the polarization electric field in this embodiment originates from the intrinsic spontaneous polarization of the wide-bandgap semiconductor in the wurtzite structure (i.e., the GaN-type ultraviolet detector of this application) and the piezoelectric polarization caused by lattice mismatch, resulting in a higher electric field strength. Furthermore, the passivation layer 8 achieves band bending at the interface through the polarization electric field. Conduction band shift forms an electron barrier, preventing photogenerated electrons from escaping to the passivation layer 8, while valence band shift forms a hole barrier, confining photogenerated holes at the interface between the passivation layer 8 and the channel layer 5. This effectively suppresses the recombination of photogenerated carriers on the surface of the nano-uneven array (since defects are introduced on the surface during the fabrication of the nano-uneven array 51 to form carrier recombination centers), while also avoiding the problem of long response times caused by the slow release of carriers trapped by interface traps.

[0039] In this embodiment, the built-in electric field formed by the p-GaN gate layer 31 at least covers part of the sidewalls of the nano-rough array 51 (i.e., part of the outer surface and part of the internal space of the nano-rough array 51), that is, the built-in electric field formed by the p-GaN gate layer 31 at least partially covers the polarization electric field formed by the nano-rough array 51 and the passivation layer 8. At this time, the built-in electric field formed by the p-GaN gate layer 31 and the polarization electric field formed by the nano-rough array 51 work together to promote the separation of photogenerated carriers in the region of the nano-rough array 51. Specifically, the built-in electric field formed by the p-GaN gate layer 31 covers at least part of the sidewalls of the nano-bump array 51 (i.e., part of the outer surface and part of the internal space of the nano-bump array 51), promoting carrier separation in the bulk phase of the nano-bump array 51 (i.e., carrier separation inside the nano-bump array 51); while the polarized electric field generated by the heterojunction formed on the surface of the nano-bump array 51 and the passivation layer 8 has a small range of action and can only act on the carrier separation on the surface of the nano-bump array 51, but the intensity of the polarized electric field is high, several times stronger than the aforementioned built-in electric field. This strong polarized electric field can rapidly separate electron-hole pairs near the surface of the nano-bump array 51.

[0040] The ultraviolet detector provided by this invention features a built-in electric field formed by the p-GaN gate layer 31, barrier layer 4, and channel layer 5, and a polarized electric field formed by the nano-bump array 51 and passivation layer 8. The built-in electric field at least covers a portion of the sidewalls of the nano-bump array 51. Through the synergistic effect of the built-in electric field introduced by the p-GaN gate layer 31 and the polarized electric field introduced by the passivation layer 8, the separation of photogenerated carriers in the region where the nano-bump array 51 is located is promoted, achieving ultraviolet detection functions such as low dark current, high responsivity, and high response speed. It is suitable for ultraviolet detection systems with high sensitivity, low power consumption, and high integration. In addition, the passivation layer 8 can passivate the surface traps of the channel layer 5, suppress the degradation of the on-resistance of the ultraviolet detector, and improve the stability and reliability of the device.

[0041] The specific structure of an ultraviolet detector provided by this invention will be described in detail in the following embodiments.

[0042] Example 2

[0043] Please refer to Figure 3 , Figure 3 This is a schematic diagram of another ultraviolet detector provided in an embodiment of the present invention.

[0044] See Figure 3 To enhance the absorption of ultraviolet light by the nano-protrusion array 51, in this embodiment, the nano-protrusion array 51 includes multiple spaced nanostructure units. Each nanostructure unit is a nanoprotrusion structure with tilted sidewalls, the sidewalls of which are tilted at an angle to the thickness direction. In this case, the nanoprotrusion structure with tilted sidewalls can resonate and absorb ultraviolet light effectively. To further enhance ultraviolet light absorption, the spacing between the nano-protrusion array 51 in this embodiment is smaller than the wavelength of the ultraviolet light absorbed by the ultraviolet detector. This embodiment does not impose specific limitations on the height, spacing, or number of nanostructure units in the nano-protrusion array 51; these can be adjusted according to actual needs. For example, in this embodiment, the diameter of the nanostructure unit is 80 nm, the height is 100 nm, the spacing between adjacent nanostructure units is 40 nm, and the number of nanostructure units in the nano-protrusion array 51 is no less than 500.

[0045] When the plane containing the sidewalls of the nano-protrusion array 51 is tilted at an angle to the thickness direction of the ultraviolet detector (i.e., the c-axis direction of the wurtzite structure), the plane containing the sidewalls of the nano-protrusion array 51 is a semi-polar surface. In this case, the polarized electric field formed by the nano-protrusion array 51 and the passivation layer 8 can completely cover the outer surface of the nano-protrusion array 51, thus significantly improving the photoresponsivity of the ultraviolet detector. When the plane containing the spacing of the nano-protrusion array 51 is perpendicular to the thickness direction of the ultraviolet detector (i.e., the c-axis direction of the wurtzite structure), the plane containing the spacing of the nano-protrusion array 51 is a polar surface. In this case, the polarized electric field is strongest, enabling the polarized electric field formed by the spacing of the nano-protrusion array 51 and the passivation layer 8 to assist in the depletion of the channel layer 5; in this case, the ultraviolet detector can significantly reduce dark current.

[0046] Based on the above embodiments, the channel layer 5 further includes a channel layer 53 located in the second region; the sum of the thickness of the remaining channel layer 52 located in the first region and the height of the nano-protrusion array 51 is less than the thickness of the channel layer 53 located in the second region. Specifically, in this embodiment, the channel layer 5 includes a nano-protrusion array 51 located in the first region, a remaining channel layer 52 located in the first region, and a channel layer 53 located in the second region, wherein the remaining channel layer 52 located in the first region is disposed between the nano-protrusion array 51 and the barrier layer 4. Specifically, in order to facilitate the chemical mechanical planarization during the fabrication process of the ultraviolet detector, the sum of the thickness of the remaining channel layer 52 located in the first region and the height of the nano-protrusion array 51 is less than the thickness of the channel layer 53 located in the second region.

[0047] Based on the above embodiments, the barrier layer 4 is an AlGaN barrier layer 4. In order to generate a high-density two-dimensional electron gas at the interface between the barrier layer 4 and the channel layer 5, the molar composition of Al is 20%-25%, and the thickness is 20nm-30nm. If the thickness of the barrier layer 4 is too large or the molar composition is too high, it will cause the stress of the AlGaN barrier layer to increase, resulting in more defects. On the other hand, if the barrier layer 4 is too thin, it will lead to insufficient two-dimensional electron gas density. In this embodiment, the molar composition of Al in the barrier layer 4 is 23%, and the thickness of the barrier layer is 20nm.

[0048] In this embodiment, the thickness of the channel layer 5 and the thickness of the remaining channel layer 52 in the first region can be adjusted according to the coverage range of the built-in electric field and the polarization electric field to ensure that the built-in electric field at least partially covers the nano-bump array 51. In this embodiment, the p-GaN gate layer 31 is a Mg-doped GaN layer with a Mg atom concentration of 1×10⁻⁶. 19 cm -3 -1×10 20 cm -3 The thickness of the Mg-doped GaN layer ranges from 50 nm to 500 nm. The range of the built-in electric field formed by the Mg-doped GaN layer can be controlled by adjusting the concentration of magnesium atoms and the thickness of the Mg-doped GaN layer. Specifically, the Mg atom concentration in the Mg-doped GaN layer is set to 3 × 10⁻⁶. 19 cm -3 The thickness of the Mg-doped GaN layer is set to 90 nm. At this time, the depth of the depletion region of the built-in electric field formed by the Mg-doped GaN layer, barrier layer 4, and channel layer 5 can reach 200 nm. In order to achieve the built-in electric field formed by the Mg-doped GaN layer covering the entire area of ​​the nano-rough array 51, the thickness of the channel layer 5 in this embodiment is 120 nm-130 nm. At this time, the thickness of the remaining channel layer 52 located in the first region is 20 nm-30 nm.

[0049] Based on the above embodiments, the ultraviolet detector includes a source electrode 6 and a drain electrode 7; the source electrode 6 and the drain electrode 7 are respectively located on the surface of the channel layer 53 in the second region facing away from the substrate 1. In this embodiment, the source electrode 6 and the drain electrode 7 can be composite metal layers composed of the following combinations: a titanium metal layer, an aluminum metal layer, a nickel metal layer, and a gold metal layer. In this embodiment, both the source electrode 6 and the drain electrode 7 are composite metal layers composed of a titanium metal layer, an aluminum metal layer, a nickel metal layer, and a gold metal layer, with thicknesses of 20 nm, 120 nm, 40 nm, and 120 nm, respectively.

[0050] Based on the above embodiments, the passivation layer 8 includes a passivation layer 8 on the surface of the nano-rough array 51 in the first region and a passivation layer 8 on the surface of the channel layer 53 in the second region other than the source electrode 6 and the drain electrode 7. Specifically, the passivation layer 8 includes a passivation layer 8 on the spacer surface of the nano-rough array 51 in the first region, a passivation layer 8 on the surface of the nanostructure unit of the nano-rough array 51 in the first region, and a passivation layer 8 on the surface of the channel layer 53 in the second region other than the source electrode 6 and the drain electrode 7, that is, the passivation layer 8 completely covers the exposed surface of the channel layer 5 and the surface of the nano-rough array 51. In this embodiment, the thickness of the passivation layer 8 is 3nm-5nm, such as 4nm in this embodiment.

[0051] At this time, the spacing of the nano-bump array 51 in the first region and the passivation layer 8 on the spacing surface form a polarized electric field, which has a gate-like effect. It can help deplete the channel layer 5, thereby reducing dark current and suppressing the persistent photoconductivity effect (the polarized electric field rapidly depletes the electrons in the channel layer 5 after the light disappears). Referring to the foregoing, the thickness of the remaining channel layer 52 in the first region in this embodiment is 20nm-30nm. To verify the depletion effect of the polarized electric field formed by the spacing of the nano-bump array 51 in the first region (i.e., GaN channel layer 5) and the passivation layer 8 on the spacing surface (i.e., AlN passivation layer 8) on the channel, this embodiment uses Sentaurus TCAD software (a semiconductor simulation software) for simulation. See [link to relevant documentation]. Figure 4 , Figure 4This is a schematic diagram of the electron concentration distribution near the two-dimensional electron gas channel of an ultraviolet detector provided in an embodiment of the present invention. Specifically, it is a comparison diagram of the electron concentration distribution near the two-dimensional electron gas channel of a GaN / AlGaN heterostructure used in an ultraviolet detector before and after the introduction of an AlN passivation layer. The highest electron concentration values ​​of the two curves in the figure are around a depth of 0.024 micrometers, which corresponds to the two-dimensional electron gas at the AlGaN / GaN layer interface. The GaN layer thickness is set to 20 nm, corresponding to the remaining channel layer 52 in the first region. By comparison, the electron concentration of the channel layer is significantly reduced after the introduction of the passivation layer 8. The polarization electric field formed by the spacing of the nano-rough array 51 in the first region (i.e., the GaN layer with a thickness of 20 nm) and the passivation layer 8 (i.e., the AlN layer with a thickness of 4 nm) on the surface of the spacing has a depletion effect on the channel layer 5. See also Figure 5 , Figure 5 This is a schematic diagram of the electron concentration distribution near the two-dimensional electron gas channel of another ultraviolet detector provided in this embodiment of the invention. Specifically, it is a comparison diagram of the electron concentration distribution near the two-dimensional electron gas channel of the GaN / AlGaN heterostructure used in another ultraviolet detector before and after the introduction of the AlN passivation layer. The GaN layer thickness is set to 30nm, corresponding to the remaining channel layer 52 in the first region. By comparison, the electron concentration of the channel layer 5 is significantly reduced after the introduction of the passivation layer 8. The polarization electric field formed by the spacing of the nano-rough array 51 in the first region (i.e., the GaN layer with a thickness of 30nm) and the passivation layer 8 (i.e., the AlN layer with a thickness of 4nm) on the surface of the spacing has a depletion effect on the channel layer 5.

[0052] Based on the above embodiments, the ultraviolet detector further includes a dielectric layer 2, which is located between the substrate 1 and the p-GaN layer 3, and is stacked with the substrate 1. In this embodiment, the dielectric layer 2 is a SiO2 dielectric layer 2.

[0053] The ultraviolet detector provided by this invention features a built-in electric field formed by the p-GaN gate layer 31, barrier layer 4, and channel layer 5, and a polarized electric field formed by the nano-bump array 51 and passivation layer 8. The built-in electric field at least covers a portion of the sidewalls of the nano-bump array 51. Through the synergistic effect of the built-in electric field introduced by the p-GaN gate layer 31 and the polarized electric field introduced by the passivation layer 8, the separation of photogenerated carriers in the region where the nano-bump array 51 is located is promoted, achieving ultraviolet detection functions such as low dark current, high responsivity, and high response speed. It is suitable for ultraviolet detection systems with high sensitivity, low power consumption, and high integration. In addition, the passivation layer 8 can passivate the surface traps of the channel layer 5, suppress the degradation of the on-resistance of the ultraviolet detector, and improve the stability and reliability of the device.

[0054] The method for fabricating an ultraviolet detector provided by this invention will be described in detail in the following embodiments.

[0055] Example 3

[0056] Please refer to Figure 6 and Figures 7a-7h , Figure 6 This is a flowchart illustrating a method for fabricating an ultraviolet detector according to an embodiment of the present invention. Figures 7a-7h This is a process flow diagram of a method for fabricating an ultraviolet detector according to an embodiment of the present invention.

[0057] See Figure 6 The fabrication methods for ultraviolet detectors include: S110. A buffer layer, a channel layer, a barrier layer, and a p-GaN layer are sequentially grown on the surface of the second substrate to form the first epitaxial structure.

[0058] This embodiment does not provide a detailed description of the method for forming the first epitaxial structure; however, relevant technologies can be referenced. In this step, see... Figure 7a A buffer layer 10, a channel layer 5, a barrier layer 4, and a p-GaN layer 3 are sequentially grown on the surface of the second substrate 9 using metal-organic chemical vapor deposition (MOCVD). The epitaxial parameters of each layer are matched to ensure crystal quality and interface flatness, thus obtaining the first epitaxial structure, such as the gallium nitride-based epitaxial wafer obtained in this embodiment.

[0059] S120. A dielectric layer is deposited on the surface of the first epitaxial structure. The substrate and the dielectric layer are wafer-bonded. After wafer bonding, the second substrate is peeled off and the buffer layer is removed to form the second epitaxial structure.

[0060] In this embodiment, the p-GaN layer 3 further includes a GaN layer 32 located in the second region. The fabrication of the GaN layer 32 includes: treating the GaN layer 32 located in the second region with hydrogen plasma using inductively coupled plasma to passivate the p-type doping of the GaN layer 32, thereby forming the GaN layer 32. In this embodiment, hydrogen plasma is used to treat the p-GaN layer 3 outside the gate region, passivating the Mg doping of the p-GaN layer 3 and restoring the two-dimensional electron gas channel at the heterojunction interface formed by the channel layer 5 and the barrier layer 4 below this region. Moreover, this treatment method does not require the introduction of an etching process, which can ensure the flatness of the wafer surface, which is beneficial to the subsequent wafer bonding process and improves the yield of the fabrication process. At the same time, the entire fabrication process is based on mature semiconductor micro-nano fabrication technology and is suitable for mass industrial production.

[0061] This embodiment does not provide a specific description of the method for forming the second epitaxial structure, but relevant technologies can be referenced. The detailed process of forming the second epitaxial structure in this embodiment can be found in the following steps.

[0062] See Figure 7bThe p-GaN gate layer 31 was masked using photolithography, with a gate width of 2μm. The p-GaN layer 3 in the second region was then treated with hydrogen plasma using inductively coupled plasma (ICP) at a power of 60W for 120 seconds, forming a high-resistivity GaN region (i.e., GaN layer 32). After treatment, the photoresist was removed using acetone.

[0063] See Figure 7c A dielectric layer 2 is deposited on the surface of the first epitaxial structure treated in the above steps using plasma-enhanced chemical vapor deposition (PECVD), and the layer is then chemically mechanically polished.

[0064] See Figures 7d-7e The substrate 1 and the dielectric layer 2 are wafer bonded. After bonding is completed, the second substrate 9 is peeled off using an acidic solution to achieve wafer flipping.

[0065] See Figure 7f The GaN buffer layer 10 was removed using an inductively coupled plasma (ICP) process, exposing the surface of the GaN channel layer 5.

[0066] S130, etching part of the channel layer on the surface of the second epitaxial structure to form a nano-uneven array in the first region, and depositing a passivation layer to complete the fabrication of the ultraviolet detector.

[0067] In this embodiment, etching a portion of the channel layer 5 to form a nano-bump array 51 located in the first region includes: defining a pattern of the nano-bump array 51 in the channel layer 5 located in the first region using electron beam lithography; etching the nano-bump array 51 using plasma etching; and repairing the etching damage using tetramethylammonium hydroxide (TMAH) solution after etching. The specific preparation process of this step can be referred to the following steps.

[0068] See Figure 7g The pattern of the nano-bump array 51 is defined in the channel layer 5 located in the first region using electron beam lithography. The nano-bump array 51 is formed by Cl-based plasma etching using inductively coupled plasma etching (ICP) process with a radio frequency power of 600W. After etching, TMAH solution is used to repair the etching damage.

[0069] See Figure 7hA passivation layer 8 is deposited on the surface of the channel layer 5 using atomic layer deposition (ALD). The passivation layer 8 has a thickness of 4 nm, so that the passivation layer 8 completely covers the nano-bump array 51.

[0070] A mesa structure was defined on the channel layer 53 in the second region using photolithography and dry etching processes. Source electrodes 6 and drain electrodes 7 were fabricated at both ends of the channel layer 53 in the second region using electron beam evaporation. The wafer containing the source electrodes 6 and drain electrodes 7 was then subjected to rapid thermal annealing in a nitrogen atmosphere at 850°C for 5 minutes, forming ohmic contacts between the source electrodes 6 and drain electrodes 7 and the channel layer 53 in the second region, thus completing the fabrication of the ultraviolet detector. (See [link to documentation]). Figure 1 and Figure 3 .

[0071] The ultraviolet detector fabricated by the method of the present invention forms a built-in electric field in the p-GaN gate layer 31, barrier layer 4, and channel layer 5, and a polarized electric field in the nano-bump array 51 and passivation layer 8. The built-in electric field at least covers part of the sidewalls of the nano-bump array 51. Through the synergistic effect of the built-in electric field introduced by the p-GaN gate layer 31 and the polarized electric field introduced by the passivation layer 8, the separation of photogenerated carriers in the region where the nano-bump array 51 is located is promoted, realizing ultraviolet detection functions such as low dark current, high responsivity, and high response speed. It is suitable for ultraviolet detection systems with high sensitivity, low power consumption, and high integration. In addition, the passivation layer 8 can passivate the surface traps of the channel layer 5, suppress the degradation of the on-resistance of the ultraviolet detector, and improve the stability and reliability of the device. At the same time, the entire fabrication process is based on mature semiconductor micro-nano fabrication technology, which is suitable for mass industrial production.

[0072] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0073] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0074] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0075] The ultraviolet detector and its fabrication method provided by this invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of this invention.

Claims

1. An ultraviolet detector, characterized in that, Along the thickness direction, it includes, in sequence: Substrate; A p-GaN layer located on one side of the substrate, the p-GaN layer including a p-GaN gate layer located in a first region; A barrier layer located on the surface of the p-GaN layer facing away from the substrate; A channel layer is located on the surface of the barrier layer facing away from the substrate. The channel layer includes a nano-bump array in a first region and a remaining channel layer in the first region. The remaining channel layer in the first region is disposed between the nano-bump array and the barrier layer. A passivation layer located on the surface of the channel layer facing away from the substrate; The barrier layer and the channel layer form a two-dimensional electron gas, and the p-GaN gate layer, the barrier layer and the channel layer form a built-in electric field; the nano-bump array and the passivation layer form a polarized electric field; the built-in electric field at least covers part of the sidewalls of the nano-bump array.

2. The ultraviolet detector according to claim 1, characterized in that, The nano-convex-concave array comprises multiple spaced nanostructure units; The nanostructure unit is a nanoprotrusion structure with inclined sidewalls, and the sidewalls of the nanoprotrusion structure are inclined at an angle to the thickness direction.

3. The ultraviolet detector according to claim 1, characterized in that, The trench layer also includes a trench layer located in the second region; The sum of the thickness of the remaining channel layer in the first region and the height of the nano-bump array is less than the thickness of the channel layer in the second region.

4. The ultraviolet detector according to claim 3, characterized in that, It includes a source electrode and a drain electrode; the source electrode and the drain electrode are respectively located on the surface of the channel layer in the second region facing away from the substrate.

5. The ultraviolet detector according to claim 4, characterized in that, The passivation layer includes the passivation layer on the surface of the nano-rough array located in the first region and the passivation layer on the surface of the channel layer located in the second region other than the source electrode and the drain electrode.

6. The ultraviolet detector according to claim 1, characterized in that, The p-GaN gate layer is a Mg-doped GaN layer with a Mg atom concentration of 1×10⁻⁶. 19 cm -3 -1×10 20 cm -3 The thickness of the Mg-doped GaN layer is 50nm-500nm.

7. The ultraviolet detector according to claim 1, characterized in that, It also includes a dielectric layer, which is located between the substrate and the p-GaN layer and is stacked with the substrate.

8. A method for fabricating an ultraviolet detector, used to fabricate the ultraviolet detector as described in any one of claims 1 to 7, characterized in that, include: A buffer layer, a channel layer, a barrier layer, and a p-GaN layer are sequentially grown on the surface of the second substrate to form the first epitaxial structure. A dielectric layer is deposited on the surface of the first epitaxial structure, and the substrate and the dielectric layer are wafer-bonded. After wafer bonding, the second substrate is peeled off, the buffer layer is removed, and the second epitaxial structure is formed. The channel layer is etched on the surface of the second epitaxial structure to form a nano-uneven array in the first region and a passivation layer is deposited to complete the fabrication of the ultraviolet detector.

9. The method for preparing an ultraviolet detector according to claim 8, characterized in that, The p-GaN layer further includes a GaN layer located in the second region, and the fabrication of the GaN layer includes: The p-GaN layer in the second region is subjected to hydrogen plasma treatment using inductively coupled plasma to passivate the p-type doping of the p-GaN layer and form a GaN layer.

10. The method for fabricating an ultraviolet detector according to claim 8, characterized in that, The etched portion of the channel layer forms a nano-rough array located in the first region, including: The pattern of the nano-bump array is defined in the channel layer of the first region using electron beam lithography; the nano-bump array is formed by plasma etching; and the etching damage is repaired by tetramethylammonium hydroxide solution after etching.

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