A GaN-based gradient-doped extreme ultraviolet detector and a preparation method thereof

Abstract

The application relates to the technical field of semiconductors, and provides a GaN-based gradient-doped extreme ultraviolet (EUV) detector and a preparation method thereof. The GaN-based gradient-doped EUV detector comprises a substrate, a GaN buffer layer, an n-GaN layer, an i-GaN layer, an n-type electrode, a gradient-doped p-GaN layer and a p-type electrode. From the surface of the gradient-doped p-GaN layer close to the p-type electrode to the surface of the gradient-doped p-GaN layer far from the p-type electrode, the doping concentration of the gradient-doped p-GaN layer gradually decreases. The GaN-based gradient-doped EUV detector provided by the application can induce a surface electric field by using the gradient-doped p-GaN layer, the electric field can drive the separation of the electron-hole pairs excited by photons, and thus the surface carrier collection capacity of the EUV waveband is significantly improved. The surface electric field formed by using the gradient-doped p-GaN layer improves the photocurrent and the responsivity of the detector. The structure has a wide application prospect in the EUV GaN-based detector.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a GaN-based gradient-doped extreme ultraviolet detector and a preparation method thereof. BACKGROUND

[0002] EUV (extreme ultraviolet) lithography technology based on 13.5 nm light source enables the successful implementation of 7 nm node integrated circuit manufacturing process, and the EUV detector is a key component for monitoring and calibrating the intensity of the photon beam. The mainstream silicon-based EUV detector has good quantum efficiency and relatively mature processing technology, but it is easy to be damaged in harsh environment or under high-dose ultraviolet irradiation, thereby affecting its reliability. Therefore, researching and developing semiconductor materials with high resistance to extreme ultraviolet radiation is the key to solving the radiation damage of the device. GaN-based material is a direct wide-bandgap semiconductor material, with a continuous adjustable bandgap of 0.9 eV to 6.2 eV, and has good thermal stability and chemical stability, which is an ideal material for preparing extreme ultraviolet detectors.

[0003] Due to the shallow penetration depth of extreme ultraviolet light, the quantum efficiency of the p-i-n type photodiode in the extreme ultraviolet light region is very low, and a considerable proportion of incident photons will be absorbed by the ohmic contact layer at the top of the pn junction, without contributing to the photocurrent, resulting in extremely low quantum efficiency (QE) in the EUV band. The current GaN-based p-i-n detector usually uses i-GaN as the light absorption layer, and realizes the separation and collection of photo-generated carriers under an applied electric field. At the same time, there are a large number of dislocations in the GaN-based material itself, and these defects and damages will cause device damage and increase of device dark current, which will damage the performance and stability of the device.

[0004] Based on the defects of the current GaN-based p-i-n detector, it is necessary to improve it. SUMMARY

[0005] In view of this, in order to reduce the strong surface absorption loss of the extreme ultraviolet detector and improve the photocurrent and responsivity thereof, the present application provides a GaN-based gradient-doped extreme ultraviolet detector and a preparation method thereof.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] In the first aspect, the present application provides a GaN-based gradient-doped extreme ultraviolet detector, comprising:

[0008] a substrate;

[0009] a GaN buffer layer located on the surface of the substrate;

[0010] an n-GaN layer located on the surface of the GaN buffer layer away from the substrate;

[0011] an i-GaN layer located on a surface of the n-GaN layer away from the substrate;

[0012] an n-type electrode located on a surface of the n-GaN layer away from the substrate, the i-GaN layer and the n-type electrode being located on two sides of the surface of the n-GaN layer respectively;

[0013] a gradient-doped p-GaN layer located on a surface of the i-GaN layer away from the substrate;

[0014] a p-type electrode located on a surface of the gradient-doped p-GaN layer away from the substrate;

[0015] wherein, from a surface of the gradient-doped p-GaN layer close to the p-type electrode to a surface of the gradient-doped p-GaN layer away from the p-type electrode, the doping concentration of the gradient-doped p-GaN layer gradually decreases.

[0016] Preferably, from the surface of the gradient-doped p-GaN layer close to the p-type electrode to the surface of the gradient-doped p-GaN layer away from the p-type electrode, the doping concentration of the gradient-doped p-GaN layer decreases from (2~3)×10 19 cm -3 to (1~2)×10 16 cm -3 .

[0017] Preferably, the thickness of the gradient-doped p-GaN layer is 50~150nm.

[0018] Preferably, the thickness of the n-GaN layer is ≥400nm, and the doping concentration is ≥5×10 18 cm -3 .

[0019] Preferably, the i-GaN layer is an unintentionally doped GaN layer, and the thickness of the i-GaN layer is 400~500nm.

[0020] Preferably, the substrate is a heterogeneous substrate or a homogeneous substrate;

[0021] The heterogeneous substrate includes any one of a sapphire substrate, a silicon carbide substrate, and a silicon substrate;

[0022] The homogeneous substrate includes a GaN substrate or an AlN substrate.

[0023] Preferably, the material of the n-type electrode includes at least one of Pt, Ti, Ni, and Au;

[0024] The material of the p-type electrode includes at least one of Ni, Pt, and Au.

[0025] Preferably, the thickness of the n-type electrode is 50-300 nm.

[0026] The thickness of the p-type electrode is 3-5 nm.

[0027] The thickness of the GaN buffer layer is 50-200 nm.

[0028] In a second aspect, the application further provides a preparation method of the GaN-based gradient-doped EUV detector, comprising the following steps:

[0029] Growth of a GaN buffer layer on the surface of the substrate by epitaxy;

[0030] Deposition of an n-GaN layer on the surface of the GaN buffer layer;

[0031] Deposition of an i-GaN layer on one side of the surface of the n-GaN layer;

[0032] Deposition of a gradient-doped p-GaN layer on the surface of the i-GaN layer;

[0033] Etching of a device mesa to expose the n-GaN layer;

[0034] Deposition of an n-type electrode on the surface of the n-GaN layer under the mesa;

[0035] Deposition of a p-type electrode on the surface of the gradient-doped p-GaN layer.

[0036] Preferably, the method comprises the following steps:

[0037] Sequential growth of a GaN buffer layer, an n-GaN layer on the surface of the substrate by epitaxy;

[0038] Growth of i-GaN material, gradient-doped p-GaN material on the surface of the n-GaN layer, growth of a SiO2 mask layer outside the gradient-doped p-GaN material, photoetching of a mesa pattern on the SiO2 mask layer, etching of the SiO2 mask layer not covered by photoresist in the non-mesa pattern area, etching of the area not covered by the SiO2 mask layer to the n-GaN layer, removal of the SiO2 mask layer in the mesa area, to obtain the gradient-doped p-GaN layer and the i-GaN layer;

[0039] Preparation of a photoresist mask pattern of the n-type electrode on the n-GaN layer by photoetching, removal of the photoresist in the electrode pattern area after development, retention of the photoresist in the non-electrode pattern area, then evaporation of the n-type electrode material on the photoresist mask pattern, removal of the photoresist and the electrode material covered thereon, and finally annealing treatment to obtain the n-type electrode;

[0040] The photoresist mask pattern of the p-type electrode is prepared on the gradient-doped p-GaN layer by using a photoetching technology, the photoresist in the electrode pattern area is removed after development, the photoresist in the non-electrode pattern area is reserved, then the p-type electrode material is evaporated on the photoresist mask pattern, the photoresist and the electrode material covered thereon are removed, and finally annealing treatment is performed to obtain the p-type electrode.

[0041] The GaN-based gradient-doped EUV detector has the following beneficial effects relative to the prior art:

[0042] The GaN-based gradient-doped EUV detector comprises a substrate, a GaN buffer layer, an n-GaN layer, an i-GaN layer, an n-type electrode, a gradient-doped p-GaN layer and a p-type electrode, wherein the doping concentration of the gradient-doped p-GaN layer gradually decreases from the surface close to the p-type electrode to the surface far from the p-type electrode; the gradient-doped p-GaN layer induces a surface electric field, which can drive the separation of the electron-hole pairs excited by photons, thereby significantly improving the surface carrier collection capability in the EUV band; the gradient-doped p-GaN layer serves as an absorption layer of the detector and absorbs the ultraviolet signal; the GaN-based gradient-doped EUV detector of the application utilizes the surface electric field induced by the gradient-doped p-GaN layer, which can drive the separation of the electron-hole pairs excited by photons, thereby significantly improving the photocurrent and responsivity of the detector; this structure has a wide application prospect in the EUV GaN-based detector. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0044] Figure 1 It is a structural schematic diagram of the GaN-based gradient-doped EUV detector of the present application;

[0045] Figure 2 It is a flow chart of the preparation method of the GaN-based gradient-doped EUV detector of the present application;

[0046] Figure 3 It is the electric field intensity at the position under the table of the detector with different thicknesses in Example 1 and Comparative Example 1;

[0047] Figure 4A plot of the photo-current of the detector in Example 1 and Comparative Example 1 as a function of voltage;

[0048] Figure 5 A plot of the responsivity of the detector in Example 1 and Comparative Example 1 as a function of voltage. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0050] It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0051] In the description of the present application, it should be understood that the positional or location relationship indicated by terms such as "upper" is based on the positional or location relationship shown in the drawings, or the positional or location relationship commonly placed when the product of the present application is used, or the positional or location relationship commonly understood by those skilled in the art, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0052] The following are described in detail respectively. It should be noted that the order of the following embodiments is not a limitation on the preferred order of the embodiments. In addition, in the description of the present application, the term "comprising" means "including but not limited to". Various embodiments of the present application can exist in a range form; it should be understood that the description in a range form is only for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this text, it means that any cited number (fraction or integer) within the indicated range is included.

[0053] The present application provides a GaN-based gradient-doped extreme ultraviolet detector, as shown in Figure 1 comprising:

[0054] a substrate 1;

[0055] GaN buffer layer 2, located on the surface of substrate 1;

[0056] n-GaN layer 3, located on the surface of GaN buffer layer 2 away from substrate 1;

[0057] i-GaN layer 4, located on the surface of n-GaN layer 3 away from substrate 1;

[0058] n-type electrode 5, located on the surface of n-GaN layer 3 away from substrate 1, i-GaN layer 4 and n-type electrode 5 are respectively located on both sides of the surface of n-GaN layer 3;

[0059] Gradient-doped p-GaN layer 6, located on the surface of i-GaN layer 4 away from substrate 1;

[0060] p-type electrode 7, located on the surface of gradient-doped p-GaN layer 6 away from substrate 1;

[0061] Wherein, from the surface of the gradient-doped p-GaN layer close to the p-type electrode to the surface away from the p-type electrode, the doping concentration of the gradient-doped p-GaN layer 6 gradually decreases.

[0062] The GaN-based gradient-doped extreme ultraviolet detector of the application comprises a substrate 1, a GaN buffer layer 2, an n-GaN layer 3, an i-GaN layer 4, an n-type electrode 5, a gradient-doped p-GaN layer 6, and a p-type electrode 7; wherein the substrate 1, the GaN buffer layer 2, and the n-GaN layer 3 are sequentially stacked, the i-GaN layer 4 and the n-type electrode 5 are respectively located on both sides of the surface of the n-GaN layer 3; the gradient-doped p-GaN layer 6 is located on the surface of the i-GaN layer 4; the p-type electrode 7 is located on the surface of the gradient-doped p-GaN layer 6; wherein, from the surface of the gradient-doped p-GaN layer 6 close to the p-type electrode 7 to the surface away from the p-type electrode 7, the doping concentration of the gradient-doped p-GaN layer 6 gradually decreases, that is, in the thickness direction of the gradient-doped p-GaN layer 6 and Figure 1 The doping concentration gradually decreases from top to bottom; the n-GaN layer serves as an n-type region of the detector and forms an ohmic contact with the n-type electrode; the gradient-doped p-GaN layer induces a surface electric field, which can drive the separation of the photo-excited electron-hole pairs, thereby significantly improving the surface carrier collection capability in the EUV waveband; the gradient-doped p-type GaN layer serves as an absorption layer of the detector and absorbs ultraviolet signals; the gradient-doped p-GaN layer forms a low-barrier Schottky contact with the p-type electrode; the GaN-based gradient-doped extreme ultraviolet detector of the application utilizes the gradient-doped p-GaN layer to induce a surface electric field (such as Figure 3As shown in the figure, the electric field can drive the separation of photon-excited electron-hole pairs, thereby significantly improving the surface carrier collection capability in the EUV band; the detector of the present application utilizes the surface electric field formed by the gradient-doped p-GaN layer to improve the photocurrent (as shown in the figure) and responsivity (as shown in the figure) of the detector, and this structure has a broad application prospect in the extreme ultraviolet GaN-based detector. Figure 4 As shown in the figure, the electric field can drive the separation of photon-excited electron-hole pairs, thereby significantly improving the surface carrier collection capability in the EUV band; the detector of the present application utilizes the surface electric field formed by the gradient-doped p-GaN layer to improve the photocurrent (as shown in the figure) and responsivity (as shown in the figure) of the detector, and this structure has a broad application prospect in the extreme ultraviolet GaN-based detector. Figure 5

[0063] Specifically, the n-GaN layer, i.e., the n-type gallium nitride layer, is formed by doping specific impurity atoms into gallium nitride to make it a conductive layer mainly with electrons as carriers; these impurity atoms are usually silicon (Si) and other donor impurities; the i-GaN layer, i.e., the intrinsic gallium nitride layer, is a gallium nitride layer basically free of intentionally doped impurities; and the p-GaN layer, i.e., the p-type gallium nitride layer, is formed by doping acceptor impurities such as magnesium (Mg) into gallium nitride to make the material a conductive layer mainly with holes as carriers.

[0064] In some embodiments, the doping concentration of the gradient-doped p-GaN layer decreases from the surface of the gradient-doped p-GaN layer close to the p-type electrode to the surface of the gradient-doped p-GaN layer far from the p-type electrode. Figure 1 In the gradient-doped p-GaN layer 6, the doping concentration of the gradient-doped p-GaN layer decreases from (2~3)×10 19 cm -3 to (1~2)×10 16 cm -3 , for example, from 2×10 19 cm -3 to 1×10 16 cm -3 , for example, from 2×10 19 cm -3 to 1.5×10 19 cm -3 , 1×10 19 cm -3 , 5×10 18 cm -3 , 1×10 18 cm -3 , 5×10 17 cm -3 , 1×10 17 cm -3 , 5×10 16 cm -3 , 4×10 16 cm -3 , 3×10 16 cm -3 , 2×10 16 cm -3 , 1×10​16 cm -3 .

[0065] In some embodiments, the gradient-doped p-GaN layer 6 comprises a plurality of doped p-GaN layers from top to bottom, and the doping concentration of the plurality of doped p-GaN layers from top to bottom decreases from 2x10 19 cm -3 to 1x10 16 cm -3 , i.e., the doping concentration of the uppermost doped p-GaN layer is 2x10 19 cm -3 , and the doping concentration of the lowermost doped p-GaN layer is 1x10 16 cm -3 .

[0066] In some embodiments, the thickness of the gradient-doped p-GaN layer is 50-150 nm.

[0067] In some embodiments, the thickness of the n-GaN layer 3 is ≥400 nm, and the doping concentration is ≥5x10 18 cm -3 .

[0068] In some embodiments, the i-GaN layer 4 is an unintentionally doped GaN layer, and the thickness of the i-GaN layer is 400-500 nm.

[0069] In some embodiments, the substrate 1 is a hetero-substrate or a homo-substrate.

[0070] The hetero-substrate comprises any one of a sapphire substrate, a silicon carbide substrate, and a silicon substrate.

[0071] The homo-substrate comprises a GaN substrate or an AlN substrate.

[0072] In some embodiments, the n-type electrode 5 is an ohmic contact electrode, and the material of the n-type electrode 5 comprises at least one of Pt, Ti, Ni, and Au. Specifically, the material of the n-type electrode 5 is any one of Pt, Ti, Ni, and Au, or an alloy of two or more of Pt, Ti, Ni, and Au.

[0073] In some embodiments, the p-type electrode 7 is a super-thin semi-transparent electrode or a grid-shaped electrode, and the material of the p-type electrode 7 comprises at least one of Ni, Pt, and Au.

[0074] In some embodiments, the thickness of the n-type electrode 5 is 50-300 nm.

[0075] In some embodiments, the thickness of the p-type electrode 7 is 3-5 nm.

[0076] In some embodiments, the GaN buffer layer 2 has a thickness of 50-200 nm.

[0077] Based on the same inventive concept, the application further provides a preparation method of the GaN-based gradient-doped EUV detector as above, as shown in the accompanying drawings, comprising the following steps: Figure 2

[0078] S1, epitaxially growing a GaN buffer layer on the surface of a substrate;

[0079] S2, depositing an n-GaN layer on the surface of the GaN buffer layer;

[0080] S3, depositing an i-GaN layer on one side of the surface of the n-GaN layer;

[0081] S4, depositing a gradient-doped p-GaN layer on the surface of the i-GaN layer;

[0082] S5, etching a device mesa to expose the n-GaN layer;

[0083] S6, depositing an n-type electrode on the surface of the n-GaN layer under the mesa in the etching area;

[0084] S7, depositing a p-type electrode on the surface of the gradient-doped p-GaN layer.

[0085] In some embodiments, the preparation method of the GaN-based gradient-doped EUV detector comprises the following steps:

[0086] S1, growing a device epitaxial material: epitaxially growing a GaN buffer layer, an n-GaN layer, an i-GaN material, and a gradient-doped p-GaN material on the surface of a substrate in sequence;

[0087] S2, preparing a mesa structure: growing a SiO2 mask layer on the outside of the gradient-doped p-GaN material, using photolithography to pattern the mesa on the SiO2 mask layer, using RIE technology to etch and remove the SiO2 mask layer not covered by photoresist in the non-mesa pattern area, using ICP technology to etch the area not covered by the SiO2 mask layer to the n-GaN layer, and using HF to remove the SiO2 mask layer in the mesa area to obtain the gradient-doped p-GaN layer and the i-GaN layer;

[0088] S3, preparing an n-type electrode: using photolithography to prepare a photoresist mask pattern of the n-type electrode on the n-GaN layer, removing the photoresist in the electrode pattern area after development, retaining the photoresist in the non-electrode pattern area, then evaporating n-type electrode material on the photoresist mask pattern, removing the photoresist and the electrode material covered thereon using Lift Off technology, and finally performing annealing treatment to obtain the n-type electrode;

[0089] ​S4, preparing p-type electrode: using photolithography technology to prepare photoresist mask pattern of p-type electrode on gradient doped p-GaN layer, after development, removing photoresist of electrode pattern area, retaining photoresist of non-electrode pattern area, then evaporating p-type electrode material on photoresist mask pattern, removing photoresist and electrode material covered thereon by using Lift Off technology, finally performing annealing treatment, obtaining p-type electrode.

[0090] In some embodiments, the method for growing the device epitaxial material in step S1 is MOCVD or MBE.

[0091] In some embodiments, in step S2, photolithography technology is used, and the selection of positive and negative photoresists is determined according to the window design of the photomask pattern, so that the photoresist of the mesa area is retained after development, and the photoresist of the non-mesa area is removed.

[0092] In some embodiments, in steps S3 and S4, photolithography technology is used, and the selection of positive and negative photoresists is determined according to the window design of the photomask pattern, so that the photoresist of the electrode pattern area is removed after development, and the photoresist of the non-electrode area is retained.

[0093] In some embodiments, in steps S3 and S4, the method for evaporating n-type electrode material and p-type electrode material is electron beam evaporation or thermal evaporation technology.

[0094] In some embodiments, the annealing treatment is: using an annealing furnace to anneal the n-type electrode and the p-type electrode in a nitrogen atmosphere, and the annealing temperature and time are determined by the electrode material; for example, when the n-type electrode and the p-type electrode material is Pt, the annealing temperature is 400-600℃, and the annealing time is 5-10min; when the n-type electrode material is Ti, the annealing temperature is 300-500℃, and the annealing time is 5-15min; when the n-type electrode and the p-type electrode material is Ni, the annealing temperature is 300-500℃, and the annealing time is 10-15min; when the n-type electrode and the p-type electrode material is Au, the annealing temperature is 200-400℃, and the annealing time is 10-20min.

[0095] In some embodiments, the GaN buffer layer is deposited using ammonia and a gallium source (commonly trimethyl gallium (TMGa)) as raw materials, the carrier gas is usually hydrogen (H2) or nitrogen (N2), the flow rate is 5-20 slm, the growth temperature is 500-600℃, the TMGa flow rate is 50-150 sccm, and the NH3 flow rate is 3000-5000 sccm.

[0096] In some embodiments, the i-GaN layer is deposited using ammonia and a gallium source (typically trimethylgallium (TMGa)) as raw materials, the growth temperature is 1000-1100°C, the reaction chamber pressure is controlled at 100-300 Torr, and the gas flow rate is: TMGa flow rate: 50-150 sccm, NH3 flow rate: 3000-5000 sccm, and H2 flow rate: 10-15 slm.

[0097] In some embodiments, the n-GaN layer is prepared using an n-type doping source: silane (SiH4), and the process parameters are: growth temperature: 1000-1100°C, reaction chamber pressure: 100-300 Torr, and gas flow rate: TMGa flow rate: 50-150 sccm, NH3 flow rate: 3000-5000 sccm, SiH4 flow rate: 0.1-10 sccm, and H2 flow rate: 10-15 slm.

[0098] In some embodiments, the p-GaN layer is prepared using a p-type doping source: biscyclopentadienyl magnesium (Cp2Mg), and the process parameters are: growth temperature: 800-900°C, reaction chamber pressure: 100-300 Torr, and gas flow rate: TMGa flow rate: 50-150 sccm, NH3 flow rate: 3000-5000 sccm, Cp2Mg flow rate: adjusted according to the required doping concentration, typically 1-10 sccm, and H2 flow rate: 10-15 slm.

[0099] The GaN-based gradient-doped extreme ultraviolet detector and the preparation method thereof of the present application are further described below with specific embodiments. This part further describes the content of the present application in combination with specific embodiments, but should not be understood as a limitation of the present application. If not specifically stated, the technical means adopted in the embodiments are conventional means familiar to those skilled in the art. Unless specifically stated, the reagents, methods and equipment adopted in the present application are conventional reagents, methods and equipment in the art.

[0100] Embodiment 1

[0101] The embodiment of the present application provides a GaN-based gradient-doped extreme ultraviolet detector, which comprises:

[0102] a substrate;

[0103] a GaN buffer layer located on the surface of the substrate;

[0104] an n-GaN layer located on the surface of the GaN buffer layer away from the substrate;

[0105] an i-GaN layer located on the surface of the n-GaN layer away from the substrate;

[0106] n-type electrode, located on the surface of the n-GaN layer away from the substrate 1, the i-GaN layer and the n-type electrode are located on both sides of the surface of the n-GaN layer respectively;

[0107] Gradiently doped p-GaN layer, located on the surface of the i-GaN layer away from the substrate;

[0108] p-type electrode, located on the surface of the gradiently doped p-GaN layer away from the substrate;

[0109] The gradiently doped p-GaN layer comprises 10 doped p-GaN layers from top to bottom, and the doping concentration of the 10 doped p-GaN layers from top to bottom decreases from 2×10 19 cm -3 to 1×10 16 cm -3 , and the doping concentration of the 10 doped p-GaN layers from top to bottom is 2×10 19 cm -3 , 1.5×10 19 cm -3 , 1×10 19 cm -3 , 5×10 18 cm -3 , 1×10 18 cm -3 , 5×10 17 cm -3 , 1×10 17 cm -3 , 5×10 16 cm -3 , 3×10 16 cm -3 , 1×10 16 cm -3 respectively; the total thickness of the gradiently doped p-GaN layer is 150 nm, and the thickness of each doped p-GaN layer is 15 nm;

[0110] The thickness of the n-GaN layer is 500 nm, and the doping concentration is 8×10 18 cm -3 ;

[0111] The i-GaN layer is an unintentionally doped GaN layer, and the thickness of the i-GaN layer is 400 nm;

[0112] The substrate is a sapphire substrate, and the thickness is;

[0113] The n-type electrode comprises a Pt layer (thickness 50 nm), a Ti layer (thickness 50 nm), a Ni layer (thickness 50 nm) and an Au layer (thickness 50 nm) which are stacked in sequence, and the Pt layer is in contact with the n-GaN layer;

[0114] The p-type electrode is Ni, and the thickness is 5 nm;

[0115] The thickness of the GaN buffer layer is 100 nm.

[0116] The preparation method of the GaN-based gradient-doped extreme ultraviolet detector comprises the following steps:

[0117] S1, growing an epitaxial material of a device: using a MOVCD method to epitaxially grow, on a substrate surface, a GaN buffer layer, an n-GaN layer, an i-GaN material, and a gradient-doped p-GaN material in sequence;

[0118] S2, preparing a mesa structure: growing a SiO2 mask layer on the outer side of the gradient-doped p-GaN material, using a photolithography technology to photoetch a mesa pattern on the SiO2 mask layer, using an RIE technology to etch and remove the SiO2 mask layer that is not covered by the photoresist in the non-mesa pattern area, using an ICP technology to etch the area not covered by the SiO2 mask layer to the n-GaN layer, and using HF to remove the SiO2 mask layer in the mesa area, so as to obtain a gradient-doped p-GaN layer and an i-GaN layer;

[0119] S3, preparing an n-type electrode: using a photolithography technology to prepare a photoresist mask pattern of the n-type electrode above the n-GaN layer, removing the photoresist in the electrode pattern area after development, retaining the photoresist in the non-electrode pattern area, then evaporating an n-type electrode material on the photoresist mask pattern, removing the photoresist and the electrode material covered thereon by using a Lift Off technology, and finally performing annealing treatment, so as to obtain the n-type electrode;

[0120] S4, preparing a p-type electrode: using a photolithography technology to prepare a photoresist mask pattern of the p-type electrode above the gradient-doped p-GaN layer, removing the photoresist in the electrode pattern area after development, retaining the photoresist in the non-electrode pattern area, then evaporating a p-type electrode material on the photoresist mask pattern, removing the photoresist and the electrode material covered thereon by using a Lift Off technology, and finally performing annealing treatment, so as to obtain the p-type electrode;

[0121] During preparation of the n-type electrode, the annealing temperature is 450 DEG C, and the annealing time is 5 min;

[0122] During preparation of the p-type electrode, the annealing temperature is 400 DEG C, and the annealing time is 10 min;

[0123] The process parameters for preparing the GaN buffer layer are as follows: the nitrogen flow is 15 slm, the growth temperature is 550 DEG C, the TMGa flow is 100 sccm, and the NH3 flow is 4000 sccm;

[0124] The i-GaN layer preparation process parameters are: growth temperature is 1100℃, reaction cavity pressure is 150 Torr, gas flow: TMGa flow is 120 sccm, NH3 flow is 4500 sccm, carrier gas flow: H2 flow is 12 slm;

[0125] The n-GaN layer preparation process parameters are: growth temperature is 1050℃, reaction cavity pressure is 200 Torr; gas flow: TMGa flow is 80 sccm, NH3 flow is 4200 sccm, SiH4 flow is determined according to the doping concentration, carrier gas flow: H2 flow is 12 slm;

[0126] The p-GaN layer preparation process parameters are: growth temperature is 850℃, reaction cavity pressure is 150 Torr; gas flow TMGa flow is 120 sccm, NH3 flow is 4000 sccm, Cp2Mg flow: adjusted according to the required doping concentration, carrier gas flow: H2 flow is 10 slm.

[0127] Comparative Example 1

[0128] The present comparative example provides a GaN-based extreme ultraviolet detector, comprising:

[0129] a substrate;

[0130] a GaN buffer layer located on the surface of the substrate;

[0131] an n-GaN layer located on the surface of the GaN buffer layer away from the substrate;

[0132] an i-GaN layer located on the surface of the n-GaN layer away from the substrate;

[0133] an n-type electrode located on the surface of the n-GaN layer away from the substrate 1, and the i-GaN layer and the n-type electrode are respectively located on both sides of the surface of the n-GaN layer;

[0134] a p-GaN layer located on the surface of the i-GaN layer away from the substrate;

[0135] a p-type electrode located on the surface of the gradient-doped p-GaN layer away from the substrate;

[0136] Performance test

[0137] Figures 3-5 The presence of a gradient-doped layer means the detector in Example 1, and the absence of a gradient-doped layer means the detector in Comparative Example 1.

[0138] It can be seen from Figure 3 that the electric field intensity at the position of the mesa bottom of the detector in Example 1 is greater than that of the detector in Comparative Example 1.

[0139] As can be seen from Table 1, the photoelectric current of the detector in Example 1 is greater than that of the detector in Comparative Example 1. Figure 4 As can be seen from Table 2, the responsivity of the detector in Example 1 is greater than that of the detector in Comparative Example 1.

[0140] Figure 5 As can be seen from Table 2, the responsivity of the detector in Example 1 is greater than that of the detector in Comparative Example 1.

[0141] The above description is merely preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.​

Claims

1. A GaN-based gradient-doped extreme ultraviolet detector, characterized in that, The application relates to an ultraviolet photodetector, which comprises the following components: a substrate; a GaN buffer layer on the surface of the substrate; an n-GaN layer on the surface of the GaN buffer layer away from the substrate; an i-GaN layer on the surface of the n-GaN layer away from the substrate; an n-type electrode on the surface of the n-GaN layer away from the substrate; the i-GaN layer and the n-type electrode are respectively located on the two sides of the surface of the n-GaN layer; a gradient-doped p-GaN layer on the surface of the i-GaN layer away from the substrate; a p-type electrode on the surface of the gradient-doped p-GaN layer away from the substrate; wherein the doping concentration of the gradient-doped p-GaN layer gradually decreases from the surface of the gradient-doped p-GaN layer close to the p-type electrode to the surface of the gradient-doped p-GaN layer away from the p-type electrode; the gradient-doped p-GaN layer serves as an absorption layer of the ultraviolet photodetector and absorbs ultraviolet signals; the gradient-doped p-GaN layer and the p-type electrode form a low-barrier Schottky contact; the gradient-doped p-GaN layer induces a surface electric field, and the electric field drives the separation of a photon-excited electron-hole pair, thereby significantly improving the surface carrier collection capability of the EUV waveband. The thickness of the gradient-doped p-GaN layer is 50-150 nm. The i-GaN layer is an unintentionally doped GaN layer, and the thickness of the i-GaN layer is 400-500 nm. The substrate is a hetero-substrate or a homo-substrate; The hetero-substrate comprises any one of a sapphire substrate, a silicon carbide substrate and a silicon substrate; The homo-substrate comprises a GaN substrate or an AlN substrate. The material of the n-type electrode comprises at least one of Pt, Ti, Ni and Au; The material of the p-type electrode comprises at least one of Ni, Pt and Au. The thickness of the n-type electrode is 50-300 nm; The thickness of the p-type electrode is 3-5 nm; 2. The GaN-based graded-doped EUV detector of claim 1, wherein, The doping concentration of the gradient-doped p-GaN layer is reduced from (2~3)×10 19 cm -3 to (1~2)×10 16 cm -3 from the surface of the p-type electrode to the surface away from the p-type electrode.

3. The GaN-based graded-doped EUV detector of claim 1, wherein the n-type GaN layer is formed by a metal-organic chemical vapor deposition (MOCVD) method. The thickness of the GaN buffer layer is 50-200 nm.

4. The GaN-based graded-doped EUV detector of claim 1, wherein the n-type GaN layer is formed by a metal-organic chemical vapor deposition (MOCVD) process. The thickness of the n-GaN layer is ≥ 400 nm, and the doping concentration is ≥ 5 x 1018 cm-3. 18 cm -3 .

5. The GaN-based graded-doped EUV detector of claim 1, wherein the n-type GaN layer is formed by a metal-organic chemical vapor deposition (MOCVD) process. The application further discloses a preparation method of the ultraviolet photodetector, which comprises the following steps: epitaxially growing a GaN buffer layer on the surface of a substrate; depositing an n-GaN layer on the surface of the GaN buffer layer; depositing an i-GaN layer on one side of the surface of the n-GaN layer; depositing a gradient-doped p-GaN layer on the surface of the i-GaN layer; etching a device mesa to expose the n-GaN layer; depositing an n-type electrode on the surface of the n-GaN layer in the etching area under the mesa; and depositing a p-type electrode on the surface of the gradient-doped p-GaN layer.

6. The GaN-based graded-doped EUV detector of claim 1, wherein the n-type GaN layer is formed by a metal-organic chemical vapor deposition (MOCVD) process. The application further discloses a preparation method of the ultraviolet photodetector, which comprises the following steps: epitaxially growing a GaN buffer layer, an n-GaN layer, an i-GaN material and gradient-doped p-GaN material on the surface of a substrate in sequence; growing a SiO2 mask layer outside the gradient-doped p-GaN material, and then performing photoetching on the SiO2 mask layer to form a mesa pattern; etching and removing the SiO2 mask layer in a non-mesa pattern area without photoresist coverage, and then etching the area without the SiO2 mask layer coverage to the n-GaN layer; removing the SiO2 mask layer in the mesa area to obtain a gradient-doped p-GaN layer and an i-GaN layer. ​ ​ 7. The GaN-based graded-doped EUV detector of claim 1, wherein the n-type GaN layer is formed by a metal-organic chemical vapor deposition (MOCVD) process. ​ ​ 8. The GaN-based graded-doped EUV detector of claim 1, wherein the n-type GaN layer is formed by a metal-organic chemical vapor deposition (MOCVD) process. ​ ​ ​ 9. A method for fabricating a GaN-based gradient-doped Ech-VUV detector according to any one of claims 1-8, characterized in that, ​ ​ ​ ​ ​ ​ ​ ​ 10. The method for fabricating a GaN-based gradient-doped extreme ultraviolet detector as described in claim 9, characterized in that, ​ ​ ​ The photoresist mask pattern of the n-type electrode is prepared on the n-GaN layer by using the photoetching technology, the photoresist of the electrode pattern area is removed after development, the photoresist of the non-electrode pattern area is reserved, then the n-type electrode material is evaporated on the photoresist mask pattern, the photoresist and the electrode material covered on the photoresist are removed, finally annealing treatment is carried out, and the n-type electrode is obtained; The photoresist mask pattern of the p-type electrode is prepared on the gradient-doped p-GaN layer by using the photoetching technology, the photoresist of the electrode pattern area is removed after development, the photoresist of the non-electrode pattern area is reserved, then the p-type electrode material is evaporated on the photoresist mask pattern, the photoresist and the electrode material covered on the photoresist are removed, finally annealing treatment is carried out, and the p-type electrode is obtained.

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