Ultraviolet photocathode based on gallium oxide and preparation method thereof

Abstract

The invention discloses an ultraviolet photocathode based on gallium oxide and a preparation method thereof. The ultraviolet photocathode is provided with an Ag reflecting layer, a substrate layer, a p-type gallium oxide layer and an activation layer from bottom to top in sequence; the Ag reflecting layer is used for reflecting unabsorbed light back to the p-type gallium oxide layer; the substrate layer is a c-plane sapphire substrate and is used for depositing a gallium oxide thin film; the p-type gallium oxide layer is a Cu-N co-doped gallium oxide film and is used as an emission layer of the photoelectric cathode; the activation layer is a Cs adsorption layer, is adsorbed on the upper surface of the p-type gallium oxide layer, and is used for reducing the electron affinity and improving the electron emission efficiency of the photoelectric cathode. Through Cu-N co-doping, the hole carrier concentration of the gallium oxide thin film is improved and reaches 6.2 * 10 < 15 >-1.1 * 10 < 18 > cm <-3 >, the hole Hall mobility is improved and reaches 12.5-41.7 cm < 2 > / Vs, and the quantum efficiency of a photoelectric cathode is improved and can reach 52% at most.

Description

Technical Field

[0001] The invention relates to the field of p-type gallium oxide photocathode, and in particular to an ultraviolet photocathode based on gallium oxide and a preparation method thereof. Background Art

[0002] Ultraviolet photocathode is a key optoelectronic device that can generate photoelectrons under ultraviolet light irradiation, and is widely used in ultraviolet detection, imaging, space science and other fields. With the continuous development of ultraviolet photoelectric technology, the demand for ultraviolet photocathodes with high performance, wide spectral response and high sensitivity is increasing.

[0003] In recent years, wide bandgap semiconductor materials such as gallium oxide (Ga2O3), gallium nitride (GaN), diamond and silicon carbide (SiC) have been widely studied for use in ultraviolet photocathodes. Their wide bandgap characteristics enable these materials to effectively respond to deep ultraviolet light (wavelength in the range of 200-280nm) while suppressing interference from visible light and infrared light. At present, GaN and its alloy materials have been intensively studied and put into use, but since GaN p-type doping is still a problem, the doping efficiency is low, the surface state density is high, and there are many intrinsic defects, the photoelectric conversion efficiency of GaN-based photocathodes is low, the quantum efficiency is low (only about 40%), the dark current is large, and the device performance is not good. CN113964003A proposes a method of using a nanotube structure to increase the surface area of ​​photoelectric emission, thereby improving the photoelectric conversion efficiency and quantum efficiency, but it still does not solve the fundamental problem of low GaN p-type doping efficiency.

[0004] The bandgap of gallium oxide is about 4.8-4.9eV, which is significantly larger than that of gallium nitride, which is about 3.4eV. This makes gallium oxide photocathodes have higher photoresponsivity and quantum efficiency in the higher energy ultraviolet region, and can detect photons with shorter wavelengths, thus performing well in deep ultraviolet band applications. However, achieving efficient p-type doping is still a hot topic and difficulty in current research.

[0005] Therefore, in view of the above problems, it is necessary to propose a gallium oxide-based photocathode with more efficient p-type doping to meet market demand and promote the rapid development of gallium oxide photocathode. Summary of the invention

[0006] The purpose of the present invention is to provide a gallium oxide-based ultraviolet photocathode and a preparation method thereof, which can not only improve the quantum efficiency of the photocathode, but also enhance the absorption of ultraviolet light by the photocathode.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] On the one hand, the present invention provides a gallium oxide-based ultraviolet photocathode, which is sequentially arranged from bottom to top as an Ag reflection layer, a substrate layer, a p-type gallium oxide layer, and an activation layer;

[0009] The Ag reflective layer is used to reflect unabsorbed light back to the p-type gallium oxide layer;

[0010] The substrate layer is a c-plane sapphire substrate for depositing a gallium oxide thin film;

[0011] The p-type gallium oxide layer is a Cu-N co-doped gallium oxide film, which is used as an emission layer of the photocathode;

[0012] The activation layer is a Cs adsorption layer, which is adsorbed on the upper surface of the p-type gallium oxide layer and is used to reduce the electron affinity and improve the electron emission efficiency of the photocathode.

[0013] As a further preference of the present invention, the Cu-N co-doped gallium oxide film is prepared by a dual-target magnetron sputtering method, wherein the Cu doped target material is Ga2O3 or CuO target material, and the Cu doping concentration is controlled by changing the sputtering time, and the N doping is achieved by mixing N2 in the sputtering gas Ar, and the N doping concentration is controlled by changing the sputtering gas pressure and flow rate.

[0014] On the other hand, the present invention also provides a method for preparing the above-mentioned gallium oxide-based ultraviolet photocathode, comprising the following steps:

[0015] Step 1: Select c-plane sapphire as the substrate and ultrasonically clean the substrate with acetone, ethanol and deionized water for 10 minutes respectively to remove organic matter on the surface of the substrate;

[0016] Step 2: Install the Ga2O3 target and CuO target respectively, and place the cleaned substrate into the deposition chamber;

[0017] Step 3: Start the vacuum pump and reduce the pressure in the sputtering chamber to less than 10 -6 Torr, to remove residual gas and impurities;

[0018] Step 4: Select a mixture of nitrogen and argon as the working gas, and adjust the pressure and flow of the working gas;

[0019] Step 5: Heat the substrate and start the sputtering target, and perform pre-sputtering for 5-10 minutes to clean the target surface and stabilize the sputtering conditions;

[0020] Step 6: Re-adjust the sputtering power and sputtering time, open the shutter, and start timing growth;

[0021] Step 7: After the film growth is completed, take out the sample and perform annealing treatment;

[0022] Step 8: After annealing, the Cs adsorption layer is tightly adsorbed on the gallium oxide film through an ultra-high vacuum activation process;

[0023] Step 9: Bond the gallium oxide film and the Ag reflector together to complete the preparation.

[0024] As a further preferred embodiment of the present invention, the distance between the target and the substrate in step 2 is 6 to 7 cm.

[0025] As a further preferred embodiment of the present invention, in step 4, the N2 / Ar flow ratio in the working gas is 10-50%, the pressure of the working gas is set to 0.5-1.5 Pa, and the flow rate of the working gas is set to 20-80 sccm.

[0026] As a further preferred embodiment of the present invention, in step 5, the temperature of the substrate is set to 700-800°C.

[0027] As a further preferred embodiment of the present invention, the sputtering power in step 6 is set to 40-150W.

[0028] As a further preference of the present invention, the sputtering time in step 6 is set to multiple time periods. In each time period, the sputtering time of the Ga2O3 target is fixed at 8 minutes, the sputtering time of the CuO target is fixed at 1 to 8 minutes, and the total sputtering time is set to 1 to 4 hours.

[0029] As a further preferred embodiment of the present invention, in step 7, the annealing atmosphere is one of nitrogen or oxygen, the annealing temperature is 600-900° C., and the time is 1.5 h.

[0030] As a further preferred embodiment of the present invention, the thickness of the Cs adsorption layer in step 8 is 1 to 3 atomic layers.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention proposes a Cu-N co-doped gallium oxide efficient p-type doping method and prepares a Ga2O3-based NEA photocathode, which replaces the traditional GaAs and GaN-based photocathodes and realizes the application of Ga2O3 materials in the field of ultraviolet photocathodes;

[0033] 2. The present invention reduces the defect states in the energy band through Cu-N co-doping, inhibits the compensation effect of electrons, and increases the hole carrier concentration of the gallium oxide film to 6.2×10 15 ~1.1×10 18 cm -3 ;

[0034] 3. The present invention uses Cu-N co-doping. Cu doping can adjust the acceptor energy level formed by N by changing the local electronic structure of gallium oxide, making the energy level shallower, thereby reducing the activation energy of holes;

[0035] 4. The hole Hall mobility of the p-type gallium oxide film obtained by Cu-N co-doping in the present invention is significantly improved to 12.5-41.7 cm2 / Vs;

[0036] 5. The present invention introduces band edge states at the top of the valence band or the bottom of the conduction band through Cu-N co-doping. These band edge states have shallow energy levels, so that more electrons can be excited under the action of lower energy photons, thereby increasing the absorption of ultraviolet light and improving the quantum efficiency (QE) of the photocathode, which can reach up to 52%;

[0037] 6. The photocathode prepared by the present invention is less affected by the ambient temperature and has more stable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the specific structure of the present invention, in which: 1-Ag reflective plate layer; 2-substrate layer; 3-p-type gallium oxide layer; 4-activation layer.

[0039] Figure 2 This is an AFM image of the medium concentration Cu-N doped p-type Ga2O3 thin film prepared in Example 2 of the present invention.

[0040] Figure 3 This is the ultraviolet light (200-280nm) absorption diagram of the medium concentration Cu-N doped p-type Ga2O3 film prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0041] The present invention provides a gallium oxide-based ultraviolet photocathode, such as Figure 1 As shown, from bottom to top, the Ag reflective layer 1, the substrate layer 2, the p-type gallium oxide layer 3, and the activation layer 4 are arranged in sequence;

[0042] The Ag reflective layer 1 is used to reflect the unabsorbed light back to the p-type gallium oxide layer 3;

[0043] The substrate layer 2 is a c-plane sapphire substrate for depositing a gallium oxide thin film;

[0044] The p-type gallium oxide layer 3 is a Cu-N co-doped gallium oxide film, which is used as an emission layer of the photocathode;

[0045] The activation layer 4 is a Cs adsorption layer adsorbed on the upper surface of the p-type gallium oxide layer 3 to reduce the electron affinity and improve the electron emission efficiency of the photocathode.

[0046] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] The purity of the Ga2O3 target and the CuO target in the following examples is 99.99%.

[0048] Example 1

[0049] This example explores the performance of gallium oxide photocathode when doped at low concentration. The specific steps include:

[0050] Step 1: Select c-plane sapphire as the substrate and ultrasonically clean the Al2O3 substrate with acetone, ethanol and deionized water for 10 minutes respectively to remove organic matter on the substrate surface;

[0051] Step 2: Install the Ga2O3 target and CuO target respectively, and place the cleaned substrate into the deposition chamber (the distance between the target and the substrate is 6.5 cm);

[0052] Step 3: Start the vacuum pump and reduce the pressure in the sputtering chamber to less than 10 -6 Torr, to remove residual gas and impurities;

[0053] Step 4: Select Ar and N2 mixed gas as the working gas, adjust the working gas pressure to 0.5 Pa, and set the flow rate to 39 sccm (N2 / Ar: 9 / 30 sccm);

[0054] Step 5: Heat the substrate to 750°C and start the sputtering target, and perform a short pre-sputtering (about 5-10 minutes) to clean the target surface and stabilize the sputtering conditions;

[0055] Step 6: Set the sputtering power to 80W, the sputtering time of the Ga2O3 target to 8min, the sputtering time of the CuO target to 1min, and the total sputtering time to 2h; open the baffle and start timing growth;

[0056] Step 7: After the film growth is completed, take out the sample and anneal it in a nitrogen atmosphere at 800°C for 1.5h;

[0057] Step 8: After annealing, the Cs adsorption layer is tightly adsorbed on the gallium oxide film through an ultra-high vacuum activation process, with a thickness of 2 atomic layers;

[0058] Step 9: Bond the gallium oxide film and the Ag reflector together to complete the preparation.

[0059] The electrical performance of the prepared gallium oxide photocathode was tested, and it was found that the hole carrier concentration was 6.2×10 15 cm -3 , the hole Hall mobility is 22.8 cm2 / Vs, the quantum efficiency can reach up to 37%.

[0060] Example 2

[0061] This example explores the performance of the gallium oxide photocathode at a moderate doping concentration. The specific steps include:

[0062] Step 1: Select c-plane sapphire as the substrate and ultrasonically clean the Al2O3 substrate with acetone, ethanol and deionized water for 10 minutes respectively to remove organic matter on the substrate surface;

[0063] Step 2: Install the Ga2O3 target and CuO target respectively, and place the cleaned substrate into the deposition chamber (the distance between the target and the substrate is 6.5 cm);

[0064] Step 3: Start the vacuum pump and reduce the pressure in the sputtering chamber to less than 10 -6 Torr, to remove residual gas and impurities;

[0065] Step 4: Select Ar and N2 mixed gas as the working gas, adjust the working gas pressure to 1Pa, and set the flow rate to 52sccm (N2 / Ar: 12 / 40sccm);

[0066] Step 5: Heat the substrate to 750°C and start the sputtering target, and perform a short pre-sputtering (about 5-10 minutes) to clean the target surface and stabilize the sputtering conditions;

[0067] Step 6: Set the sputtering power to 80W, the sputtering time of the Ga2O3 target to 8min, the sputtering time of the CuO target to 4min, and the total sputtering time to 2h; open the baffle and start timing growth;

[0068] Step 7: After the film growth is completed, take out the sample and anneal it in a nitrogen atmosphere at 800°C for 1.5h;

[0069] Step 8: After annealing, the Cs adsorption layer is tightly adsorbed on the gallium oxide film through an ultra-high vacuum activation process, with a thickness of 2 atomic layers;

[0070] Step 9: Bond the gallium oxide film and the Ag reflector together to complete the preparation.

[0071] Figure 2 This is an AFM image of the medium concentration Cu-N doped p-type Ga2O3 film prepared in this example. The RMS is only 3.48nm, indicating that the gallium oxide film doped at this concentration has good quality.

[0072] Figure 3This is the ultraviolet light (200-280nm) absorption diagram of the medium concentration Cu-N doped p-type Ga2O3 film prepared in this example. Compared with the undoped gallium oxide film, the absorption rate in the range of 260-280nm is significantly improved up to about 95%.

[0073] The electrical performance of the prepared gallium oxide photocathode was tested, and it was found that the hole carrier concentration was 7.6×10 16 cm -3 , the hole Hall mobility is 41.7 cm 2 / Vs, the quantum efficiency can reach up to 52%.

[0074] Example 3

[0075] This example explores the performance of gallium oxide photocathode when doped at high concentration. The specific steps include:

[0076] Step 1: Select c-plane sapphire as the substrate and ultrasonically clean the Al2O3 substrate with acetone, ethanol and deionized water for 10 minutes respectively to remove organic matter on the substrate surface;

[0077] Step 2: Install the Ga2O3 target and CuO target respectively, and place the cleaned substrate into the deposition chamber (the distance between the target and the substrate is 6.5 cm);

[0078] Step 3: Start the vacuum pump and reduce the pressure in the sputtering chamber to less than 10 -6 Torr, to remove residual gas and impurities;

[0079] Step 4: Select Ar and N2 mixed gas as the working gas, adjust the working gas pressure to 1.5 Pa, and set the flow rate to 78 sccm (N2 / Ar: 18 / 60 sccm);

[0080] Step 5: Heat the substrate to 750°C and start the sputtering target, and perform a short pre-sputtering (about 5-10 minutes) to clean the target surface and stabilize the sputtering conditions;

[0081] Step 6: Set the sputtering power to 80W, the sputtering time of the Ga2O3 target to 8min, the sputtering time of the CuO target to 8min, and the total sputtering time to 2h; open the baffle and start timing growth;

[0082] Step 7: After the film growth is completed, take out the sample and anneal it in a nitrogen atmosphere at 800°C for 1.5h;

[0083] Step 8: After annealing, the Cs adsorption layer is tightly adsorbed on the gallium oxide film through an ultra-high vacuum activation process, with a thickness of 2 atomic layers;

[0084] Step 9: Bond the gallium oxide film and the Ag reflector together to complete the preparation.

[0085] The electrical performance of the prepared gallium oxide photocathode was tested, and it was found that the hole carrier concentration was 1.1×10 18 cm -3 , the hole Hall mobility is 12.5 cm 2 / Vs, the quantum efficiency can reach up to 29%.

[0086] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A gallium oxide-based ultraviolet photocathode, characterized in that: The ultraviolet photocathode is sequentially arranged from bottom to top as a Ag reflection layer, a substrate layer, a p-type gallium oxide layer, and an activation layer; The Ag reflective layer is used to reflect unabsorbed light back to the p-type gallium oxide layer; The substrate layer is a c-plane sapphire substrate for depositing a gallium oxide thin film; The p-type gallium oxide layer is a Cu-N co-doped gallium oxide film, which is used as an emission layer of the photocathode; The activation layer is a Cs adsorption layer, which is adsorbed on the upper surface of the p-type gallium oxide layer and is used to reduce the electron affinity and improve the electron emission efficiency of the photocathode.

2. The gallium oxide-based ultraviolet photocathode according to claim 1, characterized in that: The Cu-N co-doped gallium oxide film is prepared by a dual-target magnetron sputtering method, wherein the Cu doping target material is Ga2O3 and CuO target material, and the Cu doping concentration is controlled by changing the sputtering time. N doping is achieved by mixing N2 in the sputtering gas Ar, and the N doping concentration is controlled by changing the sputtering gas pressure and flow rate.

3. A method for preparing a gallium oxide-based ultraviolet photocathode according to claim 1 or 2, characterized in that: The steps include: Step 1: Select c-plane sapphire as the substrate and ultrasonically clean the substrate with acetone, ethanol and deionized water for 5-10 minutes respectively to remove organic matter on the surface of the substrate; Step 2: Install Ga2O3 target and CuO target respectively, and place the cleaned substrate into the deposition chamber; Step 3: Start the vacuum pump and reduce the pressure in the sputtering chamber to less than 10 -6 Torr, to remove residual gas and impurities; Step 4: Select a mixture of nitrogen and argon as the working gas, and adjust the pressure and flow of the working gas; Step 5: Heat the substrate and start the sputtering target, and perform pre-sputtering for 5-10 minutes to clean the target surface and stabilize the sputtering conditions; Step 6: Re-adjust the sputtering power and sputtering time, open the shutter, and start timing growth; Step 7: After the film growth is completed, take out the sample and perform annealing treatment; Step 8: After annealing, the Cs adsorption layer is tightly adsorbed on the gallium oxide film through an ultra-high vacuum activation process; Step 9: Bond the gallium oxide film and the Ag reflector together to complete the preparation.

4. The method for preparing a gallium oxide-based ultraviolet photocathode according to claim 3, characterized in that: In step 2, the distance between the target and the substrate is 6 to 7 cm.

5. The method for preparing a gallium oxide-based ultraviolet photocathode according to claim 3, characterized in that: In step 4, the N2 / Ar flow ratio in the working gas is 10-50%, the pressure of the working gas is set to 0.5-1.5 Pa, and the flow rate of the working gas is set to 20-80 sccm.

6. The method for preparing a gallium oxide-based ultraviolet photocathode according to claim 3, characterized in that: In step 5, the temperature of the substrate is set to 700-800°C.

7. The method for preparing a gallium oxide-based ultraviolet photocathode according to claim 3, characterized in that: In step 6, the sputtering power is set to 40-150W.

8. The method for preparing a gallium oxide-based ultraviolet photocathode according to claim 3, characterized in that: In step 6, the sputtering time is set to multiple time periods. In each time period, the sputtering time of the Ga2O3 target is fixed at 8 minutes, the sputtering time of the CuO target is fixed at 1 to 8 minutes, and the total sputtering time is set to 1 to 4 hours.

9. The method for preparing a gallium oxide-based ultraviolet photocathode according to claim 3, characterized in that: In step 7, the annealing atmosphere is one of nitrogen or oxygen, the annealing temperature is 600-900° C., and the time is 1.5 h.

10. The method for preparing a gallium oxide-based ultraviolet photocathode according to claim 3, characterized in that: The thickness of the Cs adsorption layer in step 8 is 1 to 3 atomic layers.

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