Method for reducing dark current of aluminum gallium nitrogen ultraviolet photoelectric detector
Through chemical treatment and heat treatment technology, the leakage channel problem caused by the silicon impurity layer at the growth interface of the aluminum gallium nitrogen ultraviolet photodetector is solved, which significantly reduces the dark current and improves the device performance.
Patent Information
- Application Number
- CN202411535812.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-31
- Publication Date
- 2025-02-11
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
The aluminum gallium nitrogen ultraviolet photodetector naturally adsorbed silicon impurity layer at the growth interface of heterogeneous substrates such as sapphire forms a leakage channel, resulting in an increase in dark current and reducing device performance.
Chemical treatment, including immersing the pre-cleaned sapphire substrate in a mixed solution, oxidative etching, to form a dense oxidized film, followed by heat treatment in a mixed atmosphere of nitrogen, hydrogen and ammonia, to remove silicon contaminants on the surface of the sapphire, and An aluminum gallium nitrogen epitaxial layer is epitaxially grown in a hydride gas phase epitaxial device.
It effectively reduces the dark current of the aluminum gallium nitrogen ultraviolet photodetector, which can be reduced by an order of magnitude at the growth interface, while maintaining the carrier concentration at the growth interface without increasing, ensuring the improvement of device performance.
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Figure CN119421539A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of semiconductor technology, and in particular relates to a method for reducing the dark current of an aluminum gallium nitrogen ultraviolet photodetector. Background Art
[0002] Traditionally, UV detection has relied on photomultiplier tubes and silicon photodiodes. Although photomultiplier tubes have the advantages of high gain and low noise, they are bulky, costly, and have high power consumption. With the maturity of high-quality AlGaN ternary materials, AlGaN-based materials have become ideal for UV detection due to their tunable band gap. By adjusting the aluminum content, AlGaN materials are able to cover the entire mid-UV and near-UV bands. AlGaN UV photodetectors are unique in that they do not respond to background radiation from the sun because solar radiation within its spectral range (<280nm) is filtered out by the ozone layer before reaching the lower atmosphere. This feature enables AlGaN solar-blind detectors to be unaffected by solar noise and specifically used to detect artificial UV sources. In recent years, AlGaN-based solar-blind photodetectors have gradually become a powerful alternative to photomultiplier tubes and silicon photodiodes with their inherent spectral selectivity.
[0003] The dark current of a photodetector refers to the current generated by the detector itself when there is no light irradiation. Large dark currents will have an adverse effect on the performance of the photodetector. First, dark currents will reduce the signal-to-noise ratio of the detector, making the detector less sensitive at low light levels. Second, dark currents will affect the response speed of the detector, causing errors in the detector's high-speed signal detection. The leakage current caused by the manufacturing process and material defects of the detector itself is the main source of the detector's dark current. At present, aluminum gallium nitride ultraviolet photodetectors are usually grown heteroepitaxially on substrates such as sapphire. The naturally adsorbed silicon impurity layer at the growth interface will form a leakage channel, increase the dark current of the detector, and reduce the performance of the device. Summary of the invention
[0004] In order to solve the problem in the prior art that the silicon impurity layer naturally adsorbed at the growth interface of the epitaxial layer of the aluminum gallium nitride ultraviolet photodetector on a heterogeneous substrate such as sapphire will form a leakage channel and increase the dark current of the detector, the present invention provides a method for reducing the dark current of the aluminum gallium nitride ultraviolet photodetector by chemical treatment, which is simple and easy to operate. The specific scheme is as follows:
[0005] A method for reducing the dark current of an AlGaN ultraviolet photodetector comprises the following steps: immersing a pre-cleaned sapphire substrate in a mixed solution for oxidation etching, taking out the etched sapphire substrate, rinsing it and drying it; transferring the dried sapphire substrate into a hydride vapor phase epitaxy device for heat treatment, and then introducing a gallium source, an aluminum source and a nitrogen source to epitaxially grow an AlGaN epitaxial layer to form an AlGaN / sapphire template; and preparing an AlGaN ultraviolet photodetector on the AlGaN / sapphire template through ultraviolet photolithography and electron beam evaporation processes.
[0006] Furthermore, the mixed solution includes an oxidant and an etchant; the volume ratio of the oxidant to the etchant is 1 to 4:1.
[0007] Furthermore, the oxidant is hydrogen peroxide or sulfuric acid with a mass fraction of 20-30%; the etchant is potassium hydroxide or sodium hydroxide solution with a concentration of 1-3 mol / L.
[0008] Furthermore, the mixed solution is ultrasonicated and heated; the pre-cleaned sapphire substrate is immersed in the mixed solution, so that the sapphire surface is etched by 1 to 2 nm, and the sapphire substrate is taken out and rinsed with running water. At this time, due to the presence of a strong oxidizing agent, the sapphire surface is oxidized to form a uniform and dense oxide film that can block the air.
[0009] Blow dry with nitrogen to obtain a dried sapphire substrate.
[0010] Furthermore, the ultrasonic and heating step is to ultrasonically heat the mixed solution to 80-100° C. at 500-1000 W; and immerse the sapphire substrate to be cleaned in the mixed solution for 20-60 minutes.
[0011] Furthermore, the heat treatment is carried out in a mixed atmosphere at 900-1000° C. for 5-10 minutes.
[0012] Furthermore, the mixed atmosphere includes nitrogen, hydrogen and ammonia; the flow rate of the nitrogen is 2.5-4slm; the flow rate of the hydrogen is 2.5-4slm; and the flow rate of the ammonia is 0.1-0.5slm.
[0013] Furthermore, the gallium source is metallic gallium, the aluminum source is metallic aluminum, and the nitrogen source is ammonia; and the temperature of the epitaxial growth is 1300-1400°C.
[0014] An AlGaN ultraviolet photodetector prepared by the above method for reducing the dark current of an AlGaN ultraviolet photodetector comprises a sapphire template, an electrode, and an AlGaN epitaxial layer disposed between the sapphire template and the electrode.
[0015] Furthermore, the surface of the sapphire substrate after heat treatment is atomically clean and free of silicon contaminants.
[0016] By adopting the above scheme, the method of the present invention has the following advantages:
[0017] 1. The present invention uses ultrasonic assisted heating to promote the etching reaction on the surface of the sapphire substrate, speed up the etching speed, and remove the pollutants that fall off the surface of the sapphire substrate. Then, the sapphire substrate is rinsed with deionized water for 10 to 20 minutes. At this time, due to the presence of a strong oxidizing agent, the sapphire surface is oxidized to form a uniform and dense oxide film, which can block secondary pollution from the air.
[0018] 2. The present invention heat treats the oxidized etched sapphire in a mixed gas atmosphere, and the pollutants and oxide film on the sapphire surface are decomposed and carried away with the air flow. Therefore, the surface of the sapphire substrate does not contain silicon pollutants, becomes atomically clean, and will not be polluted by the air again.
[0019] 3. The dense oxide film generated by the surface cleaning of the sapphire substrate in the present invention prevents pollutants in the air from directly contacting the sapphire surface, and the heat treatment and aluminum gallium nitride deposition are both carried out in the same container, which is simple to operate with fewer steps and avoids secondary contamination caused by transferring the sapphire substrate container, thereby ensuring the purity of the sapphire substrate surface.
[0020] 4. The present invention uses hydrogen chloride as a reaction gas and reacts chemically with metal gallium and aluminum under the carrier of hydrogen or nitrogen to generate aluminum gallium nitride, which then reacts with ammonia above a sapphire substrate under the carrier of hydrogen or nitrogen to generate aluminum gallium nitride, and is deposited on the substrate to form an aluminum gallium nitride layer, and the layer thickness can be controlled by the deposition time as required.
[0021] 5. The carrier concentration at the growth interface of the AlGaN ultraviolet photodetector obtained by the method of the present invention does not increase, indicating that there is no leakage caused by silicon impurities at the growth interface.
[0022] 6. The dark current of the aluminum gallium nitride ultraviolet photodetector prepared by the method of the present invention is significantly reduced, and can be reduced by up to one order of magnitude.
[0023] 7. The method of the present invention has few steps, is simple and easy to operate, and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 It is a schematic structural diagram of the aluminum gallium nitrogen ultraviolet photodetector of the present invention.
[0025] Figure 2 This is the impurity distribution diagram at the growth interface of Example 1.
[0026] Figure 3 This is the impurity distribution diagram at the growth interface of Comparative Example 1.
[0027] Figure 4 This is the impurity distribution diagram at the growth interface of Comparative Example 2.
[0028] Figure 5 This is the impurity distribution diagram at the growth interface of Comparative Example 3.
[0029] Figure 6 It is a comparison diagram of carrier concentration at the growth interface of Example 1 and Comparative Examples 1-3.
[0030] Figure 7 It is a comparison diagram of the dark current of the aluminum gallium nitride ultraviolet photodetector of Example 1 and Comparative Examples 1 to 3. DETAILED DESCRIPTION
[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0032] Embodiment 1:
[0033] (1) taking a sapphire substrate, and cleaning it in acetone and ethanol in turn to obtain a pre-cleaned sapphire substrate; mixing 30% hydrogen peroxide and 2 mol / L sodium hydroxide solution in a volume ratio of 2:1 to obtain a mixed solution; ultrasonicating the mixed solution at 700 W and heating it in a water bath to 95° C., immersing the pre-cleaned sapphire substrate in the mixed solution for 30 minutes to etch 1 to 2 nm from the sapphire surface, taking out the sapphire substrate and rinsing it with running deionized water for 10 to 20 minutes, and drying it with nitrogen to obtain a dried sapphire substrate;
[0034] (2) The dried sapphire substrate is transferred into a hydride vapor phase epitaxy device, and heat treated at 950° C. for 10 min in a mixed atmosphere of 3 slm nitrogen, 3 slm hydrogen and 0.3 slm ammonia. Then, a gallium source, an aluminum source and a nitrogen source are introduced into the hydride vapor phase epitaxy device, and an aluminum gallium nitrogen epitaxial layer is epitaxially grown at 1350° C. to form an aluminum gallium nitrogen / sapphire template;
[0035] (3) The AlGaN / sapphire template is prepared into an ultraviolet photodetector by ultraviolet lithography and electron beam evaporation. Figure 1 As shown, the ultraviolet photodetector includes a sapphire template, an electrode, and an aluminum gallium nitride epitaxial layer arranged between the sapphire template and the electrode.
[0036] The impurity distribution results of the AlGaN / sapphire template growth interface are shown in Figure 2. Figure 2 As shown. Figure 2It can be seen that the carrier concentration at the growth interface of the AlGaN / sapphire template prepared by the method of the present invention does not increase, indicating that there is no silicon contaminant on the growth interface.
[0037] Embodiment 2:
[0038] The difference from Example 1 is:
[0039] The volume ratio of hydrogen peroxide and sodium hydroxide solution is 4:1.
[0040] Embodiment 3:
[0041] The difference from Example 1 is:
[0042] The volume ratio of hydrogen peroxide and sodium hydroxide solution is 1:1.
[0043] Embodiment 4:
[0044] The difference from Example 1 is:
[0045] (2) The dried sapphire substrate is transferred into a hydride vapor phase epitaxy device, and heat treated at 950° C. for 5 min in a mixed atmosphere of nitrogen with a flow rate of 2.5 slm, hydrogen with a flow rate of 2.5 slm, and ammonia with a flow rate of 0.5 slm. Then, a gallium source, an aluminum source, and a nitrogen source are introduced into the hydride vapor phase epitaxy device, and an aluminum gallium nitrogen epitaxial layer is epitaxially grown at 1350° C. to form an aluminum gallium nitrogen / sapphire template;
[0046] Comparative Example 1:
[0047] (1) taking a sapphire substrate, and cleaning it in acetone and ethanol in sequence to obtain a pre-cleaned sapphire substrate; taking out the sapphire substrate and rinsing it with flowing deionized water for 10 min to 20 min, and drying it with nitrogen to obtain a dried sapphire substrate;
[0048] (2) The dried sapphire substrate is transferred into a hydride vapor phase epitaxy device, and heat treated at 950° C. for 10 min in a mixed atmosphere of 3 slm nitrogen, 3 slm hydrogen and 0.3 slm ammonia. Then, a gallium source, an aluminum source and a nitrogen source are introduced into the hydride vapor phase epitaxy device, and an aluminum gallium nitrogen epitaxial layer is epitaxially grown at 1350° C. to form an aluminum gallium nitrogen / sapphire template;
[0049] (3) The AlGaN / sapphire template is prepared into an ultraviolet photodetector by ultraviolet lithography and electron beam evaporation process.
[0050] The impurity distribution at the AlGaN / sapphire template growth interface of Comparative Example 1 was detected. Figure 3 As shown, only the existing common organic reagents are used for cleaning Figure 3It contains a large amount of silicon contaminants in the form of siloxane. It can be seen from this that since there is no etchant in the cleaning process of Comparative Example 1, the silicon contaminants on the sapphire surface cannot be etched away; since there is no oxidant, a dense oxide film cannot be formed on the sapphire surface, so secondary air pollution cannot be avoided, and the silicon contaminants on the sapphire surface will increase. Even after heat treatment, the silicon contaminants on the sapphire surface cannot be completely decomposed. Therefore, there are still a large number of silicon contaminants on the exposed sapphire substrate surface. The impurity and carrier concentration distribution results of Example 1 and Comparative Example 1 show that the method of the present invention can effectively remove silicon impurities on the surface of the sapphire substrate.
[0051] Comparative Example 2:
[0052] (1) taking a sapphire substrate, and cleaning it in acetone and ethanol in turn to obtain a pre-cleaned sapphire substrate; ultrasonically treating a 30% hydrogen peroxide oxidant at 700 W and heating it in a water bath to 95° C., immersing the pre-cleaned sapphire substrate in the oxidant and keeping it for 30 minutes, taking out the sapphire substrate and rinsing it with running deionized water for 10 minutes to 20 minutes, and drying it with nitrogen to obtain a dried sapphire substrate;
[0053] (2) The dried sapphire substrate is transferred into a hydride vapor phase epitaxy device, and heat treated at 950° C. for 10 min in a mixed atmosphere of 3 slm nitrogen, 3 slm hydrogen and 0.3 slm ammonia. Then, a gallium source, an aluminum source and a nitrogen source are introduced into the hydride vapor phase epitaxy device, and an aluminum gallium nitrogen epitaxial layer is epitaxially grown at 1350° C. to form an aluminum gallium nitrogen / sapphire template;
[0054] (3) The AlGaN / sapphire template is prepared into an ultraviolet photodetector by ultraviolet lithography and electron beam evaporation process.
[0055] The impurity distribution at the AlGaN / sapphire template growth interface of Comparative Example 2 was detected. Figure 4 As shown, the types of silicon pollutants on the interface are slightly reduced compared with comparative example 1, but are still significantly more than those in Example 1. This indicates that due to the absence of an etchant, the silicon pollutants on the sapphire surface cannot be etched away. Although the silicon pollutants on the sapphire surface are not completely removed, a dense oxide film can be formed under the action of an oxidant to block secondary air pollution. After heat treatment, the oxide film will be decomposed and carried away with the airflow, but there are still unetched silicon pollutants on the exposed sapphire surface, so the pollutants are reduced compared with comparative example 1, but are still relatively large.
[0056] Comparative Example 3:
[0057] (1) taking a sapphire substrate, and cleaning it in acetone and ethanol in turn to obtain a pre-cleaned sapphire substrate; ultrasonically treating a 2 mol / L sodium hydroxide solution etchant at 700 W and heating it in a water bath to 95° C., immersing the pre-cleaned sapphire substrate in the mixed solution, and keeping it for 30 minutes to etch 1 to 2 nm, taking out the sapphire substrate and rinsing it with running deionized water for 10 to 20 minutes, and drying it with nitrogen to obtain a dried sapphire substrate;
[0058] (2) The dried sapphire substrate is transferred into a hydride vapor phase epitaxy device, and heat treated at 950° C. for 10 min in a mixed atmosphere of 3 slm nitrogen, 3 slm hydrogen and 0.3 slm ammonia. Then, a gallium source, an aluminum source and a nitrogen source are introduced into the hydride vapor phase epitaxy device, and an aluminum gallium nitrogen epitaxial layer is epitaxially grown at 1350° C. to form an aluminum gallium nitrogen / sapphire template;
[0059] (3) The AlGaN / sapphire template is prepared into an ultraviolet photodetector by ultraviolet lithography and electron beam evaporation process.
[0060] The impurity distribution at the AlGaN / sapphire template growth interface of Comparative Example 3 was detected. Figure 5 As shown in the figure, the types of silicon pollutants on the interface have slightly decreased, but are still significantly more than in Example 1. Compared with Example 1, it can be seen that due to the use of an etchant, the sapphire surface is etched away by 1nm to 2nm, and the silicon pollutants on the surface are etched away, but due to the lack of an oxidant, a dense oxide film cannot be formed on the sapphire surface, and it will be polluted by air again to form silicon pollutants. After heat treatment, the silicon pollutants on the sapphire surface cannot be completely decomposed, and the sapphire surface is still not clean. This shows that the etchant and the oxidant need to be used together to produce a synergistic effect, and the use of a single one cannot achieve the effect of completely cleaning the growth interface.
[0061] Example sample test:
[0062] The carrier concentration at the aluminum gallium nitride / sapphire template growth interface of Example 1 and Comparative Example 1 was tested. The results are as follows Figure 4 As shown in the figure, it can be seen that at the growth interface (about 550nm), the carrier concentration of comparative examples 1 to 3 increases sharply, while the carrier concentration of embodiment 1 at this point does not increase, indicating that there is no leakage current caused by silicon impurities at the growth interface of embodiment 1.
[0063] The dark current of Example 1 and Comparative Example 1 was tested using a semiconductor analyzer. The results are as follows Figure 5As shown, the dark current of the aluminum gallium nitride ultraviolet photodetector prepared by the method of the present invention is significantly smaller than that of comparative examples 1 to 3, and can be reduced by an order of magnitude at most. This shows that the method of the present invention can effectively remove silicon impurities at the interface of aluminum gallium nitride heteroepitaxial growth, and will not be polluted by air again. The method of the present invention can significantly reduce the dark current of the aluminum gallium nitride ultraviolet photodetector.
[0064] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.
Claims
1. A method for reducing dark current of an aluminum gallium nitride ultraviolet photodetector, characterized in that: The pre-cleaned sapphire substrate is immersed in the mixed solution for oxidation etching, and the etched sapphire substrate is taken out, rinsed and dried; the dried sapphire substrate is transferred to a hydride vapor phase epitaxy device for heat treatment, and then a gallium source, an aluminum source and a nitrogen source are introduced to epitaxially grow an aluminum gallium nitride epitaxial layer to form an aluminum gallium nitride / sapphire template; an aluminum gallium nitride ultraviolet photodetector is prepared on the above aluminum gallium nitride / sapphire template through ultraviolet lithography and electron beam evaporation processes.
2. The method for reducing dark current of an AlGaN ultraviolet photodetector according to claim 1, characterized in that: The mixed solution includes an oxidant and an etchant; the volume ratio of the oxidant to the etchant is 1 to 4:
1.
3. The method for reducing dark current of an AlGaN ultraviolet photodetector according to claim 2, characterized in that: The oxidant is hydrogen peroxide or sulfuric acid with a mass fraction of 20-30%; the etchant is potassium hydroxide or sodium hydroxide solution with a concentration of 1-3 mol / L.
4. The method for reducing dark current of an AlGaN ultraviolet photodetector according to claim 1, characterized in that: The mixed solution is ultrasonically treated and heated; the pre-cleaned sapphire substrate is immersed in the mixed solution to etch 1 to 2 nm of the sapphire surface; the sapphire substrate is taken out and rinsed with flowing water, and blown dry with nitrogen to obtain a dried sapphire substrate.
5. The method for reducing dark current of an AlGaN ultraviolet photodetector according to claim 4, characterized in that: The ultrasonic and heating method comprises ultrasonically heating the mixed solution to 80-100° C. at 500-1000 W; and immersing the sapphire substrate to be cleaned in the mixed solution for 20-60 minutes.
6. The method for reducing dark current of an AlGaN ultraviolet photodetector according to claim 1, characterized in that: The heat treatment is carried out in a mixed atmosphere at 900-1000° C. for 5-10 minutes.
7. The method for reducing dark current of an AlGaN ultraviolet photodetector according to claim 6, characterized in that: The mixed atmosphere includes nitrogen, hydrogen and ammonia; the flow rate of the nitrogen is 2.5-4slm; the flow rate of the hydrogen is 2.5-4slm; and the flow rate of the ammonia is 0.1-0.5slm.
8. The method for reducing dark current of an AlGaN ultraviolet photodetector according to claim 1, characterized in that: The gallium source is metallic gallium, the aluminum source is metallic aluminum, and the nitrogen source is ammonia; the temperature of the epitaxial growth is 1300-1400°C.
9. An AlGaN ultraviolet photodetector prepared by the method for reducing dark current of an AlGaN ultraviolet photodetector according to any one of claims 1 to 8, characterized in that: The invention comprises a sapphire template, an electrode, and an aluminum gallium nitride epitaxial layer arranged between the sapphire template and the electrode.
10. The AlGaN ultraviolet photodetector prepared by the method for reducing the dark current of an AlGaN ultraviolet photodetector according to claim 9, characterized in that: The surface of the sapphire substrate after heat treatment is atomically clean.