P-type ohmic contact electrode in gallium nitride-based Micro-LED and preparation method of P-type ohmic contact electrode

Abstract

The invention discloses a P-type ohmic contact electrode in a gallium nitride-based Micro-LED and a preparation method of the P-type ohmic contact electrode, and belongs to the technical field of semiconductors. The method comprises the following steps: carrying out inorganic cleaning (H2SO4: H2O2 = 3: 1) on a sapphire-based gallium nitride epitaxial wafer, carrying out photoetching to form a transmission line model pattern, carrying out electron beam evaporation on a 5nm nickel / 5nm gold double-layer electrode, carrying out metal stripping, and then carrying out rapid annealing (preheating at 200 DEG C for 30 seconds and annealing at 500 DEG C for 60 seconds) in an oxygen atmosphere. Through a transmission line model test, the specific contact resistivity is calculated to be as low as 2.495 * 10 <-5 > omega.cm < 2 >. By optimizing annealing process parameters (temperature, time and oxygen flow), the contact resistance of Ni / Au and p-GaN is remarkably reduced, the electrical property and luminous efficiency of the Micro-LED are improved, and the method is suitable for manufacturing high-density display devices.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and specifically to a P-type ohmic contact electrode in a gallium nitride-based Micro-LED and a preparation method thereof. By optimizing the annealing process, the contact resistance is reduced, and the device performance is improved. Background Art

[0002] Micro-LED (Micro Light Emitting Diode) is an emerging display technology based on self-luminous semiconductor materials. Compared with traditional LCD and OLED display technologies, it has many advantages. Micro-LED consists of tiny inorganic LEDs, and each LED pixel can emit light independently, thus eliminating the need for a backlight. Its core advantages include high brightness, low power consumption, long service life, high contrast, and a wider color gamut. This technology performs excellently in achieving higher resolution, response speed, and stability at extreme temperatures, and is therefore widely used in future high-end display devices such as smartphones, smartwatches, AR / VR devices, and large display screens.

[0003] For GaN-based Micro-LEDs, compared with the more mature ohmic contact between metal and n-GaN, more attention should be paid to the ohmic contact between metal and p-GaN. The Ni / Au electrode can be widely used here, mainly because it can provide excellent electrical properties and reliable ohmic contact, ensuring high current injection efficiency and low resistance, thereby improving the light emission efficiency of the device. In addition, the Ni / Au thin film has good optical transparency, especially in the application of semi-transparent electrodes, allowing partial light to penetrate, which helps to improve the light extraction efficiency. Its chemical stability and thermal stability also enable the electrode to maintain stable performance in high-temperature and long-term use environments, reducing the risk of degradation. Moreover, the Ni / Au electrode is compatible with conventional semiconductor manufacturing processes, easy to mass-produce on a large scale, reduces the process complexity, and at the same time ensures the balance of performance and reliability of Micro-LED devices.

[0004] In summary, the Micro-LED display technology has attracted much attention due to its advantages such as high brightness and low power consumption, but the problem of high P-type ohmic contact resistance restricts its electrical performance. The existing annealing process of the Ni / Au electrode has defects such as unstable contact resistance and many interface defects. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a P-type ohmic contact electrode in a gallium nitride-based Micro-LED and a preparation method thereof. By precisely controlling the annealing temperature (500 °C) and oxygen flow rate (4 - 10 sccm), combined with the optimization of the transmission line model (TLM), the specific contact resistivity is significantly reduced.

[0006] Technical solution: A method for preparing a P-type ohmic contact electrode in a gallium nitride-based Micro-LED, comprising the following steps:

[0007] Perform inorganic cleaning on a sapphire-based gallium nitride epitaxial wafer;

[0008] Form a transmission line model pattern by lithography;

[0009] Evaporate a nickel-gold alloy (Ni / Au, 5nm / 5nm) on the surface of the epitaxial wafer;

[0010] After metal lift-off, perform rapid annealing in an oxygen atmosphere. The annealing process includes:

[0011] Purge with O2 for 60 s at room temperature (flow rate 10 sccm);

[0012] Raise the temperature to 200 °C within 30 s (O2 flow rate 4 sccm) and maintain for 30 s;

[0013] Raise the temperature to 500 °C within 30 s (O2 flow rate 4 sccm) and maintain for 60 s;

[0014] Increase the O2 flow rate to 10 sccm and cool down to room temperature.

[0015] Preferably, the inorganic cleaning uses a solution of H2SO4:H2O2 = 3:1, soak overnight and then rinse and blow dry.

[0016] Preferably, the transmission line model includes 6 electrodes with a width of 100 μm and spacings of 8 μm, 10 μm, 12 μm, 14 μm, and 16 μm respectively.

[0017] Preferably, the metal lift-off includes soaking in acetone, ultrasonic oscillation (15 min), and isopropyl alcohol cleaning (10 min).

[0018] Preferably, the total duration of the rapid annealing is 180 s.

[0019] The present invention also provides a P-type ohmic contact electrode in a gallium nitride-based Micro-LED, prepared by the above method.

[0020] Preferably, its specific contact resistivity is 2.495×10 -5 Ω·cm 2 .

[0021] The principle of the present invention is as follows: an interfacial reaction occurs between Ni and P-GaN, resulting in the diffusion of Ni atoms into the semiconductor surface. This reaction helps to reduce the Schottky barrier, thereby forming a better ohmic contact. Annealing causes an alloying reaction at the Ni-GaN interface, forming a compound. This alloyed structure can improve the stability and conductivity of the interface. The high conductivity and stability of Au ensure that the annealed electrode can maintain low resistance and high current conduction ability. Since Au is inert, it does not react with GaN during annealing but retains its original conductivity and corrosion resistance. During the annealing process, thermal energy drives the atomic diffusion at the interface between the metal layer and the semiconductor, making the interface between the electrode material and the semiconductor smoother and more uniform. This diffusion mechanism can reduce interface defects, improve contact characteristics, and optimize current distribution, ultimately enhancing the electrical performance and light-emitting efficiency of Micro-LEDs.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The method of the present invention enables current to be injected into the LED device more efficiently, significantly reducing the contact resistance between the electrode and the semiconductor. The chemical stability and adhesion of Ni are also enhanced during annealing, thereby improving the mechanical stability and durability of the electrode. The control of appropriate annealing temperature and time is crucial for the influence on the surface morphology of the electrode. This annealing condition can improve the ohmic contact while controlling the surface roughness of the electrode, avoiding excessive roughness from affecting the optical performance of the electrode or increasing the series resistance of the device.

[0023] In the GaN-based Micro-LED prepared by the present invention, the specific contact resistivity of the P-type ohmic contact electrode is as low as 2.495×10 -5 Ω·cm 2 , which is reduced by one order of magnitude compared with the traditional process; the electrode surface is flat and dense, without voids (attached Figure 1 ).

[0024] The annealing process of the present invention is compatible with mass production and the cost is controllable. Description of the Drawings

[0025] Figure 1 is the surface morphology diagram of Example 1;

[0026] Figure 2 is the schematic diagram of the I-V curve test of Example 1;

[0027] Figure 3 is the fitting diagram of the total resistance between electrodes and the distance between electrodes of Example 1;

[0028] Figure 4 is the schematic diagram of the I-V curve test of Comparative Example 1;

[0029] Figure 5The fitting graph of the total resistance between electrodes and the distance between electrodes for Comparative Example 1;

[0030] Figure 6 Schematic diagram of the I-V curve test for Comparative Example 2;

[0031] Figure 7 The fitting graph of the total resistance between electrodes and the distance between electrodes for Comparative Example 2;

[0032] Figure 8 Schematic diagram of the I-V curve test for Comparative Example 3;

[0033] Figure 9 The fitting graph of the total resistance between electrodes and the distance between electrodes for Comparative Example 3. Detailed implementation manners

[0034] Example 1

[0035] The present invention can be used in the preparation method of P-type ohmic contact electrodes in gallium nitride-based Micro-LEDs, and specifically includes the following steps:

[0036] (1) Select a suitable sapphire-based GaN epitaxial wafer, and perform inorganic cleaning on the epitaxial wafer using H2SO4:H2O2 = 3:1. This can remove the particles and organic contaminants on the surface of the epitaxial wafer. Immerse it in the solution overnight, and after cleaning, rinse it with a large amount of deionized water and dry it with a nitrogen gun;

[0037] (2) Spin-coat a negative photoresist on the surface of the epitaxial wafer, expose it, and develop it to leave the required pattern on the surface of the epitaxial wafer;

[0038] (3) Use electron beam evaporation to deposit a nickel-gold alloy on the surface of the epitaxial wafer, with the thickness of nickel and gold being 5 nm each;

[0039] (4) Perform metal lift-off. Place the sample with the deposited metal into an acetone solution to remove the photoresist, so that the excess metal on the surface of the sample detaches from the surface of the sample. After repeating several times, place the sample into an ultrasonic cleaner for ultrasonic oscillation for 15 min, then place it into an isopropyl alcohol solution for ultrasonic oscillation for 10 min, rinse the surface of the sample with a large amount of deionized water, and dry it with a nitrogen gun;

[0040] (5) Place the sample into a rapid annealing furnace for rapid annealing. In the rapid annealing furnace, first purge the sample with O2 for 60 s at room temperature, with a flow rate of 10 sccm; rapidly heat up to 200 °C within 30 s, with an O2 flow rate of 4 sccm; maintain for 30 s under this condition; rapidly heat up to 500 °C within 30 s, with the O2 flow rate unchanged; maintain for 60 s at 500 °C, with the O2 flow rate unchanged; increase the O2 flow rate to 10 sccm and purge and cool the sample.

[0041] Through Figure 1It can be found that the surface is smooth and dense under this condition, and no obvious cavities appear on the surface.

[0042] The I-V test was carried out on the total resistance between electrodes after annealing in Example 1 using a probe station, and the results are as Figure 2 shown. When the electrode spacing is 8 μm, the total resistance between electrodes is 6427.5 Ω; when the electrode spacing is 10 μm, the total resistance between electrodes is 8184.5 Ω; when the electrode spacing is 12 μm, the total resistance between electrodes is 9769.3 Ω; when the electrode spacing is 14 μm, the total resistance between electrodes is 11194 Ω; when the electrode spacing is 16 μm, the total resistance between electrodes is 12743 Ω.

[0043] According to the transmission line model theory, a linear relationship was fitted between the total resistance between electrodes and the electrode spacing. The slope and intercept were obtained from the fitted results, and then the specific contact resistivity was calculated according to the calculation formula. The test results are as Figure 3 shown, and the specific contact resistivity is obtained as 2.495×10 -5 Ω·cm 2 .

[0044] Comparative Example 1

[0045] (1) Select a suitable sapphire-based GaN epitaxial wafer, and perform inorganic cleaning on the epitaxial wafer using H2SO4:H2O2 = 3:1. This can remove the particles and organic contamination on the surface of the epitaxial wafer. Immerse it in the solution overnight, and after cleaning, rinse it with a large amount of deionized water and dry it with a nitrogen gun;

[0046] (2) Spin-coat a negative photoresist on the surface of the epitaxial wafer, expose it, and develop it to leave the required pattern on the surface of the epitaxial wafer;

[0047] (3) Use electron beam evaporation to deposit a nickel-gold alloy on the surface of the epitaxial wafer, with the thicknesses of nickel and gold being 5 nm each;

[0048] (4) Perform metal lift-off. Put the sample with the deposited metal into an acetone solution to remove the photoresist, so that the excess metal on the surface of the sample detaches from the surface of the sample. After repeating several times, put the sample into an ultrasonic cleaner and ultrasonically vibrate it for 15 min, then put it into an isopropanol solution and ultrasonically vibrate it for 10 min, rinse the surface of the sample with a large amount of deionized water, and dry it with a nitrogen gun;

[0049] (5) Put the sample into a rapid annealing furnace for rapid annealing. First, purge the sample with O2 for 60 s at room temperature in the rapid annealing furnace, with a flow rate of 10 sccm; rapidly heat up to 200 °C within 30 s, with an O2 flow rate of 4 sccm; maintain it for 30 s under this condition; rapidly heat up to 400 °C within 30 s, with the O2 flow rate unchanged; maintain it for 60 s at 400 °C, with the O2 flow rate unchanged; increase the O2 flow rate to 10 sccm and purge and cool the sample.

[0050] The I-V test was performed on the total resistance between the electrodes after annealing in Comparative Example 1 using a probe station. The results are as follows: Figure 4 When the electrode spacing was 8 μm, the total resistance between the electrodes was 7471.8 Ω; when the electrode spacing was 10 μm, the total resistance between the electrodes was 11333 Ω; when the electrode spacing was 12 μm, the total resistance between the electrodes was 10980 Ω; when the electrode spacing was 14 μm, the total resistance between the electrodes was 12708 Ω; when the electrode spacing was 16 μm, the total resistance between the electrodes was 15581 Ω.

[0051] According to the transmission line model theory, a linear relationship was fitted between the total resistance between the electrodes and the electrode spacing. The slope and intercept were obtained from the fitted results, and then the specific contact resistivity was calculated according to the calculation formula. The test results are as follows: Figure 5 As shown, the specific contact resistivity was obtained as 3.185×10 -4 Ω·cm 2 .

[0052] Comparative Example 2

[0053] (1) A suitable sapphire-based GaN epitaxial wafer was selected, and inorganic cleaning of the epitaxial wafer was carried out using H2SO4:H2O2 = 3:1. This can remove the particles and organic contaminants on the surface of the epitaxial wafer. It was soaked in the solution overnight. After cleaning, it was rinsed with a large amount of deionized water and dried with a nitrogen gun;

[0054] (2) A negative photoresist was spin-coated on the surface of the epitaxial wafer, exposed, and developed to leave the required pattern on the surface of the epitaxial wafer;

[0055] (3) Nickel-gold alloy was evaporated on the surface of the epitaxial wafer using electron beam evaporation, with the thickness of nickel and gold being 5 nm each;

[0056] (4) Metal lift-off was performed. The sample after evaporating the metal was placed in an acetone solution to remove the photoresist, so that the excess metal on the surface of the sample was detached from the surface of the sample. After repeating several times, the sample was placed in an ultrasonic cleaner and ultrasonically vibrated for 15 min, then placed in an isopropanol solution and ultrasonically vibrated for 10 min, and the surface of the sample was rinsed with a large amount of deionized water and dried with a nitrogen gun;

[0057] (5) The sample was placed in a rapid annealing furnace for rapid annealing. In the rapid annealing furnace, the sample was first purged with O2 for 60 s at room temperature, with a flow rate of 10 sccm; it was rapidly heated to 200 °C within 30 s, with an O2 flow rate of 4 sccm; under this condition, it was maintained for 30 s; it was rapidly heated to 500 °C within 30 s, with the O2 flow rate remaining unchanged; it was maintained at 500 °C for 30 s, with the O2 flow rate remaining unchanged; the O2 flow rate was increased to 10 sccm to purge and cool the sample.

[0058] The I-V test was performed on the total resistance between the electrodes after annealing in Comparative Example 2 using a probe station. The results are as follows:Figure 6 As shown in the figure. When the electrode spacing is 8μm, the total resistance between the electrodes is 6381.8Ω; when the electrode spacing is 10μm, the total resistance between the electrodes is 7951.1Ω; when the electrode spacing is 12μm, the total resistance between the electrodes is 9469.6Ω; when the electrode spacing is 14μm, the total resistance between the electrodes is 10936Ω; when the electrode spacing is 16μm, the total resistance between the electrodes is 12304Ω.

[0059] According to the transmission line model theory, a linear relationship is fitted between the total resistance between the electrodes and the electrode spacing. The slope and intercept are obtained from the fitted results, and then the specific contact resistivity is calculated according to the calculation formula. The test results are as Figure 7 shown, and the specific contact resistivity is obtained as 8.801×10 -5 Ω·cm 2 .

[0060] Comparative Example 3

[0061] (1) Select a suitable sapphire-based GaN epitaxial wafer, and perform inorganic cleaning on the epitaxial wafer using H2SO4:H2O2 = 3:1. This can remove the particles and organic contaminants on the surface of the epitaxial wafer. Immerse it in the solution overnight, and after cleaning, rinse it with a large amount of deionized water and dry it with a nitrogen gun;

[0062] (2) Spin-coat a negative photoresist on the surface of the epitaxial wafer, expose it, and develop it to leave the required pattern on the surface of the epitaxial wafer;

[0063] (3) Use electron beam evaporation to deposit a nickel-gold alloy on the surface of the epitaxial wafer, with the thicknesses of nickel and gold being 5nm each;

[0064] (4) Perform metal lift-off. Place the sample with the deposited metal into an acetone solution to remove the photoresist, so that the excess metal on the surface of the sample detaches from the surface of the sample. After repeating several times, place the sample into an ultrasonic cleaner and ultrasonically vibrate it for 15 minutes, then place it into an isopropyl alcohol solution and ultrasonically vibrate it for 10 minutes, rinse the surface of the sample with a large amount of deionized water, and dry it with a nitrogen gun;

[0065] (5) Place the sample into a rapid annealing furnace for rapid annealing. In the rapid annealing furnace, first purge the sample with O2 at room temperature for 60s, with a flow rate of 10sccm; rapidly heat up to 200℃ within 30s, with an O2 flow rate of 4sccm; maintain under this condition for 30s; rapidly heat up to 600℃ within 30s, with the O2 flow rate remaining unchanged; maintain at 600℃ for 60s, with the O2 flow rate remaining unchanged; increase the O2 flow rate to 10sccm and purge and cool the sample.

[0066] Use a probe station to perform an I-V test on the total resistance between the electrodes after annealing in Comparative Example 3. The results are as Figure 8As shown. When the electrode spacing is 8 μm, the total resistance between the electrodes is 9432.2 Ω; when the electrode spacing is 10 μm, the total resistance between the electrodes is 11930 Ω; when the electrode spacing is 12 μm, the total resistance between the electrodes is 13070 Ω; when the electrode spacing is 14 μm, the total resistance between the electrodes is 15014 Ω; when the electrode spacing is 16 μm, the total resistance between the electrodes is 17136 Ω.

[0067] According to the transmission line model theory, a linear relationship is fitted between the total resistance between the electrodes and the electrode spacing. The slope and intercept are obtained from the fitted results, and then the specific contact resistivity is calculated according to the calculation formula. The test results are as Figure 9 shown, and the specific contact resistivity of 1.334×10 -3 Ω·cm 2 is obtained.

Claims

1. A preparation method of a P-type ohmic contact electrode in a gallium nitride-based Micro-LED, characterized in that, It includes the following steps: Perform inorganic cleaning on the gallium nitride epitaxial wafer on sapphire substrate; Form a transmission line model pattern by photolithography; Evaporate nickel-gold alloy (Ni / Au, 5nm / 5nm) on the surface of the epitaxial wafer; After metal lift-off, perform rapid annealing in an oxygen atmosphere. The annealing process includes: Purge with O2 for 60 s at room temperature (flow rate 10 sccm); Raise the temperature to 200 °C within 30 s (O2 flow rate 4 sccm) and maintain for 30 s; Raise the temperature to 500 °C within 30 s (O2 flow rate 4 sccm) and maintain for 60 s; Increase the O2 flow rate to 10 sccm and cool down to room temperature.

2. The method according to claim 1, wherein The inorganic cleaning uses a solution of H2SO4:H2O2 = 3:1, soak overnight and then rinse and blow dry.

3. The method according to claim 1, wherein The transmission line model includes 6 electrodes with a width of 100 μm and spacings of 8 μm, 10 μm, 12 μm, 14 μm, and 16 μm respectively.

4. The method according to claim 1, wherein The metal lift-off includes soaking in acetone, ultrasonic oscillation (15 min), and isopropanol cleaning (10 min).

5. The method according to claim 1, characterized in that The total duration of the rapid annealing is 180 s.

6. A P-type ohmic contact electrode in a gallium nitride-based Micro-LED, characterized in that, Prepared by using the method according to any one of claims 1-5.

7. The electrode according to claim 6, characterized in that, Its specific contact resistivity is 2.495×10 -5 Ω·cm 2 .

Images