A method for making ohmic contacts to p-type iii-v semiconductor materials with low specific contact resistance

Abstract

The application relates to a preparation method of a low specific contact resistance p-type III-V semiconductor material and an ohmic contact of a conductive electrode. The method uses a delta doping technology to grow a Mg high-doping contact layer of a p-type III / V nitride semiconductor material, effectively improves the doping concentration of Mg, thereby improving the hole concentration of a contact interface, thinning the potential barrier of the semiconductor interface, enabling electrons to pass through the interface potential barrier through a tunneling effect, forming a good ohmic contact, reducing the contact resistance, and further reducing the heat generation, and improving the device life. The application has excellent effects on reducing the specific contact resistance, and has the characteristics of high preparation efficiency and more extensive material adaptability, thereby being more valuable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor, and particularly relates to a preparation method of ohmic contact of p-type III-V semiconductor material with low specific contact resistivity and conductive electrode. BACKGROUND

[0002] At present, the third generation semiconductor materials represented by gallium nitride (GaN) have been widely used in many important fields, such as semiconductor lasers, early warning radar, fast chargers and the like. Many semiconductor devices are composed of n-type and p-type semiconductors, and the connection with external circuits also needs to use contact electrodes. Generally, the preparation process of the electrode needs to be adjusted to ensure ohmic contact. Good ohmic contact is beneficial to reduce the series resistance, thereby reducing the heat accumulation of the contact interface in the large current working state. If the contact is poor and the contact resistance is large, heat is easy to accumulate and burn out the device. Therefore, good ohmic contact is one of the important indicators to improve the service life and working performance of III-V semiconductor devices.

[0003] Due to the difference in work function between III-V semiconductor materials and conductive electrode materials such as metals, a contact potential barrier is often formed at the interface of the contact, which hinders the transport of carriers, increases the contact resistance and reduces the electrical performance of the device. Taking p-GaN as an example, it has always been difficult to prepare an electrode with low specific contact resistivity. The reasons for this difficulty mainly include the following aspects: firstly, the work function of p-GaN is high, and it is almost impossible to find a metal material with a matching work function; secondly, it is difficult to increase the doping concentration of p-GaN, and it is also difficult to activate the hole carriers, so it is difficult to obtain a hole concentration higher than 10 19 / cm 3 ; thirdly, p-GaN often has a high density of surface states, thereby forming pinning of the Fermi level, which is not conducive to the preparation of ohmic contact conductive electrodes. In order to reduce the specific contact resistivity, the common solutions mainly start from the following aspects: 1) selecting a metal with a more similar work function and performing alloying treatment, thereby reducing the interface potential barrier; 2) preparing a heavily doped contact layer to increase the carrier concentration, thereby thinning the interface potential barrier and allowing the carriers to tunnel through; 3) reducing the interface potential barrier or repairing the surface state through surface treatment means; 4) increasing the density of interface defect energy levels and using deep level defects to assist carrier tunneling.

[0004] For the problem of high-quality ohmic contact preparation of p-GaN, domestic and foreign researchers have proposed a variety of improved solutions. For the optimization direction of electrode material selection, there are multiple patents that can be referred to. For example, the patent of Japan Rayon Company "Gallium nitride-based III-V compound semiconductor device with ohmic electrode and method for manufacturing the same" (patent publication number 1102507) provides a method for preparing an ohmic contact electrode using a Ni / Au electrode; the patent of Shanghai Beida Blue Light "Preparation method of low resistance p-type GaN-based material ohmic contact" (patent number ZL02155062.X) proposes a method for reducing the contact resistance by treating the Ni / Au electrode with oxygen plasma. The influence of these electrode material selection and processing methods on the final low contact resistance is relatively small, while the influence of the carrier concentration of the semiconductor material itself is greater. Therefore, another important technology is to improve the carrier concentration of the semiconductor material, for example, the patent "Preparation method of p-type GaN low resistance ohmic contact layer" (application number 201410520243.8) proposes a method for preparing a heavy-doped contact layer, which improves the carrier concentration on the semiconductor side by appropriate activation conditions. However, as we know, it is difficult to heavily dope Mg during the growth of p-GaN by MOCVD (metal organic chemical vapor deposition), and it is difficult to exceed 10 20 / cm 3 , and because the acceptor activation energy of Mg ions is high, and it is easy to form ion pairs with H ions, the activation rate of Mg is low, usually less than 10%, and the self-compensation effect under high doping further reduces the activation rate, so it is difficult to exceed 10 19 / cm 3, which is not conducive to the preparation of ohmic contact electrodes. The method used in the patent "p-GaN ohmic contact electrode with low specific contact resistance and its preparation method and application" (application number 201910943294.4) is to inject a large dose of Mg ions by ion implantation, thereby reducing the formation of Mg-H complex pairs and increasing the activation rate of Mg. The disadvantage of this method is that high-energy and large-dose ion implantation can cause surface damage, resulting in a decrease in the crystal quality of the semiconductor material near the interface, an increase in defect scattering, and a decrease in conductivity. And ion implantation needs to rely on special equipment, increasing the process steps, equipment cost and manufacturing time cost, which is not conducive to reducing production cost and improving production efficiency. In terms of treating the surface of semiconductor materials to improve contact effect, the patent "Method for realizing low resistance ohmic contact between metal and p-type GaN" (application number 201911198532.X) proposes using F plasma for surface treatment, which can use F ion strong electronegativity to repair interface state, so that the Fermi level is unpinned, thereby reducing the contact resistance. The patent "Improved method for ohmic contact of GaN device" (application number 201910095568.9) proposes using a proper dose of proton irradiation of semiconductor materials to reduce the surface barrier and improve the contact performance. However, both of these methods require special equipment, increasing the process steps, which is not conducive to reducing production cost and improving production efficiency.

[0005] Therefore, for III-V nitride semiconductor materials represented by GaN, the specific contact resistance of the p-type electrode contact is usually >10 -3 Ω·cm 2 , and it is generally believed in the industry that the specific contact resistance needs to reach 10 -4 Ω·cm 2 order of magnitude or lower to ensure good electrical performance. However, there is still a lack of low specific contact resistance ohmic contact electrode preparation methods with high production efficiency and without increasing cost. SUMMARY

[0006] The purpose of the present application is to solve the difficulty of preparing low specific contact resistance ohmic contact between p-GaN and conductive electrodes, while not increasing the production process and production cost. The ohmic contact of the p-electrode is very important for the electrical performance of III / V nitride semiconductor devices. Due to the characteristics of p-GaN itself, the bottleneck of many devices is in the p-region, such as high series resistance, high contact resistance, high heat generation, etc. Obviously, high-quality ohmic contact can effectively reduce the overall series resistance, while reducing the power consumption and heat generation of the p-region, thereby improving the efficiency and life of the device. The key to ohmic contact is the preparation method of the contact layer. The core of the present application is to improve the preparation method of the contact layer, and then use appropriate electrode materials to obtain a specific contact resistance of less than 10 -4 Ω·cm2 The specific contact resistivity of the p-type III-V semiconductor material is low.

[0007] The technical solutions adopted by the present application are as follows:

[0008] The present application provides a method for preparing an ohmic contact electrode of a p-type III-V semiconductor material with low specific contact resistivity, which comprises the following steps:

[0009] Further, the step of growing the heavily doped contact layer by delta doping is performed once or multiple times during the process of growing the p-type III-V semiconductor material by MOCVD.

[0010] Further, the step of growing the heavily doped contact layer by delta doping is performed once or multiple times during the process of growing the p-type III-V semiconductor material by MOCVD. 20 / cm 3 The above.

[0011] Further, the growth rate of the contact layer is controlled to be 5-15 nm / min, and the growth temperature is controlled to be 700-900℃.

[0012] Further, after the growth of the contact layer is started, 0-5 nm of the contact layer is grown normally, and then the first delta doping growth is performed, and then the periodic delta doping growth is performed, and the interval thickness between the two delta dopings is 1-10 nm, and the more preferable interval thickness is 1-3 nm.

[0013] Further, the number of times of delta doping is determined by the thickness of the contact layer and the periodic interval, and the thickness of the contact layer is 1-30 nm, and the more preferable thickness of the contact layer is 2-10 nm.

[0014] Further, after the growth of the contact layer by delta doping is completed, the acceptor energy level of the doped element is activated.

[0015] The present application also provides an ohmic contact electrode with low specific contact resistivity, which comprises a contact layer and a conductive electrode layer on the contact layer, and the contact layer is prepared by the method of the present application.

[0016] Further, the conductive electrode layer can be made of metal alloys such as Ni / Au or Pd / Pt / Au, or transparent conductive oxides such as ITO (indium tin oxide) and AZO (aluminum zinc oxide).

[0017] The present application also provides a semiconductor device comprising the ohmic contact electrode with low specific contact resistivity.

[0018] The key point of the present application is that the Mg high-doped contact layer of p-type III / V nitride semiconductor material is grown by using the delta-doping technology, which effectively increases the average doping concentration of Mg, thereby increasing the hole concentration of the contact interface, thinning the Schottky barrier between the conductive electrode and the semiconductor interface, allowing electrons to pass through the interface barrier by tunneling effect, forming a good ohmic contact, reducing the contact resistance, and further reducing the heat generation, and improving the device life.

[0019] The semiconductor contact layer preparation method based on the delta-doping technology provided by the present application is used for optimizing the specific contact resistivity of III-V nitride materials such as GaN and conductive electrodes. Compared with the prior art, the present application provides a more optimized ohmic contact electrode preparation method, which has excellent effect on reducing the specific contact resistivity, and has the characteristics of high preparation efficiency and more extensive material adaptability, thereby being more valuable. The present application has the following advantages compared with the prior art:

[0020] 1. High-doped Mg can be achieved in a relatively thin thickness, and the average doping concentration of Mg can exceed 10 20 / cm 3 in a thickness of less than 5nm, and good crystal quality can also be maintained, which is difficult to achieve by other methods. Even if the ion implantation method forcibly implants Mg ions in a large dose, although a high doping amount can be achieved, the crystal structure will be severely damaged due to the bombardment effect, resulting in low hole mobility and large series resistance. In other conventional MOCVD growth methods, the doping concentration of Mg is only gradually increased, and a relatively thick contact layer needs to be grown to achieve a high concentration, and even if a relatively thick contact layer is grown, it is still difficult to achieve a doping amount of 10 20 / cm 3 order of magnitude. A thinner contact layer has at least two advantages, one is to reduce the series resistance in the vertical film direction, and the other is that the interface between the metal and the contact layer can be closer to the contact layer and the p-GaN layer, so as to make full use of the hole aggregation effect caused by the band bending at the interface to increase the hole concentration. Therefore, the use of delta-doping technology to grow the contact layer has great advantages in improving the electrical properties of the p-GaN and high-conductive electrode contact, thereby effectively reducing the heat generation at the electrode interface and improving the life of the device. This method can not only be used for the contact of light-electricity devices such as LEDs and lasers, but also can be used for other electronic devices such as HEMT and MOSFET.

[0021] 2. No new process steps and instruments are needed. In comparison, many surface treatment techniques or ion implantation techniques need to introduce new process steps, which reduces the production efficiency and increases the overall production cost due to the use of special equipment. Thinner contact layer means shorter growth time, which improves the production efficiency. Thinner contact layer also means smaller series resistance, which can further improve the overall electrical performance.

[0022] 3. The method is suitable for a wider range of materials. As we know, with the increase of Al composition in AlGaN, the doping and activation of Mg will be more difficult, and higher Al composition p-type AlGaN is needed in some devices, so the preparation of ohmic contact is more difficult. The method of delta doping is used to grow the contact layer, which can effectively dope Mg in high Al composition AlGaN, so as to prepare a conductive electrode with lower specific contact resistivity. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of a common III / V semiconductor device contact region structure.

[0024] Figure 2 is a schematic diagram of the concentration distribution of delta-doped Mg atoms in the device structure.

[0025] Figure 3 is a schematic diagram of a common blue-green LED structure.

[0026] Figure 4 is a schematic diagram of the diffusion overlap of the delta-doped layer.

[0027] Figure 5 is a schematic diagram of a common structure of the p region of a laser.

[0028] Figure 6 is a schematic diagram of a circular transmission line pattern.

[0029] Figure 7 is a circular transmission line data fitting diagram according to the data in Table 1.

[0030] Figure 8 is the specific contact resistivity of different blocks of two experimental samples. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below through specific examples and drawings.

[0032] The technical scheme of the present application mainly starts from the material growth method of the contact layer. Taking p-GaN as an example, because of the difficulty in Mg doping and activation, the p-type region doping concentration is usually not particularly high (less than 10 19 / cm 3 ) in order to have better crystal quality, and because the acceptor level activation energy of Mg ion is high, only less than 10% of the Mg impurities can be activated, so the p-type region carrier concentration is usually less than 10 18 / cm 3 , which is not conducive to direct contact with the metal to form an ohmic contact. In view of this, the common practice in the industry is to add a contact layer between the p-type region and the conductive electrode, which is specifically used to improve the interface carrier concentration, as shown in Figure 1 . The contact layer has the following characteristics: 1. The Mg doping concentration in the semiconductor material of the contact layer is high, which needs to reach 10 20 / cm 3 or more, in order to increase the hole carrier concentration at the contact interface; 2. The thickness of the contact layer cannot be too thick, generally in the range of 1-30 nm, on the one hand because too thick will deteriorate the crystal quality, on the other hand because the interface between the lower doped p-type semiconductor and the highly doped contact layer will bend the energy band downward, forming a low energy valley, thereby gathering holes to form a two-dimensional hole gas-like structure, greatly improving the local hole concentration, which is conducive to forming an ohmic contact with the metal, and if the thickness is too thick, the hole gathering area will be far away from the interface between the contact layer and the metal, and will not achieve the effect of increasing the carrier concentration at the contact interface.

[0033] In the usual contact layer growth method, it is difficult to achieve high doping when the thickness of the contact layer is less than 5 nm, because the incorporation of Mg atoms has a gradual change process, even if a large flow of Mg source is suddenly introduced during growth, it will not immediately reach a high doping concentration, and the doping concentration will gradually increase with the increase of thickness. Therefore, in the conventional method, it is impossible to achieve a very high doping concentration when the thickness of the contact layer is too small. On the other hand, it is also difficult to accurately control the thickness during growth when the thickness is too thin. This is because at a lower growth rate, Mg atoms have enough time to resolve and are not conducive to the incorporation of Mg atoms, making it more difficult to achieve high doping. Although increasing the growth rate is conducive to the incorporation of Mg atoms, it is difficult to accurately control the growth thickness to less than 5 nm, because the entire growth time is very short.

[0034] Even if the structure of the contact layer is used, there are still great difficulties in the preparation process, that is, in the process of MOCVD material growth, the Mg doping amount needs to reach 10 20 / cm 3The above is difficult, since the Mg atom incorporation is gradual, it is more difficult to achieve high doping in very thin thickness. The problem to be solved by the present application is the growth method of the contact layer.

[0035] In order to improve the doping concentration of Mg ions as much as possible, the present application adopts the method of delta doping to grow the contact layer. The principle of delta doping is that in the process of growing GaN by MOCVD, the supply of Ga source is cut off at the designed place, and the supply of Mg source is maintained, so that Mg impurity atoms almost completely cover the surface, Mg atoms occupy a large number of Ga atom positions, greatly improving the Mg proportion of the atomic layer, and then the Ga source supply is restored to continue the growth of the crystal. During the interruption of the Ga source, the crystal basically stops growing, so the large number of Mg atom replacements only occur in a few atomic layers. Therefore, the final Mg atom content is very high in the place where delta doping is performed, and the concentration can reach 10 21 / cm 3 above, and lower on both sides, showing a delta function form, as shown in Figure 2 , so it is called delta doping technology. In actual growth, since atoms can diffuse, the Mg of delta doping will diffuse to both sides to form a high-doped distribution zone, and the distance of Mg atom diffusion to both sides is generally less than 5 nm. In order to improve the overall Mg doping level, it is usually necessary to perform multiple delta doping operations during MOCVD growth. In the present application, multiple delta doping can be performed to grow the contact layer. According to our experimental experience, using delta doping can not only solve the difficulty of doping amount exceeding 10 20 / cm 3 , but also solve the purpose of achieving high doping in very thin layers (thickness less than 5 nm).

[0036] In the process of growing the contact layer using the delta doping technology, there are multiple parameters that can be adjusted, such as contact layer growth temperature, growth thickness, gas source flow ratio, delta doping position and cycle number, etc. These parameters will jointly affect the final doping effect, and only appropriate parameter combination can make the method produce good effect. The following will be explained in specific examples.

[0037] Example 1:

[0038] In common blue-green light high-power LED devices, due to the large power, the current density during device operation is large, so the contact performance between the electrode and the contact layer must be optimized, so the contact layer is often set as a structure to improve the contact performance, and the common device structure is as shown in Figure 3 , the Mg doping concentration of the p-GaN layer is less than 10 19 / cm3 After the growth of the p-GaN layer is completed, the temperature and gas flow are adjusted, and the flow of the Mg source is increased to start the growth of the contact layer. The growth rate of the contact layer GaN is controlled in the range of 5-15 nm / min, and more preferably 10 nm / min, by adjusting the gas flow of the Ga source. Since the quantum well region contains InGaN, which is prone to decomposition at high temperatures, in order to protect the quantum well region from decomposition damage at high temperatures, the growth temperature is generally controlled in the range of 700-900°C, and more preferably set to be consistent with the growth temperature of the p-GaN layer, which can reduce the temperature change time, thereby reducing the thermal damage to the quantum well and improving the growth efficiency.

[0039] After the growth of the contact layer is started, 0-5 nm is first grown conventionally, and more preferably 1-2 nm, and then the first delta-doping growth is started. Then, periodic delta-doping growth is performed, and the interval thickness between two delta-doping layers is 1-10 nm, and more preferably 1-3 nm. A smaller thickness interval is to make the Mg atom diffusion regions of the two delta-doping layers overlap each other, as shown in FIG. 2, thereby increasing the overall doping concentration and avoiding the increase of the vertical film surface direction series resistance caused by the independent high-doped regions. However, the thickness interval of the two adjacent delta-doping layers should not be too small, because a large number of Mg atoms replace Ga atoms in the delta-doping layer, and the diameter of Mg atoms is smaller than that of Ga atoms, which will generate a certain stress. If the interval between the two adjacent delta-doping layers is too small, the stress will quickly accumulate to generate a large number of defects, and the crystal quality will be reduced. Figure 4

[0040] ​The number of delta doping depends on the thickness of the contact layer and the interval of the delta doping. The thickness of the contact layer is usually in the range of 1-30 nm, and more preferably in the range of 2-5 nm. For example, for a set of optimized design parameters, the thickness of the contact layer is 5 nm, the interval of the delta doping is 2 nm, and the initial thickness is 2 nm, only two times of delta doping is needed. When the delta doping is performed, the Ga source is cut off for 5-15 s, more preferably for 10 s, and then the Ga source is resumed for further growth. After the growth of the contact layer with delta doping, a suitable method is needed to activate the Mg ion acceptor level. The commonly used activation method is to anneal the sample in a tube furnace at 600-700 °C for 5-10 min in a nitrogen atmosphere or a mixture of nitrogen and oxygen. The rapid annealing furnace can also be used. After activation, a conductive electrode, such as a metal alloy electrode, is needed. In order to reduce the interface Schottky barrier height as much as possible, the alloy electrode is usually selected to be Ni / Au, which has a work function close to that of the p-GaN material. The Ni / Au electrode is usually prepared by electron beam evaporation. The thickness of the Ni layer is 1-20 nm, and more preferably 5-10 nm. The thickness of the Au layer is 1-50 nm, and more preferably 10-30 nm. The sample is then annealed at 500-600 °C, and more preferably at 520-560 °C, for 1-5 min. Under suitable conditions, an ohmic contact with a specific contact resistivity of less than 10 -4 Ω·cm 2 can be prepared. Other suitable conductive electrode materials can also be selected.

[0041] Example 2:

[0042] In another type of optoelectronic device, the current density during operation is also very high, which is a semiconductor laser. Generally, the threshold current density of the gallium nitride-based laser is in the order of thousands of amperes per square centimeter. In order to improve the lifetime of the device, the thermal effect of the p-electrode must be reduced, that is, the contact performance of the p-electrode must be improved, and the specific contact resistivity is usually required to be less than 10 -4 Ω·cm 2 order of magnitude, and the lower the specific contact resistivity, the better. The common structure of the laser is as follows Figure 5As shown. In order to produce a good light confinement effect, reduce light field leakage, light confinement layer (cladding) needs to be sufficient thickness, generally light confinement layer in the order of hundreds of nanometers, so its light absorption effect can not be ignored. Generally in order to reduce the light absorption effect of light confinement layer on the light field, the Mg doping concentration of the light confinement layer is not too high, because a large number of Mg impurities will produce a larger light absorption. At the same time in order to improve the contact effect with the conductive electrode, and the p-type semiconductor layer with metal contact is required to have a higher hole concentration. In order to solve this contradiction, the common processing method is to set the contact layer, the layer has a higher doping concentration, can meet the demand of high hole concentration with metal contact, in addition, the layer also needs to be as thin as possible, so as to reduce the longitudinal series resistance. With such a function of the contact layer, it is relatively difficult to realize, because it is difficult to increase the doping concentration of Mg atoms to 10 20 / cm 3 Above. The technical scheme of the application can be used to prepare the contact layer required by the laser.

[0043] After the growth of the light confinement layer is completed, the temperature and gas flow are adjusted, and the flow of the Mg source is increased to start the growth of the contact layer. By adjusting the gas flow of the Ga source, the growth rate of the contact layer GaN is controlled in the range of 5-15 nm / min, and more preferably 10 nm / min. Since the quantum well region contains InGaN, which is easy to decompose at high temperature, in order to protect the quantum well region from decomposition and damage at high temperature, the growth temperature is generally controlled in the range of 700-900℃, and more preferably set to be consistent with the growth temperature of the p-GaN layer, which can reduce the temperature change time, thereby reducing the thermal damage to the quantum well and improving the growth efficiency.

[0044] After starting the contact layer growth, a conventional growth of 0–5 nm is performed first, preferably 1–2 nm, followed by the first delta-doping growth. Then, periodic delta-doping growth is carried out, with an interval thickness of 1–10 nm between two delta-doping operations, preferably 1–3 nm. The typical contact layer thickness is in the range of 1–30 nm, preferably 2–5 nm. For example, with optimized design parameters of a 5 nm contact layer thickness, a 2 nm delta-doping interval, and an initial thickness of 2 nm, only two delta-doping operations are required. During delta-doping, the Ga source supply needs to be interrupted for 5–15 s, preferably 10 s, before resuming the Ga source supply and continuing growth. After completing the delta-doped contact layer growth, a suitable method is needed to activate the incorporated Mg ion acceptor levels. Common activation methods include annealing in a tube furnace at 600–700 °C for 5–10 min under a nitrogen atmosphere or a nitrogen-oxygen mixed atmosphere, or using a rapid annealing furnace. After activation, conductive electrodes need to be fabricated. To minimize the Schottky barrier height at the interface, Ni / Au, with a work function close to that of p-GaN, is typically chosen as the electrode. Pd / Pt / Au can also be used. For example, Ni / Au electrodes are commonly deposited using electron beam evaporation, depositing 1–20 nm of Ni (ideally 5–10 nm), followed by 1–50 nm of Au (ideally 10–30 nm), and then annealing at 500–600 °C (ideally 520–560 °C) for 1–5 minutes. Under suitable parameters, electrodes with a specific contact resistivity below 10⁻⁶ can be fabricated. -4 Ω·cm 2 The ohmic contact effect is excellent. With further optimization using more conductive electrodes, it can achieve 10... -6 ~10 -5 Ω·cm 2 Magnitude.

[0045] A commonly used method for measuring electrodes and semiconductor materials is the circular transmission line model (CTLM). For example... Figure 6 As shown, there are 6 rings, with a fixed inner diameter of r0 and an outer diameter of r. n By gradually increasing the value of each element, and passing a current I through both sides of the ring during measurement while measuring the voltage V, the corresponding resistance R can be calculated. tot R tot Satisfying the formula:

[0046]

[0047] In the formula, r0, r n L represents the inner and outer radii, respectively. T Let r be the transmission line length. n -r0 is very small, so r can be approximated as rn =r0, therefore theoretically R tot -ln(r n The / r0) curve is a straight line. R can be obtained from the experimental data through linear fitting. S and L T , and then by Find ρ c The advantages of this method are that the sample does not require mesa insulation, the fabrication is simple, and data processing using graphical methods is also convenient. Considering the difference between the actual ohmic contact dimensions and the design dimensions, compared to other transmission line models, the theoretical and actual contact resistivity values ​​obtained using the dotted transmission line model differ the least (for comparison, see the reference <Methods for Measuring and Calculating Contact Resistivity of Metals and Semiconductors>, Li Hongjian, Shi Ying, Semiconductor Technology Vol. 133 No. 12).

[0048] According to the method of the present invention, we prepared two samples, denoted as Sample 1 and Sample 2. Two blocks were randomly selected from each sample for CTLM testing, denoted as Block 1 and Block 2. On the contact layer prepared according to the method of the present invention, the following patterns were photolithographically etched... Figure 6 The circular transmission line pattern is shown, followed by electrode material deposition. The electrode material is a Ni / Au alloy electrode, prepared by electron beam evaporation to first deposit a 10 nm Ni film, then a 20 nm Au film, followed by rapid annealing at 450 °C in air for 5 min. Table 1 records the actual measured r0 and r... n R tot This allows for the calculation of the contact resistance. Based on the principle, R needs to be calculated. tot -ln(r n Fitting of the straight line / r0).

[0049] Table 1. Contact resistance test data for circular transmission line model

[0050]

[0051] Figure 7 The data fitting results for CTLM tests on two blocks of each of the two samples are shown, from which the slope and intercept of the fit can be obtained. According to formula (1), R tot -ln(r n In the straight line / r0), the slope = R S / 2π, therefore R S =Slope * 2π; take r n ≈r0, therefore

[0052] according to Figure 7From the fitting results, we statistically determined the slope and intercept of each block in the two samples, and then calculated R based on the corresponding formulas and data. S and L T Then, the specific contact resistivity is calculated. Figure 8 This refers to the specific contact resistivity of different sections of two experimental samples. Table 2 records the relevant calculation data, showing that for each sample, the calculated specific contact resistivity for both sections is less than 10. -4 Quantity, entering 10 -5 Within a certain order of magnitude, it exhibited excellent contact performance. It should be noted that the data from this experiment is limited and cannot represent the best results achievable by the method described in this invention. However, it demonstrates that it at least achieves the effects recorded in this experiment. We believe that by combining more electrode optimization techniques, the method described in this invention can achieve even better contact results.

[0053] Table 2 is based on Figure 7 The specific contact resistivity was calculated based on the fitting results.

[0054]

[0055] In the technical solution of the present invention, during the growth process of p-GaN between delta doping, Mg can be doped or not.

[0056] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A method of making ohmic contact to a low specific contact resistance p-type III-V semiconductor material with a conductive electrode, characterized by, The delta doping technique is used to grow the heavily doped contact layer; the delta doping technique is to cut off the supply of Ga source, keep the supply of Mg source, make Mg atoms occupy the positions of Ga atoms, increase the Mg proportion of the atomic layer, and then restore the supply of Ga source to continue the growth of the crystal during the MOCVD growth of GaN; the average doping concentration of Mg is more than 10 20 / cm 3 in the thickness range of less than 5nm; the delta doping technique used to grow the heavily doped contact layer is one or more times of delta doping operation during the growth of p-type III-V semiconductor material by using MOCVD process.

2. The method of claim 1, wherein, The growth rate of the contact layer is controlled at 5-15 nm / min, and the growth temperature is controlled at 700-900℃.

3. The method of claim 1, wherein, After starting to grow the contact layer, first grow 0-5 nm normally, then start to grow by first delta-doping, and then grow by periodic delta-doping, with a interval thickness of 1-10 nm between two delta-doping.

4. The method of claim 3, wherein, The number of times of delta-doping is determined by the thickness of the contact layer and the interval, and the thickness of the contact layer is 1-30 nm.

5. The method of claim 1, wherein, After the growth of the contact layer by delta-doping is completed, the acceptor energy level of the doped element is activated.

6. An ohmic contact electrode of low specific contact resistance, characterized by, An ohmic contact electrode with low specific contact resistance is prepared by the method of any one of claims 1-5.

7. The low specific contact resistance ohmic contact electrode of claim 6, wherein, The conductive electrode layer uses Ni / Au or Pd / Pt / Au or transparent conductive material ITO, AZO as electrode.

8. A semiconductor device, characterized by, An ohmic contact electrode with low specific contact resistance is prepared by the method of any one of claims 1-5.

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