Superlattice structure, GaN HEMT device epitaxial structure and preparation method

Abstract

The invention discloses a superlattice structure, a GaN HEMT (High Electron Mobility Transistor) device epitaxial structure and a preparation method, the superlattice structure is formed by periodically and alternately stacking an AlN thin layer, an Al < x > Ga < 1-x > N thin layer and an Al < y > Ga < 1-y > N thin layer, 50, y < lt >; 50; the thicknesses of the AlN thin layer, the Al < x > Ga < 1-x > N thin layer and the Al < y > Ga < 1-y > N thin layer are t1, t2 and t3 respectively, and the thickness ratio of the three layers is that (t1 + t2): t3 is more than or equal to 1: 15 and less than or equal to 1: 50. By increasing the thickness ratio of the AlN thin layer to the AlGaN thin layer, the surface roughness of the superlattice structure is obviously improved, the vertical collapse pressure of the device from inside to outside is obviously improved, the poor vertical collapse pressure in the central area in the device can be obviously improved, the overall uniformity of the vertical collapse pressure of the device is greatly improved, and the performance of the device is improved. Therefore, the electrical property of the device is obviously improved, and no edge crack defect is generated in the range.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a superlattice structure, an epitaxial structure of GaN HEMT devices, and a method for their fabrication. Background Technology

[0002] The description in this section provides only background information relevant to the disclosure of this application and does not constitute prior art.

[0003] Figure 1 It is a typical epitaxial structure of GaN HEMT (gallium nitride high electron mobility transistor) device, which includes, from bottom to top: substrate 1, buffer layer 2, high-resistivity buffer layer 3, channel layer 4, barrier layer 5, and cap layer 6.

[0004] The substrate 1 is typically made of materials such as silicon, SiC, or sapphire to provide physical support or electrical insulation. The high-resistivity buffer layer 3 is typically made of carbon-doped GaN to provide insulation properties and prevent the diffusion of two-dimensional electron gas (2-DEG) towards the substrate. The channel layer 4 and the barrier layer 5 are used to generate two-dimensional electron gas through polarization. The cap layer 6 is used to cover the barrier layer 5 and prevent its oxidation. Because the substrate 1 and the high-resistivity buffer layer 3 have problems such as lattice mismatch and thermal expansion coefficient mismatch, the buffer layer 2 can reduce defects such as interfacial tension caused by these lattice mismatches.

[0005] Buffer layer structures are diverse. Generally, a superlattice layer (SLs) 23 can be introduced into the buffer layer 2 region, such as... Figure 2 As shown, superlattice structures are generally formed by the periodic alternation of thin layers of different materials, such as GaN / AlGaN, AlN / AlGaN, AlN / GaN, InAs / GaSb, etc. The role of superlattices is to increase epitaxial thickness, thereby increasing the insulation of the underlying layer, reducing the probability of vertical leakage current, and improving VBV (vertical breakdown voltage) characteristics. However, the increase in thickness and the multilayer SLs will be accompanied by an increase in stress accumulation, which may lead to quality problems such as increased device cracks. Therefore, a proper superlattice structure design can increase epitaxial thickness, reduce edge crack problems, and maintain lattice quality while releasing the lattice mismatch stress accumulated between the AlGaN / GaN active layer stacked between the high-resistivity buffer layer and the substrate.

[0006] The selection of thin-layer materials, thin-layer thickness, periodicity and number of repeating units, and thin-layer interface quality (such as roughness) in superlattice structures can all have a significant impact on device performance. Therefore, the structural design of superlattice structures is very important. Otherwise, introducing superlattice structures may not only fail to improve device characteristics but may also increase device quality defects. Summary of the Invention

[0007] The purpose of this invention is to provide a superlattice structure, a GaN HEMT device epitaxial structure, and a fabrication method to overcome the shortcomings of existing technologies.

[0008] This invention provides a superlattice structure consisting of a thin layer of AlN and Al x Ga 1-x N thin layer and Al y Ga 1-y N thin layers are periodically stacked alternately, where X>50, y<50; the AlN thin layers, the Al x Ga 1-x N thin layer and the Al y Ga 1-y The thicknesses of the N thin layers are t1, t2, and t3, and the thickness ratio between the three layers is 1:15≤(t1+t2):t3≤1:50.

[0009] Preferably, the superlattice is formed by repeated stacking of thin layers with the same thickness ratio, or by alternating stacking of thin layers with different thickness ratios;

[0010] Preferably, when the thickness ratios are the same, the thickness ratio between the three layers is (t1+t2):t3=1:(15~25);

[0011] Preferably, the superlattice structure is formed by alternating stacking of two pairs of SLs1 and SLs2 thin layers with different thickness ratios;

[0012] The thickness ratio between the three layers of the SLs1 thin layer is: (t1+t2):t3=1:(15~25);

[0013] The thickness ratio between the three layers of the SLs2 thin layer is: (t1+t2):t3=1:(40~50).

[0014] Preferably, the surface roughness Ra of the superlattice structure is: 0.3nm≤Ra≤1nm.

[0015] Preferably, the superlattice structure consists of one thin-layer pair, namely the AlN thin layer and the Al... x Ga 1-x N thin layer and the Al y Ga 1-y The total thickness t of the three thin layers N is: 25nm ≤ t ≤ 45nm.

[0016] Preferably, the total thickness T of the superlattice structure is: 1500nm≤T≤10000nm.

[0017] Preferably, the superlattice structure is doped with C and / or Fe; the C doping concentration is not less than 1E18 cm⁻¹.-3 .

[0018] Another aspect of the present invention provides a method for preparing the above-mentioned superlattice structure, wherein the superlattice structure is formed by stacking AlN epitaxial layers and AlGaN epitaxial layers;

[0019] The deposition parameters of the AlN thin layer in the superlattice structure are: V / III ratio of 2500 to 6000.

[0020] Preferably, the growth temperature of the superlattice structure is 950℃~1150℃.

[0021] A third aspect of the present invention provides a GaN HEMT device epitaxial structure, including a substrate and a nucleation transition layer, a superlattice layer, a high-resistivity buffer layer, a channel layer, a barrier layer and a cap layer sequentially deposited on the substrate, wherein the superlattice layer adopts the superlattice structure described above.

[0022] Preferably, the nucleation transition layer comprises, from bottom to top, an AlN nucleation layer and an AlGaN transition layer;

[0023] The AlGaN transition layer comprises four AlGaN layers;

[0024] Preferably, the substrate is made of Si, SiC or Al2O3 material;

[0025] The high-resistivity buffer layer is a C-GaN layer;

[0026] The barrier layer is an AlGaN layer;

[0027] The cap layer is a GaN layer.

[0028] This application significantly improves the surface roughness of the superlattice structure by increasing the thickness ratio of AlN and AlGaN thin layers, significantly improves the vertical breakdown of the device from the inside out, and can significantly improve the poor vertical breakdown in the central region of the device, thereby greatly improving the overall uniformity of the vertical breakdown and thus significantly improving the electrical performance of the device. Moreover, no edge crack defects will be generated within this range. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a typical GaN HEMT device epitaxial structure.

[0030] Figure 2 This is a schematic diagram of a typical superlattice layer structure;

[0031] Figure 3 This is a TEM image of the sample obtained in Comparative Example 1;

[0032] Figure 4This is a schematic diagram of the vertical breakdown voltage (VBV) measurement location of the GaN HEMT device in this application;

[0033] Figure 5 This is a graph showing the vertical collapse volume (VBV) test results of the sample obtained in Comparative Example 1;

[0034] Figure 6 This is a graph showing the vertical collapse volume (VBV) test results of the sample obtained in Example 1;

[0035] Figure 7 This is a graph showing the vertical collapse volume (VBV) test results of the sample obtained in Example 2;

[0036] Figure 8 This is a comparison chart of the vertical collapse volume (VBV) test results of the samples obtained in Comparative Example 1 and Examples 1-2.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1-Substrate; 2-Buffer layer; 21-AlN nucleation layer; 22-AlGaN transition layer; 221-First AlGaN layer; 222-Second AlGaN layer; 223-Third AlGaN layer; 224-Fourth AlGaN layer; 23-Superlattice layer; 230-One thin layer pair (1-pairSLs); 231-AlN thin layer; 232-Al x Ga 1-x N thin layer; 233-Al y Ga 1-y N-Thin layer; 3-High-resistivity buffer layer; 4-Channel layer; 5-Barrier layer; 6-Cap layer. Detailed Implementation

[0039] The following description, in conjunction with the accompanying drawings, further illustrates this application.

[0040] like Figures 1-2 The image shows a typical GaN HEMT epitaxial structure and superlattice structure, where the superlattice structure is generally formed by the periodic alternating stacking of thin layers of different materials. Currently, a typical superlattice structure consists of AlN thin layers (Al231, Al231, Al231) and... x Ga 1-x N thin layer 232 and Al y Ga 1-y N thin layers 233 are periodically stacked alternately, X>50, y<50, where each thin layer corresponds to an AlN thin layer and an Al thin layer in 230. x Ga 1-x N thin layer and Al y Ga 1-y The thicknesses of the N thin layers are t1, t2, and t3, respectively.

[0041] In this context, an AlN thin layer on the substrate can create a tensile stress, while an AlGaN thin layer stacked on top of an AlN thin layer can provide a compressive stress. x Ga 1-x N thin layer and Al y Ga 1-y The Al content varies in the N thin layer, Al x Ga 1-x The aluminum content of the N thin layer is located in Al y Ga 1-y The aluminum content of the N thin film is between that of the AlN thin film and the AlN thin film, and it is located between the AlN thin film and the Al y Ga 1-y Between the N thin layers, stress transition can be used, and the entire superlattice structure is a stack of compressive stress and tensile stress that is as stress-balanced as possible.

[0042] Studies have shown that the thickness ratio of AlN to AlGaN thin layers in a superlattice structure has a significant impact on the mechanical and electrical properties of the device. When the AlN to AlGaN thin layer thickness ratio is low, the vertical breakdown voltage from the inside to the outside of the device is low, especially the vertical breakdown voltage at the center of the device is lower than that at the edges, resulting in poorer electrical performance. Figure 5 The figure shown is the vertical breakdown voltage result obtained by the device when (t1+t2):t3=1:6. The vertical breakdown voltage is distributed from the inside to the outside from 425V to 885V, and the vertical breakdown voltage at the center is less than that at the edge (generally, the higher the vertical breakdown voltage at the center, the better the electrical performance of the device, and for the sake of yield, it is desirable to have the center as the good die rather than the edge).

[0043] This application effectively improves the aforementioned problems by optimizing the thickness ratio between superlattice thin layers. Specifically:

[0044] The superlattice structure provided in this application consists of an AlN thin layer and Al x Ga 1-x N thin layer and Al y Ga 1-y N thin layers are periodically stacked alternately, where X>50 and y<50; the thicknesses of AlN thin layers, AlxGa1-xN thin layers and AlyGa1-yN thin layers are t1, t2 and t3 respectively, and the thickness ratio between the three layers is 1:15≤(t1+t2):t3≤1:50.

[0045] Experiments have shown that increasing the thickness ratio of AlN and AlGaN thin layers can significantly improve the surface roughness of the superlattice structure, significantly improve the vertical breakdown of the device from the inside out, and significantly improve the poor vertical breakdown in the central region of the device, thereby greatly improving the overall uniformity of the vertical breakdown and thus significantly improving the electrical performance of the device. Moreover, no edge crack defects will occur within this range.

[0046] When (t1+t2):t3 is relatively large, the AlN layer is relatively thin. Although this can improve surface roughness and the uniformity of vertical voltage breakdown (VBV), the reduced AlN layer thickness also means a decrease in the device's insulation properties (AlN has a bandgap of 6.1 eV, which provides relatively high insulation), and the overall strength of the VBV is relatively lower. Therefore, the thickness ratio of (t1+t2):t3 should be controlled within a certain range, and the AlN layer should not be too thin.

[0047] Experiments have verified that when (t1+t2):t3 = 1:50, the overall vertical crushing strength is lower than when (t1+t2):t3 = 1:15. Therefore, preferably, (t1+t2):t3 = 1:15. Under this condition, the roughness can be reduced to improve the uniformity of the VBV (Vacuum-Vacuum Composite Material), while maintaining high-strength vertical crushing. This application has also experimentally discovered that the superlattice structure can be formed by repeatedly stacking pairs of thin layers with the same thickness ratio, or by alternately stacking pairs of thin layers with different thickness ratios. The thin layer pair described herein is one AlN thin layer and one Al... x Ga 1-x N thin layer and 1 Al y Ga 1-y Repeating units formed by N thin layers.

[0048] Preferably, when the thickness ratio of the thin layers is the same, the thickness ratio between the three layers is (t1+t2):t3=1:(15~25).

[0049] Preferably, the superlattice structure is formed by alternating stacking of two pairs of SLs1 and SLs2 thin layers with different thickness ratios;

[0050] The thickness ratio between the three layers in the SLs1 thin layer is: (t1+t2):t3=1:(15~25);

[0051] The thickness ratio between the three layers of the SLs2 thin layer is: (t1+t2):t3=1:(40~50).

[0052] Experiments have shown that, under the premise that the thickness ratio is 1:15≤(t1+t2):t3≤1:50, whether using thin layer pairs with the same thickness ratio or using thin layer pairs with different thickness ratios, the vertical breakage of the device can be effectively improved without producing edge crack defects.

[0053] This application's experiments revealed that adjusting the thickness ratio primarily affects the vertical breakdown voltage of the device by influencing the surface roughness of the superlattice structure. Theoretically, surface roughness is the main cause of deteriorating vertical breakdown voltage. The surface roughness of the superlattice structure also affects the subsequent epitaxial quality. When the surface roughness is high, more defects are easily introduced during the growth process, leading to increased leakage current and decreased vertical breakdown voltage in the device.

[0054] After experimental optimization, the surface roughness Ra of the superlattice structure in this application is: 0.3nm≤Ra≤1nm.

[0055] Experiments have revealed that epitaxial parameters influencing the surface roughness of superlattice structures include the V / III ratio (5 / 3 ratio, the molar ratio of nitrogen to aluminum gallium), growth temperature, and superlattice thickness. These parameters determine whether AlN / AlGaN superlattice structures can effectively maintain good epitaxial quality and surface flatness during growth. For AlN, generally, a low V / III ratio is suitable for two-dimensional growth (2D growth), i.e., lateral or sideways growth, easily forming a flat epitaxial film. Conversely, a high V / III ratio is suitable for three-dimensional growth (3D growth), i.e., island-like growth, easily forming an epitaxial film with uneven surface roughness, which is the opposite of the growth trend of GaN. Furthermore, in addition to affecting epitaxial growth, the growth temperature also influences the ease with which carbon (C) from the MO source (metal-organic source) is incorporated into the structure. Lower epitaxial growth temperatures tend to introduce more C doping, but this also leads to poorer epitaxial quality. Therefore, given these interconnected influences, how to properly match these epitaxial parameters to obtain the best characteristics is one of the key points of this application.

[0056] Based on the above, this application also provides a method for preparing a superlattice structure, which uses a superlattice structure formed by stacking AlN epitaxial layers and AlGaN epitaxial layers.

[0057] The deposition parameters for the AlN thin layer are: a V / III ratio of 2500–6000. Increasing the V / III ratio, such as by increasing the nitrogen source flow rate or decreasing the aluminum source flow rate, can thin the AlN layer and reduce its surface roughness. Experiments have shown that when the V / III ratio is in the range of 2500–6000, the (t1+t2):t3 thickness ratio can be maintained between 1:(15–50), reducing the surface roughness Ra to below 1, thereby effectively improving the vertical breakdown strength and uniformity of the device and reducing device defects. The conclusion of this application that "increasing the V / III ratio can reduce surface roughness" is the opposite of the general conclusion that "a high V / III ratio results in an epitaxial film with higher surface roughness." It is speculated that under such AlN growth conditions, this thickness ratio of AlN / Al...x Ga 1-x N / Al y Ga 1-y The stress state formed by N contributes to the improvement of the roughness of the superlattice stack.

[0058] Experiments revealed that when the V / Ⅲ ratio of the AlN layer was adjusted, the AlN grown immediately adjacent to the AlN layer... x Ga 1-x N also changes depending on the growth conditions of the AlN layer; therefore, this application will use Al x Ga 1-x Correlate the thickness between the N thin layer and the AlN thin layer with Al y Ga 1-y The thickness of the N thin layer was compared.

[0059] Preferably, the growth temperature of the superlattice structure is 950℃ to 1150℃. As mentioned above, a suitable temperature can achieve a balance between C doping and epitaxial quality.

[0060] Deposition methods can include MOCVD, etc.

[0061] Experiments have shown that when the thickness of the thin layer pair and the total thickness of the superlattice are large, the surface roughness is easily affected, resulting in significant differences between the internal and external surfaces of the device during vertical collapse, poor uniformity, and increased stress accumulation due to the large thickness, which easily leads to threading dislocation defects. Preferably, the thickness t of one thin layer pair in the superlattice structure is: 25nm ≤ t ≤ 45nm.

[0062] Preferably, the total thickness T of the superlattice structure is: 1500nm≤T≤10000nm, that is, there are approximately 60 to 200 pairs of thin layers in the superlattice structure of this application.

[0063] Superlattice structures doped with C and / or Fe can increase insulation and reduce vertical leakage current. The C doping concentration is not less than 1E18 cm⁻¹. -3 .

[0064] Doping can be done using either an "external doping source" or "internal doping." An "external doping source" involves using alkanes such as C2H4 for carbon doping or CP2Fe for Fe doping. In this case, the doping primarily affects the AlGaN layer, specifically the Al layer. x Ga 1-x N / Al y Ga 1-y Nitrogen is doped.

[0065] "Internal doping" involves introducing a carbon source by adjusting the V / III ratio, temperature, and growth rate, resulting in C doping throughout the entire superlattice structure. This application can employ either internal or external doping for C doping.

[0066] The superlattice structure described above can be well applied to conventional GaN HEMT device epitaxial structures. This application provides a preferred GaN HEMT device epitaxial structure, including a substrate 1 and a nucleation transition layer, a superlattice layer 23, a high-resistivity buffer layer 3, a channel layer 4, a barrier layer 5, and a cap layer 6 sequentially deposited on the substrate 1, wherein the superlattice layer adopts the superlattice structure described above.

[0067] The nucleation transition layer and the superlattice layer together form buffer 2, reducing the lattice adaptation problem between the substrate and the high-resistivity buffer layer.

[0068] The nucleation transition layer consists of an AlN nucleation layer 21 and an AlGaN transition layer 22 from bottom to top.

[0069] Substrate 1 can be made of materials such as Si, SiC, or Al2O3;

[0070] Barrier layer 5 is an AlGaN layer;

[0071] The cap layer 6 is a GaN layer.

[0072] The AlGaN transition layer consists of four AlGaN layers.

[0073] As those skilled in the art will understand, in order to achieve other technical effects, other corresponding structures may be introduced on the basis of the extensional structure of this application.

[0074] Example 1

[0075] Using a silicon substrate, AlN layer 21, AlGaN layer 221, AlGaN layer 222, AlGaN layer 223, AlGaN layer 224, AlN / AlGaN superlattice layer 23, C-GaN high-resistivity buffer layer 3, GaN channel layer 4, AlGaN barrier layer 5, and GaN cap layer 6 are sequentially deposited on substrate 1 using conventional MOCVD methods.

[0076] The AlN / AlGaN superlattice layer consists of a thin AlN layer (231) and an Al... x Ga 1-x N thin layer 232 and Al y Ga 1-y N233 thin layers are formed by periodic alternating stacking, with a total of 90 pairs of 230 thin layers, of which X is 65 and y is 30; the superlattice layer is grown at a temperature of 1000℃.

[0077] One thin layer is used to align an AlN thin layer and an Al layer. x Ga1-x N thin layer and Al y Ga 1-y The thicknesses of the N thin layer are t1, t2, and t3, respectively;

[0078] The AlN and AlGaN layers in each thin-layer pair have the same thickness ratio, (t1+t2):t3 is 1:20, and t1:t2 = 1:2.5.

[0079] The specific growth conditions and structural parameters of the AlN / AlGaN superlattice layer are shown in Table 1.

[0080] Example 2

[0081] Using a silicon substrate, AlN layer, AlGaN layer 1, AlGaN layer 2, AlGaN layer 3, AlGaN layer 4, AlN / AlGaN superlattice layer, C-GaN high-resistivity buffer layer, GaN channel layer, AlGaN barrier layer, and GaN cap layer are sequentially deposited on the substrate using conventional MOCVD method.

[0082] The AlN / AlGaN superlattice layer is formed by alternating stacking of two thin-layer pairs with different thickness ratios (SLs1 and SLs2 thin-layer pairs, respectively). Each thin-layer pair includes an AlN thin layer and an Al... x Ga 1-x N thin layer and Al y Ga 1-y N thin layers, with a total of 90 thin layer pairs, of which X is 65 and y is 30; the superlattice layer growth temperature is 1000℃;

[0083] One thin layer is used to align an AlN thin layer and an Al layer. x Ga 1-x N thin layer and Al y Ga 1-y The thicknesses of the N thin layer are t1, t2, and t3, respectively.

[0084] The thickness ratio between the three layers of the SLs1 thin layer is: (t1+t2):t3=1:20, t1:t2=1:2.5; the thickness ratio between the three layers of the SLs2 thin layer is: (t1+t2):t3=1:50, t1:t2=1:2.5.

[0085] The specific growth conditions and structural parameters of the AlN / AlGaN superlattice layer are shown in Table 1.

[0086] Comparative Example 1

[0087] Using a silicon substrate, AlN layer, AlGaN layer 1, AlGaN layer 2, AlGaN layer 3, AlGaN layer 4, AlN / AlGaN superlattice layer, C-GaN high-resistivity buffer layer, GaN channel layer, AlGaN barrier layer, and GaN cap layer are sequentially deposited on the substrate using conventional MOCVD method.

[0088] Compared to Example 1, the thickness ratio of AlN and AlGaN layers (t1+t2):t3 for each layer pair was adjusted to 1:6. The superlattice layer growth temperature was 1000℃.

[0089] The specific growth conditions and structural parameters of the AlN / AlGaN superlattice layer are shown in Table 1.

[0090] Except for the defined structural parameters and superlattice growth parameters, Examples 1-2 and Comparative Example 1 used the same technical conditions.

[0091] After the samples were cooled to room temperature, the performance of the samples obtained in Examples 1 and 2 and the sample obtained in Comparative Example 1 was tested using conventional methods. The results are shown in Table 1. Figure 3 and Figures 5-8 As shown (where the superlattice surface roughness is the result of the test after the superlattice growth is completed, and the sample TEM image is the TEM image obtained after the entire epitaxial growth is completed).

[0092] Table 1

[0093]

[0094] Figure 3 The TEM image shows that the thickness of one thin layer pair in Comparative Example 1 is 35 nm, and the thickness of one thin layer pair in Comparative Example 1 shown in Table 1 is 35.3 nm (the thickness of the thin layer pairs in Table 1 was obtained by XRD detection, and TEM detection data is generally more accurate). The two are quite close, which proves that the thickness data of the three samples in Table 1 are relatively accurate and can be compared.

[0095] Table 1 shows that the V / Ⅲ ratio of AlN thin film growth in the superlattice structure of Comparative Example 1 is 1735, while the V / Ⅲ ratios of Example 1 and Example 2 are increased to 2890 and 5785, respectively.

[0096] Table 1 shows that the thickness of one thin layer pair in the superlattice of Comparative Example 1 is 35.3 nm, and the total structural thickness is 5.46 μm. In contrast, the thickness of one thin layer pair in the Example 1 sample after adjusting the superlattice thickness is 33.1 nm, and the total structural thickness is 5.36 μm. The thicknesses of two thin layer pairs in Example 2 sample are 33.1 nm and 31.3 nm, respectively, and the total structural thickness is 5.22 μm. The thickness of the thin layer pairs and the total structural thickness in the superlattice of Examples 1 and 2 samples are all smaller than those of Comparative Example 1 sample.

[0097] Table 1 shows that the surface roughness Ra C of the sample in Comparative Example 1 is 1.7 nm, while the surface roughness of Example 1 is reduced to 0.42 nm and that of Example 2 is reduced to 0.59 nm.

[0098] Summarizing the experimental results presented in the table, we found that different conclusions were reached even at relatively low growth temperatures. Generally, AlN growth requires a relatively low V / III ratio to obtain AlN films with low roughness. Conversely, in this application, a relatively high V / III ratio can reduce the overall SLs roughness. It is speculated that under these AlN growth conditions, an AlN / Al film with such a thickness ratio... x Ga 1-x N / Al y Ga 1-y The stress state formed by N throughout the process helps improve the roughness of the superlattice stack.

[0099] As shown in Table 1, the edge cracks of Comparative Example 1 and Examples 1-2 were all less than 2 mm.

[0100] Figure 4 This is a schematic diagram of the vertical crush measurement position of the sample.

[0101] Figure 5 The comparative example 1 sample showed a vertical voltage drop distribution from the inside out of 425V to 885V (under 1μA conditions), while Figure 6 The vertical breakdown voltage distribution of the sample in Example 1, from the inside out, is 1050V to 790V (under 1μA conditions), which is a significant improvement compared to the vertical breakdown voltage of the sample in Comparative Example 1. Figure 7 The vertical collapse distribution of the sample in Example 2 from the inside to the outside is 970–660 V (under 1 μA conditions), which is also significantly improved compared to the vertical collapse of the sample in Comparative Example 1.

[0102] The results of the vertical collapse are summarized as follows: Figure 8As shown, both Examples 1 and 2 significantly improve the poor vertical breakdown in the internal region of the device. Although the vertical breakdown at the outermost edge is slightly reduced, the overall uniformity is greatly improved. Therefore, this application can effectively improve the vertical breakdown of the device by optimizing the thickness ratio of AlN thin layer to AlGaN thin layer in the superlattice, especially significantly improving the vertical breakdown at the center. Moreover, the edge cracks are maintained at <2mm.

[0103] Table 1 shows that the XRD (102) FWHM of the samples in Example 1 and Example 2 is slightly improved compared to that of the sample in Comparative Example 1. (102) FWHM is known to be related to threading dislocation defects, and the lower the value, the lower the density of threading dislocation.

[0104] The above data shows that by increasing the V / Ⅲ ratio of the AlN thin layer growth conditions in the superlattice structure, the thickness ratio of the AlN thin layer to the AlGaN thin layer in the superlattice layer can be increased, thereby significantly improving the surface roughness of the superlattice structure. When the surface roughness of the superlattice structure is reduced, defects introduced during the growth process due to excessive roughness can be effectively mitigated, resulting in reduced leakage current and improved vertical breakdown voltage. In particular, the distribution of vertical breakdown voltage from the inside to the outside is improved, reducing the difference between the inside and outside of the vertical breakdown voltage and enhancing overall uniformity. Furthermore, it can reduce the XRD (102) FWHM, thereby reducing threading dislocation defects.

[0105] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A superlattice structure, characterized in that, Composed of AlN thin layer, Al x Ga 1-x N thin layer and Al y Ga 1-y N thin layers are periodically stacked alternately, where X>50, y<50; the AlN thin layers, the Al x Ga 1-x N thin layer and the Al y Ga 1-y The thicknesses of the N thin layers are t1, t2, and t3, and the thickness ratio between the three layers is 1:15≤(t1+t2):t3≤1:

50.

2. The superlattice structure as described in claim 1, characterized in that, The superlattice is formed by repeated stacking of thin layers with the same thickness ratio, or by alternating stacking of thin layers with different thickness ratios. Preferably, when the thickness ratios are the same, the thickness ratio between the three layers is (t1+t2):t3=1:(15~25); Preferably, the superlattice structure is formed by alternating stacking of two pairs of SLs1 and SLs2 thin layers with different thickness ratios; The thickness ratio between the three layers of the SLs1 thin layer is: (t1+t2):t3=1:(15~25); The thickness ratio between the three layers of the SLs2 thin layer is: (t1+t2):t3=1:(40~50).

3. The superlattice structure as described in claim 1, characterized in that, The surface roughness Ra of the superlattice structure is: 0.3nm≤Ra≤1nm.

4. The superlattice structure as described in claim 1, characterized in that, The superlattice structure contains one thin-layer pair, namely the AlN thin layer and the Al... x Ga 1-x N thin layer and the Al y Ga 1-y The total thickness t of the three thin layers N is: 25nm ≤ t ≤ 45nm.

5. The superlattice structure as described in claim 4, characterized in that, The total thickness T of the superlattice structure is: 1500nm≤T≤10000nm.

6. The superlattice structure as described in claim 1, characterized in that, The superlattice structure is doped with C and / or Fe; the C doping concentration is not less than 1E18 cm⁻¹. -3 .

7. The method for preparing the superlattice structure according to any one of claims 1 to 6, characterized in that, The superlattice structure is formed by stacking AlN epitaxial layers and AlGaN epitaxial layers; The deposition parameters of the AlN thin layer in the superlattice structure are: V / Ⅲ ratio of 2500 to 6000.

8. The method for preparing the superlattice structure as described in claim 7, characterized in that, The growth temperature of the superlattice structure is 950℃~1150℃.

9. An epitaxial structure for a GaN HEMT device, comprising a substrate and a nucleation transition layer, a superlattice layer, a high-resistivity buffer layer, a channel layer, a barrier layer, and a cap layer sequentially deposited on the substrate, characterized in that, The superlattice layer adopts the superlattice structure as described in any one of claims 1 to 6.

10. The GaN HEMT device epitaxial structure as described in claim 9, characterized in that, The nucleation transition layer comprises, from bottom to top, an AlN nucleation layer and an AlGaN transition layer; The AlGaN transition layer comprises four AlGaN layers; Preferably, the substrate is made of Si, SiC or Al2O3 material; The high-resistivity buffer layer is a C-GaN layer; The barrier layer is an AlGaN layer; The cap layer is a GaN layer.

Images