Method for inhibiting Si-delta doping diffusion in molecular beam epitaxial growth PHEMT (Pseudomorphic High Electron Mobility Transistor)

Abstract

The invention relates to a method for inhibiting Si-delta doping diffusion in molecular beam epitaxy growth of a PHEMT (Pseudomorphic High Electron Mobility Transistor). The method comprises the following steps: growing a PHEMT structure on a GaAs substrate through a molecular beam epitaxy technology; wherein the growth temperature difference between the second Si-delta doping layer and the covering layer in the PHEMT structure is 80-110 DEG C, and the covering layer is grown by adopting a low-temperature growth process, so that the effect of inhibiting the second Si-delta doping layer from diffusing towards the growth direction is achieved. According to the invention, diffusion of Si-delta doping to the epitaxial layer is inhibited by using a low-temperature growth mode, Si atoms entering a heterojunction interface are reduced, the scattering probability of electrons is reduced, the accuracy of the concentration of the delta doping layer can be effectively improved, and the electrical performance of a device is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials technology, and specifically relates to a method for suppressing Si-delta doping diffusion in molecular beam epitaxy (PHEMT). Background Technology

[0002] In recent years, with the rapid development of technologies such as high-speed communication, radar detection, millimeter-wave imaging, and satellite communication, higher performance requirements have been placed on radio frequency and microwave power devices, including higher cutoff frequencies, greater power densities, lower noise figures, and better linearity. Against this backdrop, high electron mobility transistor (HEMT) technology has attracted widespread attention due to its excellent high-frequency characteristics and carrier mobility. In particular, pseudomorphic high electron mobility transistors (PHEMTs), with their high mobility characteristics of two-dimensional electron gases (2DEGs) realized in compound semiconductor systems, have become an important research and application direction for contemporary high-frequency, high-power electronic devices.

[0003] PHEMT devices are typically based on compound semiconductor materials such as GaAs, InP, or GaN. By introducing a bandgap difference between the channel layer and the barrier layer, a two-dimensional electron gas channel is formed. This conductive channel and the doped layer are spatially separated, significantly reducing carrier scattering and improving electron mobility and saturation drift velocity. This characteristic gives PHEMTs extremely high transconductance gain and low noise in the microwave and millimeter-wave bands, making them particularly suitable for low-noise amplifiers (LNAs), power amplifiers (PAs), mixers, and high-speed switching circuits. Furthermore, with continuous optimization of manufacturing processes, PHEMT devices have achieved significant improvements in operating voltage, thermal stability, and reliability, laying the foundation for their long-term application in complex environments. In applications, PHEMT technology is widely used in satellite communication receiver front-ends, 5G / 6G millimeter-wave transceiver modules, phased array antenna T / R components, and low-noise radar front-end systems. Their low noise and high gain characteristics make them key active devices in the receiver link, while improvements in linearity and power density directly affect the system's dynamic range and signal fidelity. With the continuous improvement of system integration, the miniaturization and monolithic integration of PHEMT devices are becoming increasingly apparent, driving the development of RF front-end modules towards high performance and low power consumption.

[0004] Currently, mainstream PHEMT processes mostly employ AlGaAs / InGaAs / GaAs or InAlAs / InGaAs / InP structures. Among these, the AlGaAs / InGaAs system is mature and low-cost, suitable for large-scale integration, while the InP system offers higher carrier mobility and lower noise performance, making it suitable for ultra-high frequency and ultra-low noise applications. In PHEMT structures, introducing silicon (Si) in the form of a delta-doped layer is a common and crucial process for realizing high-quality two-dimensional electron gas (2DEG) channels. The fundamental role of Si-delta doping is as a charge supply source "away from the channel"—by forming extremely narrow doping peaks in the barrier layer (i.e., areal density typically around 10). 12 -10 13 cm -2 The PHEMT (density on the order of magnitude of 2DEG) provides electrons to quantum wells / channels near the heterostructure interface, while simultaneously using an isolation layer to spatially separate charged ions from the 2DEG to reduce ionic impurity scattering, thereby maintaining high mobility while ensuring high carrier density. This "delta-doped + spacer layer" growth method is the fundamental reason why PHEMT can simultaneously achieve high areal density and high mobility, directly determining transconductance g_m, noise figure, and high-frequency characteristics.

[0005] However, the "narrow and precise" spatial distribution of delta doping is a prerequisite for its effectiveness: once the Si doped layer diffuses or shifts during subsequent high-temperature growth, it will affect the key electrical and radio frequency performance of PHEMT, mainly manifested in the following ways: 1. Decreased two-dimensional electron gas mobility (μ) - enhanced scattering of ionized impurities and background impurities; 2. Changes in carrier effective areal density (Ns) and threshold / bias characteristics; 3. Decreased noise performance and receiver sensitivity; 4. Degradation of radio frequency limits and linearity; 5. Reliability and thermal stability issues. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for suppressing Si-delta doping diffusion in molecular beam epitaxy (PHEMT), thereby suppressing Si-delta diffusion and maintaining high-quality two-dimensional electron gas, high carrier density and high mobility in the PHEMT structure.

[0007] This invention provides a method for suppressing Si-delta doping diffusion in molecular beam epitaxy (PHEMT) growth, comprising: growing a PHEMT structure on a GaAs substrate using molecular beam epitaxy; wherein the growth temperature difference between the second Si-delta doped layer and its capping layer in the PHEMT structure is 80-110°C, and the capping layer is grown using a low-temperature growth process, thereby achieving the effect of suppressing the diffusion of the second Si-delta doped layer in the growth direction.

[0008] Preferably, the concentration distribution of Si atoms in the PHEMT structure is measured by secondary ion mass spectrometry (SIMS) to determine the growth direction of Si atoms.

[0009] Preferably, the capping layer is a second AlGaAs barrier layer and a GaAs cap layer.

[0010] Preferably, the PHEMT structure comprises, from bottom to top, a GaAs buffer layer, an AlGaAs / GaAs superlattice layer, a first AlGaAs barrier layer, a first Si-delta doped layer, a first AlGaAs isolation layer, an InGaAs channel layer, a second AlGaAs isolation layer, a second Si-delta doped layer, a second AlGaAs barrier layer, and a GaAs cap layer.

[0011] Furthermore, the growth temperature of the GaAs buffer layer is 670-680℃, the growth temperature of the AlGaAs / GaAs superlattice layer, the first AlGaAs barrier layer, the first Si-delta doped layer, the first AlGaAs isolation layer, the second AlGaAs isolation layer, and the second Si-delta doped layer are all 685-695℃, the growth temperature of the InGaAs channel layer is 450-460℃, and the growth temperature of the second AlGaAs barrier layer and the GaAs cap layer is 580-610℃.

[0012] Beneficial effects

[0013] This invention utilizes a low-temperature growth method to suppress the diffusion of Si-delta doping into the epitaxial layer, reduce the entry of Si atoms into the heterojunction interface, lower the electron scattering probability, effectively improve the accuracy of delta doping layer concentration, and enhance the electrical performance of the device. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of PHEMT in this invention.

[0015] Figure 2 The results are obtained by secondary ion mass spectrometry measurement of each atom in PHEMT sample No. 1 in Comparative Example 1.

[0016] Figure 3 The results are obtained by secondary ion mass spectrometry measurement of Si atoms in PHEMT sample No. 1 in Comparative Example 1.

[0017] Figure 4 These are the secondary ion mass spectrometry measurement results of each atom in PHEMT sample No. 2 in Example 1.

[0018] Figure 5The results are obtained by secondary ion mass spectrometry measurement of Si atoms in PHEMT sample No. 2 in Example 1.

[0019] Figure reference numerals: 1-GaAs substrate, 2-GaAs buffer layer, 3-AlGaAs / GaAs superlattice layer, 4-First AlGaAs barrier layer, 5-First Si-delta doped layer, 6-First AlGaAs isolation layer, 7-InGaAs channel layer, 8-Second AlGaAs isolation layer, 9-Second Si-delta doped layer, 10-Second AlGaAs barrier layer, 11-GaAs cap layer. Detailed Implementation

[0020] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0021] In the embodiments and comparative examples of this invention, the epitaxial growth of indium arsenide quantum dots uses a solid-state source molecular beam epitaxy (SSMBE) system, which has two solid-state group V sources, As and Sb, three group III sources, Ga, Al and In, and three doping sources, Si, GaTe and Be.

[0022] This invention utilizes molecular beam epitaxy to grow a PHEMT structure on a GaAs substrate 1; such as Figure 1 As shown, the PHEMT structure includes, from bottom to top, a GaAs buffer layer 2, an AlGaAs / GaAs superlattice layer 3, a first AlGaAs barrier layer 4, a first Si-delta doped layer 5, a first AlGaAs isolation layer 6, an InGaAs channel layer 7, a second AlGaAs isolation layer 8, a second Si-delta doped layer 9, a second AlGaAs barrier layer 10, and a GaAs cap layer 11.

[0023] Comparative Example 1

[0024] First, on the GaAs substrate, according to Figure 1 A PHEMT test piece was grown on the structure and named PHEMT sample 1. The growth temperature of each layer was measured by thermocouples and is shown in Table 1. The growth temperature of the GaAs buffer layer was 675℃, the growth temperature of the AlGaAs / GaAs superlattice layer, the first AlGaAs barrier layer and the second AlGaAs barrier layer, the first Si-delta doped layer and the second Si-delta doped layer, the first AlGaAs isolation layer and the second AlGaAs isolation layer, and the GaAs cap layer were all 690℃, and the growth temperature of the InGaAs channel layer was 460℃.

[0025] Table 1. Growth temperatures of each layer in PHEMT sample No. 1

[0026] Secondary ion mass spectrometry measurements were performed on PHEMT sample No. 1, and the concentrations of different atoms were calibrated. The test results are as follows: Figure 2 As shown in the figure; the test results indicate that the concentration distributions of Al, Ga, and As atoms all conform to the structural design, while the doping peaks of the first and second Si-delta doped layers show significant differences in Si atom concentration. Therefore, the concentration of Si atoms was separately tested and calibrated, and the test results are shown in the figure. Figure 3 As shown. In secondary ion mass spectrometry data analysis, the two core quantities are Integral and Average. The specific meanings of Integral and Average are as follows: Integral represents the integral value of the concentration curve, and its unit is atoms / cm². 2 (i.e., at / cm) 2 ), representing the "total number of atoms per square centimeter," also known as surface density. It is commonly used to describe the total elemental content in a doped layer; Average represents the average concentration over the measured depth range, with units of atoms / cm². 3 (i.e., at / cc), representing the "total number of atoms per cubic centimeter," or volume concentration, is commonly used to describe doping concentration. According to... Figure 3 The test results show that the average volume concentration of the doping peak in the second Si-delta doped layer is 1.02 × 10⁻⁶. 18 at / cc corresponds to an Integral areal density of 3.94 × 10⁻⁶. 12 at / cm 2 The peak intensity was 4.85 × 10⁻⁶. 18 at / cc. Furthermore, the Si-delta doping on both sides of the channel exhibits significant differences. The first Si-delta doped layer has a narrower doping peak and a steeper slope along the growth direction, indicating that the low-temperature growth of the channel layer inhibits Si diffusion. The second Si-delta doped layer shows a different pattern. The high-temperature growth of the second AlGaAs barrier layer leads to intense Si diffusion along the growth direction, resulting in a slow slope decrease on the left side of the Si-delta doping peak. This difference is due to the high-temperature growth of the top layer (second AlGaAs barrier layer and GaAs cap layer), and the subsequent high-temperature growth of the capping layer causes Si-delta doping to diffuse along the growth direction.

[0027] Example 1

[0028] To address this issue, the growth temperature of the second AlGaAs barrier layer and the GaAs cap layer at the top was optimized.

[0029] First, on the GaAs substrate, according to Figure 1 A PHEMT test piece was grown using the structure described above, and named PHEMT sample No. 2. The growth temperature of each layer was measured using thermocouples, as shown in Table 2. To suppress the diffusion of Si-delta doping caused by high temperature, the growth temperature of the second AlGaAs barrier layer and GaAs cap layer at the top was optimized to 580℃. Compared with PHEMT sample No. 1, the growth temperature of the capping layer of the second Si-delta doped layer in PHEMT sample No. 2 was reduced by 110℃.

[0030] Table 2. Growth temperatures of each layer in PHEMT sample No. 2

[0031] Secondary ion mass spectrometry measurements were performed on PHEMT sample No. 2, and the concentrations of different atoms were calibrated. The test results are as follows: Figure 4 As shown in the figure. Test results indicate that the concentration distributions of As and H atoms conform to the structural design. However, for the concentration of Si atoms, the doping peak of the second Si-delta doped layer is significantly different compared to sample 1. The concentration of Si atoms was separately calibrated, and the test results are shown in the figure. Figure 5 As shown. According to Figure 5 The test results show that the average volume concentration of the doping peak in the second Si-delta doped layer is 2.26 × 10⁻⁶. 18 at / cc corresponds to an Integral areal density of 4.78 × 10⁻⁶. 12 at / cm 2 The peak intensity was 8.72 × 10⁻⁶. 18At / cc. Compared with PHEMT sample No. 1, PHEMT sample No. 2 shows improved bulk concentration and areal density, with higher and narrower doping peaks. Under low-temperature growth conditions, the doping curve of the second Si-delta doped layer in PHEMT sample No. 2 exhibits a steeper distribution on the left side, while the right side distribution is the same as that of PHEMT sample No. 1. This is because the low-temperature growth of the capping layer effectively suppresses Si diffusion, which is conducive to forming a steep distribution interface. Furthermore, for PHEMT sample No. 2, the doping peaks of the second Si-delta doped layer show the same trend as those of the first Si-delta doped layer, and the doping patterns on both sides of the channel show consistency. This indicates that low-temperature growth of the capping layer can more precisely control the spatial distribution of Si-delta doping and effectively suppress Si diffusion in the growth direction, forming a steep distribution interface. This provides a reference for optimizing the growth process of PHEMT.

Claims

1. A method for suppressing Si-delta doping diffusion in molecular beam epitaxy (PHEMT), comprising: A PHEMT structure is grown on a GaAs substrate using molecular beam epitaxy. The growth temperature difference between the second Si-delta doped layer and the capping layer in the PHEMT structure is 80-110°C. The capping layer is grown using a low-temperature growth process to suppress the diffusion of the second Si-delta doped layer in the growth direction.

2. The method according to claim 1, characterized in that, The concentration distribution of Si atoms in the PHEMT structure was measured by secondary ion mass spectrometry to determine the diffusion direction of Si atoms.

3. The method according to claim 1, characterized in that, The capping layer consists of a second AlGaAs barrier layer and a GaAs cap layer.

4. The method according to claim 1, characterized in that, The PHEMT structure, from bottom to top, includes a GaAs buffer layer, an AlGaAs / GaAs superlattice layer, a first AlGaAs barrier layer, a first Si-delta doped layer, a first AlGaAs isolation layer, an InGaAs channel layer, a second AlGaAs isolation layer, a second Si-delta doped layer, a second AlGaAs barrier layer, and a GaAs cap layer.

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