Recently, Zhou Bing's research group at Taiyuan University of Technology and Yuan Chao's research group at Wuhan University have cooperated to publish an article entitled "Effect of bias-enhanced nucleation on the microstructure and thermal" in the international authoritative journals "Materials Characterization" and "Diamond & Related Materials". Boundary Resistance of Gan Sinx Diamond Multilayer Composites" and "Modulating Microstructure and Thermal Properties of Diamond Sinx Gan Multilayer Structure by Diamond Growth Temperature"**.
GaN high electron mobility transistors (HEMTS) have broad application prospects in the field of high-power RF devices due to their excellent high-power and high-frequency performance. However, the rapid increase in the active temperature of the device during operation makes it difficult to take full advantage of the high power advantage, and the actual power density is much lower than the theoretical value, which limits the further improvement of the device performance.
At present, it is an effective and feasible solution to take advantage of the excellent thermal conductivity of polycrystalline diamond films (a thickness of 1-3 m with a thermal conductivity of about 300-500 W m K at room temperature) to help GaN hemts efficiently diffuse heat from the active region to the diamond layer. Therefore, reducing the interfacial thermal resistance of the diamond GaN structure is very important for GaN hemts. There are many conditions in the diamond growth process that affect the thermal properties of the diamond GaN multilayer structure and the formation of defects. Among them, the bias pressure during diamond nucleation and the diamond growth temperature are extremely important parameters, which have not been fully studied in the past.
In order to solve the problems existing in the current process of diamond nucleation, a bias enhanced nucleation technology based on microwave plasma chemical vapor deposition (MPCVD) diamond was proposed, which controlled the nucleation of diamond under different bias voltages (400-700 V) to regulate the interfacial thermal resistance. The optimization of the bias voltage is conducive to the establishment of a stable plasma environment and the acquisition of a complete diamond-gallium nitride multilayer structure and interface.
The self-developed high-resolution pump-probe thermal reflectance (TTR) was used to characterize the interfacial thermal resistance and thermal conductivity of diamond films grown at different bias voltages. In addition, the microstructure and thermophysical properties (thermal conductivity and interfacial thermal resistance) of the multilayer structure of diamond gallium nitride were controlled by controlling the diamond growth temperature (740-860), which were verified and explained by TTR characterization and structural characterization. The results of the thermal characterization of TTR show that the lowest interfacial thermal resistance and the highest thermal conductivity of polycrystalline diamond films can be obtained at the same time at a bias voltage of 700 V and a growth temperature of 800 V.
These two results systematically study the regulation of microstructure and thermophysical properties in the multilayer structure of diamond gallium nitride by controlling nucleation bias and growth temperature in MPCVD. The results show that it is feasible and effective to control the thermophysical properties in the multilayer structure of diamond gallium nitride by controlling the process conditions of diamond growth. These two works further optimize the MPCVD growth process of GaN surface diamonds, and are expected to provide a potential solution for GaN HEMTs to achieve efficient heat dissipation and improve device performance.
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