Research On Preparation And Performance Of Heat Dissipation Layer Based On GaN-on-Diamond Structure

With the increasing power of Gallium Nitride(GaN)devices,the "self-heating effect" of the devices become more and more obvious,which puts forward an urgent need for the heat dissipation of high-frequency and high-power electronic devices.CVD diamond instead of traditional substrate material can effectively meet the heat dissipation requirements of high frequency and high power devices,and effectively improve the performance,life and reliability of device.However,there are some technical problems in diamond film deposited on GaN surface,such as poor stability,large thermal mismatch and stress accumulation,which lead to the cracking of the epitaxial layer.Moreover,the problems affecting the thermal transport of the GaN/diamond interface have not been clarified,limiting the further application and development of the GaN-on-diamond.This paper studies the stable nucleation and diamond grown on the surface of GaN/protective layer in high temperature hydrogen plasma environment.Based on electrostatic enhanced self-adsorption effect and double diamond layer method,low stress diamond/GaN composite materials were prepared.In addition,the heat transfer mechanism affecting the interface between GaN and diamond was studied,and the thermal boundary resistance of diamond/GaN was measured.The mechanism of induced decomposition of GaN epitaxial layer by high-temperature hydrogen plasma and the ways of inhibiting decomposition are studied.Hydrogen plasma and temperature are the inducement and driving force of GaN decomposition.Therefore,the stability of the GaN epitaxial layer in high temperature hydrogen plasma environment is extremely poor.Adding a protective layer on the GaN surface and increasing the nitrogen partial pressure in hydrogen plasma can effectively improve the stability of GaN.In addition,the amorphous SiNx and AlN protective layer with low roughness,dense and non-porous are deposited by magnetron sputtering technology.Diamond films deposited on the surface of GaN/protective layer by microwave chemical vapor deposition is studied.A dense diamond film can be formed to further resist hydrogen plasma penetration,when the CH4 is 12%and the temperature is 800℃.Based on the electrostatic self-adsorption effect of GaN/protective layer and nano diamond powder,high density nano-diamond particles dispersed on the substrate can be achieved.Finally,the highly dense diamond core layer is quickly obtained on the surface of the GaN/protective layer,which can effectively improve the interface bonding strength and the quality of the diamond core layer.In addition,according to the theory of interfacial heat transfer,the interface microstructure,phonon density of state mismatch and the correlation between protective layer material and interfacial heat transfer are investigated.It is suggested that the selection of protective layer material and the matching degree of acoustic density at the interface are important factors affecting the thermal transmission of the interface.To improve the roughness of the protective layer,the effective contact area of the interface can be increased,and the heat transfer ability of the interface can be further improved,and the GaN/diamond thermal boundary resistance of 35.5±5.2 m2K/GWwas obtained.A method for preparing diamond substrate GaN wafer by double diamond layer is presented.The GaN/diamond structure with low stress and low interfacial thermal resistance has been successfully prepared,and the crystal quality has not been significantly reduced before and after GaN epitaxial layer transfer.Moreover,the results of Hall test show that the diamond process parameters are obtained by two-step method:in nucleation stage,methane concentration is 12%,nucleation temperature is 800℃.After nucleation for 5 min,when methane concentration is 5%and deposition temperature is 850℃,the electron mobility attenuation of diamond substrate GaN epitaxial layer is minimal,about 14%.