Simulation Study Of AlN Adsorption On The α-Al₂O₃(0001) Surface

AlN thin film has a wide application prospect in optoelectronic devices including ultraviolet detector,ultraviolet light emitter diode,ultraviolet photoelectric apparatuses and mobility devices,etc.The high-quality AlN thin films growth on the sapphire(0001) substrate,but there is no theoretical calculation on the initial growing mechanism of theAlN thin films deposited on theα-Al₂O₃(0001) surface.The first principle is considered for AlN films heterogeneous growth simulation through an analysis of the difficulties of complex nitride films growth and a summary of the modeling and computer simulation methods of films growth.Adsorption growth models of AlN films growth on theα-Al₂O₃(0001) surface and their theoretical calculation are carried out by using the CASTEP code based on the density-functional theory(DFT).The electron-electron interaction is treated within the local density approximation(LDA) and the generalized gradient approximation(GGA).In this paper,the author attempts to have a detail discussion of the following points such as dynamics study on the adsorption and diffusion in early growth of AlN/α-Al₂O₃(0001) films.The mechanism of AlN adsorption on theα-Al₂O₃(0001) surface,the surface structure and the growing orientation,the temperature dependent influence of the atoms behavior character of the surface etc. are calculated the first time by the author.The results are well in accordance with experimental reports.The ab initio dynamic simulation of the AlN adsorption on theα-Al₂O₃(0001) surface.The theoretical calculation gives a further evidence that the adsorption process can be divided into four stages,the physical adsorption and surface migration, the chemical adsorption of(Al)N-Al,the chemical adsorption of Al-O(substrate) and the superficial stable state.In the stable adsorption position,the bonding length of (Al)N-Al is 0.172±0.01nm,after the adsorption,the bonding length of AlN is 0.189±0.010nm,chemical bonding energy achieved 4.844 eV～5.132eV,indicated that AlN has had a strong chemical adsorption on theα-Al₂O₃(0001) surface.There is a deflected angle of 30°between the chemical bonding of the AlN and the adjacent surface Al-O bonding;the stable chemical adsorption site of Al is just about 30°deflected from the O-hexagonal symmetry of theα-Al₂O₃(0001) surface.The bonding processing of a AlN molecule on the surface of Al₂O₃,adsorption energy and bonding orientation are investigated.The change in surface structure and bonding processing as well as the characters of surface chemical bonding are further investigated Through analysis of the atomic populations,density of state,and bonding electronic density before and after the adsorption,it is revealed that the chemical bonding formed by the N^3- of the A1N and the surface Al³⁺ is characterized by strong ionic bonding,and the bond of the Al³⁺ and the surface O^2- also has a obvious ionic character.Meanwhile,the AlN adsorption and diffusion on theα-Al₂O₃(0001) surface have given a further theoretical calculation.There are a analysis about the adsorption process,the system energy change,the suffision of the surface particles as well as the AlN film growth under the different temperature.With the temperature increasing, the average diffusivity of these particle atα-Al₂O₃(0001) surface is enhanced in the bonding process.The diffusion coefficient of N atom is higher than that of the Al atom,especially in the physical adsorption stage.In the higher temperature condition (over the 700℃),the desorption role of the N atom is markedly improved,so it is unfavorable to the stable absorption of AlN.The temperature between 500℃and 700℃is beneficial to the stable adsorption and the growth of the AlN onα-Al₂O₃(0001) surface.