Surface Adsorption And Diffusion Study In GaN MOVPE Growth

GaN is an important wide band-gap compound semiconductor material,widely used in the preparation of microelectronic and optoelectronic devices.MOVPE is the main method for growing GaN films.Understanding the surface reaction mechanism of GaN is essential to controlling the growth quality.In this study,the surface adsorption and diffusion processes were studied for MOVPE-grown GaN films based on the quantum chemistry calculation of density functional theory?DFT?.In particular,the adsorption and diffusion of the main reaction precursors?Ga and GaCH₃?on ideal,H-covered or NH₂-covered GaN?0001?surface are studied.Revealing the initial reaction path by calculating and comparing the geometrical structure,the adsorption energy of different adsorption sites and the diffusion energy barrier of the adsorbed particles on the surface.Firstly,building the construction of GaN?0001?supercell model and using the combination method of GGA-PW91 functional to verify based on Dmol3 module of Material studio software.Secondly,analysing the adsorption energies,Mulliken charge distribution and partial density of states when Ga atoms and GaCH₃ adsorbed on different adsorption sites for three different covering surfaces and revealing surface bonding principle of particles.Finally,the linear synchronous transit and quadratic synchronous transit?LST/QST?method are used to searching the diffusion energy barrier of the particles under different diffusion paths on the surface according to the stable adsorption sites of Ga atoms and monomethyl gallium GaCH₃ on the three surfaces.The main conclusions of the paper are as follows:?1?Ga atoms and monomethyl gallium GaCH₃ are adsorbed on the T4 and H3 sites of three different covering surfaces.The adsorption energy of the particles on the NH₂-covered surface is the largest,that on the H-covered surface is the smallest,and that on the ideal surface is in middle.?2?It is conclude through analyzing the Mulliken charge distribution of adsorbed particles and surface particles,the charge is transferred from the adsorbed particles to the surface particles and the adsorbed Ga atoms and GaCH₃ are slightly positively charged,When Ga atoms and GaCH₃ are adsorbed on NH₂-covered GaN?0001?surface.However,the conclusion on ideal and H-covered surface is opposite.?3?It is found through analysing partial density of states: the 4s and 4p orbits of absorbed Ga atoms and Ga atom from GaCH₃ show different degree of hybrid phenomenon?the 2s and 2p orbits of N atoms and the 4s and 4p orbits of surface Ga atoms are also hybridized?.Absorbed Ga atom and GaCH₃ and surface neighbor Ga atoms formed covalent bonds with lon nature,and the bond strength relationship is Ga-N> Ga-Ga> Ga-H.?4?The diffusion energy barrier of Ga atom on the NH₂-covered GaN?0001?surface is the largest,so that excessive NH₂ on the surface will suppress the diffusion of Ga atoms.There are also the same conclusion for MMG.