Quantum Chemistry Study On Bi-molecular Co-adsorption On AlN Surface

Aluminum Nitride?AlN?semiconductor thin film has the characteristics of wide band gap?6.2eV?,strong chemical bond energy,good thermal conductivity and small thermal expansion coefficient.It is widely used in the preparation of blue LED and ultraviolet photovoltaic devices.Meanwhile AlN also has a small lattice mismatch and similar thermal expansion coefficients with GaN,so it is often used as a buffer layer for heteroepitaxial growth such as GaN.In the growth of AlN metalorganic vapor phase epitaxy?MOVPE?,the reaction precursors simultaneously introduce into the reactor and decompose,adsorbe on high temperature substrate.Therefore,it is important to understand the co-adsorption mechanism of gas-phase products on the surface.Previous studies mainly focuse on the single adsorption of particles and ignore the co-adsorption of two particles.In this paper,quantum chemistry calculations are carried out on the co-adsorption of N-containing particles and Al-containing particles in the growth of AlN MOVPE.The purpose is to further understand the mechanism of the AlN surface reaction,thereby improving the film growth rate and quality of the AlN-MOVPE process.According to the previous studies,the Al-containing particles in the gas phase of AlN-MOVPE are monomethyl aluminum?MMAl?,dimethyl aluminum ammonia?DMAlNH₂?and triamino aluminum?Al?NH₂?₃?,N-containing particle is NH₃,and the stable AlN growth plane is the AlN?0001?-Al plane.Therefore,in the simulation calculation,three groups of surface reaction precursors were considered:NH₃ and MMAl,NH₃ and DMAlNH₂,NH₃ and Al?NH₂?₃co-adsorption on the ideal,H-covered and NH₂-covered AlN?0001?-Al plane.Through the comparative analysis of the surface adsorption sites,adsorption energies,Mulliken chemical bond population,partial density of states and electron density difference before and after adsorption,the basic rules of co-adsorption of different Al-containing particles and NH3 on the surface were explored.The main conclusions showen as follows:?1?When MMAl,DMAlNH₂ and Al?NH₂?₃ co-adsorption with NH₃ on different surfaces,there is similar adsorption energy when co-adsorption on ideal surface,indicating that different Al-containing particles and NH₃ have the same adsorption trends when co-adsorbed on the ideal surface.?2?There is similar adsorption situation when NH₃ and DMAlNH₂,NH₃ and Al?NH₂?₃co-adsorption on different surfaces,and easy to adsorb on the ideal and H-covered surface,but not easy to adsorb on the NH₂-covered surface.When they co-adsorption on the NH₂-covered surface,there is only the bonding reaction between the particles without adsorption reaction with the surface atoms.So when the Al-containing particles in the gas-phase product are mainly DMAlNH₂ and Al?NH₂?₃,the appearance of NH₂-covered surface should be avoided.?3?Compared with the co-adsorption of NH₃ and DMAlNH₂,NH₃ and Al?NH₂?₃ on three surfaces,NH₃ and MMAl have different adsorption trends.The adsorption tendency of NH₃ and MMAl on the ideal and NH₂-covered surfaces is same,but it is more easily to adsorb on the H-covered surface?the adsorption energy is about 15 times of the ideal and NH₂-covered surface?.Therefore,under H-rich conditions,the mainly Al-containing particles in the gas-phase product should be MMAl,which can be got by controlling the external conditions.?4?During co-adsorption,the particles will be subjected by the surface atoms and particales at the same time,and the stable adsorption structures which are obtained by co-adsorption is not necessarily more stable than the structures adsorbed by single adsorption.For example,when NH₃ and DMAlNH₂,NH₃ and Al?NH₂?₃ co-adsorption on NH₂-covered surface is not conducive to the growth of the thin film.