Atomic assembly during GaN film growth: Molecular dynamics simulations

Abstract

Molecular dynamics simulations using a recently developed Ga-N Tersoff type bond order interatomic potential have been used to investigate the growth mechanisms of ͑0001͒ wurtzite GaN films from thermalized atomic gallium and nitrogen fluxes. The crystallinity and stoichiometry of the deposited wurtzite lattice structures were determined as a function of growth temperature and N:Ga flux ratio. The lattice perfection was found to improve as the growth temperature was increased to 500 K. At a fixed growth temperature, the lattice quality and stoichiometry both reached optimum as the N:Ga ratio approached a value between two and three. The optimum flux ratio increased with increasing growth temperature. These three observations are consistent with experimental studies of growth on wurtzite phase promoting substrates. The atomic assembly mechanisms responsible for these effects have been explored using time-resolved atom position images. The analysis revealed that high quality crystalline growth only occurred when off-lattice atoms ͑which are usually associated with amorphous embryos or defect complexes͒ formed during deposition were able to move to unoccupied lattice sites by thermally activated diffusion processes. The need for a high N:Ga flux ratio to synthesize stochiometric films arises because many of the nitrogen adatoms that impact N-rich ͑0001͒ GaN surfaces are re-evaporated. Reductions of the substrate temperature reduce this reevaporation and as a result, the optimum N:Ga ratio for the stoichiometric film formation ͑and best lattice perfection͒ was reduced as the growth temperature was decreased.

High-fidelity simulations of CdTe vapor deposition from a bond-order potential-based molecular dynamics method

“…Due to the constraints of computational cost, MD simulations employ accelerated deposition rates. 51,52 As will be discussed below, the accelerated deposition rates reduce the diffusion time of surface atoms before they are buried by subsequently deposited atoms. This problem can be mitigated using elevated substrate temperatures to accelerate the surface diffusion.…”

Analytical bond-order potential for the Cd-Zn-Te ternary system

“…15 Tersoff potentials fundamentally incorporate the property trends of different phases and can also predict crystalline growth during vapor deposition simulations. 31,32 However, Tersoff potentials are difficult to parameterize to ensure the lowest energy for the ground-state phase and its crystalline growth during vapor deposition simulations. Without involving iterative vapor deposition tests in parameterization, literature Tersoff potentials often incorrectly predict amorphous growth.…”

Molecular Dynamics Simulation of MBE Growth of CdTe/ZnTe/Si

“…Typically, MD simulations of crystal growth of covalent systems have been limited to cells with substrate areas of a few tens of atoms, with only a few hundred atoms in the entire simulation cell. 58,59 The treatment of larger unit cells would be a considerable advantage. A larger substrate area, for example, would allow a greater variety of surface reconstructions, orientations, and miscuts, as well as structures of the deposited species such as quantum dots and crystal defects.…”