Theoretical study of antisite arsenic incorporation in the low temperature molecular beam epitaxy of gallium arsenide

Abstract

A stochastic model for simulating the surface growth processes in the low temperature molecular beam epitaxy of gallium arsenide is developed, including the presence and dynamics of a weakly bound physisorbed state for arsenic. The physisorbed arsenic is allowed to incorporate into the arsenic site or gallium site (antisite) and evaporate. Additionally, the antisite As is allowed to evaporate from the surface of the crystal. The arsenic flux, temperature and growth rate dependences of antisite arsenic (AsGa) concentration and the resultant % lattice mismatch obtained from our simulation are in excellent agreement with the experimental results. The activation energy of 1.16 eV for the evaporation of antisite arsenic from the crystal obtained from our model is in good agreement with theoretical estimates. At a constant substrate temperature and growth rate (Ga flux rate), the antisite arsenic concentration and hence, the % lattice mismatch increase with arsenic flux in the low flux regime and saturate for high flux regime. The critical arsenic flux at which the AsGa concentration and the % lattice mismatch saturate, increases with temperature. The AsGa concentration and % lattice mismatch saturate at lower values for higher temperatures. As the arsenic flux increases, the coverage of the physisorbed layer increases and at a critical flux dictated by the fixed temperature and growth rate, the coverage saturates at its maximum value of unity (a complete monolayer) and hence, the concentration of AsGa and % lattice mismatch saturate. Lower AsGa concentration and % lattice mismatch result at higher temperature due to more evaporation of AsGa from the surface of the growing crystal. Additionally, an analytical model is developed to predict the AsGa concentration and % lattice mismatch for various growth conditions.