The role of step kinetics in MBE of compound semiconductors

Abstract

The degree of equilibrium at the growth step during MBE is studied taking GaAs and (In,Ga)As as examples. The theoretical calculation with the assumption of near-equilibrium at the step edge gives the temperature dependence of mode transition between the 2D nucleation and the step flow on the Ga flux intensity and the inter-step distance, which agree very well with the experiments. The (In,Ga)As MBE experiment shows that there is a segregation dependency of In on the interstep distance which means a certain amount of supersaturation exists even at the step edge. The theory predicts that the supersaturation ratio is of the order of 1.5 at the step edge. From these experimental results and theoretical considerations, it is concluded that equilibrium or near-equilibrium is established at the step edge. The experiments with nonplanar substrate, which gave a very long diffusion length for atom incorporation, are discussed and it is suggested that the origin of the disagreement with the present model can be explained in terms of a large lateral flux in the growth on the nonplanar substrate.