Electric Current Induced Asymmetry of Surface Diffusion - Instability of Vicinal Crystal Surfaces

Abstract

We measured the width L_b, of a bunch, consisting of a fixed number of steps, as a function of the temperature of the Si crystal, heated by direct electric current. We carried out these measurements in three different regimes—during crystal-vapor equilibrium, during sublimation, and during crystal growth. The central result of this work is the experimentally-determined temperature-dependence g(T) of the step interaction coefficient in the expression f (ρ) = f(0) + κρ + gρ ³ for the surface free energy (per unit projected area) of a vicinal surface of Si(111) with a density of steps ρ. We evaluated g(T) in the high temperature interval on the basis of the derived expression $\frac{{g(T)}} {{g(T_0 )}} = \frac{{L_b^3 (T)}} {{L_b^3 (T_0 )}}\frac{{1(T)}} {{1(T_0 )}}$ and the measured values of L_b and I(T) during crystal-vapour equilibrium (I(T) is the electric current, flowing through the Si crystal to keep it at a temperature T). The experiments on the temperature-dependence of the bunch width L_b under non-equilibrium conditions (growth of the Si crystal) manifest a sharp peak (at T = 1230° C), which indicates a significant change of the structure of the Si(111) surface.