An ion-beam technique for measuring surface diffusion coefficients

The effective surface diffusion coefficient of Ga along the [110] direction on vicinal GaAs( 001) 2x4 surfaces during molecular-beam epitaxy was measu red using specular ion current measurements. In this technique, 3 keV Ar io ns were impinged upon the surface at a glancing angle (typically 3 degrees) , and the specularly scattered ion current was measured. Since specular ref lections require a locally flat surface, adatoms cause a decrease in the me asured current, allowing an average adatom density measurement. The time de pendence of the Ga adatom population was measured during and after Ga depos ition. Diffusion coefficients, obtained from the adatom lifetimes using a s imple model of diffusion to the step edges, were fit well by the expression D=2x10(-9) exp (-0.73 eV/kT)cm(2)/s from 400 to 600 degrees C. (C) 1999 Am erican Institute of Physics. [S0003-6951(99)04012-7].