Effect of growth rate on step structure and ordering in GaInP

CuPt ordering is widely observed in GaInP epitaxial layers grown by organometallic vapor phase epitaxy. The formation of this spontaneously ordered structure during epitaxial growth is intimately related to the atomic-scale physical processes occurring on the surface, specifically surface reconstruction and the attachment of atoms at steps. For growth on singular (001) GaAs substrates the surface structure, measured using atomic force microscopy, is seen to consist of small islands surrounded by either monolayer or bilayer steps. An increase in the growth rate from 0.25 to 2.0 μm/h with a constant tertiarybutylphosphine partial pressure at 670 °C has no effect on either the degree of order or the step structure. Only the step spacing is observed to change. It decreases systematically as the growth rate is increased, following an approximate 1/(growth rate) 1/2 dependence. As the growth rate increases, the time atoms have to rearrange before being frozen due to coverage by the next layer decreases. This leads directly to the dependence observed. These observations are consistent with previous observations which appear to show a close correlation between step structure (monolayer versus bilayer) and ordering, although the causative factor has not been determined.