Step structure and ordering in GaInP

Steps are known to affect the ordering phenomenon in GaInP; [110] steps assist ordering and [bar 110] steps retard ordering. However, the mechanism leading to this behavior has not been determined. In this paper, the step spacing is used as a semiquantitative indicator of the attachment of adatoms at the step edge for organometallic vapor phase epitaxial growth on singular (001) GaAs substrates. The step spacing and degree of order in the epitaxial layers have been studied as a function of temperature and the flow rate of the P precursor for both tertiarybutylphosphine (TBP) and phosphine. As the flow rate of the P precursor is lowered beyond a certain critical point, both the degree of order and the step spacing are seen to decrease together. The behavior is the same for TBP and for PH3. Similarly, as the growth temperature is increased above a certain value, the step spacing and order parameter decrease together. This suggests a relationship between adatom attachment at steps and the ordering mechanism. Possible explanations for these phenomena are explored. At low temperatures, the degree of order is reduced and the step spacing decreases exponentially. The data suggest that the reduction in the surface diffusion coefficient with decreasing temperature is the main factor acting to reduce both the step spacing and the degree of order. However, the increasing adatom sticking coefficient at both step edges expected at low temperatures will affect both phenomena as well. copyright 1998 American Institute of Physics