The kinetic aspects of ordering in GaAs 1- xSb x grown by organometallic vapor phase epitaxy

Abstract

Long range ordered structures have been studied in GaAs 1- x Sb x alloys with x ≈ 0.5 grown by organometallic vapor phase epitaxy (OMVPE). The emphasis of this paper is on the kinetic effects leading to the occurrence of ordering. In particular, the effects of growth temperature, growth rate, and substrate orientation are reported. The ordered simple tetragonal CuAu-I (L1 0) and the chalcopyrite (E1 1) structures were observed at the highest growth temperatures from 580 to 660°C on (100) oriented InP substrates with both high and low growth rates. The samples grown at lower temperatures, 550°C, on (100) oriented InP substrates were observed to have only the L1 0 ordered structure at a growth rate of 0.02 μm/min and principally the L1 0 ordered structure with a very small amount of E1 1 at a growth rate of 0.01 μm/min. A new superlattice structure with 3 times the normal zincblende periodicity along the [110] direction was observed for samples grown over the entire growth temperature range studied for GaAs 0.5Sb 0.5 on (100)InP substrates. Growth on (110) oriented substrates produced GaAs 0.5Sb 0.5 with only the L1 0 ordered structure. However, an additional superlattice structure with four times the normal periodicity along the [100] direction was observed for these samples. We also examined samples grown on (221) and (311) oriented InP substrates at 550°C. They showed very little ordering with only local observation of weak L1 0 superlattice electron diffraction spots. Photoluminescence measurements for the epilayers grown on (221) and (311) substrates showed much stronger intensities and narrower half-widths than for those grown on (100) and (110) oriented InP substrates, due perhaps to a higher degree of homogeneity in the absence of ordered phases.