Observation of Ga droplet formation on (311)A and (511)A GaAs surfaces

Using ( 100) GaAs substrates as a reference, we present a study of the formation of Ga droplets on ( 311) A and ( 511) A GaAs substrates in which the effect of both the substrate temperature and the amount of Ga supplied on the droplet density and height for the three different surfaces have been investigated. Droplets on ( 100) substrates show a round shape; however, they appear as elongated balls with tails along the [233] direction of the ( 311) A substrate and the [255] direction of the ( 511) A substrate. It has been found that the Ga droplets on ( 511) A surfaces have lower densities and higher heights than those on ( 100) substrates. In contrast, Ga droplets on ( 311) A surfaces have lower heights and much higher densities compared to those for both ( 100) and ( 511) A. We observed that the decrease in the droplet density with increasing growth temperature for both ( 311) A and ( 511) A is more than twice that for the ( 100) GaAs surface due to the larger drop in the nucleation rate. Based on these observations, we offer a physical explanation based on the thermodynamics and the anisotropy of the high-index surfaces.