Effect of substrate orientation on arsenic precipitation in low-temperature-grown GaAs

Arsenic precipitation in "superlattice" structures of alternately undoped and [Si] = 3 × 10¹⁸cm^--doped GaAs grown at 250°C on (100), (311)A, and (311)B GaAs substrates has been studied using transmission electron microscopy. It is found that upon postgrowth annealing at 800°C, As precipitates are nearly confined in the Si-doped regions, forming two-dimensional cluster arrays located approximately at the center of each Si-doped layer. The results also show that the As precipitates in the (311)B substrate are slightly denser and larger than those in the (311)A substrate and both are markedly denser and larger than those in the (100) substrate. This can be attributed to the varying excess arsenic incorporations in differently orientated substrates.