Precipitation of Arsenic in Doped GaAs

Precipitation processes in the p-type, n-type, and intrinsic GaAs layers grown by molecular beam epitaxy at a low tempera ture were studied by transmission electron microscopy. The average spacing, average diameter, and volume fraction of precipitates were measured as a function of the annealing time for the annealing tempera ture of 700~ Volume fractions of precipitates are nearly constant in each layer over the period of annealing, implying that the precipitation process has reached the coarsening stage in the annealing times used in the study. The volume fraction of precipitates in the n-type layer is about a hal f of those in the p-type and intrinsic layers, suggesting that the incorporation rate of excess As into the n-type layer during the growth is lower th~n those into the p-type and intrinsic layers. Despite a large difference of amounts of excess As in as-grown n-type, p-type, and intrinsic layers, the average spacings and, hence, number densities of precipitates in three layers are nearly identical for each of the annealing conditions.