The effect of arsenic overpressure on the structural properties GaAs grown at low temperature

The structural properties of GaAs grown by molecular-beam epitaxy at low temperatures have been investigated by scanning electron microscopy, transmission electron microscopy, and high-resolution x-ray double-crystal rocking curves as a function of arsenic overpressure during growth. It was found that surface smoothness and excess arsenic incorporation both depend strongly on growth temperature and on As/Ga flux ratio, For each growth temperature there is a ''window'' in the flux ratio which results in smooth surfaces. As-grown layers have an increased lattice constant in the growth direction. This relative lattice expansion increases with flux ratio at a constant growth temperature and eventually saturates, Transmission electron micrographs have revealed the presence of arsenic precipitates in material annealed at 600 degrees C. Increasing the As-4 pressure during growth results in increases in precipitate diameter by almost 50% while their density and shape remain constant. Based on these observations a model has been developed to explain the lattice expansion dependence on arsenic overpressure. (C) 1996 American institute of Physics.