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 l ow temperatures have been investigated by scanning electron microscopy , transmission electron microscopy, and high-resolution x-ray double-c rystal rocking curves as a function of arsenic overpressure during gro wth. It was found that surface smoothness and excess arsenic incorpora tion both depend strongly on growth temperature and on As/Ga flux rati o, For each growth temperature there is a ''window'' in the flux ratio which results in smooth surfaces. As-grown layers have an increased l attice constant in the growth direction. This relative lattice expansi on increases with flux ratio at a constant growth temperature and even tually 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 p recipitate diameter by almost 50% while their density and shape remain constant. Based on these observations a model has been developed to e xplain the lattice expansion dependence on arsenic overpressure. (C) 1 996 American institute of Physics.