Lattice site locations of excess arsenic atoms in gallium arsenide grown by low-temperature molecular beam epitaxy

The excess As atoms present in as-grown GaAs buffer layers grown by molecular beam epitaxy at low substrate temperature (∼200 °C) was measured by particle induced x-ray emission to be ∼4×10²⁰ atoms/cm³. The lattice site location of these excess As atoms in the layer was studied by ion channeling methods. Our results strongly suggested that the excess As atoms are located in an interstitial position close to the substitutional As atoms with a projected displacement ∼0.3 Å into the 〈110〉 channel. These results are consistent with the 〈111〉 split interstitials model suggested from TEM results. After annealing at 600 °C these excess As atoms coalesce forming As precipitates.