Enhanced precipitation of excess As on antimony delta layers in low-temperature-grown GaAs

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Delta doping with antimony isovalent impurity has been employed as a precursor for two-dimensional precipitation of excess arsenic in GaAs grown by molecular-beam epitaxy at low substrate temperature (LT-GaAs), and subsequently annealed. LT-GaAs films delta doped with indium isovalent impurity showed previously to provide two-dimensional As cluster sheets were studied for comparison. Small clusters observed by transmission electron microscopy at the Sb delta layers had an unusual lens shape and, probably, nonrhombohedral microstructure. These clusters induced strong local strains in the surrounding GaAs matrix. After annealing under the same conditions, the clusters at the Sb delta layers were found to be bigger than those at the In delta layers. Additionally, nucleation of the arsenic clusters at the Sb delta layers occurs at a relatively low annealing temperature. The observed precipitation features indicate that delta doping with Sb is more effective for two-dimensional precipitation of the excess As in LT-GaAs as compared with In delta doping.