Growth of single-crystal metastable semiconducting (GaSb)1−xGex films

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Abstract
Epitaxial metastable (GaSb)1−xGex alloys with compostions across the pseudobinary phase diagram have been grown on (100) GaAs substrates by multitarget rf sputtering. An essential feature allowing the growth of these metastable materials was low‐energy ion bombardment of the growing film during deposition to enhance surface diffusion, promote mixing, and preferentially sputter incipient second‐phase precipitates. Annealing experiments indicated that the metastable films exhibit good high‐temperature stability and that they transform through a continuous series of GaSb‐rich and Ge‐rich phases in which the solute concentrations decrease until the equilibrium two‐phase alloy is obtained. While the calculated free‐energy difference between the single‐phase metastable and equilibrium states is ∼18 meV, the measured activation barrier for the transformation is ∼3 eV. All films were p‐type with room‐temperature hole concentrations varying from 1016 to 1019 cm−3 and mobilities between 10 and 720 cm2/ V s, depending on film composition.