✍ Scribed by KC Cadien; AH Eltoukhy; JE Greene
No coin nor oath required. For personal study only.
Epitaxial metastable (GaSb) , _ xGex alloys with compositions across the pseudobinary phase diagram have been grown on (700) GaAs substrates by multitarget rf sputtering.
The maximum growth temperature T, ranged from 490 to 520°C depending on the alloy composition.
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, A phase map plotted as a function of T, showed a very narrow transition region between metastable single phase alloys and equilibrium two phase structures. 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 Mel/ atom-', the measured activation barrier for the transformation is -3 eV. All films were P-type with room temperature hole concentrations varying from 10' 6 to 7 0' s cm-3 and mobilities between 10 and 720 cm21V-s, depending on film composition.
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