Defect states in strain-relaxed Si0.7Ge0.3 layers grown at low temperature

Two shallow hole traps dominate the deep level transient spectroscopy (DLTS) data for strain-relaxed Si0.7Ge0.3 layers grown on Si(100) by ultrahigh vacuum chemical vapor deposition at temperatures ⩽560 °C. The trap energy levels are at Ev+0.06 and Ev+0.14 eV and trap concentrations are ⩽5×1014 cm−3 in relaxed layers having threading dislocation densities of 2–4×107 cm−2. A logarithmic dependence of the filling rate indicates that these traps are associated with extended defects and this is confirmed by their absence in a sample having no dislocations. The annealing temperature of the DLTS peaks is consistent with the interpretation of these traps as states of defect complexes at dislocations, rather than intrinsic dislocation states or isolated defect complexes. The trap concentrations are proportional to the oxygen concentration in the film, suggesting that oxygen may be a constituent of the defect complex.

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