Existence of a universal low-energy tail in the photoluminescence of a-Si1−xGex:H alloys

Abstract

Time-resolved and cw photoluminescence (PL) measurements in a-${\mathrm{Si}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Ge}}_{\mathrm{x}}$:H alloys have been performed for 0≤x≤0.52. For x≲0.4 the samples exhibit a universal tail on the low-energy side of the PL spectra. The PL efficiency in this tail region is remarkably independent of Ge content. The only apparent effect of the Ge is to shift the peak of the cw PL spectrum to lower energy with increasing Ge content in a fashion which parallels the narrowing of the optical gap. The decay of the PL after pulsed excitation becomes more rapid as the Ge content is increased.