Radiative recombination in a-Si 1− xC x:H films

Abstract

Compositional dependence of photoluminescence spectra and its decay, spectra of exitation, as well the temperature quenching of intensity are investigated on a-Si 1− x C x :H films grown by glow discharge technique. In the entire range of compositions, the photoluminescence consists of a single nearly symmetrical band, peak energy and halfwidth of which increase with increasing C content from 1.4 and 0.30 eV, respectively, at x = 0 up to 2.3 and 0.7 eV at x ≅ 0.4. Above x = 0.5, both the peak energy and halfwidth depend on growth conditions more than on x. For x ≅ 0.4, a sharp decrease of temperature and electric field quenching of intensity as well the sharp increase in decay rate occur. These data indicate a change from tunnel to exiton-like recombination. The observation and analysis of an anti-Stokes emission at ‘tail-to-tail’ exitation together with the above data prompt us to propose a new model for radiative recombination in these films. The model proposed relates the correlation with existence of nanograins in the system which have light-emitting sp 2 states. The grains are separated, one from other, by potential barriers at boundaries of phases with wide bands gaps.