Picosecond Photoluminescence: A Probe of Band-Tail Thermalization in Amorphous Semiconductors

Abstract

We have determined that the initial photoluminescence decay in $a$-Si: H (at emission energies > 1.5 eV) follows an algebraic form ${t}^{\ensuremath{-}\ensuremath{\alpha}}$, for $50 \mathrm{psec}<t<3 \mathrm{nsec}$, with $\ensuremath{\alpha}(T)={\ensuremath{\alpha}}_{0}+\ensuremath{\beta}T$. These results are interpreted with a comprehensive model of nonradiative relaxation through electron band-tail thermalization. From our data we find a maximum hopping rate of 3 \ifmmode\times\else\texttimes\fi{} ${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, an effective energy width of 20 meV for single-hop relaxation in the band tail, and that electrons have relaxed 50 meV from the conduction-band edge within 50 psec of excitation.