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

We have determined that the initial photoluminescence decay in $a$-Si: H (at emission energies > 1.5 eV) follows an algebraic form $t^{-\alpha }$, for $50 \mathrm{psec}<t<\mathrm{}3\mathrm{} \mathrm{nsec}$, with $\alpha \mathrm{}\left(T\right)={\alpha }_0+\beta T$. 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 × ${10}^{13}$ ${\sec }^{-1\mathrm{}}$, 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.