Transport and recombination properties of amorphous arsenic telluride

Abstract

Considerable information about transport and recombination properties of amorphous ${\mathrm{As}}_{2}$${\mathrm{Te}}_{3}$ has been obtained from studies of steady-state and transient photoconductivity, dark conductivity, and thermopower in the temperature range from 200 to 350\ifmmode^\circ\else\textdegree\fi{}K: (i) The conductivity is dominated by holes both in the dark and under illumination. The holes move in states 0.28 \ifmmode\pm\else\textpm\fi{} 0.02 eV below the Fermi level; the mobility is activated, with $\ensuremath{\mu}\ensuremath{\simeq}10 \mathrm{exp}(\frac{\ensuremath{-}0.16}{\mathrm{kT}}) \frac{{\mathrm{cm}}^{2}}{Vsec}$. The room-temperature concentration of holes is about ${10}^{16}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. (ii) The dependence of the lifetime on light intensity and temperature strongly suggests a direct recombination mechanism between electrons and holes. The temperature independence of the recombination constant ($b={10}^{\ensuremath{-}10}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$) implies that the process is not diffusion limited. (iii) Lack of dependence of the photoconductivity on wavelength for larger than band gap excitation shows that the recombination takes place by bulk rather than by surface processes.