Low-temperature steady-state photoconductivity in amorphous selenium films

Steady-state photocurrents are measured in amorphous selenium (a-Se) films as function of illumination intensity for temperatures between 210 K and 297 K. The Lux-Ampère characteristic, I_ph ∝ G^y, shows a maximum exponent of 1.08 ± 0.06 around 250 K while lower values are measured at room temperature and 210 K. The photocurrent overshoots its steady-state value upon initial turn-on of a high light intensity by an amount that has a minimum in the 250 K region. Both phenomena indicate the presence of a deep electron trap near the a-Se equilibrium Fermi level.