Exactly exponential-band-tall in a glassy semiconductor.

Transient photocurrent measurements in glassy As(2)Se(3) reveal an accurate power law spanning more than eight decades of time. In the Multiple-Trapping model this requires a density of valence- band-tall states which varies exponentially with energy over almost five decades. The accuracy of this exponential, and its extension to states very deep in the gap, appears to be inconsistent with existing models of band talls, but may suggest long-ranged potential fluctuations. The results demonstrate a remarkable degree of perfection in the electronic structure of this ostensibly random material.