Photocarrier drift-mobility measurements and electron localization in nanoporous silicon

Abstract

We report photocarrier time-of-flight measurements in diode structures made of highly porous crystalline silicon. The corresponding electron and hole drift mobilities are very small ð<10 � 4 cm 2 = Vs Þ compared to homogeneous crystalline silicon. The mobilities are dispersive (i.e., having a power-law decay with time or length-scale), but are only weakly temperature-dependent. The dispersion parameter lies in the range 0.55–0.65 for both electrons and holes. We conclude that the drift mobilities are limited by the nanoporous geometry, and not by disorder-induced localized states acting as traps. This conclusion is surprising in the context of luminescence models based on radiative recombination of localized excitons. 2002 Elsevier Science B.V. All rights reserved.