Observation of Geometry-Limited Mobility in Porous Silicon

TL;DR

This study demonstrates that charge carrier mobility in highly porous silicon is primarily limited by the material's geometry, exhibiting dispersive behavior and minimal temperature dependence, challenging existing nanostructure models.

Contribution

It provides direct experimental evidence of geometry-limited transport in porous silicon, contrasting with quantum confinement models.

Findings

Mobility in porous silicon is significantly lower than in crystalline silicon.

Transport is dispersive and weakly temperature-dependent.

Transport behavior is directly limited by the porous geometry.

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 compared to homogeneous crystalline silicon. They show two additional signatures of semiclassical transport that are directly limited by a porous geometry: the mobilities are dispersive (i.e. dependent on time), and have very little temperature-dependence. A pure, geometry-limited transport is surprising in the context of nanometer-scale models for electronic states such as quantum percolation or nanocrystal aggregation. In such models, confinement-induced energy shifts and localization are the dominant effects.