Barrier-limited transport in μc-Si and μc-Si,C thin films prepared by remote plasma-enhanced chemical-vapor deposition

Abstract

Systematic variations of room-temperature dark conductivities and dark conductivity activation energies for n- and p-type μc-Si and μc-Si,C thin films with optical band gaps between 1.9 and 2.2 eV and deposited by remote plasma-enhanced chemical-vapor deposition are interpreted in terms of a band alignment model. This leads to an observation that the maximum attainable dark conductivities of these microcrystalline thin films are limited by either thermally assisted transport through, or over interfacial potential barriers between Si crystallites, c-Si, and the encapsulating amorphous materials: a-Si:H and a-Si,C:H, respectively. As the doping is increased in n- or p-type μc-Si, there is a transition from thermal emission limited to thermally assisted tunneling transport. For all levels of doping so-far achieved in the μc-Si,C alloys, the transport is determined by thermionic emission over interfacial barriers at the c-Si/a-Si, C:H interface.