Controlled exfoliation of a heavily n-doped porous silicon double layer electrochemically etched for layer-transfer photovoltaics

Abstract

We demonstrate the controlled exfoliation of a heavily n-doped mesoporous Si double layer prepared using two-step electrochemical etching, which can be further utilized in Si-epitaxial growth for layer transfer. The first step of electrochemical etching was to apply a lower anodic current density to form self-organized mesoporous silicon with a small pore diameter (<= 4.5 nm). For the second step, a high anodic current density was applied to create a layer with a higher porosity beneath the first layer, which enables easier detachment from the substrate. Exfoliating the porous double layer was controllable only for heavily n-doped silicon under specific conditions of anodic current density and etching time. The differences in pore morphologies, which depended upon wafer doping levels, were analyzed using two different modes of electrical breakdowns, avalanche and Zener. (C) 2012 Elsevier Ltd. All rights reserved.