Epitaxial Lift-Off for large area thin film III/V devices

Abstract

The present work describes the study and improvement of the Epitaxial Lift-Off (ELO) technique, which is used to separate III/V device structures from their GaAs substrates. As a result the ELO method, initially able to separate millimetre sized GaAs layers with a lateral etch rate of about 0.3 mm/h, has been developed to a process capable to free entire 2 '' epitaxial structures from their substrates with etch rates up to 30 mm/h. It is shown that with the right deposition and ELO strategy, the thin-film III/V structures can be adequately processed on both sides. In this way semi-transparent, bifacial solar cells on glass were produced with a total area efficiency in excess of 20% upon front side illumination and more than 15% upon back side illumination. The cell characteristics indicate that, once the thin film processing has been optimized, ELO cells require a significantly thinner base layer than regular III/V cells on a GaAs substrate and at the same time have the potential to reach a higher efficiency. (c) 2005 WILEY-VCH Verlag GmbH T Co.