Improved GaAs metal–semiconductor–metal photodetector performance for epitaxial liftoff applications

Abstract

Deposition of thin film single crystal compound semiconductor devices onto host substrates such as silicon using epitaxial lift off (ELO) may enable low cost optical communication subassemblies. In order for ELO technology to be viable for communication systems, the detector performance must approach that of their on-wafer counterparts. The MSM detectors reported herein were designed to make use of the fact that both the front and back surfaces of the absorbing layer are accessible via use of a polyimide transfer diaphragm. To passivate the back surface of the MSM, a thin layer of titanium was evaporated and mesas were defined. The Ti/GaAs layer was then lifted off and placed on the transfer diaphragm. The device was inverted, Ti side down, onto the Si3N4/Si host, and the interdigitated finger contacts and pads were defined. We have seen an order of magnitude improvement in the dark current and modest improvement of the dc responsivity.