Low-temperature-grown MBE GaAs for terahertz photomixers

We discuss and experimentally demonstrate several approaches for output power enhancement of metal-semiconductor-metal (MSM) structures of photomixers fabricated using molecular-beam epitaxial (MBE) GaAs grown at low substrate temperature. We focus on the parameters, following from the theory describing output power from a photomixer device. While low carrier lifetime and high photoconductivity was achieved by optimised LT GaAs growth conditions, substantial breakdown voltage increase was attained by improving MSM geometry, by metallic contacts recessing, as well as transferring the thin LT GaAs layer on top of high bandgap and high thermal conductivity substrates. Our results indicate a responsivity enhancement of up, to 40% as compared to the photodetectors with standard surface contacts.