My project was based on novel optoelectronic devices using transparent Indium Tin Oxide (ITO) Schottky and Ohmic contacts to n, n+, p and p+ GaAs and InGaAs substrates: photodiodes, VCSELs, TG-HEMTs, HPTs and LEDs.

ITO is a wide bandgap degenerate semiconductor material which is practically transparent and electrically conductive. It has been used for such diverse purposes as heat reflecting mirrors, transparent electromagnetic shield coatings and in photo-voltaic devices. In addition, the thickness of the ITO layer can be easily engineered to act as an anti-reflection coating. I have used it for the fabrication of numerous novel optoelectronic devices with transparent contacts to demonstrate their enhanced performances.

The deposition of ITO on semiconductor substrates by r.f. sputtering, a technique renowned for its excellent uniformity and adhesion properties, has been optimised in our laboratory to produce exceptionally ideal (ITO/n-GaAs) Schottky Diodes as well as n and p type ohmic contacts while retaining the excellent optical and electrical properties of ITO.

I was the lead worker on an EPSRC project for the development of "GaAs based HBTs for High Temperature Applications" (beyond 300°C) on an industrial collaborative project with UK Defense Evaluation Research Agency.

We studied suitable III-V material systems such as AlGaAs/GaAs and InGaP/GaAs employing both single and double heterojunction structures. Rugged novel ohmic contacts using e-beam deposited ZrB2 as a Au diffusion barrier layer was also developed as part of the project. The devices based on various wafer designs, as part of the study, were fabricated and characterized under different temperature/current stress conditions in order to analyze pertinent reliability issues.