Dr David Wallis

The subject of my PhD was the study of the atomic structure in amorphous oxides and nitrides of silicon using electron microscopy and X-ray diffraction techniques. Following completion of my PhD in 1994 I spent 2 years working as a post doctoral researcher at Oak Ridge National Laboratory in the USA. During this time I developed electron microscopy techniques such as high angle angular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS) to enable the study of materials at the atomic level. I used these techniques to solve the atomic structure at several oxide grain boundaries for the first time.

I joined the company QinetiQ (formerly the Defence Evaluation and Research Agency (DERA) and Royal Signals and Radar Establishment (RSRE)) in 1996. In my initial role in the material characterisation group, I performed electron microscopy and X-ray diffraction studies of a wide variety of materials including, carbon nanotubes, carbon fibres, oxides, semiconductors, structural materials, nano-materials and electronic devices. I became technical lead for the materials activities for QinetiQ’s GaN and InSb transistor projects in 2006. These projects successfully developed high power GaN transistors on SiC substrates, high brightness GaN LEDs on large area (150mm) Si substrates and InSb based devices suitability for high speed low power logic applications. The focus of this work was to solve the key materials challenges such as high defect densities and control of strain to allow commercial exploitation of these technologies. During my work at QinetiQ I also developed new wafer characterisation techniques and worked with third party companies on their commercial development.

I came to work in the Cambridge Centre for GaN in May 2011 to continue the development of GaN based optoelectronic devices on large area Si substrates.