Surface preparation procedures for contacting GaN
The structure of a typical metal / GaN device contact differs significantly from the idealised concept of an epitaxial layer of a metal on top of an atomically flat, clean semiconductor surface. Practical issues such as device performance, lifetime and reproducibility are strongly related to the source GaN material quality, the sequence of metal selected to make the contact and the annealing procedure used to activate the contact. Improved understanding of the dynamic evolution of the contact microstructure is needed in order to maintain control over the integrity of the metal / semiconductor interface. In this study, attention is focused on the surface processing procedures used to prepare the GaN prior to metallisation and the variation of parameters such as GaN surface roughness and remnant surface oxide, in particular. A reproducible method of controlling the GaN surface prior to metallisation is needed for both commercial device structures and improved scientific understanding.