I. Introduction
Progress in the development of gallium nimde (GaN) high electron mobility transistors (HEMTs) puts them in the position of one of the leading technologies ready to satisfy unceasing demand for high frequency and power applications because of their excellent electronic properties, especially high electron saturation velocity and high critical electric field [1 – 4] . However, there are still a lot of areas to be investigated in order to extract and utilize the favorable GaN material properties. Among them the most important is to develop new GaN specific processes, structure design, characterization, and simulation techniques.