ABSTRACT
In recent years, improved crystal growth techniques have allowed several leading groups to reduce the high background electron concentration, persistent in the GaN grown in the seventies. These reduced electron concentrations are accompanied by enhanced carrier mobilities. Amano et al. [9] demonstrated a reduction of room-temperature optical emission thresholds in AlGaN/GaN double heterostructure to about one-twelfth of that measured in simple GaN homojunctions. This research led to the construction of first carrier injection laser working under pulsed excitation. Details of the structure of GaN films grown by electron cyclotron resonance-molecular beam epitaxy have been investigated by X-ray diffraction, using the Eulerian four-circle diffraction geometry by Lei and coworkers who made the very important observation that wurtzite and zinc blende polymorphs coexist in films. Control of electrical and optical properties of a given material plays a key role in any device application. Important factors include structural quality of the grown material, doping level, the presence of intrinsic point and extended defects.
