Limitations in MBE-grown GaN and AlGaN/GaN due to dislocations and lateralinhomogeneities

We have studied inhomogeneities in AlGaNiGaN heterostructures due to disloc ations and limitations in the growth process. The electron occupancy in acc eptor-like states along dislocations in wurtzite GaN were modelled. The red uction in free electron concentration and mobility was calculated as a func tion doping concentration, dislocation concentration and compensation. We a lso studied the mobility and PL-signal in heterostructures. Since the MBE g rowth takes place on insulating substrates, in a charged nitrogen plasma, e ffects due to substrate size may be expected. We report Hall effect measure ments on Al0.2Ga0.8N/GaN HFET structure grown on 2 " sapphire and 1/4 and 1 /8 pieces. The mobility was a factor of 2, larger on 2 " substrates compare d to the pieces. Also photoluminescence variation that depend on substrate size and shape were presented. (C) 2001 published by Elsevier Science B.V.