Microstructure and field mapping of AlInN-based heterostructures and devices

The microstructure, composition and electrostatic fields of near-lattice-matched Al_1-xIn_xN/AlN/GaN heterostructures and devices have been characterized using a variety of electron microscopy techniques. A thin parastic Ga-rich layer was often observed immediately above the AlN spacer and was attributed to GaN nucleation during specimen cooling. Mapping of electrostatic potential profiles across a GaN/Al_0.85In_0.15N/AlN/ GaN heterostructure using off-axis electron holography showed polarization-induced fields of 7.5MV/cm within the AlN layer, and 2.2MV/cm within the Ga-rich layer. A two-dimensional electron gas with a density of ~9.8×10¹² cm^-2 was observed in the underlying GaN layer located very close to the AlN/GaN interface. Contact inclusions were observed extending into the AlInN and GaN layers along mixed-type threading dislocations under the source and drain regions of HFET devices. The density and size of the contact inclusions was determined by the annealing temperature.