Microstructure and Polarization Properties of III-Nitride Semiconductors
Much research in the past five decades has been done on the group III nitrides comprising the Al-Ga-In-N alloys, which have a characteristic wide bandgap necessary for many applications, such as short-wavelength visible-light emission. The atomic arrangement of these materials is tetrahedrally coordinated, in a similar fashion as in other semiconductor materials such as silicon, GaAs, and ZnO. This is due to the s and p orbitals in the outer electron shells that combine and produce four sp3 hybrid orbitals. The III-nitride semiconductors, with the hexagonal wurtzite crystal structure, have a tendency to grow along the direction, and in the simplest configuration, the substrates should accommodate the hexagonal symmetry of the basal planes. The lattice of silicon carbide is very similar to AlN and GaN. It is tetrahedrally coordinated, with each basal plane arranged in the same fashion. The lattice image shows a sharp transition between the aluminum oxide lattice of sapphire to an aluminum nitride lattice.