Physics of GaN devices (Keynote Address)

We review the physics of GaN-based devices including pyroelectric and piezoelectric sensors, GaN-based Heterostructure Field Effect Transistors (HFETs); SAW and acousto-optics devices; UV Light Emitting Diodes, and THz plasma wave electronics devices using GaN HFETs, paying special attention to polarization effects. We also discuss oscillating electron and hole islands in semiconductor GaN or AlGaN grains embedded into a pyroelectric matrix with a larger spontaneous polarization.