Introduction

III-Nitride wide bandgap semiconductors have been recognized as technologically very important materials. They have recently attracted considerable interest due to their applications in optical devices that are active in the blue/green and ultraviolet (UV) wavelength regions and in electronic devices capable of operation at high temperatures, at high power levels, and in harsh environments. Silicon- and GaAs-based devices operate only in the red and near-infrared spectral regions and cannot tolerate elevated temperatures or chemically hostile environments due to their low bandgap, uncontrolled generation of intrinsic carriers, and low resistance to caustic chemicals. Bright blue light-emitting diodes (LEDs) based on III-nitrides paved the way for full-color displays as well as for the mixing of the three primary colors to obtain white light for illumination by semiconductor LEDs. If used in place of incandescent light bulbs, these LEDs would provide compactness and longer lifetimes (> 10,000 hours for LEDs compared with 2000 hours for incandescent light bulbs) while consuming only 15-20% of the power for the same luminous flux, resulting in significant energy savings. Short-wavelength laser diodes (LDs) based on III-nitrides are essential for high-density optical storage applications because the diffraction-limited optical storage density increases quadratically as the probe laser wavelength is reduced. Due to their large dielectric strengths, GaN-based devices can operate at much higher voltages for any dimensional configuration. Furthermore, they are virtually immune from environmental attack.