The addition of GaN, A1N, InN, and related alloys to the family of device-quality semiconductors has opened up new opportunities in short-wavelength (visible and ultraviolet [uv]) photonic devices for display and data-storage applications, solar-blind uv detectors, and high-temperature/high-power electronics. Silicon will of course continue to dominate in microelectronics applications, and InP and GaAs and their related alloys will be the mainstays of long-wavelength lightwave communication systems and red, orange, and yellow light-emitting-diode (LED) technology, respectively. There are however many existing and emerging uses for wide-bandgap semiconductors with good electrical and optical characteristics. The purpose of this issue of MRS Bulletin is to furnish a background and summary on the exciting new developments involving GaN and related materials.
Strong efforts on the synthesis and device aspects of GaN took place in the 1960s and 1970s because of the potential for realization of blue lasers and LEDs that would extend the existing wavelength range of photonic devices. Progress was hampered because of several severe materials problems. First there was no bulk crystal growth technology for producing substrates, and epitaxial material was grown on highly lattice-mismatched substrates such as sapphire. This heteroepitaxial material was invariably highly conducting because of residual shallow donor defects or impurities. These high n-type backgrounds, combined with the relatively deep ionization levels of all of the common p-type dopant impurities, prevented the achievement of p-type doping and therefore of bipolar or injection devices.