An Overview of the GaN Material System and Devices

Audra Rice
Center for High Technology Materials
University of New Mexico

The achievement of p-type, Mg-doped GaN in 1989 generated much interest in high power and high temperature devices, solar blind and visible blind ultraviolet (UV) detectors, and UV sources such as laser diodes and light emitting diodes (LED+IBk-s). However, magnesium is a deep acceptor in GaN with activation energy of +AH4- 150 +IBM- 200 meV and, at room temperature, only 1 percent of the Mg concentration is electrically active. Additionally, p-type GaN:Mg is compensated, highly resistive, possesses a low mobility and is difficult to fabricate an ohmic contact to. These properties manifest themselves in high series resistance originating from the bulk spreading resistance and the poor ohmic contact resistance. For example, the short lifetime of GaN blue laser diodes, the high threshold voltages of light emitting diodes, and the degraded performance of npn bipolar junction transistors, are thought to be associated with the high series resistance and poor ohmic contacts of p-type GaN:Mg. Sapphire is an important substrate for GaN due to its economic cost. However, the lattice mismatch between the sapphire and GaN epilayer is 14+ACU-, and the GaN epilayer generally possesses 108 +IBM- 1010 cm-2 dislocations. This leads to a microstructure of GaN-on-sapphire resembling that of an ordered polycrystal in which individual grains are of high crystalline quality but are slightly tilted and twisted with respect to one another. An overview of the GaN material system will be presented, and the technological importance of GaN devices, such as, LED+IBk-s, laser diodes, photodetectors, and high power transistors, addressed.

12:30 p.m., Friday, April 7, 2000

Room 184, Physics and Astronomy Building

Northeast Corner of Lomas and Yale, Albuquerque, New Mexico