Totally Solar-Blind UV Detectors from GaN and A1N Alloys

Gallium Nitride has been known for many years to have excellent physical and electronic properties which are well suited to the production of electronic devices that can emit radiation in the blue-to-green region of the spectrum, detect UV radiation, and operate at significantly higher temperatures than devices produced from GaAs or Si. The larger bandgap of GaN offers several performance advantages in the realization of UV detectors. Devices can operate at high temperature, dark currents are many orders of magnitude smaller, and response can be solar-blind. UV detectors have already been fabricated at Cree research in the 6H polytype of SiC for the USAF. These devices exhibit a 96% quantum efficiency with a peak responsivity at 270 nm. The pn junction leakage currents were found to be 10(super4) - 10(super5) times smaller, with sensitivities up to 10(super4) times greater than for common Si based UV photodetectors. However, these devices required the use of an external filter for solar blind operation. We propose expanding on this work by fabricating UV photodetectors in GaN and AlGaN alloys. The wider bandgap energies available with these materials will move the detector response to shorter wavelengths, permitting solar blind operation without the use of external filters. In Phase I , the use of existing GaN and AlGaN epitaxial growth, fabrication and testing technology available at Cree, will permit rapid fabrication and evaluation of the performance advantages offered by these materials.