Small-area GaN detector produces large gain

Researchers at the United States Military Academy (West Point, NY) and the University of Texas at Austin (Austin, TX) have fabricated a gallium nitride (GaN) photodetector that has avalanche gain. Because avalanche photodiodes have low noise, they provide an attractive alternative to higher-noise metal-semiconductor-metal GaN detectors.

The device is constructed on sapphire and contains five epitaxial layers. Avalanche gain is achieved when the gain region is subjected to a high electrical field. When driven by a high electrical field, GaN can experience the creation of microplasmas at defect locations; because GaN has a large number of defects, the resulting microplasmas can induce breakdown at a voltage below that needed to reach high gain. To solve this problem, the researchers reduced the detector diameter to 25 mm, producing gain areas with relatively defect-free regions. Such detectors can be driven by an electric field of up to 3 MV/cm and reach a gain of 25 for a 363-nm wavelength without forming microplasmas. Contact John Carrano at [email protected].--Paula Noaker