Growth and Characterization of High-Performance GaN and Al x Ga 1-x N Ultraviolet Avalanche Photodiodes Grown on GaN Substrates Russell D. Dupuis 1,2 , Dongwon Yoo 1,2 , Jae-Hyun Ryou 1 , Yun Zhang 1 , Shyh-Chinag Shen 1 , Jae Limb 1 , Paul D. Yoder 3 , A. Drew Hanser 4 , Edward Preble 4 , and Keith Evans 4 1 School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Dr. NW, Atlanta, GA, 30332-0250 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0245 3 School of Electrical and Computer Engineering, Georgia Institute of Technology, Savannah, 210 Technology Circle, Savannah, GA, 31407 4 Kyma Technologies, 8829 Midway West Road, Raleigh, NC, 27617 ABSTRACT Wide-bandgap III-nitride-based avalanche photodiodes (APDs) are important for photodetectors operating in UV spectral region. For the growth of GaN-based heteroepitaxial layers on lattice-mismatched substrates such as sapphire and SiC, a high density of defects is introduced, thereby causing device failure by premature microplasma breakdown before the electric field reaches the level of the bulk avalanche breakdown field, which has hampered the development of III-nitride based APDs. In this study, we investigate the growth and characterization of GaN and AlGaN-based APDs on free-standing bulk GaN substrates. Epitaxial layers of GaN and Al x Ga 1-x N p-i-n ultraviolet avalanche photodiodes were grown by metalorganic chemical vapor deposition (MOCVD). Improved crystalline and structural quality of epitaxial layers was achieved by employing optimum growth parameters on low-dislocation- density bulk substrates in order to minimize the defect density in epitaxially grown materials. GaN and AlGaN APDs were fabricated into 30 m- and 50 m-diameter circular mesas and the electrical and optoelectronic characteristics were measured. APD epitaxial structure and device design, material growth optimization, material characterizations, device fabrication, and device performance characteristics are reported. INTRODUCTION The detection of UV radiation is important to a number of broad areas, including scientific research, environmental monitoring, space research, military systems, and commercial and medical applications [1,2]. For the detection of UV spectrum, UV-enhanced Si photodetectors (typically Si-based photodiodes with special anti-reflection coatings and filters designed for UV wavelengths) and photomultiplier tube (PMT) with specially fabricated UV filters are currently used. PMTs offer high-sensitivity UV detection with a photocurrent gain as high as 10 6 . The PMTs, however, generally require a high-voltage power supply (>1 kV) as well as a cooled photocathode and hence PMT systems are relatively large, expensive, bulky, and fragile. Also, costly filters must be used to attenuate unwanted long wavelength signal. Ultraviolet-enhanced Si photodetectors typically have higher dark currents at 300 K and require expensive or complex filters for solar-blind operation. Also, Si photodiodes may have a reliability problem due to a degradation of the SiO 2 /Si interface after prolonged UV radiation. Mater. Res. Soc. Symp. Proc. Vol. 1040 © 2008 Materials Research Society 1040-Q03-03