INTRODUCTION Wide-bandgap materials, such as III-N-based semiconductors, have attracted much attention for applications in high-power and high-temperature electronic devices because of their superior physical properties. 1–3 Conventional p-i-n rectifiers and Schottky-barrier diodes are the primary devices for demonstrating the high-power handling capability of semiconductor materials. The GaN p-i-n and Schottky-barrier rectifier de- vices are often grown on insulating sapphire sub- strates, so the device contacts are made from the top of the wafer; thus, etching of the device structure is indispensable. Therefore, excess leakage current in- duced by etching damage is unavoidable and should be reduced. In contrast to our previous study, 4 we use an n-i-p structure to study the effect of mesa etching by reactive-ion etching (RIE), inductively coupled plasma (ICP) etching, and photoelectro- chemical (PEC) etching on the device characteris- tics. A possible AlGaN/GaN heterostructure has been studied to exploit the wider bandgap of AlGaN. 5 We have studied the effect of varying the Al-alloy composition on the AlGaN-rectifier charac- teristics by fabricating multiple Al x Ga 1-x N p-i-n with 0  0.45. Because SiC is more closely lat- tice matched to GaN compared with sapphire and will produce fewer dislocations in the GaN film, it is believed that this could greatly reduce the leakage current. 6 The GaN p-i-n and Schottky rectifiers have been grown on both sapphire and 6H-SiC substrates with the same device structure; their respective de- vice performance is compared. Also, the results of our studies of the use of Mg ion implantation for p- guard rings as planar-edge terminations in mesa- geometry GaN Schottky rectifiers are presented. EXPERIMENTAL The epitaxial device structures for this study were grown in an EMCORE D125 University of Texas Mod- ified (UTM) metal-organic chemical vapor deposition system at a pressure of 100 torr and temperatures in the range 1030°C  T g  1100°C. Hydrogen was the main process gas and the carrier gas for the metal alkyl sources. Ammonia was used as the N source and Journal of ELECTRONIC MATERIALS, Vol. 31, No. 5, 2002 Special Issue Paper GaN and AlGaN High-Voltage Rectifiers Grown by Metal-Organic Chemical-Vapor Deposition TING GANG ZHU, UTTIYA CHOWDHURY, MICHAEL M.WONG, JONATHAN C. DENYSZYN, and RUSSELL D. DUPUIS Microelectronics Research Center, The University of Texas at Austin, Austin, TX 78758 In this paper, we report the study of the electrical characteristics of GaN and AlGaN vertical p-i-n junctions and Schottky rectifiers grown on both sapphire and SiC substrates by metal-organic chemical-vapor deposition. For GaN p-i-n rectifiers grown on SiC with a relatively thin “i” region of 2 m, a breakdown voltage over 400 V, and forward voltage as low as 4.5 V at 100 A/cm 2 are exhib- ited for a 60-m-diameter device. A GaN Schottky diode with a 2-m-thick un- doped layer exhibits a blocking voltage in excess of 230 V at a reverse-leak- age current density below 1 mA/cm 2 , and a forward-voltage drop of 3.5 V at a current density of 100 A/cm 2 . It has been found that with the same device structure and process approach, the leakage current of a device grown on a SiC substrate is much lower than a device grown on a sapphire substrate. The use of Mg ion implantation for p-guard rings as planar-edge terminations in mesa- geometry GaN Schottky rectifiers has also been studied. Key words: GaN,AlGaN, p-i-n rectifier, Schottky-barrier rectifier, metal-or- ganic chemical-vapor deposition, p-n junction, ideality factor, Schottky-barrier height, ion implantation (Received September 15, 2001; accepted December 9, 2001) 406