High Speed GaN Schottky Diodes

Power electronic devices based on gallium nitride (GaN) have a wide range of advantageous properties. However, to date, GaN-based electronics have been limited by substrate quality, size and cost. The two substrates that are used most widely are sapphireand silicon carbide (SiC). Sapphire is available in large diameters but has a large thermal coefficient of expansion (TCE) and lattice mis-match to GaN and a low thermal conductivity. This results in high defect levels and reduced device and circuitperformance. SiC substrates have high thermal conductivity, but are extremely expensive and available only in small diameters. Also SiC is not lattice or TCE matched to GaN (the mis-matches are smaller than to sapphire however). This proposal describesa novel approach to eliminate these defects, and make highly conductive GaN wafers of large diameter at commercially acceptable cost that are TCE matched to the device layers and provide high thermal conductivity. These substrates will be used for thedevelopment and commercialization of GaN-based Schottky diodes. A key application is to replace silicon PIN diodes; in this case GaN Schottky diodes will match the breakdown voltages but provide much higher switching speeds and lower losses. Thisdevelopment will result is a process to make high power GaN Schottky diodes on large area substrates with improved characteristics at a low cost, permitting widespread use of these devices in both Government and commercial applications.