BLUE LEDS, UV PHOTODIODES AND HIGH-TEMPERATURE RECTIFIERS IN 6H-SIC

Single junction devices in silicon carbide have been developed for use as blue LEDs, UV photodiodes and high-temperature rectifiers. As a li ght emitter, 6H-SiC junctions can be tailored to emit light across the visible spectrum. The most widely commercialized device is the blue L ED. Over the past two years, the quantum efficiency of the Cree blue L ED has increased significantly. The devices emit light with a peak wav elength of 470 nm with a spectral halfwidth of approximately 70 nm. Th e optical power output is typically between 12 and 18 muW for a forwar d current of 20 m A at 3V. This represents a power efficiency of appro ximately 0.02-0.03%. In addition to blue emission, the energy bandgap of approximately 3.0 eV allows for inherently low dark currents and hi gh quantum efficiencies for ultraviolet photodiode detectors made in 6 H-SiC, even at high temperatures. These devices typically exhibit a qu antum efficiency of 80-100% and peak response of approximately 250-280 nm. These characteristics are maintained to at least 623 K. The dark current density at -1.0 V and 473 K is approximately 10(-11) A/cm2 . T his corresponds to an extrapolated room temperature current density of approximately 2 x 10(-17) A/cm2 at -1.0 V. Rectifiers with blocking v oltages as high as approximately 1400 V and a forward current rating o f 400 mA at approximately 3.0 V have been fabricated. For a 710 V rect ifier, the reverse bias leakage current density at 200 V is shown to i ncrease from approximately 10(-9) to approximately 10(-7) A/cm2 from 3 00 to 673 K, respectively. The reverse bias breakdown appears to occur via avalanche multiplication processes exhibiting a sharp knee at bre akdown. For a approximately 1400 V rectifier, the reverse bias leakage current at 1375 V is less than 1 muA at room temperature.