Blue LEDs, UV photodiodes and high-temperature rectifiers in 6H-SiC

Abstract

Single junction devices in silicon carbide have been developed for use as blue LEDs, UV photodiodes and high- temperature rectifiers. As a light emitter, 6H-SiC junctions can be tailored to emit light across the visible spectrum. The most widely commercialized device is the blue LED. Over the past two years, the quantum efficiency of the Cree blue LED has increased significantly. The devices emit light with a peak wavelength of 470 nm with a spectral halfwidth of ∼70 nm. The optical power output is typically between 12 and 18 μW for a forward current of 20 mA at 3 V. This represents a power efficiency of ∼0.02–0.03%. In addition to blue emission, the energy bandgap of ∼3.0 eV allows for inherently low dark currents and high quantum efficiencies for ultraviolet photodiode detectors made in 6H-SiC, even at high temperatures. These devices typically exhibit a quantum efficiency of 80–100% and peak response of ∼250–280 nm. These characteristics are maintained to at least 623 K. The dark current density at -1.0 V and 473 K is ∼10 -11 A/cm 2. This corresponds to an extrapolated room temperature current density of ∼2 × 10 -17 A/cm 2 at -1.0 V. Rectifiers with blocking voltages as high as ∼1400 V and a forward current rating of 400 mA at ∼3.0 V have been fabricated. For a 710 V rectifier, the reverse bias leakage current density at 200 V is shown to increase from ∼10 -9 to ∼10 -7 A/cm 2 from 300 to 673 K, respectively. The reverse bias breakdown appears to occur via avalanche multiplication processes exhibiting a sharp knee at breakdown. For a ∼1400 V rectifier, the reverse bias leakage current at 1375 V is less than 1 μA at room temperature.