High-Temperature Rectifiers, UV Photodiodes, and Blue LEDs in 6H-SiC
Single junction devices in silicon carbide have been developed for use as high temperature rectifiers, UV photodiodes and blue LEDs. Rectifiers with blocking voltages from 15–1400 V and a forward current rating of 400 mA at ~3.0 V have been fabricated, packaged for 350°C operation and tested. The reverse bias breakdown appears to occur via avalanche multiplication processes exhibiting a sharp knee at breakdown. For a 710 V rectifier, the reverse bias leakage current density at 650 V is shown to increase from ~10−5 to ~10−4 A/cm2 from 300 to 673K, respectively.
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. Preliminary devices exhibit quantum efficiencies as high as ~100% with a tunable peak response from ~250–280 nm. The wavelength cut-off is at ~420 nm corresponding to the bandgap energy. The dark current density at -1.0 V and 473K is ~10−11 A/cm2. This corresponds to an extrapolated room temperature current density of ~2×l0−17 A/cm2 at -1.0 V.
As a light emitter, 6H-SiC junctions can be tailored to emit light across the visible spectrum. Currently, only blue LEDs are commercially available in this material. Over the past year, the quantum efficiency of the Cree blue LED has been 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 17 µW at a forward current of 20 mA and 3 V. This represents a power efficiency of ~0.020–0.028%, the highest for any commercially available blue LED in the world today.
KeywordsReverse Bias Ideality Factor Forward Bias Deep Level Transient Spectrometry Blue Lead
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