6H-Silicon Carbide Light Emitting Diodes and UV Photodiodes

Abstract

Silicon carbide has been used to fabricate a variety of short wavelength optoelectronic devices including blue LEDs, green LEDs and UV photodiodes. 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 years, the quantum efficiency of the Cree Research 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 25 and 35 μW at a forward current of 20 mA and 3.2 V. This represents an external quantum efficiency of ≈︂0.05 to 0.07%. Green LEDs have been demonstrated which emit with a peak wavelength of 530 nm. As opposed to the epitaxial junction used in the blue LED, the green devices use ion implanted junctions. The typical output power is similar to that of the blue LED. However, with respect to photometric units, the die luminous intensity is a factor of two higher than the blue LED, 1.2 mcd (millicandela) for a radiant flux output of 33 μW. In addition to short wavelength light 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 to 100% and peak response of ≈︂250 to 280 nm. These characteristics are maintained to at least 350 °C. The dark current density at —1.0 V and 473 K is ≈︂10—11 A/cm2. This corresponds to an extrapolated room temperature current density of ≈︂2 × 10—17 A/cm2 at —1.0 V.