Performance of thin 4H-SiC UV avalanche photodiodes

The large bandgap of 4H-SiC (3.25 eV) makes it a suitable material for visible-blind UV detection. In the paper, the performance of 4H-SiC avalanche photodiodes (APDs) with a thin avalanche width of 0.1 μm is evaluated. Avalanche photodiodes with thin multiplication regions can greatly improve the signal-to-noise ratio of photoreceiver systems by providing internal gain while maintaining a high operating speed and low operating voltage. The diodes exhibit a peak unity-gain responsivity of 144 mA/W at a wavelength of 265 nm. Photomultiplication measurements carried out on these diodes showed that β>α in 4H-SiC, where β and α are the hole and electron ionisation coefficients, respectively. The 4H-SiC APDs also exhibit very low excess noise corresponding to k=0.1 (where k=α/β for hole multiplication) in the local model when illuminated by 325 nm light. This is much lower than that of commonly used Si APDs with identical thickness and indicates that 4H-SiC is well suited for high gain, low noise UV detection. In view of the large β/α ratio measured in these thin 4H-SiC APDs, multiplication must be initiated by hole injection to ensure a low excess-noise performance.