Detection of low-level ultraviolet (UV) light has been the focus of numerous research and development efforts in recent
years. To date, the most promising solid-state solution is SiC avalanche photodiodes. We report 4H-SiC avalanche
photodiodes with low dark current and high gain. Geiger mode operation with high single photon detection efficiency
and low dark count probability has been achieved. The dark current behavior of a 4x4 array of SiC APDs is also
Sensitive ultraviolet photodetectors are essential components for a growing number of civilian and military applications.
In this paper, we report 4H Silicon Carbide (SiC) avalanche photodiodes (APDs) with a p-i-n structure. These APDs,
range in diameter from 180 μm to 250μm, exhibit very low dark current (10s of pA at avalanche gain of 1000) and high
gain in linear-mode operation. An external quantum efficiency of 48% at 280 nm is achieved at unity gain with a
recessed-window structure. The differential resistance of a 250 μm recessed-window device at zero bias is estimated to
be 6×10<sup>14</sup> ohms. As a result of high external quantum efficiency, large area, and large differential resistance, a record
high specific detectivity of 4.1×10<sup>14</sup> cmHz <sup>1/2</sup> W<sup>-1</sup>, has been achieved. Single ultraviolet photon detection in Geiger-mode
operation with gated quenching is also described. In this paper, we report single photon detection efficiency (SPDE) of
30% at 280 nm with a dark count probability (DCP) of 8×10<sup>-4</sup>.