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A large-area, 250 [micro]M-diameter, 4H-SiC avalanche photodiodes with low dark current and high gain is described. The differential resistance of the recessed-window device at zero bias is estimated and a record high specific detectivity is achieved due to high external quantum efficiency, large area, and large differential resistance.

Spatial nonuniformity of responsivity of 4H-SiC avalanche photodiodes at high gain is reported that results from variation in the doping density. Two-dimensional raster scans show a steady decline laterally across the device.

Temperature-dependent current-voltage (I-V) measurements are used to determine the reverse dark current mechanisms in 4H-SiC avalanche photodiodes (APDs). A pn junction vertical mesa structure, passivated with SiO2 grown by plasma enhanced chemical vapor deposition, exhibits predominate leakage current along the mesa sidewall.

Addition of silicon barrier enhancement layers to a-Si:H/a-SiC:H double barrier structure results in a negative differential resistance current/voltage curve having a high peak-to-valley ratio. The addition is done in the collecting and injecting diode regions. The enhancement layers reduce leakage current and increase resonant tunneling current, and are more effective than crystalline AlGaAs/GaAs double barrier diodes. A primary model simulating these data account for the validity of enhancement layers.