SiC Avalanche Photodiodes - Crystal Orientation and Spatial Uniformity

We are investigating 4H-SiC avalanche photodiodes for use as solar-blind, single-photon UV detectors, which could enable low cost, size, weight, and power devices that are reliable and robust, suitable for many sensing applications. One concern for these devices is the spatially-nonuniform gain which limits the useful device area and impedes the scaling necessary to compete with leading UV sensor architectures. We examined various potential sources of the nonuniformity, and conclude that the typically observed phenomenon is likely caused by impact ionization anisotropy and the 4° wafer offcut angle needed to maintain a consistent polytype during epitaxial growth. Additionally, we present both linear and Geiger-mode spatial maps on the same devices to explain the observed differences in each.