AlGaN Solar-Blind Avalanche Photodiodes with Enhanced Multiplication Gain Using Back-Illuminated Structure

Schottky Al 0.4 Ga 0.6 N solar-blind avalanche photodiodes with back-illuminated structure have been demonstrated. The fabricated devices with a mesa diameter of 150 µm exhibited dark currents as low as 1 pA at reverse biases below 100 V. Peak external quantum efficiencies of 21 and 46% were obtained at 262 nm and zero bias under the front and back illumination conditions, respectively. Multiplication gain in excess of 4000 has been achieved under back illumination, while the gain is ∼2000 under front illumination. The higher gain obtained under back illumination is ascribed to the hole-initiated avalanche process.