High Quantum Efficiency at Low Bias AlxGa1-xN p-i-n Photodiodes

There has been a growing interest in back-illuminated solar-blind AlxGa1—xN photodiodes for flip-chip mounting to silicon read-out circuits. These devices not only need to have high external quantum efficiencies, but these efficiencies must be achieved at, or less than, the operating voltage of the readout display. We report the growth, fabrication, characterization, and comparison of two AlxGa1—xN heteroepitaxial back-illuminated p–i–n photodiodes. The first device is visible-blind with an Al0.20Ga0.80N active region and shows an external quantum efficiency of 53% at zero bias and 64% at 5 V at a wavelength of λ = 290 nm. The second device is solar-blind and has an Al0.35Ga0.65N active region with 0 V and 5 V external quantum efficiencies of 26% and 32% at 279 nm, respectively. Detectivities of D* = 8.40 × 1012 cm Hz1/2 W—1 and D* = 5.30 × 1012 cm Hz1/2 W—1 were demonstrated for the Al0.20Ga0.80N and Al0.35Ga0.65N devices, respectively.