Improved solar-blind external quantum efficiency of back-illuminated Al x Ga 1− x N heterojunction pin photodiodes

Improved external quantum efficiency for AlxGa1−xN solar-blind pin photodiodes is reported. The zero-bias external quantum efficiency was 53% (Rλ=0.12 A/W) at 275 nm, and increased to 58% (Rλ=0.13 A/W) at a reverse bias of 5 V. In addition, the photodiodes exhibited a low dark current density of 8.2×10−11 A/cm2 at a reverse bias of 5 V, which resulted in a large differential resistance. The high zero-bias responsivity and large differential resistance combine to yield a high detectivity of D*∼3.0×1014 cmċHz1/2ċW−1. These results are attributed to an improved Al0.6Ga0.4N window n-region.