Improved solar-blind detectivity using an AlxGa1−xN heterojunction p–i–n photodiode

We report the improved detectivity of ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ -based solar-blind $\mathrm{p–i–n}$ photodiodes with high zero-bias external quantum efficiency. The zero-bias external quantum efficiency was ∼42% at 269 nm, and increased to ∼46% at a reverse bias of −5 V. In addition, the photodiodes exhibited a low dark current density of ${\text{8.2×10}}^{\text{−11}}\hspace{0.17em}{\mathrm{A/cm}}^2$ at a reverse bias of −5 V, which resulted in a large differential resistance. The high quantum efficiency and large differential resistance combine to yield a high detectivity of $D^{*}{\text{∼2.0×10}}^{14}\hspace{0.17em}\mathrm{cm} {\mathrm{Hz}}^{\text{1/2}} {\mathrm{W}}^{\text{−1}}.$ These results are attributed to the use of an ${\mathrm{Al}}_{\text{0.6}}{\mathrm{Ga}}_{\text{0.4}}\mathrm{N}$ window n region, which allows improved transmission to the absorption region, and to improved material quality.