Low-noise photodetectors based on heterojunctions of AlGaN–GaN

We describe detailed current–voltage and noise measurements carried out on AlGaN–GaN heterojunction photodetectors. Dark current densities below ${\text{1×10}}^{\text{−10}} {\mathrm{A/cm}}^{\mathrm{2}}$ are measured at a bias level of −5 V, at room temperature. In diodes with a diameter of 50 μm, low leakage currents result in the zero-bias noise spectral density as low as ${\text{3.6×10}}^{\text{−32}} {\mathrm{A}}^{\mathrm{2}}\mathrm{/Hz}.$ Based on the combined electrical and noise measurements, we calculate room-temperature thermally limited specific detectivity greater than ${\text{2.4×10}}^{14} {\mathrm{cm Hz}}^{\mathrm{1/2}}{\mathrm{ W}}^{\mathrm{-1}}.$ Background-limited specific detectivity exceeds ${\text{3.5×10}}^{13} {\mathrm{cm Hz}}^{\mathrm{1/2}}{\mathrm{ W}}^{\mathrm{-1}}.$