Back illuminated AlGaN solar-blind photodetectors

We report the growth, fabrication, and characterization of ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}\text{\hspace{0.05em}(0⩽x⩽0.60)}$ heteroepitaxial back-illuminated solar-blind p-i-n photodiodes on (0001) sapphire substrates. The group III-nitride heteroepitaxial layers are grown by low-pressure metalorganic chemical vapor deposition on double polished sapphire substrates using various growth conditions. The back-illuminated devices exhibit very low dark current densities. Furthermore, they exhibit external quantum efficiencies up to 35% at the peak of the photoresponse $\text{(λ∼280\hspace{0.05em}}\mathrm{nm}\mathrm{).}$ Improvements were made to the growth technique in order to achieve crack-free ${\mathrm{Al}}_{\mathrm{0.4}}{\mathrm{Ga}}_{\mathrm{0.6}}\mathrm{N}$ active regions on a thick ${\mathrm{Al}}_{\mathrm{0.6}}{\mathrm{Ga}}_{\mathrm{0.4}}\mathrm{N}$ window layer and to obtain activated p-type ${\mathrm{Al}}_{\mathrm{0.4}}{\mathrm{Ga}}_{\mathrm{0.6}}\mathrm{N}$ layers.