Selective regrowth of Al0.30Ga0.70N p–i–n photodiodes

We report on the device performance of selective-area regrown ${\mathrm{Al}}_{\mathrm{0.30}}{\mathrm{Ga}}_{\mathrm{0.70}}\mathrm{N}\mathrm{ p–i–n}$ photodiodes. Tensile strain, induced by the lattice mismatch between ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ and GaN, leads to cracking above the critical thickness in layers with high aluminum concentration. Selective-area regrown devices with ⩽70 μm diameters were fabricated without signs of cracking. These devices show low dark current densities with flat photoresponse and a forward turn-on current of ∼25 A/cm² at 7 V. A quantum efficiency greater than 20% was achieved at zero bias with a peak wavelength of $\text{λ=315\hspace{0.05em}}\mathrm{nm}.$ A differential resistance of $R_0{\text{=3.46×10}}^{14}\mathrm{ \Omega }$ and a detectivity of $D^{*}{\text{=4.85×10}}^{13} {\mathrm{cm Hz}}^{\text{1/2}} {\mathrm{W}}^{\mathrm{-1}}$ was demonstrated.