Pt/AlGaN metal semiconductor ultra-violet photodiodes on crack-free AlGaN layers

Schottky-type solar-blind ultra-violet photodetectors were designed and fabricated by employing an unintentionally doped AlGaN layer, grown on a sapphire substrate by metal-organic chemical vapor deposition (MOCVD). When a low-temperature grown AlGaN interlayer was inserted between the GaN and AlGaN active layers, it was found to play an important role in decreasing the thermal and lattice mismatch-induced crack density in the active AlGaN layer. The Schottky-type photodetectors fabricated on the crack-free AlGaN layer then exhibited excellent electrical characteristics and UV sensing behavior. Accordingly, the resulting Pt/AlGaN metal semiconductor photodiode had a dark current of 9 nA at -5 V, cut-off wavelength of 310 nm, and quantum efficiency of 65% at 280 nm, plus the UV/visible extinction ratio was ∼10⁴ in the band edge, which is one of the highest values recorded for an AlGaN photodetector.