Solar-Blind AlGaN Heterostructure Photodiodes

A backside-illuminated solar-blind UV detector based on an AlGaN p-i-n heterostructure has been successfully synthesized, fabricated and tested. The p-i-n photodiode structure consists of a 1.0 μm n-type Al 0.64 Ga 0.36 N:Si layer grown by MOVPE onto a low temperature AlN buffer layer on a polished sapphire substrate. On top of this base layer is a 0.2 μm undoped Al 0.47 Ga 0.53 N active layer and a 0.5 μm p-type Al 0.47 Ga 0.53 N:Mg top layer. Square mesas of area A = 4 × 10 −4 cm 2 were obtained by reactive ion etching using BCl 3 . The solar-blind photodiode exhibits a very narrow UV spectral responsivity band peaked at 273 nm with a FWHM = 21 nm. Maximum responsivity R = 0.051 A/W at 273 nm, corresponding to an internal quantum efficiency of 27%. R 0 A values up to 8 × 10 7 Ω-cm 2 were obtained, corresponding to D* = 3.5 × 10 12 cm Hz 1/2 W −1 at 273 nm.