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 mum n-type Al0.64Ga0.36N: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 mum undoped Al0.47Ga0.53N active layer and a 0.5 mum p-type Al0.47Ga0.53N: Mg top layer. Square mesas of area A = 4 x 10(-4) cm(2) were obtained by reactive ion etching using BCl3. 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 x 10(7) Ohm -cm(2) were obtained, corresponding to D* = 3.5 x 10(12) cm Hz(1/2) W-1 at 273 nm.