Solar-Blind AlGaN Heterostructure Photodiodes

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Abstract
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 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 μm undoped Al0.47Ga0.53N active layer and a 0.5 μm p-type Al0.47Ga0.53N:Mg top layer. Square mesas of area A = 4 × 10−4 cm2 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%. R0A values up to 8 × 107Ω-cm2 were obtained, corresponding to D* = 3.5 × 1012 cm Hz1/2W−1 at 273 nm.