Solar-blind AlGaN-based inverted heterostructure photodiodes

True solar-blind operation with a sharp responsivity cutoff at similar to 3 00 nm has been demonstrated in AlGaN-based photodiodes using an "inverted h eterostructure photodiode" design. This structure utilizes an AlxGa1-xN(x > 0.3) intrinsic or lightly doped active layer surrounded by p- and/or n-typ e contact layers having a narrower band gap than the active layer. By utili zing narrow band gap (e.g., GaN) contact layers, the difficulties associate d with achieving high doping efficiencies in wide band gap contact layers a re circumvented. This basic structure is applicable to both front- and back -side illuminated detector geometries. Front-side illuminated solar-blind p hotodiodes were demonstrated with a peak responsivity of 0.08 A/W at 285 nm , while back-side illuminated detectors yielded a peak responsivity of 0.03 3 A/W at 275 nm (both are measured without antireflection coating). Both ty pes of detectors offered sharp spectral responsivity cutoff of at least thr ee orders of magnitude by 325 nm. (C) 2000 American Institute of Physics. [ S0003-6951(00)00829-9].