Bias-Controlled Spectral Response in GaN/AlN Single-Nanowire Ultraviolet Photodetectors.

We present a study of GaN single-nanowire ultraviolet photodetectors with an embedded GaN/AlN superlattice. The heterostructure dimensions and doping profile were designed in such a way that the application of positive or negative bias leads to an enhancement of the collection of photogenerated carriers from the GaN/AlN superlattice or from the GaN base, respectively, as confirmed by electron beam-induced current measurements. The devices display enhanced response in the ultraviolet A (≈ 330-360 nm)/B (≈ 280-330 nm) spectral windows under positive/negative bias. The result is explained by correlation of the photocurrent measurements with scanning transmission electron microscopy observations of the same single nanowire and semiclassical simulations of the strain and band structure in one and three dimensions.