Narrow-band photodetection based on M-plane GaN films

Rapid identification of a range of hazardous airborne biological and chemical agents requires simultaneous detection at several specific wavelengths, and consequently a set of photodetectors with very narrow-band spectral responsivity. We demonstrate two ultraviolet photodetection configurations based on strained M-plane GaN films on LiAlO(2)(100) substrates grown by molecular-beam epitaxy with a detection bandwidth below 8 nm. The optical band gap of the film depends on the orientation of the linear polarization of the incident light relative to the c-axis of GaN, which lies in the film plane. The first configuration consists of a polarization-sensitive planar Schottky photodetector and a filter. An orthogonal alignment of the c-axis of the photodetector and the filter produces a detection system, with a peak responsivity at 360 nm and a bandwidth of 6 nm. The second one consists of two planar Schottky photodetectors; with their c-axes oriented perpendicular to each other. The difference signal between the two photodetectors produces a peak responsivity at 358 nm and a bandwidth of 7.3 nm.