Si-doped AlxGa1-xN photoconductive detectors

We report on the fabrication and characterisation of ultraviolet photocondu ctive detectors based on Si-doped AlxGa1-xN (0 less than or equal to x less than or equal to 0.35) epitaxial layers grown on sapphire. The peak respon sivity shifts from 365 nm to 300 nm for increasing Al contents. The devices present high responsivities (similar to 100 A W-1 for P-opt = 1 W m(-2)), which strongly depend on the incident optical power. This behaviour is expl ained by a light-induced modulation of the conductive area. In addition, th e responsivity increases with carrier concentration and mobility, as also p redicted by this model. Persistent photoconductivity decreases with doping, whatever the Al content, because of the enhancement of tunnel recombinatio n across the potential barriers generated by surface and defects. Photocurr ent decays have been successfully modelled by taking into account both the thermoionic and tunnel relaxation mechanisms, the latter being dominant eve n for undoped GaN.