Responsivity of GaN and (GaAl)N band-gap-graded ultraviolet p-n detectors

摘要

Abstract: Calculation has been carried out on the current responsivity of an Al$-x$/Ga$-1-x$/N(n)-GaN(p) photodiode ultraviolet (UV) detector in which the Al$-x$/Ga$-1-x$/N layer has an energy band-gap grading (EBGG). The analytical solution to the one- dimensional continuity equation was used in the calculations. The spatial dependence of the material properties, such as energy band-gap and absorption coefficient of the photodiode's n-type layer is included in the solution. The band-gap grading due to a reduced absorption coefficient at the surface region (where recombination occurs) and the built in electric field results in the increase of the minority carrier generation in the vicinity of the junction resulting the enhancement of carrier collection efficiency. Within the range of small values of EBGG there is a substantial rise in the detector responsivity with increasing grading. In the case of surface recombinationless Al$-x$/Ga$-1-x$/N(n) front side layer the further increase of the grading does not result the significant rise of responsivity especially in the spectral region near the cutoff. Much more pronounced the increase in responsivity with the grading has been found when the surface recombination was present. !34