Quantum yield of energy-band-gap-graded AlGaN(n)/GaN(p) UV photodetector

Abstract

Numerical analysis has been carried out on the spectral dependence of the quantum yield for an AlGaN(n)-GaN(p) photodiode ultraviolet (UV) detector in which the AlGaN layer is an energy band-gap graded (EBGG). The latter has been achieved by variation of Al content. The spatial dependence of the material properties, such as energy band- gap and absorption coefficient of the photodiode's n-type layer is considered in the calculation. The band-gap grading, due to a reduced absorption coefficient at the surface region 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. In order to improve the quantum yield, it was found that there is no need to fabricate the structures exhibiting the large gradients. Within the range of small values of EBGG there is a substantial rise in the detector quantum yield with increasing the grading. Much more extended the dependence in quantum yield with the grating has been found when the recombination was present at the illuminated surface. The carried out study enabled to determine the optimal grading and the graded layer thickness with regard to the detector response to the selected UV wavelengths.