Impact of energy band-gap grading on responsivity of an Al xGa 1− xN ultraviolet p–n detector

Abstract

A theoretical study has been carried out on the responsivity of an Al x Ga 1− x N(n)–GaN(p) photodiode ultraviolet detector in which the Al x Ga 1− x N layer has an energy band-gap grading. The analytical solution to the one-dimensional continuity equation was used in the calculations. The spatial dependence of the material properties, such as the absorption coefficient and the energy band-gap of the photodiode n-type layer was included in the solution. In the calculations the minority carrier diffusion length and lifetime determined from a homogeneous n–p GaN photodiode were used. Since a moderate grading is considered this seems to be justified. The effect of n-type front layer thickness of energy band-gap graded photodiodes on the responsivity was analyzed and compared to that of the ungraded photodiodes. Compared to ungraded photodiodes an enhanced current responsivity and its much reduced dependence on graded layer thickness and on the surface recombination rate are found.