The effects of built-in electric field on the performance of compositionally graded P-on-n HgCdTe heterojunction photodiodes

The results of a study of the optical and electrical performance of P-on-n HgCdTe heterojunctions, with a linear gradient in composition, are presented. First presented is a solution of the one-dimensional continuity equation which includes the spatial dependencies of the material properties, such as absorption coefficient, band gap, and intrinsic carrier concentration, in the graded layer. Using the above solution, diodes with different grading profiles (and hence different electric fields), but with the same cutoff wavelength, are compared. The advantages of the built-in electric field formed by the grading in composition are presented and discussed. It is shown that the major consequence of the electric field is the reduction of the effects caused by the imperfect CdTe/HgCdTe interface at the backside.