Delta Doping in HgCdTe-Based Unipolar Barrier Photodetectors

A method is described whereby the valence band (VB) discontinuitythat is present in mercury cadmium telluride (HgCdTe)-based alloy-barrier nBn detectors can be minimized. It is numerically demonstrated that compositionally graded layers can provide the required transition between the wide bandgap CdTe barrier layer and the latticematched HgCdTe absorber and contact layers, although a large VB discontinuity is present. In addition, the incorporation of delta-doped (δ-doped) layers in the vicinity of the barrier region can minimize the VB discontinuity, thus blocking the flow of majority carriers and allowing unimpeded flow of photogenerated minority carriers. This strategy results in diffusion-limited dark current at low reverse bias combined with efficient collection of photogenerated carriers. The nBn structure proposed in this paper can be applied to other semiconductor materials operating in various infrared wavelength bands. The method is not limited to the nBn structure and can be applied to any xBx barrier detector structure (with x = n, p) configuration in order to minimize the energy band discontinuity in the corresponding minority carrier band.