Experimental and theoretical analysis of the contribution of the graded region to the current and RoA of HgCdTe diodes

The validity of the assumption that the contribution of the n region to the current of Hg_1-xCd_xTe diodes is negligible was examined. By placing such diodes in a magnetic field we were able to separate between the current component originating in the p-type substrate, and that from the graded n region. Experimental results show that the ratio between these currents is 0.5 - 3, depending on temperature. The theoretical analysis reveals the influence of the electric field present outside the depletion region on the current generated by the graded region. This field not only produces a drift component, which drives the minority carriers into the junction, it also greatly modifies the excess carrier distribution, thereby changing diffusion part of the current. The analysis shows the importance of the lifetime profile in the graded region, which is a function of the specific recombination mechanism and its dependence on the local dopant concentration. The effect of parameters such as substrate concentration, surface concentration, and junction depth on this current is discussed.