Analysis of effect of HgCdTe passivant on the performance of long-wavelength infrared(LWIR) detectors

The performance of HgCdTe infrared photoconductors is strongly dependent on the semiconductor surface conditions. In this paper, the effect of fixed charge density(Qox) due to passivation on the responsivity of HgCdTe photoconductive detectors is analysed both theoretically and experimentally. A profile responsivity model is used here for calculation, which mainly includes the contribution of minority carrier lifetime and the shunt resistance resulting from the accumulation layer at the surface. In this model, the profiles of surface majority carrier concentration and surface mobility are taken into consideration. A gate-controlled photoconductor structure is designed and fabricated to investigate surface effects on HgCdTe infrared photoconductive detectors. And it is used to evaluate and optimize surface passivation layers. Minority carrier lifetime, resistance and responsivity of the device have been measured as a function of the gate potential in this structure. The measured variations have shown a reasonable agreement with our model. It is predicted that the optimization of surface fixed charges at the MCT-passivant interface can bring a great improvement in the responsivity of photoconductive detectors.