Surface recombination velocity of anodic sulfide and ZnS coated p-HgCdTe

The surface recombination velocity s has been determined for Hg1 _xCdxTe (x~Q.2) for two different surface passivations: (i) anodic sulfide with an overcoating of ZnS and (ii) ZnS coating on freshly etched samples. The method used was photoelectromagnetic effect, in which a magnetic field is applied perpendicular to the diffusion current of optically generated injected carriers. Analysis of the magnetic field dependence of the resulting current can yield s, as well as carrier mobility, lifetime, etc. The temperature dependence of s is very similar for the two passivations at temperatures higher than 50 K, and is increasing with decreasing temperature. At low temperatures s continues to rise for ZnS passivation and stays flat for the native anodic sulfide. Two activation energies are determined: 12.5 ± 1.5 meV at temperatures higher than 60 K, and 2.3 + 0.2 meV at temperatures lower than 30 K. The high-temperature activation energy is identical for both passivations. It is concluded that the same surface traps control the surface recombination rate for the two passivations, and their concentration is equal in both cases. The traps are apparently “intrinsic,” and can be related to lattice defects, most probably vacancies. Their concentration at the surface is similar to that in the bulk.