HEAVILY ACCUMULATED SURFACES OF MERCURY CADMIUM TELLURIDE DETECTORS - THEORY AND EXPERIMENT

Some processes used to passivate n-type mercury cadmium telluride photoconductive infrared detectors produce electron accumulation layers at the surfaces, which result in 2D electron gases. The dispersion relations for the electric subbands that occur in these layers have been calculated from first principles. Poisson's equation for the built-in potential and Schroedinger's equation for the eigenstates have been solved self-consistently. The cyclotron effective masses and Fermi energies have been computed for each subband density for 12 total densities between 0.1 to 5.0 X 10(12) cm-2. The agreement with Shubnikov-de Haas measurements is very good at lower densities with possible improvement if band-gap narrowing effects were to be included. At higher densities, larger differences occur. The simple 2D description is shown to break down as the density increases because the wave functions of the conduction and valence bands cannot be well separated by the narrow band gap of long-wavelength detectors. These results provide a basis for characterizing the passivation processes, which greatly affect device performance.