High magnetic field characterisation of (Hg, Cd)Te surface layers

Abstract

A description is given of the use of the Shubnikov-De Haas effect, parallel-field magnetoresistance and cyclotron resonance to give a rather complete characterisation of (Hg, Cd)Te surface accumulation layers. The Shubnikov-De Haas and parallel-field magnetoresistance enable one to distinguish the separate contributions to conductivity from surface layers and bulk, the measure surface carrier densities and very accurately deduce the number of populated subbands. The parallel-field causes depopulation of the subbands, and is particularly sensitive to subbands with very low carrier densities (n ∼ 1 x 1010 cm-2). Cyclotron resonance is used to make a very accurate determination of the x-value of the bulk material, and to measure the effective masses of the surface electrons. Separate resonances can be detected for each of the electric subbands. The structures studied are infra-red detector elements passivated with an anodic oxide. We have found that the oxide is sensitive to above band gap UV ( ∼ 3.3 eV) illumination, which causes a persistant discharge of the oxide surface states below 77 K. This allows us continuously to decrease the surface carrier concentration and make accurate studies of the systematic surface charge density dependence of the subband populations, effective masses and resistance.