RELATIONSHIP OF MBE GROWTH-PARAMETERS WITH THE ELECTRICAL-PROPERTIES OF THIN (100) INAS EPILAYERS

A study of the electrical properties of InAs heteroepitaxial layers grown on (100) GaAs and their dependence upon growth parameters has been undertaken. InAs films 1 mu m thick were grown by molecular beam deposition at a substrate temperature of 370 degrees C. Layers with residual n-type carrier concentrations in the range 5*1016-2*1018 cm-3 at room temperature were obtained. These mobile carriers in arise from both bulk dopants and interface effects. It has been observed that the electrical properties of the InAs epilayers are critically dependent upon the incident indium and arsenic fluxes. High values of In and As4 fluxes produced residual bulk n-type doping levels in the 1018 cm-3 range and caused additional scattering. The lowest carrier concentrations and highest mobilities were obtained for the lowest value of indium flux used (1*1014 atoms cm-2 s-1) and with the smallest arsenic flux consistent with the deposition of stoichiometric layers. Depth profile measurements on the best films indicated that the residual carriers primarily arose from donor centres situated at the film-substrate interface. The material remote from this interface had bulk-like mobilities and near-intrinsic carrier concentrations. The use of a 0.1 mu m GaAs buffer layer isolated the films from a further source of donor centres. The presence of gaseous oxygen during film growth has been found to degrade film electrical properties. No effects were observed when hydrogen was present.