ELECTRONIC-TRANSPORT PROPERTIES OF UNHYDROGENATED AMORPHOUS GALLIUM-ARSENIDE

Hall mobility, mu(H), and electrical conductivity, sigma, of unhydrogenated amorphous-gallium-arsenide films, prepared by r.f. sputtering, have been measured. Conductivity as a function of temperature shows a variable-range hopping mechanism at T < 260 K, while at high temperature, conductivity and Hall mobility are both thermally activated. The results are interpreted in terms of the presence of defect complexes due to an excess of Ga. The stoichiometry and the structure of the films are used to explain the behaviour and the values Of mu(H). The values of the activation energy of the conductivity seem in agreement with theoretical calculations on the position of electronic states created by defect complexes in the mobility-gap of a-GaAs.