Electronic transport in ion-bombarded amorphous silicon

dc-conductivity and thermopower of ion-bombarded amorphous silicon have been measured as a function of temperature. At 300 K and below the conductivity exhibits and exp[-(T0/T)sup(n)] dependence with n approx. equal to 1/2, and the thermopower is vanishingly small. While the characteristic temperature varies strongly with the preparation conditions, the prefactor sigma0 remains approximately constant at about 50 Ω-1 cm-1 for all samples. The data can be explained by a mechanism based on electronic transport in a two-phase solid. It is assumed that the carriers tunnel between microvoids embedded in a high resistivity matrix. (orig.)