Effect of impurity band conduction on the electrical characteristics of n-type CuInSe2

Abstract

The Hall effect and electrical resistivity of n-type CuInSe2 single crystals are measured between 4.2 and 300 K. Using a single conduction band model, the variation of the electron concentration with temperature above 100 K is explained in terms of the thermal activation of a shallow donor. The density of states effective mass me*=0.09me of the electrons, the activation energy of the donors around 7 meV, their concentration, and the compensation ratio are estimated. The temperature dependence of the electron mobility in conduction band is analyzed by taking into account the scattering of the charge carriers by ionized impurities and acoustic and polar optical phonon modes. The adjustable parameters, thus obtained, are compared with those reported earlier. On the other hand, by considering the two-band model with electrons in both the conduction and impurity bands, the change in the Hall coefficient with temperature between 300 and 40 K is explained. It is found that at the temperature where the Hall coefficient is maximum, the mobility in the impurity band is about 20% as compared to its value in the conduction band. The width of the impurity band is found to increase with increasing impurity concentration and the electron mobility below 20 K is explained by considering the effect of Mott-type variable range hopping conduction.