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

The Hall effect and electrical resistivity of n-type CuInSe2 single crystal s 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 i s explained in terms of the thermal activation of a shallow donor. The dens ity of states effective mass m(e)*=0.09m(e) of the electrons, the activatio n energy of the donors around 7 meV, their concentration, and the compensat ion ratio are estimated. The temperature dependence of the electron mobilit y in conduction band is analyzed by taking into account the scattering of t he charge carriers by ionized impurities and acoustic and polar optical pho non modes. The adjustable parameters, thus obtained, are compared with thos e reported earlier. On the other hand, by considering the two-band model wi th electrons in both the conduction and impurity bands, the change in the H all coefficient with temperature between 300 and 40 K is explained. It is f ound that at the temperature where the Hall coefficient is maximum, the mob ility in the impurity band is about 20% as compared to its value in the con duction band. The width of the impurity band is found to increase with incr easing impurity concentration and the electron mobility below 20 K is expla ined by considering the effect of Mott-type variable range hopping conducti on. (C) 2001 American Institute of Physics.