Conducting mechanism in the epitaxial p-type transparent conducting oxide Cr2O3:Mg

Epitaxial p-type transparent conducting oxide (TCO) Cr2O3:Mg was grown by electron-beam evaporation in a molecular beam epitaxy system on c-plane sapphire. The influence of Mg dopants and the oxygen partial pressure were investigated by thermoelectric and electrical measurements. The conduction mechanism is analyzed using the small-polaron hopping model, and hopping activation energies have been determined, which vary with doping concentration in the range of 210-300 +/- 5 meV. Films with better conductivity were obtained by postannealing. The effect of postannealing is discussed in terms of a crystallographic reordering of the Mg dopant. The highest Seebeck mobilities obtained from thermoelectric measurements are of the order of 10(-4) cm(2)V(-1)s(-1). We investigate the fundamental properties of a Mg dopant in a high crystalline quality epitaxial film of a binary oxide, helping us understand the role of short range crystallographic order in a p-type TCO in detail.