Epitaxial $p$-type transparent conducting oxide (TCO) $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3:\mathrm{Mg}$ 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 ${10}^{-4}{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$. 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.

• Received 10 October 2014
• Revised 4 February 2015

DOI:https://doi.org/10.1103/PhysRevB.91.125202