Synthesis, electronic transport and optical properties of Si:alpha-Fe2O3 single crystals

We report the synthesis of silicon-doped hematite (Si:alpha-Fe2O3) single crystals via chemical vapor transport, with Si incorporation on the order of 1019 cm(-3). The conductivity, Seebeck and Hall effect were measured in the basal plane between 200 and 400 K. Distinct differences in electron transport were observed above and below the magnetic transition temperature of hematite at similar to 265 K (the Morin transition, T-M). Above 265 K, transport was found to agree with the adiabatic small-polaron model, the conductivity was characterized by an activation energy of similar to 100 meV and the Hall effect was dominated by the weak ferromagnetism of the material. A room temperature electron drift mobility of similar to 10(-2) cm(2) V-1 s(-1) was estimated. Below TM, the activation energy increased to similar to 160 meV and a conventional Hall coefficient could be determined. In this regime, the Hall coefficient was negative and the corresponding Hall mobility was temperature-independent with a value of similar to 10(-1) cm(2) V-1 s(-1). Seebeck coefficient measurements indicated that the silicon donors were fully ionized in the temperature range studied. Finally, we observed a broad infrared absorption upon doping and tentatively assign the feature at similar to 0.8 eV to photon-assisted small-polaron hops. These results are discussed in the context of existing hematite transport studies.