The inherent transport anisotropy of rutile tin dioxide (SnO2) determined by van der Pauw measurements and its consequences for applications

The anisotropic electron mobility of unintentionally doped, single crystalline, bulk, rutile SnO2(100) and (110) wafers is investigated by van der Pauw-Hall measurements. The room temperature average Hall electron mobility of mu approximate to 220 cm(2)/V s at a Hall electron concentration of n approximate to 10(18) cm(-3) suggests high-quality samples. The extracted 1.26 times higher mobility in the c-direction than perpendicular to it is in very good agreement with the corresponding anisotropy of the effective electron mass, which is 1.28 times higher perpendicular to c than parallel to c, suggesting rather isotropic scattering mechanisms. At temperatures below 100 K, a higher mobility anisotropy is found and tentatively attributed to low-angle grain boundaries with a surprisingly low energy barrier. Thus, the efficiency of mobility-sensitive applications, such as field effect transistors, increases by aligning the transport direction with the c-direction of the crystal. For transparent contact applications, such as Sb-or F-doped SnO2 (termed ATO or FTO, respectively), this benefit is expected to be even larger due to the increasing effective mass anisotropy with the increasing electron concentration. Published by AIP Publishing.