Transport properties of copper-doped indium oxide and indium tin oxide ceramics

The transport properties of undoped and copper-doped indium oxide and indium tin oxide ceramics are investigated. The correlation between density, carrier concentration, and mobility is analysed. The density of IO ceramics can be considerably increased by copper doping and approaches that of single crystals for 5 mol% of CuO. The increase of density results in an enhancement of carrier mobility. However, a lowering of the electron concentration, as the copper concentration increases, occurs because a small amount of copper enters the lattice as Cu(I). The density of ITO is also enhanced by copper doping but, most interestingly, both the carrier concentration and carrier mobility increase as the copper content becomes more important. Results of optical absorbance are also reported and are discussed in relation with the transport properties. For IO:Cu ceramics, the absorbance in the free-carrier absorption region decreases as the CuO amount increases as a result of the lowering of the carrier concentration. As for ITO and ITO:Cu ceramics, the free-carrier absorption is stronger than for IO:Cu, because the carrier concentration is much higher.