Density-of-states effective mass and scattering parameter measurements by transport phenomena in thin films

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Abstract
A novel machine has been developed to measure transport coefficients in the temperature range of 50–350 K of thin films deposited on electrically insulating substrates. The measured coefficients—resistivity, Hall, Seebeck, and Nernst—are applied to solutions of the Boltzmann transport equation to give information about the film’s density-of-states effective mass, the Fermi energy level, and an energy-dependent scattering parameter. The machine is designed to eliminate or compensate for simultaneously occurring transport phenomena that would interfere with the desired measured quantity, while allowing for all four coefficients to be measured on the same sample. An average density-of-states effective mass value of 0.29±0.04me was measured on the transparent conductive oxide, cadmium stannate (CTO), over a carrier concentration range of 2–7×1020 cm−3. This effective mass value matched previous results obtained by optical and thermoelectric modeling. The measured scattering parameter indicates that neutral impurities or a mixture of scattering mechanisms may inhibit the transport of carriers in CTO.