Electron mobility in CdO films

Abstract

Electron mobility in degenerate CdO thin films has been studied as a function of carrier concentration. The “optical” mobility has been determined from infrared reflectance measurements of the conduction band plasmon lifetime. The acquired values vary from ∼209 to ∼1116 cm2 V-1 s-1 for carrier concentrations between 2.5×1020 and 2.6×1019 cm-3. Ionized impurity scattering is shown to be the dominant effect reducing the intra-grain mobility of the electrons at room temperature. The transport mobilities from Hall effect measurements range between ̃20 and ̃124 cm2 V-1 s-1 which are much lower than the optical mobilities. Simulation of grain boundary scattering-limited mobility is commonly based on models that assume a depletion layer at the boundaries which causes an inter-grain potential barrier. These models are found not to be applicable to CdO as it has been previously shown to have surface electron accumulation. Therefore, simulation of the transport mobility has been performed using the Fuchs-Sondheimer and Mayadas-Shatzkes models to take into account the grain boundary and surface scattering mechanisms, in addition to intra-grain scattering. The results indicate that electron scattering at grain boundaries with ̃95 % reflection is the dominant mechanism in reducing the mobility across the layer. The effect of surface scattering plays only a minor role in electron transport.