Conduction band modifications by d states in vanadium doped CdO

Abstract 3d transition metal ions have been shown to act as donors and to introduce highly localized d-levels when incorporated in CdO. In this work, we synthesized CdO thin films doped with a 3d metal V (CVO) with a V mole fraction x up to 0.1 by radio-frequency magnetron sputtering. CVO thin films exhibit a monotonic increase in the electron concentration n with x up to a saturation value of ∼1.0 × 1021 cm−3 at a dopant concentration x > 0.045. In contrast to CdO doped with shallow donors such as In where the electron mobility μ is > 100 cm2/V-s even at a high In doping level of >5%, in CVO the μ decreases continuously from ∼100 to  0.045 is consistent with transitions from the valence band to the empty E+ subband while the much reduced μ can be explained by the increase in effective mass due to flattening of the E- subband. Such band anticrossing interaction is a common phenomenon for most transition metal dopants with d electrons in metal oxides and can explain the optoelectronic properties of these materials.