The physical and electrical properties of non-crystalline Ta- and Hf-alumiunates, (Ta2O5),(Al2O3)(1-x) and (HfO2)(x)-(Al2O3)(1-x), respectively, were studied. As-deposited films were homogeneous and pseudo-binary in character with increased thermal stability with respect to the respective end-member oxides. Capacitance-voltage and current density-voltage data as a function of temperature demonstrate that the Ta and Hf d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta2O5 and HfO2 with respect to Si. This work correlates the studies of Ta- and Hf-aluminates to develop a qualitative conduction band energy level scheme for the two alloys where the interfacial electrical properties are dominated by electron traps of the respective transition metal atoms, and/or or network defects associated with the alloy. (C) 2002 Elsevier Science Ltd. All rights reserved.