DC electronic transport mechanisms in some manganese-oxide insulator thin films grown on Si substrates

Thin films of crystalline of Mn2O3, MnO, and their mixture have been prepared on Si(P) substrates by evaporation of MnO2 powder followed by calcination in air and in vacuum. The structure of the prepared oxide films was studied by X-ray diffraction (XRD). For electrical studies, the samples were constructed in the form of Al/oxide/Si MOS structures. Those MOS devices have been electrically characterised by the measurement of their capacitance as a function of gate voltage. The MOS capacitors exhibited the charge regimes of accumulation, depletion, and inversion. The net surface charge density was measured to be in the range of 10(14) to 10(15) m(-2) The dc current-voltage characteristic measurements at room temperature and in the temperature range (290-370 K) show that the mechanisms controlling the current flow in those oxides were the Richardson-Schottky (RS) mechanism and the trap-charge-limited space-charge-limited conductivity (TSCLC) mechanism characterised by exponential distribution of traps, depending on the film structure and hence the preparation conditions. The temperature dependence of leakage current in films, of alpha-Mn2O3 and MnO has interesting property that higher temperatures reduce the current. This may be important in the application in circuits that operate under extreme conditions. The parameters of those mechanisms like the activation energy of electrical conduction, dynamic relative permittivity, and traps concentration were determined. (c) 2005 Elsevier B.V. All rights reserved.