DC-conduction mechanism in crystalline oxidised La and La-Mn films grown on p-Si substrate

摘要

Crystalline lanthanum oxide (LAO) and lanthanum-manganese (La-Mn) oxide thin films were prepared on p-Si substrates and characterised by X-ray fluorescence (XRF) and X-ray diffraction (XRD) methods. Hydroxide compounds [La(OH)_3 and LaOOH] in addition to La_2O_3 structure were detected in the prepared crystalline LAO films. Those hydroxide compounds reduced the dielectric constant of the prepared LAO to 6.4. The XRD study of La-Mn oxide films shows that La oxide and Mn oxide crystallised each alone at 600 deg C without forming one complex compound or a solid solution. Furthermore, lanthanum hydroxide compounds were not detected in La-Mn oxide samples. The oxide-voltage dependence of the DC-current density for both LAO and La-Mn oxide films were found to follow the voltage dependent part of Richardson-Schottky (RS) equation, and therefore, the field-lowering coefficient and the dynamic relative permittivity were determined. On the other hand, the temperature dependence of the DC-leakage current density for both types of films was not obeying the temperature-dependence part of RS formula. It shows that the leakage current in crystalline LAO and La-Mn oxide insulating films have a metallic-temperature behaviour. This behaviour was explained due to the superimposing of RS mechanism with another conduction mechanism that was suggested to be the carrier-trapping mechanism. Generally, the experimental data demonstrated that addition of Mn oxide to La oxide forming La-Mn oxide that almost terminate the hygroscopic products does not change the DC-conduction nature and does not improve the insulating quality towards that of pure La_2O_3.