Isothermal-Dielectric-Relaxation Currents in Thin-Film Al-CeF3-Al Samples

Abstract

A new technique based on isothermal-dielectric-relaxation currents (IDRC) had been successfully used to study the defect properties of thin-film Al-Ce${\mathrm{F}}_3$-Al samples. The IDRC technique consists of applying a step voltage to the sample to induce a non-steady state and then measuring the non-steady-state current as a function of time as the system decays to the steady state. It is found that at low temperatures ($T<\mathrm{}250\mathrm{}$ °K), the displacement charge $Q_d$ circulating the external circuit is associated with the geometrical capacitance. Thus, it is inversely proportional to the thickness of the sample and linearly dependent on the voltage. At higher temperatures ($T>\mathrm{}280\mathrm{}$ °K) a pronounced dielectric-relaxation current flows through the insulator. The displacement charge $Q_r$ associated with the relaxation current is found to be 20-40 times the magnitude of $Q_d$ and independent of the thickness of the insulator at low voltages, indicating the existence of Schottky barriers at the electrode insulator and, thus, that the conduction process is electrode limited. At higher voltages $V\gtrsim 4$ V, $Q_r$ saturates showing that the conduction process is bulk limited. From the $Q_r-V$ characteristic, the trapping density is found to be 6 × ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The $\mathrm{It}-{log}_{10}t$ characteristic is shown to manifest a pronounced peak. From this characteristic, it is determined that the occupied trap levels are contained in a band of energy of width approximately 0.02 eV, which is centered about an energy 0.63 ± 0.03 eV below the bottom of the conduction band. The results are shown to be consistent with IDRC theory and previous stimulated-dielectric-relaxation-current studies on the same samples.