Detection of a piezoelectric effect in thin films of thermally grown SiO2 via lock-in ellipsometry
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Scheme of the measurement setup: He-Ne laser, polarizer, quarter-wave plate, analyzer, and a photo-detector (PD: Si photodiode) form the null ellipsometer. The sample is subjected to alternating voltage and the oscillating photodiode signal is detected with a lock-in amplifier. To increase sensitivity, the analyzer was shifted from the null position by ≈2° during the measurements.
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(a) and (b) Dependence of the photo-detector current on the amplitude of the applied (177 Hz) for samples S1 and S2 respectively; Inset in (b): Frequency dependence (1–1000 Hz) of the piezoelectric response of sample S2, = 4 V. (c) Dependence of the detector current for sample S1 on the superimposed (−1.6 to 1.6 V) with = 0.5 V, 177 Hz at 100 °C (maximum electric field 840 kV/cm). The voltage (both DC and AC) was switched on and off, thereby illustrating that, in the absence of voltage applied to the sample, no signal was recorded (the noise level is negligible) and no “memory” effect related to charge injection/trapping and electret-like behavior is observed. One can see that the value of the does not affect the amplitude of the detector current.
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