11 February 2008 Responsivity modulation of thin-film CdS by means of lock-in technique
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Thin-film CdS was deposited onto glass with nanosecond pulsed-laser (PLD) deposition using 355 nm for only 2 minutes resulting in a 200 nm thick film. X-ray analysis revealed a peculiar texture consisting of crystallites embedded in an amorphous matrix. Employing alternating and constant light sources, i.e., chopped light and a light emitting diode (LED) in conjunction with lock-in technique, we introduce here a straightforward way to modulate the alternating responsivity (AR) of the CdS film at room temperature. The arrangement was the following: Aluminum contacts were evaporated on the film surface and were electrically connected to a power supply and a lock-in amplifier. The chopped light was exciting the film surface between the contacts and a blue (465 nm) LED was directed to the same area. In this way, it was possible to measure the AR of the film under the influence of blue background irradiation. Notably, the efficiency of the bleaching effect depends on the applied electric field, intensity of blue LED and chopped photon energy. Around 50% quenching is observed at 100 V/cm in the vicinity of CdS band gap. The per cent quenching is decreased with increase in bias and increase with increase in the blue LED intensity. The modulation is attributed to the shortening of the available AR carriers due to the generation of direct current channels in the film. Summarizing, the work demonstrates the use of the lock-in principle for modulation and quenching techniques in optoelectronics rather than for applications in metrology only.
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K. P. Acharya, K. P. Acharya, B. Ullrich, B. Ullrich, "Responsivity modulation of thin-film CdS by means of lock-in technique", Proc. SPIE 6890, Optical Components and Materials V, 68900Q (11 February 2008); doi: 10.1117/12.761852; https://doi.org/10.1117/12.761852

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