Synthesis And Characterization Of Nanocrystalline Cds Thin Films By Microwave-Assisted Chemical Bath Deposition For Photodetectors Application
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Date
2015-10
Authors
Mohammed Ali, Mohammed Husham
Journal Title
Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
This study aimed to synthesize nanostructured cadmium sulfide (CdS) thin films for efficient photodetector (PD) devices using a simple and low-cost method. Nanocrystalline CdS thin films were grown on Si(100) substrates by microwave-assisted chemical bath deposition. The properties of the grown CdS thin films were optimized by controlling the growth parameters such as the molar concentration of ion (Cd2+ and S2−) sources, the growth duration, and the molar ratios of the precursors. Analyses revealed that a well-characterized nanocrystalline CdS thin film was obtained using 0.08 M precursors at a deposition time of 20 min. The surface morphology of the grown thin film became more compact and uniform and showed higher roughness. The properties of the grown thin films were further improved by increasing the S/Cd precursors molar ratio. The structural quality of the prepared CdS thin film was significantly enhanced at a S/Cd molar ratio of 1.875. Photoluminescence measurement revealed an efficient emission at 510 nm, which corresponds to the near-band-edge emission of CdS. Moreover, the density of defects was reduced, as suggested by the low intensity defect-related emission. The crystallinity of the grown thin films was also increased, as suggested by the increasing of the average crystallite (D) grain size. The D value was increased from 36 to 42 nm when the S/Cd molar ratio was increased from 1 to 1.875. The effect of the preparation parameters on the photodetection properties of the grown CdS thin films was investigated. Ni–CdS–Ni metal–semiconductor–metal photodetectors were fabricated and characterized. A PD was fabricated based on optimum CdS thin film conditions (prepared using 0.08 M precursor at a deposition time of 20 min). The fabricated PD showed, respectively, a photosensitivity and response time of 1440% and 9 ms to 500 nm light at an applied reverse bias of −1 V. The photodetection properties of the fabricated PDs were improved by varying the S/Cd precursor molar ratios. A maximum photosensitivity of 25.28×103% with a response time of 8 ms was obtained for the fabricated PD based on a nanocrystalline CdS thin film prepared using a S/Cd molar ratio of 1.875 at a reverse bias of −1 V. The fabricated PD exhibited a small leakage (dark) current (1.3 μA) compared to the obtained photocurrent (330 μA) upon illumination, which led to an enhancement of the device photosensitivity. The fabricated PDs based on nanocrystalline CdS thin films prepared using S/Cd molar ratios of 1.25 and 1.875 exhibited a measurable photocurrent at zero applied bias, which demonstrate that the fabricated devices are self-powered PDs. The built-in field, which formed within the depletion region of the Ni/CdS Schottky junction, acts as the driving force to separate the photogenerated electron–hole pairs from recombination and generate a photocurrent without any external bias. Photoresponse measurements revealed that the fabricated PDs can function as self-powered devices with high photosensitivity and rapid response time values of 9.72×104% and 9 ms, respectively, to low-power (1.20 mW/cm2, 500 nm) light. The present study introduced a cost-effective and simple approach to fabricate efficient devices in terms of photosensitivity and response speed with low power consumption, even down to zero.
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Keywords
Nanocrystalline CdS thin films