Growth, characterization and application of CdS thin films deposited by chemical bath deposition

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Abstract
The recent advance in soft solution processing of inorganic materials offers an exciting opportunity to develop large‐area manufacturing technologies for inorganic thin‐film transistors (TFTs). In this paper, we report our recent progress in fabricating CdS TFTs using chemical bath deposition (CBD) to deposit CdS channel layers. Device analysis of an enhancement‐mode CdS metal–insulator–semiconductor field effect transistor (MISFET) with a field‐effect mobility of ∼1.5 cm2 V−1 s−1 and a threshold voltage of VT ∼ 14 V is reported here. An on‐to‐off ratio of ∼106 is achieved. This rather large drain current on‐to‐off ratio indicates that this device will function well as a switch. An examination of the CdS film morphology by scanning electron microscopy indicates that the films deposited by CBD and used for our current device fabrication are dominated by a particle sticking growth mechanism. This is supported by a real‐time quartz crystal microbalance growth curve and atomic force microscopy characterizations of the particles formed in the CBD solution. A different bath condition for CBD was tested to obtain a dense CdS layer. A selected‐area electron diffraction pattern indicates that the CdS thin film deposited by CBD has a hexagonal structure with an optical bandgap of 2.4 eV as determined by UV–Vis absorption. Copyright © 2005 John Wiley & Sons, Ltd.