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

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 cm 2 V -1 s -1 and a threshold voltage of v T ∼ 14 V is reported here. An on-to-off ratio of ∼10 6 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.