LIQUID FLOW DEPOSITION OF PbS FILMS ON GaAs(100)

Chemical Bath Deposition (CBD) is a simple and inexpensive technique for thin film deposition of a variety of semiconductors. Nevertheless, this technique experiences some drawbacks such as change of reactant concentrations and spatial non-uniformity. Liquid flow deposition (LFD) is a variation of CBD with potentially improved performance. In the current research LFD was studied using a custom-made reactor, in which the deposition of lead sulfide (PbS) on gallium arsenide (GaAs) substrate was explored as a test case. PbS is widely studied for different applications such as photovoltaic cells, IR detectors and thermoelectric devices. The main objectives of the current research were to enhance our understanding of thin film deposition by comparing the LFD and CBD methods, and optimization of PbS thin film deposition using LFD. High resolution scanning electron microscopy (HR-SEM) and X-ray diffraction (XRD) showed oriented films for both methods. Notably, there were much less particles precipitating on the film surface in the case of LFD compared to CBD. The initial growth rate of PbS films via LFD was found to be lower than in CBD, resulting in thinner film thickness and suggesting that LFD is more suitable for growing films via the ion-by-ion mechanism. Kinetic studies showed that the maximal growth rate in the reactor was achieved when residence time corresponded to half of the induction time. Moreover, as expected, the growth rate in LFD increases with time up to 80 nm/min after 30 min of deposition after which it stays constant throughout the deposition, while in CBD the growth rate drops after half an hour of deposition.