Liquid flow deposition of PbS films on GaAs(100)

Abstract

Chemical bath deposition (CBD) is a simple and inexpensive technique for thin film deposition of a variety of semiconductors. Nevertheless, this technique has some drawbacks such as the 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 of PbS films was studied for the first time using a custom-made reactor. The reactor was made of Pyrex and has a tubular geometry, and the substrate was placed vertically on a hemi-cylindrical stage made of Teflon. The main objective of this research was to enhance our understanding of thin film deposition by comparing the results obtained in LFD and CBD methods. High resolution scanning electron microscopy and X-ray diffraction showed <110> oriented films for both methods. A notable advantage of the LFD method is the possibility to deposit films of the same quality simultaneously on both sides of the substrate, which has a variety of practical implications. Kinetic studies showed that the maximal growth rate in the reactor was achieved when the residence time corresponded to half of the induction time, which indicates that film growth occurred by direct nucleation on the substrate. LFD can provide monocrystalline films with thickness exceeding 5 μm at room temperature, whereas such a film thickness is rarely obtained in CBD. Moreover, a growth time series in LFD demonstrated autocatalytic deposition and its effect on the resulting film. The growth rate in LFD increases with time and reaches a maximum of 80 nm min⁻¹ after 30 min of deposition at 30 °C, after which it stays constant throughout the deposition, while in CBD the growth rate drops after 30 min of deposition.