The Electrochemical Formation of Semiconductor Chalcogenides

Electrochemical atomic layer deposition (E-ALD) is a technique that has been developed and advanced by the Stickney group. This method uses individual solutions at room temperature to deposit thin films layer-by-layer. Many materials have been grown and can be grown using this method. E-ALD is well suited for semiconductor materials due to its ability to achieve high quality films and its ability to control to stoichiometry of the resulting film. The quality of a semiconductor material when assembled into a device, such as a solar cell, is crucial in the efficiency of said device. This dissertation details the development and investigation of multiple chalcogenide semiconductor systems. Cyclic voltammetry (CV) studies of each individual element are first studied in order to understand the electrochemistry and aid in developing a successful E-ALD program. A typical E-ALD cycle involves first depositing one element from solution onto a substrate. Ideally a surface limited reaction such as underpotential deposition (UPD) will be used to deposit one monolayer or less of material at a time. Afterwards, the second element is introduced and then deposited on top of the other to form a binary compound. This cycle can be repeated as necessary to achieve the desired film thickness. The effect of solution pHs, potentials for deposition, and deposition duration were some of the parameters investigated to optimize the resulting thin film.

The semiconductors investigated in this work are SnSe, GeSe, and SbSe. The chalcogen group is made up of the following elements: oxygen, sulfur, selenium, tellurium, and polonium. The chalcogens have multiple oxidation states, complicating their electrochemical deposition. In the case of selenium, CVs show that it can undergo both oxidative and reductive stripping in acidic solution. When forming the aforementioned materials, different challenges arose based off of each elements individual electrochemistry. Film characterization was achieved mainly by XRD, SEM/EDS, EPMA, and Raman spectroscopy.