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Abstract
Using Electrochemical Atomic Layer Deposition (E-ALD) and its one-solution counterpart, Potential Pulse Atomic Layer Deposition (PP-ALD), programs were developed for the deposition of compound semiconductor thin films. Both E-ALD and PP-ALD utilize the property of underpotential deposition (UPD), but while E-ALD requires solution switching, PP-ALD is done from one solution bottle. The PP-ALD deposition requires careful alternation of cathodic and anodic pulses to limit the material deposited. This allows for PP-ALD to be a much faster deposition process, but it can be more challenging to design a deposition program as both solutions must be soluble in the same pH’s and deposit and strip at similar electrochemical potentials. By choosing optimal parameters governed by the Nernst equation such as pH, potential, and precursor concentration as well as physical conditions such as duty time, light exposure, and supporting electrolyte concentration, optimal deposition conditions can be achieved using both processes. Use of cyclic voltammetry and current-time traces allow for the monitoring of the deposition process in-situ while a variety of characterization methods can be used on the thin films after the deposition process is complete. Morphology of the deposits was characterized using SEM while the structural composition was analyzed with EDX and EPMA. Structural characterization was done by XRD and Raman Spectroscopy.
Many different semiconductor compounds can be formed using E-ALD processes. In2Se3 and InSe are interesting as potential photoanodes or photocathodes in a photoelectrochemical cell but can also be combined with other binary compounds into the super-structure, Copper Indium Gallium Selenide (CIGS) as well for solar cell use. GeTe is often used in Phase Change Random Access Memory (PRAM) applications as a phase change material due to its stable amorphous and crystalline states as well as its fast switching speed. Lastly, when combined with Surface Limited Redox Replacement (SLRR), E-ALD allows for the conformal deposition of epitaxial layers of noble metals such as Cu and Au which can serve as capping layers to protect the underlying films from unwanted oxidation.
Many different semiconductor compounds can be formed using E-ALD processes. In2Se3 and InSe are interesting as potential photoanodes or photocathodes in a photoelectrochemical cell but can also be combined with other binary compounds into the super-structure, Copper Indium Gallium Selenide (CIGS) as well for solar cell use. GeTe is often used in Phase Change Random Access Memory (PRAM) applications as a phase change material due to its stable amorphous and crystalline states as well as its fast switching speed. Lastly, when combined with Surface Limited Redox Replacement (SLRR), E-ALD allows for the conformal deposition of epitaxial layers of noble metals such as Cu and Au which can serve as capping layers to protect the underlying films from unwanted oxidation.