Files
Abstract
This dissertation discusses the layer-by-layer deposition of Cu2Se and In2Se3 usingpotential pulse atomic layer deposition (PP-ALD) and optimization studies of CdTe usingelectrochemical atomic layer deposition (E-ALD). PP-ALD is an electrodepositionmethodology combining concepts from techniques such as sequential monolayerdeposition (SMD) and E-ALD in order to create E-ALD quality films at increaseddeposition rates.During PP-ALD cycles, potentials are alternated between cathodic and anodicpotentials, foregoing cyclic voltammetry (CV) or solution alternation required in SMD andE-ALD. The cathodic potential is positioned at a co-electrodeposition potential for a timesufficient to form fractions of a monolayer (ML). The Anodic potential oxidatively stripselemental excess creating stoichiometric deposit surfaces. During pure co-dep,potentiostatic or galvanostatic, localized excess of an element results in stoichiometryvariations. Since the Cathodic pulse time limits the amount deposited, PP-ALD avoidsburying elemental excess as it remains accessible to stripping during the Anodic pulse.This is an ALD method since it is based on repeated application of surface limitedreactions to grow deposits an atomic layer at a time. Electrochemical surface limitedreactions are frequently referred to as underpotential deposition (UPD), which occurs at apotential that takes advantage of compound formation energetics to form a deposit of oneelement on another. In PP-ALD, the anodic potential produces UPD since onlythermodynamically stable compound remains. The resulting Cu2Se and In2Se3 filmproperties were characterized using coulometry, electron probe microanalysis (EPMA),CV, x-ray diffraction (XRD), and spectroscopic ellipsometry. In2Se3 deposits made frompH 1 solution were preferable to those made from pH 3 solution due to stoichiometry andhomogeneity improvements. A PP-ALD solution made with Se+6 precursor was vetted asa replacement for the more reactive Se+4 ion. Selenic acid solution resulted in 0.1-0.3 MLof Se deposition when compared to selenous acid, which deposited 0.6 ML at the samepotential. The lack of deposition limits the practicality of selenic acid as a replacementPP-ALD precursor. Finally, CdTe deposits were improved by excluding O2 and H2 gasformed during the deposition process through the use of CO2 purging and less permeablegasket material.