Low Temperature Electrodeposition of Epitaxial Films of Covalent Semiconductors

Abstract

This thesis describes two major advancements in electrodeposition by ec-LLS. The first is a new low temperature (< 90 ℃) epitaxial growth technique, termed electrochemical liquid phase epitaxy (ec-LPE), for group IV covalent semiconductors. The ec-LPE technique is based on an electrodeposition strategy, electrochemical liquid liquid solid (ec-LLS) growth, to produce crystalline group IV and III-V materials from liquid metal electrodes, which is also discussed. The quintessential aspect that defines ec-LLS is the liquid metal electrode. The liquid metal acts as an electrode for reducing the ionic precursor, a solvent medium to promote crystal growth, and (in the case of binary semiconductors) a reactant. The second is the ec-LLS electrodeposition of Ge nanowires using a eutectic BiIn (e-BiIn) alloy as an electrode / solvent. This work represents the first case of ec-LLS with a liquid metal alloy that does not contain Ga or Hg. This thesis describes both fundamental and practical aspects of ec-LLS. Critical parameters (e.g. growth rate and supersaturation) influencing the Ge crystal growth in ec-LLS were studied in relation to temperature, applied potential and the mode of nucleation. The competition between heterogeneous and homogeneous nucleation was analyzed and the conclusions are used to develop ec-LPE. This thesis then details the first demonstration of ec-LPE. Large area epitaxial films of Ge were grown at T = 90 ℃ out on the benchtop. This thesis also describes the ec-LLS growth of Ge nanowires using a eutectic BiIn alloy. These Ge nanowires displayed a unique coiled morphology that had not been observed by ec-LLS previously. A final achievement on the concept of growing group III-V semiconductors by ec-LLS is also discussed. Crystalline GaSb was grown by electrodepositing Sb0 at Ga(l) electrodes, followed by a spontaneous reaction between Ga0 and Sb0 to form GaSb. The cumulative work is then contextualized, with further directions highlighted.