Open Electrochemical Liquid Phase Epitaxial Growth of Crystalline Ge Films

Room temperature and ambient pressure electrochemical liquid phase epitaxy (ec-LPE) of macroscopic Ge(100) films using uncompressed liquid metal electrodes has been achieved. Experiments were performed in aqueous electrolytes containing dissolved GeO₂ and Na₂B₄O₇ using Hg, Hg_0.35In_0.65, Ga, or Ga_0.83In_0.17 (e-GaIn) working electrodes. The resultant crystalline Ge films were characterized via scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and selected area electron diffraction. e-GaIn was identified as the liquid metal composition that produced the most uniform and largest area Ge epi-films. Thickness profiles of the electrodeposited Ge films showed thicknesses that decreased at distances further from the three-phase boundary between the liquid metal, aqueous electrolyte, and solid seed substrate, consistent with the premise that In specifically facilitates nucleation and crystal growth via surface diffusion. This study thus establishes "open" ec-LPE as a method to synthesize single crystalline semiconductors and makes recommendations for improving the prospects of "open" ec-LPE based on the cumulative observations presented herein.