Growth of germanium crystals by reacting gold with germane and selective gold removal.

摘要

Germanium crystal growth can be achieved by the vapor-liquid-solid (VLS) method in which the crystals grow from a metal solvent that is continuously saturated with germanium atoms by the decomposition of GeH4 at the surface of the metal solvent. This thesis explores controlling the growth of germanium crystals by reacting microscopic gold particles with GeH 4 such that electronic devices can be constructed from these microscopic germanium crystals.;Micrometer-size germanium crystals were grown by reacting electrodeposited gold, at the bottom of holes etched through a silicon oxide layer on a silicon substrate, with GeH4. These etched hole structures are called local crucibles and they determined the location of the germanium crystals. The size of the germanium crystals was determined by the amount of electrodeposited gold. X-ray diffraction from these germanium crystals shows that their crystal orientation is the same as the crystal orientation of the silicon substrate. The selectivity of germanium deposition onto gold particles versus onto the silicon oxide surface was increased by the addition of gaseous HCl during crystal growth.;Because gold can deleteriously affect electronic devices made from germanium, removal of the gold from germanium crystals grown from nanometer-size gold particles was explored. The removal of gold from these germanium crystals is particularly challenging because gold is a noble metal and germanium is known to be quite reactive. Liquid etchants that contain an iodine species and aqueous HC1 selectively removed the gold from these germanium crystals. Electron microscopy shows that all visible gold is removed from germanium crystals treated with these liquid etchants. Photoemission spectroscopy (PES) shows that the oxidation of germanium is minimized by the HCl in these liquid etchants. Inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) were used to quantify the residual gold after germanium crystals were treated with the liquid etchants. These techniques show that a significant fraction (as much as 99%) of the gold was removed from the germanium crystals.