The critical thickness of silicon-germanium layers grown by liquid phase epitaxy

Silicon-germanium layers are grown from metallic solution on (100) and (111 ) silicon substrates. On (111) Si, coherently strained dislocation-free SiG e layers are obtained with thicknesses larger than predicted by the current models of misfit-induced strain relaxation. A comprehensive characterisati on by imaging, diffraction, and analytical electron microscopy techniques i s carried out to determine the critical thickness, study the onset of plast ic relaxation, and explain the particular growth mechanisms leading to an u nexpectedly high thickness of elastically strained SiGe layers. A vertical Ge concentration gradient and the formation of step edges on the layers, wh ere lateral strain relaxes locally, explain the high critical thickness. Th e model of Matthews and Blakeslee is modified in order to match the experim ental observations for solution-grown SiGe layers.