Formation mechanism of high Ge content SiGe epilayer on Si by liquid phase epitaxy using Ge-Sn solution

Abstract

High germanium (Ge) content silicon germanium (Si1−xGex) epilayers with the composition x over 0.9 were prepared on Si(111) substrate by liquid phase epitaxy (LPE). As known, a lattice mismatch high to the degree of 4.2% between Ge and Si has made the direct growth of high Ge content Si1−xGex on Si substrate quite challenging for LPE. However, self-organized Si1−xGex films grown with a grading composition were recognized by cross-sectional scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The film structure obtained could be further divided into three layers according to the distribution variation of elemental composition. The initial Si1−xGex layer showed a tardy grading in the Ge composition from 0.1 to 0.15 within a thickness of 21 - 33 μm. Then, the second layer was featured by an abrupt crossover to Ge-rich condition in the composition distribution within a thickness of about 8 - 12 μm. Finally, the top Si1−xGex layer demonstrated a consistently high Ge content (x > 0.9) within a thickness of 2 – 4 μm.It is found that using a Ge-Sn initial growth solution, commencing the LPE at 950 °C, and terminating the growth at an appropriate temperature suggested by the Ge-Sn phase diagram present a feasible methodology to prepare high Ge content SiGe epilayer on Si(111) substrate. In this work, we focus on exploring the formation mechanism of high Ge content SiGe epilayer on Si by LPE by combining the SEM/EDS analysis results with both Si-Sn and Ge-Sn phase diagrams.