High Sn-concentration (~ 8%) GeSn by low-temperature (~ 150 °c) solid-phase epitaxy of a-GeSn/c-Ge

GeSn with a high substitutional Sn concentration (> 7%) is an attractive direct band gap material for high-efficiency photodevices that can be merged with large-scale integrated circuits (LSIs). To achieve GeSn with high Sn concentration, low-temperature solid-phase epitaxy using amorphous-GeSn (a-GeSn) (Sn concentration: 10%-36%)/crystal-Ge (c-Ge) stacked structures was investigated. Solid-phase growth of GeSn was enhanced as Sn concentration was increased, which enabled epitaxial growth at very low temperature (150-200 °C). Interestingly, concentrations of substitutional Sn increased with decreasing growth temperature. As a result, epitaxial growth of GeSn with substitutional Sn concentrations of ~ 8% was achieved by decreasing the growth temperature to 150 °C using a-GeSn (Sn concentration: 36%)/c-Ge stacked structures. This technique is expected to be useful to realize multi-function LSIs, where high-efficiency photodevices are integrated with transistors.