Low-temperature heteroepitaxy of Ge_1-ySn_y binary alloy using chemical vapour deposition

Germanium tin (Ge_1-ySn_y) binary alloy is an intriguing group IV semiconducting material for various electronic and optoelectronic applications. Due to low solid solubility of Sn in Ge (0.6 at.%) and their large lattice mismatch (14.7 %), epitaxial growth of Ge_1-ySn_y alloys with Sn concentrations exceeding 0.6 at.% with low defects density has been a challenging task. Despite all challenges in the growth of Ge_1-ySn_y, researchers have succeeded in growing these epilayers using various techniques, however, chemical vapour deposition (CVD) is the most important growth technique in terms of applicability and practicability. As Ge_1-ySn_y physical and electrical properties sensitively depend on its Sn concentration and lattice strain, it is necessary to fully understand the effect of CVD growth conditions on these Ge_1-ySn_y epilayers. In this work, heteroepitaxy of Ge_1-ySn_y is achieved at a very low temperature (240 ℃) which has previously been reported to be an impossible task. Growing at such low temperature can provide a high quality fully strained Ge_1-ySn_y epilayer with high Sn concentration (over 13 at.%) which could be used to construct quantum wells and other complex structurs.