Highly strained Ge1-xSnx alloy films with high Sn compositions grown by MBE

Abstract We have grown a series of Ge1-xSnx films with high Sn compositions up to 16.6% directly on Ge (1 0 0) substrates using molecular beam epitaxy (MBE). Reciprocal space mapping (RSM) study shows that all the Ge1-xSnx alloy films are highly strained even after Sn segregation has occurred. Ellipsometry measurements confirm that increasing the Sn composition shrinks the bandgap of Ge1-xSnx. We have found that low growth temperatures and high growth rates are beneficial to achieve higher Sn compositions, and strain is an important role in limiting the Sn incorporation.