Challenges in epitaxial growth by RP-CVD of strained and relaxed GeSn epilayers on a Si substrate

High Sn fraction GeSn has been grown by RP-CVD with SnCl4. However, challenges remain in creating device quality material suitable for subsequent growth. Surface segregation of tin, which increases with increased tin fraction, raises doubts about the suitability of GeSn as a platform for subsequent growth. Surface segregation may contribute to difficulties of achieving high growth rates and the growth of alloys with an increased tin fraction. The variability of tin content with depth necessitates the use of specialized compositional characterization such as SIMS. Growth of fully relaxed GeSn epilayers remains elusive, with many grown layers are partially relaxed. However, full relaxation is necessary for a direct bandgap material.