Growth and characterization of highly tensile strained Ge_1-xSn_x formed on relaxed In_yGa_1-yP buffer layers

Ge_0.94Sn_0.06 films with high tensile strain were grown on strain-relaxed In_yGa_1-yP virtual substrates using solid-source molecular beam epitaxy. The in-plane tensile strain in the Ge_0.94Sn_0.06 film was varied by changing the In mole fraction in In_xGa_1-xP buffer layer. The tensile strained Ge_0.94Sn_0.06 films were investigated by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. An in-plane tensile strain of up to 1% in the Ge_0.94Sn_0.06 was measured, which is much higher than that achieved using other buffer systems. Controlled thermal anneal experiment demonstrated that the strain was not relaxed for temperatures up to 500 °C. The band alignment of the tensile strained Ge_0.94Sn_0.06 on In_0.77Ga_0.23P was obtained by high resolution x-ray photoelectron spectroscopy. The Ge_0.94Sn_0.06/In_0.77Ga_0.23P interface was found to be of the type I band alignment, with a valence band offset of 0.31 ± 0.12 eV and a conduction band offset of 0.74 ± 0.12 eV.