Investigation on the Formation and Propagation of Defects in GeSn Thin Films

Abstract

Defect formation and propagation in Ge1-xSnx/Ge thin films were investigated by using X-ray diffraction, transmission electron microscopy and scanning electron microscopy techniques. Samples with 0.9 to 7 % Sn mole fraction were deposited on a Si substrate with a Ge buffer layer using a chemical vapor deposition technique. The X-ray diffraction results show that the Ge1-xSnxfilms are 46-100 % compressively strained. Transmission electron microscopy images show that symmetrical and asymmetrical Lomer dislocations are formed at GeSn/Ge interface, which stops propagation of defects parallel to the growth direction. Average threading dislocation density (TDD) in the Ge buffer layer is measured to be 9.71×108 cm-2. Adding Sn to Ge made the Ge1-xSnx films to be more flexible, which traps 80 % of TDD propagating in Ge buffer layer. Reduction of TDD to 3×107cm-2 indicates achievement of higher quality of Ge1-xSnx film.