Local atomic structure of Cdse ultra-thin quantum wells examined by x-ray absorption fine structure experiments

摘要

We have employed the X-ray absorption fine structure (XAFS) technique for the investigation of the local atomic structure of CdSe/ZnSe ultra-thin quantum wells (UTQWs) with 1 and 3 ML thickness. The CdSe/ZnSe system presents a large lattice mismatch of similar to 7.3 % and the pseudomorphic UTQWs are under compressive biaxial strain. The analysis of the XAFS data indicate differences in the Cd-Se bond length of the 1 and 3 ML UTQWs, as a consequence, differences in the magnitude of the strain, in significant disagreement with the usual hypothesis of thickness independent strain for pseudomorphic thin films. Furthermore, the analysis of the XAFS experiments suggests the possibility of inhomogeneous strain in the 3ML UTQW. We conclude that even for ultra-thin pseudomorphic films the strain can be inhomogeneous and depend on film thickness if this is close to the critical thickness h(c).