Role of point defects on the optical properties of self-assembled Ge/Si hut clusters

Structural and optical characterizations via reflection high-energy electron diffraction and atomic force microscopy have been combined to investigate the kinetic formation of self-assembled Ge/Si hut clusters grown at a substrate temperature of 525 degrees C by ultra-high vacuum chemical-vapor deposition. It is shown that point defects that are induced in the epilayers grown at such a low substrate temperature greatly influence the optical properties of Ge/Si hut clusters. We have investigated two approaches of sample annealing in order to remove point defects while minimizing Ge/Si intermixing: long annealing at the growth temperature and rapid annealing up to a temperature of 900 degrees C for a very short period of time. The results obtained appear to indicate that the long annealing at the growth temperature may reduce the contribution of point defects, giving rise to the observation of the proper photoluminescence of the Ge/Si hut clusters. The rapid thermal annealing is, on the other hand, shown to be efficient for removing point defects but more controlled annealing, is probably needed in order to minimize the Ge/Si intermixing. (c) 2004 Elsevier B.V. All rights reserved.