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

The kinetic formation of self-assembled Ge/Si hut clusters grown by ultra-high vacuum chemical-vapor deposition has been investigated by means of reflection high-energy electron diffraction, atomic force microscopy and photoluminescence spectroscopy. We show that point defects that are induced in the epilayers grown at substrate temperatures below 525 °C 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: a long annealing at the growth temperature and a flash annealing at high temperatures for a very short period of time. The obtained results indicate that a well-controlled flash annealing for a very short period of time is efficient for removing point defects while minimizing Ge/Si intermixing. We have then defined a processing window to obtain proper photoluminescence signature of hut clusters, which is a well-defined gaussian band located at the energy range between 800 and 900 meV. Our experiments also illustrate a correlation between the increase of Ge/Si intermixing and the evolution of the optical properties from a quantum-dot to a quantum-well behavior.