Extended wavelength region of self-assembled Ge/Si(001) islands capped with Si at different temperatures

Abstract
We investigate the emission wavelength region of self-assembled Ge/Si(001) islands. The islands were grown between 360 and 840 °C and subsequently capped with Si at low temperatures (300 °C). Under these conditions, the island morphology is preserved as revealed by atomic force microscopy. By decreasing the capping temperature, photoluminescence measurements evidence a systematic redshift enabling us to discuss the relative contribution of Si intermixing during growth and during capping. We also find that the emission wavelength can be extended up to 2.06 μm for hut clusters grown at 400 °C. By further decreasing the Ge growth temperature to 360 °C, the emission energy evidences a blueshift. This result is explained by enhanced charge carrier confinement in extremely small Ge quantum dots.