Low temperature capping of self-assembled Ge islands was investigated by means of photoluminescence (PL) spectroscopy. The island related PL signal systematically redshifts when the capping temperature decreases [1]. For substrate temperatures below 700^OC during island growth, the emission energies are lower than the usual values reported in the literature (0.75-0.9 eV). By applying low temperature capping to Ge islands grown at different temperatures, we show that the Ge island emission wavelength can be extended up to 2.06 μm. This is related to an increased Ge content in the islands. The longest emission wavelength is obtained for hut clusters grown at 400^OC which consist of pure Ge. By further decreasing the growth temperature to 360^OC, the emission energy increases again. This result is explained by enhanced charge carrier confinement in extremely small Ge quantum dots.

References:[1] U. Denker, M. Stoffel, O.G. Schmidt, H. Sigg, Appl.Phys. Lett. 82, 454 (2003)
Corresponding author: M. Stoffel, e-mail: [email protected]

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