The photoluminescence (PL) of self-organised grown SiGe islands embedded in Si is determined by indirect transitions in real and in reciprocal space : holes are confined with the islands, electrons in the tensily strained Si above and below the islands and in compressively strained Si around their circumference. By the use of data on composition and strain gradients as obtained from x-ray diffraction data and calculations of the electron and hole confined states using the next-nano3 simulation package, the PL data of the a series of island samples with systematically varying Ge gradients can be explained. If such islands are grown on prepatterned Si substrates, a rather perfect 2D lateral island ordering with a substantial reduction of island size variation is possible, which leads to much narrower PL emission. Growing island multilayers on top of 2D ordered islands results in a 3D island ordering. For spacer layer thicknesses below 10 nm electron states in adjacent island layers start to couple, which leads to miniband formation along growth direction and quite efficient PL, even at room temperature.
(Work performed in collaboration with M. Brehm, T. Fromherz, T.U. Schülli, M.-I. Richard, J. Stangl, G. Chen, V. Holý, C. Dais, D. Grützmacher, and G. Renaud)
1) M. Brehm et al., New J. Phys. 11, 063021 (2009).
2) T. U. Schülli et al., Phys. Rev. Lett. 102, 025502 (2009)
3) V. Holý et al., Phys. Rev. B 79, 035324 (2009).