In situ STM analysis and photoluminescence of C-induced Ge dots

Molecular beam epitaxy has been utilized to grow small C-induced Ge islands in silicon. The evolution of C-induced Ge dots from nucleation to the form ation of larger dots has been studied in detail. The Ge grows in a Vollmer- Weber mode of growth in areas between the C-rich patches on the Si surface. Using in situ STM analysis as well as transmission electron microscopy (TE M) it is shown that an increase in the Ge coverage leads to the overgrowth of the C-rich patches and to island coalescence, reducing the island densit y. The strongest luminescence intensity is found in this region where the G e has buried the C-rich areas. The amount of C deposited on the Si(100) sur face prior to the growth of Ge permits the control of the lateral size and the height of Ge quantum dots. Accordingly, intense photoluminescence (PL), with a stronger confinement shift dependending on the amount of Ge deposit ed, is observed for samples prepared with large C concentrations. The impac t of the Si spacer layer width on the size of the dots has been studied by TEM and compared with PL data. The data give new insights into the structur al peculiarities of C-induced Ge dots and their consequences on the electro n and hole confinement.