SIGE WIRES AND DOTS GROWN BY LOCAL EPITAXY

SiGe quantum wells with finite lateral size have been fabricated using local molecular beam epitaxy through shadowing masks with dimensions down to 200 nm. With this growth technique, mesas of high crystalline quality with sidewalls solely determined by the growth conditions can be achieved and it is possible to grow SiGe quantum wells completely e mbedded in Si. This greatly reduces nonradiative recombination rates c ompared to other methods of lateral structuring and leads to the obser vation of clear excitonic omission even from the smallest SiGe wires. Measured absolute intensities of the SiGe related signals increase by about a factor of two when decreasing the width of the wires from 1 mu m to 200 nm. When accounting for the areal coverage of the investigat ed spot with SiGe, the so normalized intensities strongly increase wit h decreasing window size and exceed the reference signal by about one order of magnitude for the smallest structures. With decreasing mesa s ize, a pronounced blue shift is observed which is dependent on the siz e of the growth window and on the growth temperature. Lateral diffusio n effects of Ge on the surface during growth will be discussed in this context.