Optical study of germanium nanostructures grown on a Si(118) vicinal substrate
Photoluminescence (PL) measurements were carried out on Si/Ge(n)/Si0.7Ge0.3/Si structures (n is varying from 1 to 7ML) deposed by gas source molecular beam epitaxy (GS-MBE) on Si(100) surfaces and high index Si(118) vicinal surfaces. Ge nanostructures were confined on the top of the undulation of the Si0.3Ge0.7 wetting layer, according to the StranskiKrastanov growth mode. PL measurements reveal a correlation between the substrate orientation and the island morphology: square dots for (001) and wires for (118) surface orientation. The results suggest that the SiGe wetting layer is required to ensure a good dot size uniformity. The dependence of the luminescence on the excitation power and the PL decay time indicate that the luminescence transitions likely occur in a type-II band line up. Finally, the dot-related PL persists up to room temperature which is very promising for optoelectronic device applications.
germanium nanostructures photoluminescence luminescence molecular beam epitaxy high index surface type-ii recombination