Formation and characterization of multilayer GeSi nanowires on miscut Si (001) substrates.

A multilayer of GeSi nanowires separated with Si spacers was readily self-assembled on miscut Si (001) substrates with 8 degrees off toward (110). The nanowires oriented along the miscut direction were very small and compactly arranged on the vicinal surface. Systematic photoluminescence (PL) spectroscopy studies were carried out on the GeSi nanowires. With increasing excitation power, a sublinear power dependent PL intensity and a blue-shift of -7 meV/decade with nearly constant full width of half maximum (FWHM) of PL peaks from multilayer GeSi nanowires was observed. These results indicated a typical type-III band alignment of GeSi nanowires/Si. The blue-shift was attributed to band bending effect with the increase of photon-generated carriers. The nearly independent FWHM of PL peaks with the excitation power was explained in terms of the formation of mini-band due to strong coupling of holes in closely neighboring nanowires. An activation energy of -12 meV was extracted from the temperature-dependent intensity of PL peaks of the nanowires, which was assigned to be the exciton binding energy around the nanowires. Based on Raman spectra, the Ge content in GeSi nanowires was estimated to be -61%.