Photoluminescence in Strain-Engineered Si/SiGe Three Dimensional Nanostructures

The effect of strain on the degeneracy of energy band minima in composition-controlled Si/SiGe nanostructures with high germanium content ($\sim $ 50{\%}) is studied by low temperature photoluminescence (PL) spectroscopy, ultra-high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy measurements. PL spectra obtained from selective excitation of the multilayered nanostructures show a reduction in the strained-silicon fundamental energy bandgap and a splitting of energy levels presumably associated with partial removal of two-fold degeneracy of the SiGe valence band. PL kinetics recorded using different excitation wavelengths show dramatically different PL lifetimes, ranging from $\sim $ 2 $\mu $s to $<$ 10 ns. We show that it is possible to obtain high quantum efficiency luminescence at 1.3-1.6 $\mu $m.