Measurements of critical point energies in the conduction band structure of Si1−xGex

Abstract

The energies of the Δ1 and L1 conduction band minima and the L3 saddle point have been measured in Si1−xGex (x=0.0–0.95) alloys using spatially resolved electron energy-loss spectroscopy. Measurements were carried out in a scanning transmission electron microscope at a spatial resolution of better than 2 nm on specimens grown in a SiGe molecular-beam epitaxy system on Si(100) substrates. As observed in photoluminescence measurements, the Δ1 and L1 bands are seen to cross at a Ge content of approximately 85%. L3 and Δ1 maintained a nearly constant energy separation independent of alloy composition. In contrast, L1 and Δ1 approach each other rapidly with increasing Ge content. Based on these results, this technique can be used to identify the composition of thin Si1−xGex alloys with a lateral resolution of better than 2 nm.