Photoluminescence in UHV/CVD tensile-strained Si type-Ⅱ quantum wells on bulk crystal SiGe substrates

摘要

Near band-edge photoluminescence (PL) in high-quality UHV/CVD tensile-strained Si type-Ⅱ quantum wells (QWs) with varying well width grown on bulk crystal SiGe substrates has been studied. In contrast to the blue-shifts observed in the PL lines of Si_(1-x)Ge_x QWs on Si, the PL lines of Si QWs exhibit red-shifts with increasing excitation density. The PL from the SiGe substrate shows no such shift. The PL red-shifts decrease as the well width decreases, and are essentially independent of temperature up to 15K where a transition from bound exciton emission to higher energy free exciton emission occurs. The rapid thermal annealing (RTA) was found to improve the crystal quality of the samples. RTA enhances the integrated PL intensity, results in narrowing and blue-shifting of PL bands, and reduces the exponent in the excitation power dependence as well as the amount of red-shifting at a given excitation density. Possible mechanisms for the observed shifts to lower energies of the PL lines with excitation density were examined, including band bending, band-filling, and binding of excitons to impurities.