Fabrication and band alignment of pseudomorphic Si1-yCy, Si1-x-yGexCy and coupled Si1-yCy/Si1-x-yGexCy quantum well structures on Si substrates

The structural and photoluminescence (PL) properties of several types of pseudomorphic Si1-x-yGexCy quantum well (QW) structures grown by solid-source molecular beam epitaxy on (0 0 1) Si substrates are described. Optimum Si1-yCy growth takes place at a substrate temperature of about 550 degrees C and a growth rate less than or equal to 1 Angstrom/s. Well-defined alloy layers with no defects or SiC precipitates are observed by transmission electron microscopy (TEM). Excitonic band edge related PL is emitted from Si1-yCdSi multiple QWs (MWQ). The band gap of strained Si1-yCy is drastically reduced by about Delta E = -y x 6.5 eV. Reducing the width of Si0.99C0.01 layers results in a PL blueshift up to 45 meV which is attributed to the strong (weak) quantum well confinement of Delta(2) valley electron (light hole) states. The band alignment in Si1-yCy/Si QWs is basically explained by the strain-induced shift of levels due to C incorporation. In Si1-x-yGexCy QWs, compressive strain caused by Ge is partially compensated by C and the band gap increases by Delta E = y x 2.4 eV. Si1-yCy as well as Si1-x-yGexCy QWs give rise to spatially direct PL transitions. Closely spaced Si1-yCy/Si1-xGex double quantum wells (DQW) give rise to spatially indirect PL recombination of Delta(2) electrons confined in the Si1-yCy layers and heavy holes localized in the Si1-xGex layers. The no-phonon transitions and the integrated PL intensity from thin DQWs are strongly enhanced compared to SQWs. In Hall transport studies, Si1-yCy and SiGeC alloys on Si reveal electron and hole mobilities which are well comparable to Si and SiGe or even improved. C alloying provides a significant extension of the possibilities in band structure engineering of Group-IV semiconductors.