Band offset predictions for strained group IV alloys:: Si1-x-yGexCy on Si(001) and Si1-xGex on Si1-zGez(001)

The band offsets for strained Si1-x-yGexCy layers grown on Si(001) substrate and for strained Si1-xGex layers grown on fully relaxed Si1-zGez virtual substrates are estimated. The hydrostatic strain, the uniaxial strain and the intrinsic chemical effect of Ge and C are considered separately. Unknown material parameters relative to the latter effect are chosen to give the best agreement with the available experimental results for Si1-xGex and Si1-yCy layers on Si. As a general trend concerning carrier confinement opportunities, it is found that a compressive strain is required to obtain a sizeable valence band offset, while a tensile strain is needed to obtain a conduction band discontinuity. In most cases the strain is responsible for a bandgap narrowing with respect to that of the substrate. The obtained results are in very good agreement with available experimental determinations of band offsets and bandgap changes for ternary alloys on Si(001).