Band-offset determination and excitons in SiGe/Si(001) quantum wells

We report both experimental and theoretical studies on ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x/\mathrm{Si}$ multiple quantum wells. A self-consistent calculation is employed to model the excitonic transition. It shows that, in the large conduction-band-offset region the ${\Delta }_2$–heavy-hole (hh) exciton is the lowest transition, while in the small-offset region the ${\Delta }_4$-hh exciton is the lower. From an analysis of the data, a type-II conduction-band-offset ratio of $30\pm 3\%$ is concluded.