Magnetoluminescence investigations of $\mathrm{Si}/{\mathrm{Si}}_{0.76}{\mathrm{Ge}}_{0.24}$ quantum wells

Photoluminescence experiments in high magnetic fields reveal diamagnetic shifts consistent with a type-II conduction band offset of about 55 meV for $\mathrm{Si}/{\mathrm{Si}}_{0.76}{\mathrm{Ge}}_{0.24}.$ We point out that for such a type-II offset a magnetic field induced changeover from ${\Delta }_2$- to ${\Delta }_4$-like recombination is expected for an 8.5 nm wide quantum well, and that this changeover can explain our measurements on this well at low excitation power. The magnetoluminescence data provide evidence for localized and free exciton recombinations, which are hardly separable without the magnetic field. For interpretation of the data we employ calculations within an effective-mass model, obtaining two-particle ground-state wave functions for excitons in quantum wells at high magnetic fields.