Millikelvin magneto-photoluminescence of isoelectronic bound excitons in type-II quantum dot superlattices

Photoluminescence (PL) spectrum of Zn-Se-Te multilayer system grown via migration enhanced epitaxy with submonolayer insertion of Te, has been reported to demonstrate coexistence of the isoelectronic centers along with the type-II quantum dots (Gu, \textit{et al.}, Phys. Rev. B \textbf{71}, 045340 (2005)). Spectrally, the band edge emission, originating from the isoelectronic bound excitons (IBE), is observed as characteristic `sharp lines' and their phonon replicas, whereas the low energy side is dominated by spatially indirect, type-II excitons. The latter exhibit robust Aharanov-Bohm oscillations in the intensity of the magneto-PL up to 30 K, while no such effect was expected for the IBEs. Here we report a high resolution spectral analysis of the magneto-PL spectra of various samples with relatively low Te content measured at millikelvin temperatures. The analysis reveals additional features in magneto-PL intensity at specific magnetic fields that appear only in the spectral region dominated by the `sharp lines'. Although the precise origin of these distinctive peaks is still unknown, they are thought to be arising due to 2-dimensional confinement of IBEs. Supported by the National Science Foundation under Award No. DMR-1006050