Level crossing of nanometer sized InAs islands in GaAs

We used polarization spectroscopy to detect level crossings in the fine structure of excitons in strained InAs islands grown on [001] GaAs. The crossings gave rise to quasi-resonant peaks, when monitoring the circularly polarized photoluminescence (PL) as a function of magnetic field. The peaks could also be detected as increases of the PL intensity. The resonant magnetic field was strongly dependent on detection energy within the PL emission peak. This energy selection is equivalent to monitoring a specific size or small interval within the broader size and shape distribution inherent to the growth process. The resonance was observed to shift to a higher magnetic field, when increasing the angle between field and sample growth direction. Basic arguments based on quantum confinement and the exciton fine structure can qualitatively account for the observations. Together with hole effective g-values the level crossing fields can be used to calculate the zero magnetic field splitting of the exciton fine structure.