Fine structure and magneto-optics of exciton, trion, and charged biexciton states in single InAs quantum dots emitting at 1.3 μm

摘要

We present a detailed investigation into the optical characteristics of individual InAs quantum dots (QDs) grown by metalorganic chemical vapor deposition, with low temperature emission in the telecoms window around 1300 nm. Using microphotoluminescence (PL) spectroscopy we have identified neutral, positively charged, and negatively charged exciton and biexciton states. Temperature-dependent measurements reveal dot-charging effects due to differences in carrier diffusivity. We observe a pronounced linearly polarized splitting of the neutral exciton and biexciton lines (～250 μeV) resulting from asymmetry in the QD structure. This asymmetry also causes a mixing of the excited trion states which is manifested in the fine structure and polarization of the charged biexciton emission; from this data we obtain values for the ratio between the anisotropic and isotropic electron-hole exchange energies of Δ_1/Δ_0 ≈ 0.2-0.5. Magneto-PL spectroscopy has been used to investigate the diamagnetic response and Zeeman splitting of the various exciton complexes. We find a significant variation in g factor between the exciton, the positive biexciton, and the negative biexciton; this is also attributed to anisotropy effects and the difference in lateral extent of the electron and hole wave functions.