Abstract
Photoluminescence (PL) and reflectivity spectroscopy in magnetic fields up to 60 Tesla are used to investigate the excitonic optical transitions within CdTe/(Cd,Mg)Te 2D electron gases. The samples are 100 A and 200 A wide quantum well (QW) wherein the electron density is varied smoothly from 1 × 1011 to 4.5 × 1011 cm-3 across the wafer. This allows us to follow the energy diagram of the neutral exciton ( X 0) and the charged exciton singlet and triplet spin states ( X - s , X - t ) versus magnetic field and the electron density. We observe a weak PL peak above 12 T (15 T) for the 200 A QW (100 A) at the low energy side of the spectra in addition to the X -0 and X - s PL. This peak could be the signature of a fundamental dark triplet state recently predicted (Phys. Rev. B62, 4630). Moreover, for high density samples a balance of PL intensity between the X -s and an other X -t occurs in the 25T-30T range. These results are interpreted on the basis of the calculations by Wojs et al. (Phys. Rev. B62 4630) taking account the Zeeman energy of the charged exciton.
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