Oscillator Strengths for Neutral, Charged, and Scattered Excitons in CdTe Quantum Wells Containing a 2D Electron Gas

Abstract

Absorption spectra have been measured for a 10 nm CdTe(0.3%Mn) quantum well with electron concentration n e variable up to 1.5 × 10 11 cm −2 . Following recent theory appropriate to low n e , here ≈ 0.1/πa 2 B , the spectra are interpreted in a "strong exciton" model, where the initial oscillator strength of the excitonic resonance (X) is conserved, with screening and phase-space filling effects negligible. As ne increases in zero-field and as the filling factor ν increases in magnetic field, the intensity of X is transferred to: (i) trion processes, namely exciton-one electron scattering and the trion resonance (T ), and (ii) quatron processes, namely exciton-two electron scattering and trion-one electron scattering. In magnetic field, the three-and four-body scattering processes become discrete, combined "exciton and cyclotron" and combined "trion and cyclotron" excitations that take all the intensity of X and T for ν > ∼ 1 and ν > 2, respectively.

Influence of free carriers on exciton ground states in quantum wells

“…In addition, starting from very low concentrations of free electrons in the quantum well, a bound trion (negatively charged exciton) state [11][12][13][14] is observed in experiments [6][7][8][9][10] . The present article will not be concerned with properties related to the trion state, but its existence provides another channel for exciton-electron interactions.…”

“…Experimental data [6][7][8][9][10] give evidence that, within a relatively narrow interval of free electron concentrations below the metallic phase, the optical absorption band associated with the bound exciton shifts and broadens, and its oscillator strength decreases as carrier concentration is increased. The dependence of these characteristics on the electron concentration allows one to relate these processes with exciton-electron interactions.…”

Magneto-optics of two-dimensional electron gases modified by strong Coulomb interactions in ZnSe quantum wells

“…the exciton binding energy in bulk ZnSe is 20 meV). Modification of the optical spectra of modulation-doped quantum wells (QW) containing a 2DEG has been the subject of extensive theoretical [2,3,4,5,6,7,8,9,10] and experimental studies [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27].…”

Optical spin orientation of minority holes in a modulation-doped GaAs/(Ga,Al)As quantum well

“…22,23,24 This is not the case, e.g., for CdTe-based QWs where trion-like multi-particle states may still reveal themselves due to a smaller exciton radius in those compounds. 25,26 Fig 1 (a) shows also the PL excitation (PLE) spectrum taken with the spectrometer position at the PL maximum. The lowest-energy PLE maximum is ~4 meV away from the maximum of the PL; also the PLE maximum at ~7 meV above the PL peak is observed.…”