Trions in ZnSe-Based Quantum Wells Probed by 50 T Magnetic Fields

Abstract

Singlet and triplet states of negatively charged excitons (trions) in ZnSe/(Zn,Be,Mg)Se quantum wells have been studied by means of photoluminescence in pulsed magnetic fields up to 50 T. Singlet state binding energies, measured for different well widths ranging from 48 to 190 A, show a monotonic increase with growing magnetic fields with a tendency to saturation. This behavior is in qualitative agreement with results of model calculations. Quantitatively, the binding energy of singlet states is underestimated by about 50%. The triplet state assigned to the "dark" triplet becomes detectable in magnetic fields above 15 T. A crossover of the triplet and singlet states is expected in magnetic fields of about 50 T.

Positively versus negatively charged excitons: A high magnetic field study of CdTe/Cd1−xMgxTe quantum wells

“…Usually, it is equal to that of neutral excitons 7,13 and its contribution can be accounted for by subtraction of the exciton diamagnetic shift (shift of the center of gravity of the exciton Zeeman doublet) from the trion field dependence.…”

“…In particular, it is shown that additionally to the ground trion state, which is an electron singlet, the trion triplet states are bound at finite magnetic fields. 5,[11][12][13] Two types of triplet states-dark and bright-are studied theoretically [14][15][16][17][18] and experimentally. 7,19,20 In magnetic fields above 20 T the binding energy of the triplet state, which is dark, may exceed the singlet state binding energy, so that the triplet state is the ground state of T − .…”

Binding energy of charged excitons in ZnSe-based quantum wells

“…spins of two carriers with the same charges (electrons in X − and holes in X + ) in the trion complex are oriented antiparallel. A triplet trion state with parallel orientation of these spins is unbound at zero magnetic field and becomes bound in high fields only [12]. When free carriers are fully polarized by magnetic field the trions can be excited optically only for one circular polarization.…”

“…Recently the triplet states have attracted considerable attention in GaAs-based QW's [51,52] and in ZnSe-based structures [12]. However, we leave this topic outside the scope of the present paper and concentrate here on the properties of the singlet state.…”

“…At present rather detailed experimental information on trions in ZnSe QW's is available: (i) negatively-and positively charged excitons were documented [5]; (ii) trions were reported for the lighthole excitons [5,8]; (iii) singlet-and triplet trion states were studied in high magnetic fields [11,12]; (iv) spin structure of trions and spin-dependent formation process of trions were investigated [11,13] dynamics in magnetic fields [14] and coherent dynamics of trions [15] were studied; (vi) oscillator strength of trion resonances was examined for different electron densities and in magnetic fields [16]. Theoretical results for this material system are limited to a calculation of the trion binding energy vs well width [17] and its variation in high magnetic fields [12]. Agreement with experiment was rather qualitative -one of the reasons for this is the uncertainty in the parameters used for the calculations.…”