Negatively charged trion in ZnSe single quantum wells with very low electron densities

Abstract

The polarization-and excitation-intensity-dependent photoluminescence of the negatively charged trion is investigated for ZnSe single quantum wells embedded in ternary and quaternary barriers. The measurements were performed in magnetic fields up to 11.8 T perpendicular to the quantum well. The spin-singlet state of the trion is clearly identified. In contrast to GaAs quantum wells, the increase of the trion binding energy through the magnetic field is found to be negligible, which is explained by the relatively small spatial extent of the trionic wave function in wide-band-gap materials. For magnetic fields beyond 7 T a resonance becomes stabilized that is identified as excited trion spin-triplet state because of its anticorrelation with the trion spin-singlet state behavior for increasing excitation energy.

Binding energy of charged excitons in ZnSe-based quantum wells

“…Only a small deviation from this dependence was found for the type D structure with ∆E g =70 meV. For very shallow 70Å ZnSe/Zn(S,Se) QW's with ∆E g =25-35 meV a trion binding energy of 2.7-2.9 meV has been reported [11]. This is consistent with our data from Fig.…”

“…However, after the first report of X − observation in Zn 0.9 Cd 0.1 Se/ZnSe QW's in 1994 [7], detailed investigations were started from 1998 only, when the high-quality ZnSe-based structures with binary quantum well layers were fabricated [8,9,10]. 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].…”

Photoluminescence ofp-doped quantum wells with strong spin splitting

“…That means that the singlet arrangement of the two holes involved in the charged exciton is replaced by a parallel arrangement of their spins (triplet state). Contrary to the case of nonmagnetic quantum wells, for which the triplet state of the charged exciton is stabilized by orbital effects at very high magnetic field 19,30,31 , in the present case the singlet state is destabilized by spin effects. This gives rise to several features which agree with a mechanism involving band-to-band transitions (double line, with the lower component having the ground state of the hole gas as its final state, and the upper one leaving the carrier gas in an excited state; and existence of a Moss-Burstein shift).…”

“…It is not clear whether a triplet state of the charged exciton could be stabilized by the Zeeman energy. Up to now, triplet states have been described in non-magnetic QWs at field values large enough to alter the orbital motion of the carriers 18,19,20,30,31 , which is not the case here. At large carrier densities, these bound states will become more and more difficult to distinguish from an uncorrelated electron-hole pair, but for the fact that in the absence of interactions, the high energy component D hi should vanish.…”

Photoluminescence of p-Doped Quantum Wells with Strong Spin Splitting

“…The spin configuration of the charged excitons usually corresponds to the singlet statethe two identical particles have opposite spins. However, it has been shown that the triplet configuration (the two identical particles having the same spin) can be stabilized in high magnetic field [17][18][19][20][21] thanks to the "shrinking" of the wave functions.…”