Photoluminescence ofp-doped quantum wells with strong spin splitting

Abstract

The spectroscopic properties of a spin polarized two-dimensional hole gas are studied in modulation doped Cd1−xMnxTe quantum wells with variable carrier density up to 5 10 11 cm −2 . The giant Zeeman effect which is characteristic of diluted magnetic semiconductors, induces a significant spin splitting even at very small values of the applied field. Several methods of measuring the carrier density (Hall effect, filling factors of the Landau levels at high field, various manifestations of MossBurstein shifts) are described and calibrated. The value of the spin splitting needed to fully polarize the hole gas, evidences a strong enhancement of the spin susceptibility of the hole gas due to carriercarrier interaction. At small values of the spin splitting, whatever the carrier density (non zero) is, photoluminescence lines are due to the formation of charged excitons in the singlet state. Spectral shifts in photoluminescence and in transmission (including an "excitonic Moss-Bustein shift") are observed and discussed in terms of excitations of the partially or fully polarized hole gas. At large spin splitting, and without changing the carrier density, the singlet state of the charged exciton is destabilized in favour of a triplet state configuration of holes. The binding energy of the singlet state is thus measured and found to be independent of the carrier density (in contrast with the splitting between the charged exciton and the neutral exciton lines). The state stable at large spin splitting is close to the neutral exciton at low carrier density, and close to an uncorrelated electron-hole pair at the largest values of the carrier density achieved. The triplet state gives rise to a characteristic double-line structure with an indirect transition to the ground state (with a strong phonon replica) and a direct transition to an excited state of the hole gas.

Photoluminescence of p-Doped Quantum Wells with Strong Spin Splitting

“…We see large changes in the relative intensities of D high and D low from sample to sample, suggesting that the indirect character is allowed by disorder or many-body interactions. Further confirmation of the indirect character of the transition is given by the LO-phonon replica that we observe for all samples in σ + polarization, and only for D high [33]. The difference between D high and D low is then a measure of the energy that is left in the system during the PL process D low : the final state of the latter transition is an excited state of the hole gas.…”

“…3 for a 8 [24,33]. When increasing the magnetic field, the intensity of this line decreases in both polarizations: the signal is zero above 0.875 T in σ − whereas a novel feature -a double line called D high and D low in the following -emerges in σ + polarization.…”

“…We also tuned the hole density from the low 10 10 cm −2 to 4 × 10 11 cm −2 by applying bias voltage of the order of 1 V in some pin structures containing a (Cd,Mn)Te QW [32]. The hole densities were calibrated from the energy difference between absorption and PL (the so-called Moss-Burstein shift), from the Hall effect or from the filling factors measured at high magnetic fields [33].…”

Coupling of Quantum Dots with Quantum Wells in a System Based on (Cd,Zn,Mg)Te

“…Thanks to combining such different objects in one structure, one can think about unusual combination of physical properties. For example, spin relaxation in QWs, and in particular semimagnetic QWs [6][7][8], is very fast, but it is rather slow in QDs [9] or QDs containing single magnetic ions [10,11]. Therefore structure with coupled QWs and QDs could be used for efficient spin orientation of carriers in QWs and further injection of such polarized carriers to QD, where spin will be preserved long time.…”

Excitonic Energy Shifts in CdMnTe/CdMgTe Quantum Wells under Resonant Excitation in Presence of 2D Carrier Gas

“…In spite of years of studies on CdTe 2D materials there are many mechanisms, especially many-body effects, to be understood, such as interactions between ground and higher excitonic states in presence or absence of free carrier gas. Until now, some work has been done regarding interactions among trions, neutral e1hh1 excitons and 2D gas of free carriers [1][2][3][4][5][6], with even higher excitonic states studied in a specially designed multi-quantum well (MQW) structure [7], but there is a wide field of phenomena to be clearly understood. One of such phenomenon is an origin of energy shift of the exciton transition after creation a high population of the excitons and an influence of the free carriers on this energy shift.…”