Photoluminescence of p-doped quantum wells with strong spin splitting

TL;DR

This study investigates the photoluminescence properties of p-doped (Cd,Mn)Te quantum wells with strong spin splitting, revealing how spin polarization affects exciton states and spectral features in a spin-polarized hole gas.

Contribution

It provides new insights into the effects of giant Zeeman-induced spin splitting on exciton states and photoluminescence in quantum wells, including the destabilization of singlet states and formation of triplet states.

Findings

Spin splitting induces full polarization of the hole gas.

Charged excitons transition from singlet to triplet states with increasing spin splitting.

Spectral shifts correlate with excitations in the polarized hole gas.

Abstract

The spectroscopic properties of a spin polarized two-dimensional hole gas are studied in modulation doped (Cd,Mn)Te quantum wells. The giant Zeeman effect 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 Moss-Burstein 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 carrier-carrier 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.