Thermal dissociation of free and acceptor-bound positive trions from magnetophotoluminescence studies of high quality GaAs/AlxGa1-xAs quantum wells

Thermal dissociation of free and acceptor-bound quasi-two-dimensional positive trions is investigated by measuring the temperature dependence of the integrated emission intensity in magnetic fields up to 17 T in high quality GaAs/AlxGa1-xAs quantum wells. Three distinct dissociation processes are observed for the well-resolved hole cyclotron replicas ("shake-up") of positive trions bound to neutral acceptors in the spin-doublet state (SU-A0Xd+). To demonstrate that the hole involved in the shake-up process is not bound by the Coulomb interaction to the charged A0X+ complex, we calculate the valence Landau levels using the Luttinger model beyond the axial approximation. The calculated value of the hole cyclotron energy agrees well with the experimental data for the energy separation of the A0X+ and SU-A0X+ lines, determined from the emission spectra. At low temperatures, below 6 K, the dominant dissociation results in a free hole and an exciton bound to the neutral acceptor in the spin-singlet or -triplet state, (A0Xd+→A0Xs+h or A0Xt+h). At higher temperatures, above 9 K, the dissociation into the free positive trion and the neutral acceptor (A0Xd+→A0+X+) predominates. From the temperature evolution of the integrated emission of the free trion lines (X+) we evaluate the transition energy between the two triplet trion states, the dark one (Xtd+) and the bright one (Xtb+). The ionization energies of all detected dissociation processes are compared with the spectral positions of the relevant radiative recombination lines from which excellent quantitative agreement is achieved.