Formation and Recombination Dynamics of Charged Excitons in a GaAs Quantum Well

Abstract

We report a time-resolved photoluminescence study of negatively charged excitons (X À ) in remotely doped GaAs/AlGaAs quantum wells. We measure the effects of temperature, electron density and magnetic field on the X À formation process (X þ e À ! X À ), thereby demonstrating that it can be regarded as a classical exciton-electron scattering process. At low electron densities we find a linear dependence of the X þ e À ! X À formation rate on electron concentration and perpendicular magnetic field. At high electron densities, for which X À formation is very fast, the PL decay time is a direct measure of the X À intrinsic lifetime t X À . We demonstrate experimentally the dependence of t X À on the X À homogeneous linewidth.

Origin of the Oscillator Strength of the Triplet State of a Trion in a Magnetic Field

“…The sample is gated with a semitransparent NiCr Schottky gate which is biased with respect to the QW Ohmic contact, allowing the electron density within the well to be varied from few 10 9 to 10 11 cm ÿ2 . In previous works [15,17] we have shown that, by varying the electric bias between the surface gate and the GaAs QW, we can observe in the PL spectra emission from X; X ÿ and eventually a two-dimensional electron gas. Notice that in the absence of a back gate bias only a negligible electric field is present across the well [18].…”

“…3. In a previous publication [17], we have demonstrated that X ÿ is mainly formed via excitons rather than directly from electron hole pairs. Thus the processes we include to describe the dynamics are the radiative decay of each of the states, characterized by lifetimes X , X ÿ t , and X ÿ s , and the feeding from X to X ÿ t and X ÿ s , with lifetimes t and s , respectively.…”

Photoluminescence of a two-dimensional electron gas in a modulation-dopedGaAs/AlxGa1−xAshkinadze1, Linder2, Cohen3 et al. 2004Phys. Rev. B120120View full textAdd to dashboardCite

“…This is because of the short recombination times of the photoexcited particles. 2,25 Nonthermalized valence band holes were detected in the PL spectra obtained at Bϭ0. Indeed, for n 2D Ͼ5ϫ10 10 cm Ϫ2 the electron-hole interaction is screened by the 2DEG, and the observed PL spectra at Bϭ0 can be well fitted by a product of the 2D electron and hole distribution functions characterized by effective electron T e and hole T h temperatures.…”

“…Under an applied magnetic field, the energy and spin relaxation rates decrease, 25 leading to a nonthermal redistribution of photogenerated particles between spin-split (n LL ϭ0) Landau Levels as well as between the excitonic (X s Ϫ ,X t Ϫ , X 0 ) states. This is detected by a low degree of the polarization of the X s Ϫ ,X t Ϫ , and X 0 lines.…”

Dynamic of Spin Triplet and Singlet Trions in a GaAs Quantum Well

“…This behaviour is not different from what has already been observed for the X ! X À transition in absence of an external magnetic field [10]. A different behaviour is observed for the spin triplet X À .…”