Dynamics of Trion Formation inInxGa1−xAsQuantum Wells

Abstract

We show a double path mechanism for the formation of charged excitons (trions); they are formed through bi-and trimolecular processes. This directly implies that both negatively and positively charged excitons coexist in a quantum well, even in the absence of excess carriers. The model is substantiated by time-resolved photoluminescence experiments performed on a very high quality In x Ga 1Àx As quantum well sample, in which the photoluminescence contributions at the energy of the trion and exciton and at the band edge can be clearly separated and traced over a broad range of times and densities. The unresolved discrepancy between the theoretical and experimental radiative decay time of the exciton in a doped semiconductor quantum well is explained by the same model. Positively and negatively charged excitons (X þ and X À trions) [1,2] are usually compared to their atomic counterpart ions of helium He þ and hydrogen H À , respectively. In astronomy, the dynamics of the formation of these atomic ions is of great importance [3]; indeed, H À is the primary source of the continuum opacity in most stellar photospheres and contributes to the production of hydrogen and other elements in various parts of the Universe. Additionally, the abundance of free electrons in the solar atmosphere is indirectly measured in terms of H À concentration. In semiconductor quantum wells (QWs), trions show a number of properties very similar to excitons [4], such as strong coupling in microcavities [5], absorption bleaching [6,7], transport [8] and diffusion [9] properties, and radiative recombination efficiency [10,11], and thus have attracted considerable interest. Moreover, trions promise to play a key role in future applications, notably in quantum-information science [12] and in the future development of all-spin-based scalable quantum computers [13,14]. They are correlated with excitons and the free carrier plasma and offer the possibility to test a model of formation of three-particle complexes.The formation process of neutral excitons (X) in QWs has been extensively investigated over the past two decades [15,16] and recently shown to be strongly density-and temperature-dependent [17]. This is a bimolecular process, in which an electron (e) and a hole (h) are bound by Coulomb interaction with the emission of the appropriate phonon. Conversely, the formation process of trions has been much less studied. It is largely believed that trions can be formed only if a population of excess carriers is trapped in the well, producing exclusively trions with the same charge. Consequently, existing models discriminate the formation channel yielding trions of opposite charge. Current models for trion formation [18,19] surmise that trions are exclusively formed through a bimolecular process, i.e., the coalescence of an exciton and a charged free carrier. While this is conceivable at low densities, nothing attests that genuine formation of the trion from an unbound electron-hole plasma (trimolecular formation) is negligible at higher densities.In...

Valley trion dynamics in monolayer MoSe2

“…In the presence of excess charges, charged excitons called trions 21,22 can be formed through the coalescence of an exciton and a free charge or directly from an unbound electron-hole plasma 23 . In monolayer TMD, strong Coulomb interactions lead to exceptionally high binding energies for excitons 24 and trions 11,25,26 , allowing them to exist even at room temperature.…”

Trion dynamics in hole-doped single-walled carbon nanotubes

“…The trion decay time of 440 fs is extremely short compared with the exciton lifetimes typically observed in isolated SWNTs [8]. In In x Ga 1 x As quantum wells the trion lifetime is of the same order of magnitude as the exciton lifetime [2]. Therefore, the short decay time observed in this study suggests that the trion annihilation in p-doped SWNTs is governed by nonradiative recombination processes such as the Auger recombination process with scattering of a hole.…”

“…The binding energy of trions in conventional semiconductors is a few meV, and they are stable only at very low temperatures [1,2]. In single-walled carbon nanotubes (SWNTs), the stable trion state at room temperature is expected because of the strong exciton effects in quasi-one dimensional systems [3].…”

The role of excitons and trions on electron spin polarization in quantum wells

“…Also, data for hole spin flip times can be found in the literature [34][35][36] . An extensive analysis of the formation, recombination and dissociation coefficients can be found in the papers of Esser et al 1 and Portella-Oberli et al 4,37 . Following these last references and considering the mass action law (Saha-Eggert relations), we have evaluated the corresponding values for our structure (Appendix A).…”