Center-of-mass quantization of excitons and polariton interference in GaAs thin layers

Abstract

We report a detailed study of the properties of exciton polaritons confined in GaAs thin layers grown by molecular-beam epitaxy. Intermediate-layer thicknesses from 150 to 600 nm between quasi-twodimensional quantum wells and bulk GaAs are considered. Both reflectance and photoluminescence measurements have been performed, and a large number of oscillation fringes and emission peaks have been detected. The spectra obtained are significantly different from those of a quantum well or of bulk GaAs, and can be attributed to quantized levels of the exciton-center-of-mass motion. The thickness dependence of the exciton peaks shows dominant contributions from the heavy-hole exciton dispersion due to its larger oscillator strength and density of states. Polariton effects and interference between different modes have to be taken into account to explain the reAectance behavior. This is done using three types of additional boundary conditions (ABC' s). From the sensitive dependence of the reflectance line shape on different ABC' s, we conclude that only Pekar's ABC gives interference fringes comparable to the experimental data. A temperature-dependence investigation gives clear evidence that the polariton effects manifest themselves in both optically thin and optically thick layers of GaAs only at low ternperatures. At higher temperatures the optical transitions are more excitonlike. The results are discussed by modeling the exciton-broadening parameter as a function of the exciton-phonon interaction.

Inversion of Zeeman splitting of exciton states in InGaAs quantum wells

“…Effect of the quantum confinement of excitons in the QWs gives rise to quasiperiodic peculiarities in optical spectra corresponding to the quantization of the centerof-mass exciton motion [31,32]. For such QWs, interfaces do not considerably affect magnetic properties of excitons, which remain similar to those for bulk crystal.…”

“…Similar technique has been used in several publications, see, e.g., Refs. [28,29,31,[37][38][39] resonantly using a Ti-sapphire or a He-Ne laser. Spectral resolution of the setup was sufficiently better than the typical width of features in the PL spectra.…”

Generation of entangled-photon pairs from biexcitons in CuCl thin films: Nano-to-bulk crossover regime

“…11,50-52 Moreover, optical responses explicitly reflects the confinement of center-of-mass motion of excitons in nano-structured materials and also in the nanoto-bulk crossover regime, [17][18][19][20][26][27][28][29][30][31][32][33][34][35][36] which we investigate in the present paper.…”

“…In principle, the biexciton RHPS process is described by the three equations of motion (9), (19), and (20), and commutation relations (10) and (12). However, in the actual calculation, we use the following approximation.…”

“…When the crystal size is larger than the exciton Bohr radius but small enough compared to the light wavelength, the center-of-mass motion of excitons are confined, and the center-of-mass kinetic energy is quantized. 19,20 When the crystal size is comparable or a few times larger than the wavelength (nano-to-bulk crossover regime), the system is characterized by exciton-photon coupled modes with peculiar resonance energy and radiative life time, and the coupled modes are gradually reduced to bulk polaritons with increasing the crystal size. 18,[21][22][23][24][25] In this crossover regime, the system shows a variety of optical responses compared to bulk materials and also to quantum dots due to the center-of-mass confinement of excitons and the spatially resonant coupling with electromagnetic fields.…”