V. A. Lovtcius

Radiative decay rate of excitons in square quantum wells: Microscopic modeling and experiment

The binding energy and the corresponding wave function of excitons in GaAs-based finite square quantum wells (QWs) are calculated by the direct numerical solution of the three-dimensional Schrodinger equation. The precise results for the lowest exciton state are obtained by the Hamiltonian discretization using the high-order finite-difference scheme. The microscopic calculations are compared with the results obtained by the standard variational approach. The exciton binding energies found by two methods coincide within 0.1 meV for the wide range of QW widths. The radiative decay rate is calculated for QWs of various widths using the exciton wave functions obtained by direct and variational methods. The radiative decay rates are confronted with the experimental data measured for high-quality GaAs/AlGaAs and InGaAs/GaAs QW heterostructures grown by molecular beam epitaxy. The calculated and measured values are in good agreement, though slight differences with earlier calculations of the radiative decay rate...

Multiple-frequency quantum beats of quantum confined exciton states

A. V. Trifonov,1 I. Ya. Gerlovin,1 I. V. Ignatiev,1 I. A. Yugova,1 R. V. Cherbunin,1 Yu. P. Efimov,2 S. A. Eliseev,2 V. V. Petrov,2 and A. V. Kavokin1, 3 Spin Optics Laboratory, Saint Petersburg State University, 198504 St. Petersburg, Russia SPbU Resource Center “Nanophotonics”, Saint Petersburg State University, 198504 St. Petersburg, Russia Physics and Astronomy School, University of Southampton, Highfield, Southampton, SO171BJ, UK (Dated: July 16, 2015)

Excitons in asymmetric quantum wells

Abstract Resonance dielectric response of excitons is studied for the high-quality InGaAs/GaAs heterostructures with wide asymmetric quantum wells (QWs). To highlight effects of the QW asymmetry, we have grown and studied several heterostructures with nominally square QWs as well as with triangle-like QWs. Several quantum confined exciton states are experimentally observed as narrow exciton resonances. A standard approach for the phenomenological analysis of the profiles is generalized by introducing different phase shifts for the light waves reflected from the QWs at different exciton resonances. Good agreement of the phenomenological fit to the experimentally observed exciton spectra for high-quality structures allowed us to reliably obtain parameters of the exciton resonances: the exciton transition energies, the radiative broadenings, and the phase shifts. A direct numerical solution of the Schrodinger equation for the heavy-hole excitons in asymmetric QWs is used for microscopic modeling of the exciton resonances. Remarkable agreement with the experiment is achieved when the effect of indium segregation is taken into account. The segregation results in a modification of the potential profile, in particular, in an asymmetry of the nominally square QWs.

Exciton scattering in heterostructures with (In,Ga)As/GaAs quantum wells

Reflectance spectroscopy is used to study exciton scattering caused by phonons, nonradiative excitons, and free carriers in a heterostructure with a wide (In,Ga)As/GaAs quantum well. Nonradiative excitons and free carriers are created via additional monochromatic illumination by a tunable laser. Constants of exciton–acoustic phonon and exciton–LO phonon scattering are determined from the temperature variations in the nonradiative broadening of exciton resonances. The excitation spectra of nonradiative broadening reveal sharp resonances associated with exciton–exciton scattering and a smooth background caused by exciton–free carrier scattering.

Microscopic modeling of exciton spectra in asymmetric quantum wells

A theoretical model of reflectance spectra is applied to the analysis of spectra of the two high-quality structures with asymmetric InGaAs/GaAs quantum wells. The analysis allows to quantitatively describe the exciton resonances related to the lowest quantum-confined exciton states. Main parameters of the quantum well potential profiles are obtained in the modeling.

Inversion of Zeeman splitting of exciton states in InGaAs quantum wells

Zeeman splitting of quantum-confined states of excitons in InGaAs quantum wells (QWs) is experimentally found to depend strongly on quantization energy. Moreover, it changes sign when the quantization energy increases with a decrease in the QW width. In the 87-nm QW, the sign change is observed for the excited quantum-confined states, which are above the ground state only by a few meV. A two-step approach for the numerical solution of the two-particle Schroedinger equation, taking into account the Coulomb interaction and valence-band coupling, is used for a theoretical justification of the observed phenomenon. The calculated variation of the g-factor convincingly follows the dependencies obtained in the experiments.

Reduction of exciton mass by uniaxial stress in GaAs/AlGaAs quantum wells

D. K. Loginov, P. S. Grigoryev, E. V. Ubiyvovk, Yu. P. Efimov, S. A. Eliseev, V. A. Lovtcius, Yu. P. Petrov, and I. V. Ignatiev Spin Optics Laboratory, St. Petersburg State University, 198504 St. Petersburg, Russia Department of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia Resource Center “Nanophotonics”, St. Petersburg State University, 198504 St. Petersburg, Russia (Dated: May 11, 2015)

Decrease of heavy-hole exciton mass induced by uniaxial stress in GaAs/AlGaAs quantum well

D. K. Loginov, P. S. Grigoryev, E. V. Ubiyvovk, Yu. P. Efimov, S. A. Eliseev, V. A. Lovtcius, Yu. P. Petrov, and I. V. Ignatiev Spin Optics Laboratory, St. Petersburg State University, 198504 St. Petersburg, Russia Department of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia Resource Center “Nanophotonics”, St. Petersburg State University, 198504 St. Petersburg, Russia (Dated: May 11, 2015)