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Journal of Applied Physics

Interband optical-absorption spectra of a finite quantum dot superlattice in a cylindrical nanowire

T. Y. Zhang, Wei Zhao, Junjie Cao, G. Qasim

Published Nov 1, 2005• 11 citations
Publisher

Abstract

Theoretical calculations of the interband optical-absorption spectra of a finite quantum dot superlattice in a wire (QDSLW) in the presence of a homogeneous dc or terahertz field are presented. The QDSLW has miniband structures of the electron states as general quantum well superlattices do and shows the two features common to one-dimensional structures, viz., strong excitonic absorption below and weak absorption above the band edge. The applied dc field causes a redshift of the location and a decrease in height of the main excitonic peak and leads to an increase in height of the minor peak next to the main peak. In the presence of a terahertz field, the Autler-Townes splitting of the main excitonic peak and the emergence of one-photon and two-photon gain peaks on the spectra are demonstrated.

DOI
10.1063/1.2131190

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Theoretical calculations of the interband optical-absorption spectra of a finite quantum dot superlattice in a wire (QDSLW) in the presence of a homogeneous dc or terahertz field are presented. The QDSLW has miniband structures of the electron states as general quantum well superlattices do and shows the two features common to one-dimensional structures, viz., strong excitonic absorption below and weak absorption above the band edge. The applied dc field causes a redshift of the location and a decrease in height of the main excitonic peak and leads to an increase in height of the minor peak next to the main peak. In the presence of a terahertz field, the Autler-Townes splitting of the main excitonic peak and the emergence of one-photon and two-photon gain peaks on the spectra are demonstrated.
Optical interband excitonic absorption of semiconductor quantum wells (QW’s) driven by a coherent pump field is investigated on the basis of semiconductor Bloch equations. The pump field has a photon energy close to the intersubband spacing between the first two conduction subbands in the QW’s. An external weak optical field probes the interband transition. The excitonic effects and pump-induced population redistribution within the conduction subbands in the QW system are included. When the density of the electron–hole pairs in the QW structure is low, the pump field induces an Autler–Townes splitting of the exciton absorption spectrum. The split size and the peak positions of the absorption doublet depend not only on the pump frequency and intensity but also on the carrier density. As the density of the electron–hole pairs is increased, the split contrast (the ratio between the maximum and the minimum values) is decreased, because the exciton effect is suppressed at higher densities owing to the many-body screening.
An approach for solving the excitonic absorption in a semiconductor quantum well driven by an intense terahertz field is presented. The formalism relies on the stationary single-photon Schrodinger equation in the full quantum mechanical framework. The optical absorption dynamics in both weak and strong couplings are discussed and compared. The excitonic absorption spectra show the Autler—Townes doublets for the resonance terahertz field, a replica peak for the non-resonance terahertz field, and the electromagnetically induced transparency phenomenon for modulating the decay rate of the second electron state in the weak coupling. In particular, the electromagnetically induced transparency phenomenon window range is discussed. In the strong coupling region, the multi-order energy level resonance splitting due to the strong optical field is found. There are three (non-resonance terahertz field) or four (resonance terahertz field) peaks in the optical absorption spectra. This work provides a simple and convenient approach to deal with the optical absorption in the exciton system.
Abstract In this paper, we examine the three-level optical Stark effect of excitons in InGaAs/InAlAs quantum dots using renormalized wavefunction formulation. The system was assumed to be irradiated by two lasers in which a strong laser dynamically couples electron-quantized levels, while a weaker laser probes interband absorption. Our results show that, in the presence of the resonant strong laser, two new absorption peaks of excitons appear in the absorption spectrum as a clear indication of the effect. In addition, we propose that the formation of the effect in low-dimensional structures could have connection to the splitting of electron levels. Furthermore, we seek to explain the essential dependence of the amplitude and position of two peaks on pump field detuning.
Nonlinear optical properties of intersubband electrons in a 3-level quantum well under intense terahertz field are investigated by using a density matrix approach. The results show that the terahertz fields with different frequencies cause the distinct modulations of the intersubband absorptions. The terahertz-induced sideband and Autler–Towns splitting in the absorption spectrum are obtained, respectively for the terahertz-photon energy below and close to the transition energy between the ground and first excited state.
This study looks at the three-level optical Stark effect of excitons in GaAs cylindrical quantum wires, utilizing the renormalized wave function theory. By applying the three-level model consisting of the first two electron levels connected via a powerful pump laser and the first hole level, we observe the appearance of the excitonic optical Stark effect through the appearance of two separated peaks in the exciton absorption spectra. In addition, the strong impact of the pump laser detuning and the wire radius on the optical Stark effect are also put under thorough examination. Finally, a brief guidance for experimental verification is also suggested.
We calculate the anisotropic two-photon absorption spectra of an AlGaAs-GaAs V-shaped quantum wire with realistic band structure, including excitonic effects. The absorption coefficient is obtained by integrating effective multiband Bloch equations accounting for the Coulomb interaction within the Hartree-Fock approximation. The various excitonic peaks are identified with respect to the involved energy subbands and the symmetry properties. Furthermore, A/sub 2/-excitons, which are dark for one-photon excitation, become bright for two-photon spectroscopy when the light is linearly polarized along a direction that is not a symmetry axis. We show that some of them may be observable.