Optical reflection and contactless electroreflection from GaAlAs layers with periodically arranged GaAs quantum wells
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Optical Reflection and Contactless Electroreflection from GaAlAs Layers with Periodically Arranged GaAs Quantum Wells V. V. Chaldysheva^, A. S. Shkol’nika, V. P. Evtikhieva, and T. Holdenb aIoffe
Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: [email protected] bBrooklyn College of the City University of New York, USA Submitted December 25, 2005; accepted for publication April 28, 2006
Abstract—Optical reflection and electroreflection for the AlGaAs layers containing the periodically arranged GaAs quantum wells of different thickness are studied at photon energies ranging from 1 to 2 eV. It is established that the spectral dependence of the reflectance involves three different contributions made by (i) the reflection from the medium–air interface; (ii) the interference reflection due to the periodically modulated refractive index, since the materials of the wells and barriers have different refractive indices; and (iii) the reflection produced by the interaction of electromagnetic waves with the exciton states in the quantum wells. Analysis of the reflection spectra shows that these contributions are characterized by different behavior with variations in temperature, angle of incidence of light, and polarization; however, quantitative separation of the spectra into individual contributions presents a rather difficult problem. To separate the contribution originating from the interaction of light with the exciton states from the optical spectra, a special approach based on contactless measurements of the optical electroreflectance over a certain spectral region is developed. It is shown that this method provides a means for determining the parameters of the exciton states in the quantum wells. PACS numbers: 78.67.De, 73.21.Fg, 78.40.Fy DOI: 10.1134/S1063782606120116
Interaction of electromagnetic waves with excitons in a semiconductor results in the formation of excitonic polaritons and in a change of resonance in the optical properties of the medium [1]. This type of resonance phenomena is of particular interest in the case of periodic quantum well (QW) structures, such that the wavelength corresponding to the exciton ground state in the QWs, λex = hc/Eexn, satisfies the Bragg condition for the interference of electromagnetic waves, λex = 2d, where d is the period of the structure, Eex is the energy of the exciton ground state, n is the refractive index of the medium, h is the Planck constant, and c is the speed of light in free space. The theoretical analysis first carried out in [2] has shown that, in such a structure, the optically active mode is only the polariton mode, for which the oscillator strength increases proportionally to the number of QWs. In more recent theoretical studies [3–9], the optical properties of these kinds of structures were treated taking into account such factors as nonradiative energy dissipation, deviations of the structural parameters from the exact Bragg condition, variations in the QW width, etc. The theoretic
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