Optical Characterization of an Array of Quantum Wires
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G. GUMBSt Department of Physics and Astronomy, Hunter College, City University of New York, 695 Park Avenue, New York, NY 10021 ABSTRACT A self-consistent many-body theory is developed to study the effect of temperature and electron density on the interband absorption coefficient and the frequency-dependent refractive index for an array of isolated quantum wires. The peaks in the absorption coefficient correspond to interband transitions resulting in the resonant absorption of light. The oscillations in the derivative spectrum are due to the quantization of the energy levels related to the in-plane confining potential for such reduced dimensional systems. There are appreciable changes in the absorption spectrum when the electron density or temperature is increased. One interband transition peak is suppressed in the high electron density limit and the thermal depopulation effect on the electron subbands can be easily seen when the temperature is high. We also find that the exciton coupling weakens the shoulder features in the absorption spectrum. This study is relevant to optical characterization of the confining potential and the areal density of electrons using photoreflectance. By using incident light with tunable frequencies in the interband excitation regime, contactless photoreflectance measurements may be carried out and the data compared with our calculations. By fitting the numerical results to the peak positions of the photoreffectance spectrum, the number of electrons in each wire may be extracted. I. INTRODUCTION Present-day nanofabrication technology, such as reactive ion etching and electron beam lithography, has made it possible to confine electrons in narrow quantum channels thereby realizing the idealized one-dimensional (MD)electron gas [1,2]. Interest in these systems is increasing because of the novel fundamental physics that presents itself and the potential device applications. Investigation of the optical properties of quantum wire structures (QWS) on a heterojunction has demonstrated that they may be used as optical detectors and lasers. Wegscheider, et al. [31 have fabricated a quantum wire laser which operates as a result of stimulated emission from excitons. The nature and properties of the collective excitations have also been examined in considerable detail (see Refs. [4-6] and references given there). Recent studies hkave shown that ID confinement becomes effective when the lateral dimension is less than 500A [7]. In this paper, we present a self-consistent field theory for the absorption coefficient of QWS consisting of a ID array of isolated wires parallel to the y axis at different electron densities and temperatures. We simulate the lateral confining potential due to etching by parabolic potentials for the electrons and holes [8]. When the derivative of the absorption coefficient is taken with respect to the light frequency, the details of the spectral features are greatly amplified. This model gives a quantitative way of determining the electron density and the frequencies of the i
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