Intra-magnetoexciton transitions in semiconductor quantum wells
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Intra-magnetoexciton transitions in semiconductor quantum wells Z. Barticevic1, M. Pacheco2, C. A. Duque3, and L. E. Oliveira4 1 Depto. de Física, Universidad Técnica Federico Santa María, Casilla 110-V, Valparaíso, Chile 2 Depto. de Física, Universidad de Santiago de Chile, Casilla 307, Santiago, Chile 3 Depto de Física, Universidad de Antioquia, AA 1226, Medellín, Colombia 4 Instituto de Física, Univ. Estadual de Campinas - Unicamp, CP 6165, Campinas-SP, Brazil ABSTRACT Highly sensitive optically detected resonance experiments have shown that magnetoexcitons in GaAs-(Ga,Al)As semiconductor quantum wells have discrete internal energy levels, with transition energies found in the far-infrared (terahertz) region. Here we are concerned with a theoretical study of the terahertz transitions of light-hole and heavy-hole confined magnetoexcitons in GaAs-(Ga,Al)As quantum wells, under a magnetic field applied in the growth direction of the semiconductor heterostructure. The various magnetoexciton states are obtained in the effective-mass approximation by expanding the corresponding exciton-envelope wave functions in terms of appropriate Gaussian functions. The electron and hole cyclotron resonances and intra-magnetoexciton transitions are theoretically studied by exciting the allowed electron, hole and internal magnetoexcitonic transitions with far-infrared radiation. Theoretical results are obtained for both the intra-magnetoexciton transition energies and oscillator strengths associated with excitations from 1s - like to 2s, 2p±, and 3p± - like magnetoexciton states, and from 2p- to 2s – like exciton states. Present results are in overall agreement with available optically detected resonance measurements and clarifies a number of queries in previous theoretical work.
INTRODUCTION The study of the optical properties of semiconductor heterostructures, such as GaAs(Ga,Al)As quantum wells (QWs) and multiple quantum wells (MQWs), provides worthy information on the physical nature of confined electrons, holes, and Coulomb-bound states such as impurities and excitons. It is well known that excitons essentially dominate the optical properties of semiconductor heterostructures and, in particular, an external perturbation such as an applied magnetic field perpendicular to the GaAs and Ga1-xAlxAs semiconductor layers is a powerful tool which is expected to provide valuable information on carrier subbands and exciton states via magneto-optical studies. Confined excitons in GaAs-Ga1-xAlxAs QWs and MQWs under magnetic fields in the growth direction reveal themselves as a series of hydrogenic-like ground and excited magnetoexciton states, with the internal transition energies among the various exciton states in the far-infrared region (FIR - of the order of 10 meV or 2.4 THz). In particular, Salib et al [1] recently observed several internal excitonic transitions and found the 1s → 2p+ heavy-hole (hh) exciton transition as dominant in GaAs-Ga0.7Al0.3As MQWs of Lw = 80 Å and Lw = 125 Å of well width. They have also assigned a “weak” fe
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