Effects of Confinement on the Optical Properties of a Shallow Acceptor and its Bound Exciton in Narrow GaAs/AIGaAs Quant
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EFFECTS OF CONFINEMENT ON THE OPTICAL PROPERTIES OF A SHALLOW ACCEPTOR AND ITS BOUND EXCITON INNARROW GaAs/AIGaAs QUANTUM WELLS P.O. HOLTZ-,--, M. SUNDARAM**, G.C. RUNE-, B. MONEMAR*, J.L. MERZ**, AND A.C. GOSSARD** * Department of Physics and Measurement Technology, Linkbping University, S-581 83 Link6ping, Sweden ** Department of Electrical and Computer Engineering and Materials Department, University of California at Santa Barbara, Santa Barbara, CA 93106 ABSTRACT Transitions from the ls ground state to 2s excited states of the Beacceptor confined in GaAs/AIGaAs quantum wells (QWs) have been observed via two independent spectroscopic techniques: Two-hole transitions of the bound exciton (BE) measured in selective photoluminescence and Resonant Raman Scattering. The dependence of the ls - 2s transition energy on the QW thickness (50 A < Lz < 140 A) has been studied for the case of acceptors in the center of the QW. The experimentally determined ls - 2s transition energies have then been added to recently calculated binding energies for the 2s excited state in order to obtain the total binding energies for the acceptor at different confinements. The derived binding energies are finally compared with theoretical predictions. The same kind of measurements have been performed for a QW with a given thickness, but in which the position of the acceptor has been varied from the center to the edge of the QW. The dependencies of the binding energies of the exciton bound to the investigated acceptor on the QW thickness and the position of the acceptor in the QW have also been studied. For the case of varying QW thickness, an almost linear relationship between the binding energies of the BE and the acceptor binding the exciton is found. This fact implies that a correspondence to Haynes' rule in bulk material could be applied to these QW systems, but in this case for the same acceptor at different binding energies due to the effect of varying confinement. INTRODUCTION The knowledge of the electronic properties of impurities confined in QWs is much more limited than the corresponding level for bulk defects. The situation is expected to be more complicated in a QW due to the reduced symmetry from Td for a point defect in bulk to D2d for an acceptor at the center of a OW and to C2 v for an off-center acceptor [13]. Electronic properties such as the binding energy of the ground state and the excited states of acceptors confined in quantum wells (QWs) Mat. Res. Soc. Symp. Proc. Vol. 163. (1990 Materials Research Society
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have been predicted in several theoretical papers. In the original calculation by G. Bastard [4] hydrogenic impurity potentials and infinite barrier heights were used, which resulted in continuously increasing binding energies with decreasing QW width. When more realistic finite heights for the barriers were used in the calculations by W.T. Masselink et al. [1, 2], it was shown that the binding energy goes through a maximum at a non-zero QW width. The acceptor energies were calculated for varying positions i
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