Light- and Heavy-Hole Bound Exciton Transitions and Free to Bound Transitions in Ga x Al 1-x As/GaAs Quantum Wells
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LIGHT- AND HEAVY-HOLE BOUND EXCITON TRANSITIONS AND FREE TO BOUND TRANSITIONS IN Ga All As/GaAs QUANJI-1 WELLS DONALD C. REYNOLDS* AND K.K. BAJAJ$ *Electronic Technology Laboratory,Wright Research and Developuernt Center, Wright-Patterson Air Force Base, OH 45433 * *Arizona State Univeristy, Tempe, AZ 86443 ABSTRACT Excitons bound to neutral donors in Alx Gat_xAs/GtA
quanttum wells were
observed by high resolution resonant excitation photoluminescence, and temperature dependent photoluminescence measurements. Changes in the binding energy of excitors are observed when the donors are located in the center of the well, at the edge of the well, or in the center of the barrier. The variations in these binding energies are reported as a function of well size from 75-350A. The binding energies irnreased as the well size was reduced to about 100A, with further reductions in well size they decreased. Light-hole free excitons bound to neutral donors were observed in The transitions were observed, using Al xl_xAs/CaAs quantum wells. selective excitation photoluminescence spectroscopy, in the energy region between the light-hole and heavy-hole free exciton transitions where no other intrinsic transitions exist. The neutral donor-bound heavy-hole free-exciton trmansitions were also observed when the light-hole bound exciton transitions were observed. Quantum well structures which showed no evidence of a heavy-hole donor bound exciton also showed no evidence of a light-hole donor bound exciton. Free to bound transitions, free hole to bound electron, have also been observed in the AlGa•lxAs/GaAs quantum wells. The diamagnetic shift of these tranisitions was used to distinguish them from excitonic transitions. Introduction There have been few measurements of the binding energy of exci tons to neutral donors (Do,X) or ionized donors (D+,X) in quantmnt wells (QWs). The original report of donor related complexes in quantum wells was by Shazabrook and Comas [11. Reynolds et al [21 reported sharp lines observed
in photoluminescence
(PL)
associated with D0 ,X transistionis
in
D0 ,X transitions were also GaAs-Alx Ga 1-xAs multiple-quanttum wells (MQWs). reported by Nomura et al [3] in Si-doped GAs-Al GaIx As single QWs (SQWs). Recently, Liu et al [4] have also observed transitions in PL associated with excitons bound to neutral and ionized donors located at the center of 0 the quaintum wells. An, impurity-bound exciton (probbly D ,X) tranlsitiorn was reported by Charbonneau el al [5] in a 180A SQ where interrupted growth was used.
We report a systetmatic study of the binding energy of Do,X in sever'al QWs of varying sizes and as altered by the physical location of the neutLral donors. The s-As x Ga1 _xAs QWsamples investigated were either niominal ly undoped,
Si-doped in the center of the well (CW),
Mat. Res. Soc. Symp. Proc. Vol. 163. ', 1990 Materials Research Society
the edges of the well
314
(EW),
or doped in
the center of the ALx Ga IxAs
barrier (CB).
We also
speculate on the binding energy of D+,X by tentatively
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