Abstract
Photoluminescence, excitation, electroreflectance and direct reflectance spectroscopy have been used to study the interband transitions in a number of modulation doped, p-type GaAs/(Al,Ga)As quantum wells. Gated samples enable a wide range of hole densities to be studied. A 150 Å `wide' quantum well sample illustrates the quenching of the neutral heavy- and light-hole exciton features, in the presence of a Fermi sea, and a transition to a charged exciton ground state (and light-hole, heavy-hole, electron bound complex). Different behaviour is found in the absorption features of the narrow (70–85 Å) quantum wells; while the charged exciton forms the ground-state threshold for photon absorption, we find the neutral exciton shifts up in energy with increasing Fermi energy. The magnitude of this blue shift is between three and four times the Fermi energy and is observed for both the heavy- and light-hole exciton.
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