INTERBAND SPECTROSCOPY OF P-TYPE GAAS (AL,GA)AS QUANTUM-WELLS AT LOW HOLE DENSITIES/

Photoluminescence, excitation, electroreflectance and direct reflectan ce spectroscopy have been used to study the interband transitions in a number of modulation doped, p-type GaAs/(Al,Ga)As quantum wells. Gate d samples enable a wide range of hole densities to be studied. A 150 A ngstrom 'wide' quantum well sample illustrates the quenching of the ne utral heavy- and light-hole exciton features, in the presence of a Fer mi sea, and a transition to a charged exciton ground state (and lighl- hole,heavy-hole, electron bound complex). Different behaviour is found in the absorption Features of the narrow (70-85 Angstrom) quantum wel ls; while the charged exciton forms the ground-state threshold for pho ton absorption, we find the neutral exciton shifts up in energy with i ncreasing Fermi energy. The magnitude of this blue shift is between th ree and four times the Fermi energy and is observed for both the heavy - and light-hole exciton. (C) 1998 Elsevier Science B.V. All rights re served.