OBSERVATION OF BOTH HEAVY-HOLE AND LIGHT-HOLE EXCITONS IN (25-60)-NM DIAMETER GAAS-(AL,GA)AS QUANTUM DOTS

Uniform arrays of free-standing quantum dots (QD's) with lateral dimen sions between 25 and 60 nm have been made from a 5-nm single-quantum-w ell (SQW) structure using electron-beam lithograpy and low-damage, ele ctron-cyclotron-resonance plasma etching. Low-temperature (5 K) photol uminescence (PL) and photoluminescence-excitation (PLE) spectroscopy h ave been used to map the samples carefully both before and after proce ssing into QD's. The PL linewidth increases with decreasing dot diamet er but remains in the range 8-4 meV (full width at half maximum) for t he diameters we have studied. This should be compared to the 3 meV tha t we see for the unprocessed SQW material. Although we have made no in tentional effort to passivate the exposed surfaces of the etched dots we continue to see strong 5-K PL from the samples when ''in-well'' exc itation is employed. Following correction for the area of QW sample re maining in the dots we see a rapid increase in the PL intensity with d ecreasing dot diameter. PLE measurements show a decrease in the Stokes shift of the heavy-hole exciton as the dot diameter is reduced. In ad dition, blueshifts of both the light-hole (lh) and heavy-hole (hh) exc iton are observed as the lateral diameter of the dot diminishes. We be lieve these are the dearest observations of both hh and lh excitons in a range of QD sizes.