DIRECT OBSERVATION OF ABOVE-QUANTUM-STEP QUASI-BOUND STATES IN GAAS ALXGA1-X/VACUUM HETEROSTRUCTURES/

In this paper we demonstrate the existence of above-quantum-step quasi bound states in GaAs/Al0.24Ga0.76As/vacuum double heterostructures usi ng a modulated photoreflection spectroscopy technique at room temperat ure. A series of clearly resolved structures was found in the spectra. Their energy positions agree well with those of transitions between q uasibound states in the state density of the heteorostructure. Further envelope wave-function analysis indicates that these quasibound state s mainly center in the GaAs/Al0.24Ga0.76As quantum-step region, and ar e found to be affected by the limited length of electron coherence. [S 0163-1829(98)08215-0].