CALCULATION OF EXCITONIC ABSORPTION-SPECTRUM OF GAAS QUANTUM-WIRE FREESTANDING IN VACUUM

The electron-hole interaction in a thin (approximate to 10 nm) GaAs qu antum wire free-standing in vacuum is strongly enhanced by the image c harge due to the abrupt permittivity drop at the wire surface. As a re sult, the exciton binding energies are much larger and the exciton wav e functions much more localised than those of the GaAs quantum wire su rrounded by the AlGaAs. The absorption spectrum of the free-standing w ire shows besides the Is exciton peak also the 3s and 5s exciton peaks , even if the peaks are 15 meV broad. The continuum absorption edge sh ows a large blue shift due to the renormalization of single-particle e nergies by the image charge.