CREATION AND ANNIHILATION OF NEGATIVELY CHARGED EXCITONS IN GAAS QUANTUM-WELLS

The electroluminescence of p-i-n GaAs double-barrier resonant tunnelli ng diodes has been investigated for various concentrations of free car riers (either holes or electrons) in the quantum well (QW). For these structures it is possible to change the relative electron or hole dens ity quasi-continuously with applied bias-voltage. New low-temperature excitonic recombinations are identified in the electroluminescence spe ctra. Continuous variation of the carrier density in the quantum well from a hole-rich into an electron-rich environment leads to the observ ation of positively charged excitons (X(2)(+)), neutral excitons (X), negatively charged excitons (X(-)) and finally an unbound electron-hol e recombination. An increased temperature causes the dissociation of t he charged excitons in favour of the neutral heavy-hole free exciton X . In high magnetic fields the unbound electron-hole recombination is t ransferred into an excitonic recombination.