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The quantum-well electroluminescence of p-i-n GaAs/AlAs double-barrier resonant tunneling diodes has been investigated. The bias-dependent tunability of the resonance conditions for electron and hole tunneling allows for a continuous change of the relative electron and hole concentrations in the quantum well. As the electron concentration is increased, the quantum-well emission line due to heavy-hole free exciton recombination is replaced by a new excitonic line, 2 meV lower in energy. This line is attributed to a negatively charged exciton X^-. The magnetic field and temperature dependence of the quantum-well emission have been used to characterize this transition.
Buhmann et al. (Wed,) studied this question.