Electron-concentration-dependent quantum-well luminescence: Evidence for a negatively charged exciton

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 ${\mathit{X}}^{\mathrm{-}}$. The magnetic field and temperature dependence of the quantum-well emission have been used to characterize this transition.