Optical spectroscopy of neutral and charged excitons in GaAs/AIGaAs quantum wells in high magnetic fields

We implement optical spectroscopy to study charged excitons in modulation-doped GaAs/AIGaAs quantum wells. We report the fLrs~ observation of the positively charged exciton and of the triplet state of the negatively charged exciton. Applyin~g a gate voltage at high magnetic fields, we investigate the transition between metallic and insulating state~ We find that while the photoluminescence fine of the metallic two-dimensional electron gas trandorms smoothly into a negatively charged exciton, the Zeeman spfitting of this line exhibits an abrupt change at the metal-insulator transition. Keyword.~Crallium arsenide; Molecular beam epitaxy;, Photoluminescencg Quantum wells; Semiconductor-se~conductor h e t e r ~