Magneto-luminescence and magneto-transport of a two-dimensional electron gas around integer filling factors

The magneto-optical emission of a high-mobility electron gas in a GaAs/AlGaAs single heterostructure shows a remarkable behavior near even filling factors in the quantum Hall regime. At low temperatures the light emission starts abruptly at filling factors v = 2, 4, 6, and is only observed in the presence of spin-down electrons in the last occupied Landau level (LL). For increasing magnetic field below filling factor 2, the emission energy remains essentially constant up to a critical field, after which it tends progressively to the usual LL-like behavior. Simultaneous transport measurements demonstrate that this critical field corresponds to the onset of extended states at the Fermi level, showing the same temperature dependence. The results are qualitatively interpreted as due to the formation of complex bound-states with the photo-created hole. (C) 2002 Elsevier Science B.V. All rights reserved.