Microwave-modulated photoluminescence of a two-dimensional electron gas

The low-temperature photoluminescence (PL) of GaAs/AlGaAs quantum wells and heterojunctions containing a high mobility two-dimensional electron gas (2DEG) is studied under microwave (mw) irradiation of 36 GHz. The analysis of the mw-modulated PL (MPL) spectra allows us to elucidate the effects of mw radiation on the 2DEG. For low magnetic field strengths (B 0.5 T), we show that the MPL spectral shape is due to energy redistribution of the photoexcited holes, as affected by the mw-heated 2DEG. For the mechanism that causes the nonequilibrium hole-energy redistribution, we propose that it is the interaction of the holes with low-energy acoustic phonons emitted by the mw-heated 2DEG. This underlying physical mechanism gives rise to the optically detected 2DEG cyclotron resonance at low B. For B > 0.5 T, optically detected resonances are observed at B values that depend on the 2DEG density, and they occur near integer electron filling factors. We argue that these resonances result from a slight 2DEG density increase under mw irradiation with a concurrent, low-energy PL spectral shift due to small band-gap narrowing.