Microwave-modulated photoluminescence of a two-dimensional electron gas

The primary effect of microwave (mw) irradiation on a two dimensional electron gas (2DEG) is heating due to mw absorption by the electrons. At low lattice temperatures, pronounced secondary effects are observed: mw-induced modification of the photoluminescence (PL) spectrum and mw-induced resistance oscillations (MIRO). We present an experimental study of mw-modulated PL (MPL) spectroscopy in modulation-doped GaAs/AlGaAs QW's. At low magnetic field strengths (B < 0.5 T), the analysis of the MPL spectra indicates that they arise of a redistribution of the photoexcited holes within the energy states of the top valence band. This is caused by absorbing low-energy acoustic phonons that are emitted by the mw-heated 2DEG. We propose that these nonequilibrium phonons also affect the 2DEG mobility leading to the MIRO's. For B > 0.5 T and intense mw-irradiation, new optically detected resonances (ODRs) are observed at magnetic fields that depend on the 2DEG density and approximately correspond to integer electron filling factors. We argue that these resonances result from a slight 2DEG density increase under mw irradiation with a concurent, low-energy PL spectral shift due to a small bandgap narrowing.