  Effects of microwave radiation on magnetoresistance are analyzed in a
balance-equation scheme that covers regimes of inter- and intra-Landau level
processes and takes account of photon-asissted electron transitions as well as
radiation-induced change of the electron distribution for high mobility
two-dimensional systems. Short-range scatterings due to background impurities
and defects are shown to be the dominant direct contributors to the
photoresistance oscillations. The electron temperature characterizing the
system heating due to irradiation, is derived by balancing the energy
absorption from the radiation field and the energy dissipation to the lattice
through realistic electron-phonon couplings, exhibiting resonant oscillation.
Microwave modulations of Shubnikov de Haas oscillation amplitude are produced
together with microwave-induced resistance oscillations, in agreement with
experimental findings. In addition, the suppression of the magnetoresistance
caused by low-frequency radiation in the higher magnetic field side is also
demonstrated.
