  In this work we address experimentally a number of unresolved issues related
to microwave induced resistance oscillations (MIRO) and the zero-resistance
states observed recently on very high-mobility 2D electron gases in GaAs/AlGaAs
heterostructures. In particular, we examine electrodynamic effects via
reflection/absorption experiments and study the exact waveform of MIRO and
their damping due to temperature. It is shown that electrodynamic effects due
to metallic-like reflection and plasmons are important producing a wide
cyclotron resonance line and a number of oscillations which do not coincide
with the MIRO. To describe the MIRO waveform a simple model was employed
involving radiation-induced scattering with displacement. A very good
correlation was found between the temperature dependencies of the quantum
lifetime from MIRO and the transport scattering time from the electron
mobility. The results are compared with measurements of Shubnikov-de Haas
oscillations down to 30 mK on the same sample.
