Using the technique of photoluminescence imaging, self-organized patterns o
f high-electron density in homogeneous n-GaAs layers under homogeneous micr
owave irradiation are studied. The structures are shown to be analogous to
current filaments in a static electric field. The symmetry of the microwave
induced patterns is not constrained by the current feeding electrodes. It
is, however, concluded that a feedback mechanism exists between the formati
on of high-conducting structures and the homogeneity of the incident microw
ave irradiation.