  We investigate the propagation and scattering of polaritons in a planar GaAs
microcavity in the linear regime under resonant excitation. The propagation of
the coherent polariton wave across an extended defect creates phase and
intensity patterns with identical qualitative features previously attributed to
dark and half-dark solitons of polaritons. We demonstrate that these features
are observed for negligible nonlinearity (i.e., polariton-polariton
interaction) and are, therefore, not sufficient to identify dark and half-dark
solitons. A linear model based on the Maxwell equations is shown to reproduce
the experimental observations.
