Summary form only given. In planar microcavity light-emitting diodes (MCLEDs), light not extracted is lost to leaky modes and also, up to 40% or more, to unavoidable laterally propagating guided modes. Photonic crystals (PCs) located around the emitting area within a distance smaller than the absorption length may act as efficient scatterers that extract guided light outside the heterostructure plane. To maximize extraction efficiency through this mechanism it is interesting to start from a microcavity based on insulating oxidised AlAs mirrors ("Alox DBRs") rather than classical AlAs-GaAs DBRs mainly because they reduce leaky modes to the benefit of guided modes.