The existence of an absolute photonic bandgap in the near-infrared for
two-dimensional periodic dielectric structures is discussed for photo
ns propagating in the plane of such 2D crystals. A special emphasis is
put on the influence of the shape and size of the filling pattern on
the absolute bandgap formation. A very large absolute photonic bandgap
is predicted for 2D crystals formed by etching into a semiconductor s
lab a periodic array of large vertical cylindric voids of circular cro
ss-section arranged in a triangular lattice. The technological feasibi
lity of such ''optimum'' air/GaAs 2D crystals by standard processing t
echniques (electron beam lithography and reactive ion etching) is demo
nstrated.