  We demonstrate that the 3.42 eV photoluminescence (PL) band in GaN is of the
same intrinsic origin as the near-edge $\sim$3.47 eV band, but arises from
regions of inversed polarity characterized by different strain and growth rate.
Two absorption edges are thermally detected at 0.35 K in nanocolumn structures,
exhibiting both bands. Micro-PL studies have shown similar temperature/power
behavior of these bands, with a competition in intensity in closely spaced
spots accompanied by alterations of exciton level ordering. Strain-induced
one-dimensional carrier confinement in small inversion domains likely explains
the discrete narrow lines observed between the bands.
