- Lateral confined epitaxy (LCE) of GaN on Si substrates results in a reduction of thermal crack density with decreasing the lateral dimensions of the growth pattern. Below a critical size, crack-free GaN on Si is obtained. The intensity of band-to-band photoluminescence (PL) peak in LCE GaN is strongly enhanced with respect to uniformly grown GaN on Si. The present study rules out the effect of crack density, internal reflections (microcavity effects), as well as enhanced light extraction efficiency, and excitation or emission through preferred facets (shape effects) as the main factor in PL enhancement. It is shown that the reduction in threading dislocation density (TDD) along the edges of the LCE patterns improves the luminescence efficiency. The relative increase in high quality material (low TDD) with the reduction of LCE unit size is, thus, the main reason for the enhanced PL intensity.