  We establish a correlation between the internal stress in InN epilayers and
their optical properties such as the measured absorption band edge and
photoluminescence emission wavelength. By a careful evaluation of the lattice
constants of InN epilayers grown on c-plane sapphire substrates under various
conditions by metalorganic vapor phase epitaxy we find that the films are under
primarily hydrostatic stress. This results in a shift in the band edge to
higher energy. The effect is significant, and may be responsible for some of
the variations in InN bandgap reported in the literature.
