  Recently, hexagonal boron nitride (hBN) layers have generated a lot of
interest as ideal substrates for 2D stacked devices. Sapphire-supported thin
hBN films of different thicknesses are grown using metalorganic vapour phase
epitaxy technique by following a flow modulation scheme. Though these films of
relatively large size are potential candidates to be employed in designing real
devices, they exhibit wrinkling. The formation of wrinkles is a key signature
of strain distribution in a film. Raman imaging has been utilized to study the
residual strain distribution in these wrinkled hBN films. An increase in the
overall compressive strain in the films with an increase in the layer thickness
has been observed. To find whether the residual lattice strain in the films can
be removed by a thermal treatment, temperature dependent Raman measurements of
these films are carried out. The study demonstrates that the thermal rate of
strain evolution is higher in the films of lower thickness than in the thicker
films. This observation further provides a possible explanation for the
variation of strain in the as-grown films. An empirical relation has been
proposed for estimating the residual strain from the morphology of the films.
We have also shown that the residual strain can be partially released by the
delamination of the films.
