  We have investigated the effect of piezoelectric (PZ) polarization property
on group velocity of phonons in binary as well as in ternary wurtzite nitrides.
It is found that with the presence of PZ polarization property, the phonon
group velocity is modified. The change in phonon group velocity due to PZ
polarization effect directly depends on piezoelectric tensor value. Using
different piezoelectric tensor values recommended by different workers in the
literature, percent change in group velocities of phonons has been estimated.
The Debye temperatures and frequencies of binary nitrides GaN, AlN and InN are
also calculated using the modified group velocities. For ternary nitrides
AlxGa(1-x)N, InxGa(1-x)N and InxAl(1-x)N, the phonon group velocities have been
calculated as a functions of composition. A small positive bowing is observed
in phonon group velocities of ternary alloys. Percent variations in phonon
group velocities are also calculated for a straightforward comparison among
ternary nitrides. The results are expected to show a change in phonon
relaxation rates and thermal conductivity of III-nitrides when piezoelectric
polarization property is taken into account.
