Ⅲ-Ⅴ compound GaN has the Wurtzite crystal structure

[1]

and belongs to symmetry group V

β

γ For GaN

group theory predicts the following lattice phonons: A

1

branch in which the Raman-active phonon is polarized in the z direction and which is infrared active also

and E

1

branch in which the phonon polarized in the x

y plane can be observed in both infrared and Raman experiments

two E

2

branches which are Raman active and two silent B

1

modes

[2

3]

. The A

1

and E

1

modes can be split into longitudinal (LO) and transverse (TO) components by the macroscopic electric field associated with the longitudinal phonon.Volia Lemos et al.

[E]

have observed three Raman active optical phonon modes E

2

A

1

(TO) and E

1

(TO) in GaN epitaxy layer grown by vapor phase epitaxy (VPE) on sapphire substrate

No E

1

(LO)mode was. observed in Raman scattering experiment previously

[4

5]

.The present work shows a Raman scattering experimental result in un-doped

N

-GaN samples grown on (0001) oriented sapphire substrate by VPE. An Ar

+

laser was used as the excitation source.