  A theoretical study of Al(1-x)Ga(x)N, based on full-potential linearized
augmented plane wave method, is used to investigate the variations in the
bandgap, optical properties and non-linear behavior of the compound with the
variation of Ga concentration. It is found that the bandgap decreases with the
increase of Ga in Al(1-x)Ga(x)N. A maximum value of 5.5 eV is determined for
the bandgap of pure AlN which reaches to minimum value of 3.0 eV when Al is
completely replaced by Ga. The static index of refraction and dielectric
constant decreases with the increase in bandgap of the material, assigning a
high index of refraction to pure GaN when compared to pure AlN. The refractive
index drops below 1 for photon energies larger than 14 eV results group
velocity of the incident radiation higher than the vacuum velocity of light.
This astonishing result shows that at higher energies the optical properties of
the material shifts from linear to non-linear. Furthermore, frequency dependent
reflectivity and absorption coefficients show that peak value of the absorption
coefficient and reflectivity shifts towards lower energy in the UV spectrum
with the increase in Ga concentration. This comprehensive theoretical study of
the optoelectronic properties of the alloys is presented for the first time
which predicts that the material can be effectively used in the optical devices
working in the visible and UV spectrum.
