  AlGaN plays a vital role in hetero-structure high electron mobility
transistor by employing a two-dimensional electron gas and as electron blocking
layer in the multi quantum well light emitting diodes. Nevertheless, the
incorporation of Al in GaN for the formation of AlGaN alloy is limited by the
diffusion barrier formed by instant nitridation of Al adatoms by reactive
atomic N. Incorporation of Al above the miscibility limit, however can be
achieved by ion beam technique. The well known ion beam mixing (IBM) technique
was carried out with the help of Ar+ irradiation for different fluences. A
novel approach was also adopted for the synthesis of AlGaN by the process of
post irradiation diffusion (PID) as a comparative study with the IBM technique.
The optical investigations of AlGaN nanowires, synthesized via two different
methods of ion beam processing are reported. The effect of irradiation fluence
and post irradiation annealing temperature on the random alloy formation were
studied by the vibrational and photoluminescence (PL) spectroscopic studies.
Vibrational studies show one-mode phonon behavior corresponding to longitudinal
optical (LO) mode of A1 symmetry (A1(LO)) for the wurtzite phase of AlGaN
nanowires in the random alloy model. Maximum Al atomic percentage ~6.3-6.7% was
calculated with the help of band bowing formalism from the Raman spectral
analysis for samples synthesized in IBM and PID processes. PL studies show the
extent of defects present in these samples.
