Optical properties of AlGaN nanowires synthesized via ion beam techniques

AlGaN plays a vital role in hetero-structure high electron mobility transistors by employing a two-dimensional electron gas as an electron blocking layer in multi-quantum well light emitting diodes. Nevertheless, the incorporation of Al into GaN for the formation of the AlGaN alloy is limited by the diffusion barrier formed by instant nitridation of Al adatoms by reactive atomic N. The incorporation of Al above the miscibility limit, however, can be achieved by the 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 was studied by the vibrational and photoluminescence (PL) spectroscopic studies. Vibrational studies show one-mode phonon behavior corresponding to the longitudinal optical (LO) mode of A 1 symmetry [A 1(LO)] for the wurtzite phase of AlGaN nanowires in the random alloy model. A maximum Al atomic percentage of ∼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.