Study of ultraviolet emission enhancement in Al_xIn _yGa_1-x-yN quaternary alloy film

The effect of indium cluster on enhanced ultraviolet luminescence in Al_xIn_yGa_1-x-yN quaternary alloys with increasing Al composition was investigated. X-ray diffraction (XRD), temperature-dependent photoluminescence (PL), transmittance spectra, and Raman scattering measurements have been employed to study the Al_xIn _yGa_1-x-yN quaternary alloy. Abnormal S-shaped temperature dependence of PL emissions in high Al content sample originated from carrier localization induced by indium nanoclusters, which is in good agreement with the pure InN mode measured by Raman scattering. A large Stokes shift between the emission peak and the absorption edge is also found in the high Al content sample. All these observations suggested that the enhancement of carrier localization by indium nanoclusters is responsible for the increase in radiative recombination probability with increasing Al composition. Our results demonstrated that Al_xIn_yGa_1-x-yN quaternary alloy can exhibit a larger band gap than that of GaN and enhanced ultraviolet luminescence due to the existence of indium nanoclusters. Meanwhile, the effect of indium clusters was increased with Al compositions increasing, even at low indium mole fraction about 4%.