Raman spectra investigation of InAlGaN quaternary alloys grown by metalorganic chemical vapor deposition

Abstract

Raman analysis of the A 1 (LO) mode of AlGaN-like phonons of the InAlGaN/GaN heterostructures in the composition range 1.38 ≦ In ≦ 2.73 and 8.01 ≦ Al ≦ 13.97 is presented. The line shape of A 1 (LO) mode of AlGaN-like phonons was observed to exhibit a significant asymmetry and Raman linewidth toward the lower energy side. The spatial correlation model is discussed and is shown to account the line shape. The spatial correlation model calculations also indicate the lack of a long-range order in the higher Al to In ratio of InAlGaN/GaN alloys. These results were confirmed by x-ray diffraction and the correlation length L decreases as the increasing of Al to In ratio corresponding to the absence of the long-range order in the alloy. The Raman linewidth of the AlGaN-like A 1 (LO) mode was found to exhibit a maximum at the higher Al to In ratio indicative of a random disordered alloy system. © 2012 American Institute of Physics.