Al incorporation, structural and optical properties of Al xGa 1−xN (0.13⩽ x⩽0.8) alloys grown by MOCVD

Abstract

The alloy Al x Ga 1− x N was grown by metal-organic chemical vapor deposition (MOCVD) using a high-temperature AlN interlayer on a thick GaN template. The Al composition ( x) of the Al x Ga 1− x N was varied in the range 0.13⩽ x⩽0.8. The in-situ reflectance spectra indicate that the growth process of AlGaN alloys is dominated by trimethylgallium (TMGa) molar flux when the molar flux of trimethylaluminium (TMAl) is kept constant. The Al compositions and growth rates of AlGaN alloys were determined by Rutherford backscattering, which indicates that the incorporation efficiency of TMAl is improved remarkably by decreasing the TMGa molar flux. The crystalline quality of these AlGaN alloys is evaluated by measuring the symmetric (0 0 2) and asymmetric (1 0 2) ω-scan X-ray diffraction peak widths. The best crystalline quality, among these Al x Ga 1− x N alloys, is for an Al composition of x=0.54 where the full-width at half-maximums of the AlGaN (0 0 2) and (1 0 2) diffraction peaks are 265 and 797 arcsec, respectively. This conclusion is consistent with the surface morphology of the AlGaN alloys probed by atomic force microscopy. Room temperature cathodoluminescence spectra show pronounced near band edge emission from these AlGaN alloys. The optical band gaps ( E g) are found to deviate from linear interpolation between E g GaN and E g AlN with a bowing parameter b=0.89.