Comparative Structural Characterization of Thin Al0.2Ga0.8 N/GaN and In0.17Al0.83N/GaN Heterostructures Grown on Si(111), by MBE, with Variation of Buffer Thickness

Abstract

We report growth, by plasma-assisted molecular beam epitaxy, of thin Al 0.2 Ga 0.8 N/GaN and In 0.17 Al 0.83 N/GaN heterostructures on Si(111) substrate with three different buffer thickness (600, 400, and 200 nm). Successful growth by critical optimization of growth conditions was followed by comparative characterization of these heterostructures by use of high resolution x-ray diffraction (HRXRD), including reciprocal space mapping (RSM), room-temperature photoluminescence (RT-PL), and high resolution transmission electron microscopy (HRTEM). The effect of different buffer thickness on the threading dislocation (TD) density of a thin 1.5 nm Al 0.2 Ga 0.8 N/In 0.17 Al 0.83 N-1.25 nm GaN-1.5 nm Al 0.2 Ga 0.8 N/In 0.17 Al 0.83 N heterostructure, was also studied. Analysis revealed increasing tensile strain with decreasing buffer thickness for AlGaN-based samples; this was confirmed by the red-shift of the GaN RT-PL peak. Reduced strain in lattice-matched InAlN-based samples resulted in a blue-shift of the GaN RT-PL peak; this was indicative of better crystallographic quality than for the AlGaN/GaN samples, which was proved by XRD-FWHM and RSM results. A substantial reduction of TD density from approximately 10 10 to 10 8 cm À2 with increasing buffer thickness resulted in a smooth thin active region for both thick buffer structures whereas the latticematched InAlN/GaN-based thick buffer resulted in less effect on TD and a smooth and prominent thin active region.