No abstract

The strain dynamic of thin film AlN is investigated before and after the deposition of a GaN epitaxial layer using plasma assisted molecular beam epitaxy. X-ray diffraction ω/2θ-scan and asymmetric reciprocal space mapping analysis show that the deposition of GaN alters the strain state of the underlying AlN template. The in-plane lattice constant of the AlN is found to increase upon growth of GaN, giving rise to a more relaxed GaN epitaxial layer. Hence, the subsequent GaN epitaxial thin film possesses better structural quality especially with lower screw dislocation density and flat surface morphology which is evidenced by the X-ray diffraction ω-scan, room temperature photoluminescence, and atomic force microscopy analysis. Such relaxation of AlN upon GaN deposition is only observed for relatively thin AlN templates with thicknesses of 20 nm–30 nm; this effect is negligible for AlN with thickness of 50 nm and above. As the thicker AlN templates already themselves relax before the GaN deposition, the localized strain fields around the misfit dislocations prohibit further change of lattice parameters.

Effect of the growth temperature and the AlN mole fraction on In incorporation and properties of quaternary IIInitride layers grown by molecular beam epitaxy J. Appl. Phys.

Thin films of the wide bandgap quaternary semiconductor InxAlyGa(1−x−y)N with low In (x = 0.01–0.05) and high Al composition (y = 0.40–0.49) were synthesized on GaN templates by plasma-assisted molecular beam epitaxy. High-resolution X-ray diffraction was used to correlate the strain accommodation of the films to composition. Room temperature ultraviolet B (280 nm–320 nm) photoluminescence intensity increased with increasing In composition, while the Stokes shift remained relatively constant. The data suggest a competition between radiative and non-radiative recombination occurs for carriers, respectively, localized at centers produced by In incorporation and at dislocations produced by strain relaxation.

We report on the impact of the preparation of the Si-face 4H-SiC(0001) Si substrate using a Ga flash-off process on the epitaxial growth of GaN by plasma-assisted molecular beam epitaxy. The nucleation, as well as the resultant structural and morphological properties of GaN grown directly on 4H-SiC(0001) Si are strongly influenced by the chemical and morphological modifications of the SiC surface induced by the Ga flash-off process. Herein we describe the impact of the specific concentration of Ga incident on the surface (quantified in terms of monolayer (ML) coverage): of 0.5 ML, 1ML and 2ML. The residual oxygen at the SiC surface, unintentional SiC nitridation and the formation of cubic GaN grains during the initial nucleation stage, are all reduced when a 2 ML Ga flash is used. All of the above factors result in structural improvement of the GaN epitaxial layers. The correlation between the SiC surface modification, the initial nucleation stage, and the GaN epitaxial layer structural quality has been articulated using x-ray photoelectron spectroscopy, xray diffraction, atomic force microscopy and spectroscopic ellipsometry data.