Strain and crystal defects in thin AlN/GaN structures on (0001) SiC

Abstract

Oxygen induced strain field homogenization in AlN nucleation layers and its impact on GaN grown by metal organic vapor phase epitaxy on sapphire: An x-ray diffraction study High-resolution x-ray diffraction was used to compare strain relaxation and defect populations in thin GaN/AlN heterostructures ͑total thickness Ϸ480 nm͒ grown on ͑0001͒ SiC using metalorganic chemical vapor deposition ͑MOCVD͒ and hydride vapor epitaxy ͑HVPE͒ techniques. The results of high-resolution x-ray diffraction measurements ͑rocking curves and reciprocal space mapping͒ were corroborated using transmission electron microscopy. Differently grown films exhibited dissimilar strain relaxation and defect populations that were related to specific growth conditions. In the MOCVD films, grown under lower deposition rates, the elastic strain in the AlN and GaN layers was fully relaxed at the initial stages of the epitaxial growth yielding nearly similar densities of threading dislocation segments ͑TDS͒ in layer volumes. Additional, "secondary" elastic stresses in these layers were attributed to the excess of point defects. In the HVPE films, grown under higher ͑five to ten times͒ deposition rates, these layers were over relaxed and the density of TDS in the GaN layer was an order of magnitude larger than that in AlN. The MOCVD-grown sample was devoid of planar defects whereas the HVPE film contains significant densities of stacking faults in both GaN and AlN layers. Formation of "secondary" extended defects was interpreted in terms of creation and structural transformation of point defects during epitaxial growth. Differences in strain levels, types, and defect populations/distributions for the two heterostructures were attributed to the different growth rates for MOCVD and HVPE.

Design rules for interfacial thermal conductance: Building better bridges

“…Other experiments reporting conductance enhancement attribute the increase to a strengthening of the bonds at the boundaries [15][16][17]. Thermal interface engineering can be critical to many technologies like integrated circuits [3], phase change memory [18] or high power electronics [19]. A systematic and microscopic understanding of the bridging properties of an interfacial layer would go a long way towards that goal.…”

The influence of reactor height adjustment on properties in GaN films grown on 6H-SiC by metal organic chemical vapor deposition

“…However, the epitaxial thin films under lower deposition rates, the elastic strain in the GaN layers were entirely relaxed at the initial stages of the epitaxial growth yielding nearly similar densities of TDs in layer volume. Therefore, under higher growth rate a mass of TDs could relaxes the more tensile stress [28]. The present results demonstrated that the chamber height emphasize the importance of this parameter for the accommodation of elastic strain and crystalline quality in the epitaxial layers and the dynamics of atom incorporation into a crystal lattice at the growth.…”

Growth of high quality ZnO thin films with a homonucleation on sapphire

“…The RHEED pattern for nucleation layer indicates the morphology of the initial annealed growth is smooth, allowing the subsequent growth of a high quality epilayer. 23,26,28,29 The creation of closed dislocation loops in the volume of the layer, just above the interface, is a final stage of defects creation process. 4(b)] yields values of $1.7 Â 10 5 cm À2 and 1.6 Â 10 7 cm À2 , respectively.…”

“…4(b)] yields values of $1.7 Â 10 5 cm À2 and 1.6 Â 10 7 cm À2 , respectively. 22,23,28,29 The created closed dislocation loops rise up, following the growth front with the lag, specified by growth conditions and elastic properties of epitaxial layer. 26 The narrow width of the central x RC peak correlates with the crystalline perfection of ZnO layer, but not directly, real more complicated situation is described below.…”