Влияние морфологии буферного слоя AlN на структурное качество полуполярного слоя GaN, выращенного на подложке Si(001), по данным просвечивающей электронной микроскопии

Structural features of the interface between semipolar gallium nitride layer and buffer layer of aluminum nitride grown on a SiC/Si(001) template misoriented by an angle of 7° were studied by high-resolution transmission electron microscopy. The effect of interface morphology on the structural quality of the gallium nitride layer is revealed: faceted structure the surface of the buffer layer reduces the threading dislocations density.

Desorption induced formation of low-density GaN quantum dots: nanoscale correlation of structural and optical properties

We report on the formation process of GaN/AlN quantum dots which arises after the deposition of 1 - 2 monolayers of GaN on an AlN/sapphire template followed by a distinct growth interruption. The influence of the duration of a growth interruption on structural and optical properties of the GaN layer has been systematically investigated. Quantum dots develop from initially bulky GaN islands, which nucleate in close vicinity to bundles of threading dislocations. For prolonged growth interruptions a decreasing island size is observed which is consistent with a systematic blue shift of the emission wavelength. In addition, a fragmentation of the bulky GaN islands into several smaller islands occurs, strongly depending on local strain fields caused by threading dislocations as well as on a different facet orientation of the islands. This morphological transition during growth interruption eventually leads to GaN quantum dot formation which assemble as clusters with a density of 108 cm-2. Desorption of GaN is identified as the major source for this morphological transition. The growth interruption time allows for tuning of the quantum dot emission wavelength in the UV spectral range.

Structural Analysis of Low Defect Ammonothermally Grown GaN Wafers by Borrmann Effect X-ray Topography

X-ray topography defect analysis of entire 1.8-inch GaN substrates, using the Borrmann effect, is presented in this paper. The GaN wafers were grown by the ammonothermal method. Borrmann effect topography of anomalous transmission could be applied due to the low defect density of the substrates. It was possible to trace the process and growth history of the GaN crystals in detail from their defect pattern imaged. Microscopic defects such as threading dislocations, but also macroscopic defects, for example dislocation clusters due to preparation insufficiency, traces of facet formation, growth bands, dislocation walls and dislocation bundles, were detected. Influences of seed crystal preparation and process parameters of crystal growth on the formation of the defects are discussed.