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

Abstract

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.

Fundamental Studies on Crystallization and Reaching the Equilibrium Shape in Basic Ammonothermal Method: Growth on a Native Lenticular Seed

“…Values of µt (µ is the linear absorption coefficient and t is the crystal thickness) were 8.6-10.3 and 8.0-9.6 for the Cu-Kα 1 and Mo-Kα 1 radiation, respectively. This meant that the XRT measurements were performed under Borrmann contrast conditions, as described in [13] and the literature referred to therein. HRXRD was applied to analyze the lattice parameters and mosaicity in various crystal regions.…”

“…They are crystallographically flat, thus with a uniform off-cut and the threading dislocation density (TDD) does not exceed 5 × 10 4 cm −2 [11]. Despite many published papers devoted to crystallization [12], as well as to the properties of ammonothermal crystals [13], a detailed investigation of the basic ammonothermal growth process has never been presented. With this paper, we aim to fill this gap.…”

Challenges of Overcoming Defects in Wide Bandgap Semiconductor Power Electronics

“…These extended defects occur in all epitaxial layers grown on c-plane substrates (the predominant and largest area substrate type) and are the result of the lack of a high-quality substrate bulk material, as well as substrate surface. Even in the best current substrate technology, low-defect seeds are scarce [66]. Point defects influence the background carrier concentration in low-doped layers and various recombination processes.…”

Large-Scale Defect Clusters with Hexagonal Honeycomb-like Arrangement in Ammonothermal GaN Crystals

“…Recently, Kirste et al demonstrated the high crystalline quality of entire 1.8-inch Am-GaN substrates by Lang-technique X-ray Bragg diffraction imaging (historically called “X-ray topography”) [ 8 ]. The main contrast mechanism for the observation of the defects was, in this case, the anomalous transmission (“Borrmann effect”) predicted by the dynamical theory of diffraction (see, for instance, Authier [ 9 ]).…”

“…The occurrence of the Borrmann effect in the studied substrates constitutes clear evidence of the high crystalline perfection of Am-GaN grown by a native seed approach. Using this laboratory X-ray Bragg diffraction imaging technique, not only microscopic defects such as threading dislocations (TDs), but also macroscopic defects, e.g., dislocation clusters due to preparation insufficiency, traces of facet formation, growth bands, dislocation walls, and dislocation bundles, were detected [ 8 ].…”