Quantitative analysis of lattice plane microstructure in the growth direction of a modified Na-flux GaN crystal using nanobeam X-ray diffraction

Abstract

We quantitatively evaluated lattice plane microstructure, which includes lattice plane tilt, spacing, twist, and their fluctuations, in a modified Na-flux GaN bulk single crystal using the synchrotron-based nanobeam X-ray diffraction method. The GaN crystal was fabricated by two-step growth; the first layer had coalescence boundaries as a consequence of faceted growth from the multipoint-seed GaN template, and the second layer grew on the first without faceted growth. Position-dependent ω-2θ-φ mapping analysis revealed in-plane distribution of local lattice plane microstructure along with dislocation morphology around the coalescence boundary and the growth-stage boundary (GSB). Faceted growth from the multipoint seed template led to concentration of a-type dislocations at the coalescence boundary. These dislocations would glide widely on basal planes above the GSB, and then homogeneously propagate toward the surface. As a result, the modified Na-flux GaN crystal had a homogeneous lattice plane microstructure with little bunching of threading dislocations.

Anomalous dislocation annihilation behavior observed in a GaN crystal grown on point seeds by the Na-flux method

“…19,20) Shida et al recently reported that in the case of the FFC technique, TDs were estimated to gather around the coalescence boundary, as well as from nanobeam X-ray diffraction measurement. 21) Nevertheless, the TDD values at the surface were not as high as in other growth techniques, and the mechanism of TD reduction was unclear. In this study, we therefore carefully evaluated the three-dimensional (3D) behavior of TDs from the inside to the surface around the coalescence region by directly capturing TDs using multiphoton excitation photoluminescence (MPPL).…”

Local strain distribution analysis in strained SiGe spintronics devices

“…In the nanoXRD measurements, an X-ray beam can be focused down to several hundred nanometers, which is known to be a very effective tool for local crystal structure analysis thanks to its small beam size. [10][11][12][13][14][15][16] The spacing and tilt of lattice planes in the device structure are simultaneously measured by threedimensional (ω-2θ-j) reciprocal lattice space mapping using a two-dimensional detector for diffracted beams. By these means, we quantitatively analyze the local crystal strain and defect structure in the strained SiGe spintronics devices to clarify the correlation between the local crystallinity and the spin transport properties.…”