Dislocation Climb in AlN Crystals Grown at Low-Temperature Gradients Revealed by 3D X-ray Diffraction Imaging

Abstract

The dislocation evolution in a cross-section a-plane cut through a sublimation-grown aluminum nitride (AlN) crystal grown with low-temperature gradients and subsequent low thermal stress is investigated with different X-ray diffraction imaging methods. Exploiting the so-called weak-beam contrast using monochromatic X-rays in combination with suitable three-dimensional (3D) interpretation and reconstruction allows the identification of individual dislocations as well as tracing their progression in the crystal volume, even in the considerably strained interface region. It is particularly striking that the laterally grown crystal volume is dislocation-free. The dislocation densities in the seed and the bulk volume are similar (1 × 103 cm–2), but while the dislocations in the seed are randomly arranged, the dislocations in the bulk volume show a uniform line shape, indicating a common mechanism of dislocation movement. Since the dislocation slings in the bulk do not lie in slip planes, it can be concluded that the lateral movement does not result from dislocation glide, but from impurity-driven climb of dislocations during growth. The absence of slip can be explained by the low-temperature gradients and the subsequent low thermal stress below the critical resolved shear stress (CRSS).

Application of laboratory micro X-ray fluorescence devices for X-ray topography

“…by Lider (2021). Recent developments show that a high-resolution 3D view of the defect distribution can be obtained using a focused sheetshaped beam (Yoneyama et al, 2023;Yildirim et al, 2023) or a rotation about the lattice-plane normal (Ha ¨nschke et al, 2017;Straubinger et al, 2023). Using monochromatic X-rays furthermore allows a high level of quantification of lattice inhomogeneities and characteristic strain fields caused by these defects (Guguschev et al, 2022;Tran Caliste et al, 2023).…”

Efficient diameter enlargement of bulk AlN single crystals with high structural quality

“…Thus, dislocation glide and subsequent dislocation generation could be avoided. 22,23) The seed temperatures were 2230 °C and the growth time was 32 h. The growth rates on the −c-plane and the m planes are both ∼200 μm h −1 , which leads to a large expansion angle of ∼45°.…”