First Bulk AlGaN Crystals Grown by the Basic Ammonothermal Method

Abstract

Bulk aluminum−gallium nitride (AlxGa1−xN) crystals were synthesized by the basic ammonothermal method using native ammonothermal GaN (Am-GaN) seeds to investigate the influence of growth geometry on structural quality. Conventional growth predominantly along the polar direction produced continuous but highly mosaic AlxGa1−xN bulk layers with numerous low-angle grain boundaries and a high dislocation density. A modified configuration promoting lateral growth produced distinct growth sectors with markedly different defect structures. One laterally grown sector exhibited homogeneous X-ray topography contrast, no observable etch pits within the investigated area, and anomalous X-ray transmission associated with the Borrmann effect. Energy-dispersive X-ray spectroscopy showed an Al content of approximately 6 at. % (x ≈ 0.06) across the investigated lateral and polar sectors within the accuracy of the method. The results demonstrate that local growth geometry strongly affects strain accommodation and defect evolution during ammonothermal AlxGa1−xN growth. High-quality lateral sectors may provide suitable seed material for subsequent regrowth toward larger, low-defect AlxGa1−xN crystals.