Fig. 3: Control of stress and strain during AlGaN/AlN epitaxial growth.
From: Progress on AlGaN-based solar-blind ultraviolet photodetectors and focal plane arrays
a Schematic diagram of relaxation process: (1) coherent growth below the critical thickness; (2) AlGaN cracks and MDs are introduced at AlGaN/GaN interface; (3) Relaxation resulted from dislocations enlarges the crack aperture; (4) cracks propagate to the GaN layer, MDs relaxing in GaN; (5) lateral growth buries cracks. Cross-sectional XTEM images of b MBE-grown AlN and c MOCVD-grown Al0.2Ga0.8N films on GaN. d SEM images of a 500-nm-thick cracked MOCVD-grown Al0.2Ga0.8N film on GaN. e Enlarged SEM image of crack overgrowth. f AFM image of a crack free Al0.2Ga0.8N film. Reprinted with permission from Bethoux et al.105. Copyright 2003 American Institute of Physics
