Relaxation mechanism of thermal stresses in the heterostructure of GaN grown on sapphire by vapor phase epitaxy

• Published in: Japanese Journal of Applied Physics Vol. 32; no. 4; pp. 1528 - 1533
• Main Authors: HIRAMATSU, K, THEERADETCH DETCHPROHM, AKASAKI, I
• Format: Journal Article
• Language: English
• Published: Tokyo Japanese journal of applied physics 01.04.1993
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid surfaces and solid-solid interfaces; Surface structure and topography; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thermal stress; Gallium Nitrides; Thermal strain; Microcrack; Theoretical study; Experimental study; Lattice parameters; Chemical vapor deposition; Inorganic compound; Dislocation; Thickness; Aluminium Oxides; Stress relaxation; Sapphire; Preparation; Thermal expansion coefficient; Crack; Heterojunction
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/jjap.32.1528

Thermal strains and stresses due to the thermal expansion coefficient difference in GaN(0001)/α-Al 2 O 3 (0001) layered structures are studied by varying the film thickness of GaN from 0.6 to 1200 µm. The strain in GaN is greater in films of less than a few microns thickness. It is decreased in films of thickness from several to about a hundred microns, and is almost completely relaxed in those thicker than 100 µm. The stresses and strains in the heterostructure are calculated using a model in which relaxation due to cracking in the sapphire is considered. Three relaxation mechanisms of the thermal strain are found for different film thicknesses as follows: (a) only lattice deformation (<4 µm), (b) enhancement of interface defects such as “microcracks” and/or dislocations (4-20 µm), and (c) generation of “macrocracks” in sapphire (>20 µm).