Cracking of GaN films

Abstract

Cracking of thick GaN films grown on sapphire is reexamined on the basis of a combination of microstructural observations of cracking and established mechanics of fracture of films. It is argued that cracking is motivated by tensile growth stresses once a critical thickness is reached. Subsequent growth on the cracked films occurs, perpetuating the cracked structure until the crack surfaces approach one another and touch. Continued film growth buries the crack. Once the crack faces touch, there are conditions under which it is energetically favorable for the cracks to close and heal. Crack healing can be kinetically limited. Whether the crack healing is complete within the growth time depends on several factors including, it is suggested, whether impurities have adsorbed to the surface during growth. Conditions under which cracks that have extended into the sapphire substrate during film growth can act as critical flaws for fracture of the substrate on cooling are also presented.

Micro-Raman Scattering From Hexagonal GaN, AlN, and AlxGa1-xN Grown on (111) Oriented Silicon: Stress Mapping of Cracks

“…Similar results have been recently reported for GaN grown on Si substrates [6]. Nevertheless, cracks in nitrides remain a persistent and [7][8][9]. These studies have mainly focused on global stresses in GaN and AlGaN deposited on sapphire, with the exception of one micro-Raman stress mapping study [8].…”

Effect of high-temperature annealing on the residual strain and bending of freestanding GaN films grown by hydride vapor phase epitaxy

“…However, a critical remaining question is the high and nonuniform distribution of dislocations, 1 impurities, 2,3 native defects, 4 and strain 5,6 across the thickness. Residual strain, 7 wafer bending, 8,9 and cracking 10,11 are the main drawbacks, hampering the reproducible production of large-area GaN substrates, and thus a proper understanding of the reasons for them is of crucial importance. The high-temperature annealing ͑HTA͒, as an important tool in materials research, is expected to lead to the redistribution of the defects and consequently to a change of electrical, optical, and structural parameters of the material.…”

Optimization of low temperature GaN buffer layers for halide vapor phase epitaxy growth of bulk GaN

“…However, in these films cracking formation has been observed. This is a common problem of heteroepitaxy of GaN on Al 2 O 3 , when tensile stress is generated by an island coalescence mechanism in the beginning of the growth on substrates with large lattice mismatch [27,28]. For HT-GaN layers grown on non-optimized LT buffers, i.e.…”