Stress control in GaN/sapphire templates for the fabrication of crack-free thick layers

Growth optimization during III-nitride multiwafer MOVPE using real-time curvature, reflectance and true temperature measurements

“…Stress control during MOVPE growth of GaN/sapphire templates was shown to be important for the fabrication of thick crack-free GaN substrates by HVPE [9]. First reports on stress control using low-temperature interlayers by Amano et al [10,11] and Han et al [5] revealed that AlN or AlGaN with a high Al-content were best suited for efficient crack suppression in overgrown layers.…”

Thick GaN layers grown by HVPE: Influence of the templates

“…According to Napierala et al [15] in HVPE layers deposited on MOCVD GaN templates the critical stress for thickness of 200 mm is about 1.5 GPa. We can conclude that the stress in our samples is below this critical stress value, therefore we did not observe cracking of the HVPE layers on both types of substrates till thicknesses of 350 mm.…”

“…The low DD and high critical thickness of the layers is connected to the low island density. The low island density can be achieved by lowering the V/III ratio in the process [15]. The crack-free thick GaN layers on MOCVD templates with small DD density using low V/III ratio are reported by Napierala et al [15].…”

“…330 mm, is because of high thermal stress built up between GaN layer and the sapphire substrate. At such thicknesses of HVPE layer, the stress is not compensated by the bowing of wafer but by the fracture of the substrate [15]. Eventually the fracture of substrate causes the GaN fracture as well.…”

“…In another publication, Richter et al [14] have reported that cracking of the layers is more pronounced when growing directly on sapphire substrate than on MOCVD templates. Napierala et al [15] showed that the crack formation in the HVPE layers is influenced by the MOCVD NL in correlation with the stress presented in the templates and can be managed by controlling the initial density of islands.…”