Different strain relief behaviors in Al0.35Ga0.65N/GaN multiple quantum wells on GaN/Sapphire templates with AlN/GaN supperlattices and low-temperature AlN interlayers

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Strain relief behaviors in Al0.35Ga0.65N/GaN multiple quantum wells (MQWs) grown on GaN/sapphire templates with either AlN/GaN supperlattices (SLs) or low-temperature AlN (LT-AlN) interlayers (ILs) between the MQWs and templates have been investigated. These two IL techniques can both effectively relieve the tensile strain in the MQWs, leading to crack-free surfaces and high crystalline quality. Further analysis shows that there are two distinct strain relief channels. In the case of adopting AlN/GaN SLs IL, microcracks and misfit dislocations account for strain relief in the MQWs. Microcracks are first generated in the IL, followed by activating formation of misfit dislocations. Then, the microcracks are immediately filled up by the subsequent epilayers. Contrastively, strain relief by using LT-AlN IL is mainly through the self relaxation process of the MQWs by surface roughening and strain compensation effect of LT-AlN IL.