Strain-Induced Band Gap Variation in InGaN/GaN Short Period Superlattices

The use of strained substrates may overcome indium incorporation limits without inducing plastic relaxation in InGaN quantum wells, and this is particularly important for short-period InGaN/GaN superlattices. By incorporating elastic strain into these heterostructures, their optoelectronic behavior is modified. Our study employed density functional theory calculations to investigate the variation in the band-gap energy of short-period InGaN/GaN superlattices that comprise pseudomorphic quantum wells with a thickness of just one monolayer. Heterostructures with equibiaxially strained GaN barriers were compared with respective ones with relaxed barriers. The findings reveal a reduction of the band gap for lower indium contents, which is attributed to the influence of the highly strained nitrogen sublattice. However, above mid-range indium compositions, the situation is reversed, and the band gap increases with the indium content. This phenomenon is attributed to the reduction of the compressive strain in the quantum wells caused by the tensile strain of the barriers. Our study also considered local indium clustering induced by phase separation as another possible modifier of the band gap. However, unlike the substrate-controlled strain, this was not found to exert a significant influence on the band gap. Overall, this study provides important insights into the behavior of the band-gap energy of strained superlattices toward optimizing the performance of optoelectronic devices based on InGaN/GaN heterostructures.

Automated summary

The use of strained substrates can overcome indium incorporation limits without causing plastic relaxation in InGaN quantum wells, which is particularly important for short-period InGaN/GaN superlattices. Elastic strain in these heterostructures modifies their optoelectronic behavior. Density functional theory calculations were used to investigate the band-gap energy variation in short-period InGaN/GaN superlattices with one monolayer thick pseudomorphic quantum wells. Heterostructures with equibiaxially strained GaN barriers were compared to those with relaxed barriers. The study reveals a reduction of the band gap with lower indium contents, attributed to the influence of highly strained nitrogen sublattice. However, above mid-range indium compositions, the band gap increases with indium content due to the reduction of compressive strain in quantum wells caused by the tensile strain of barriers. Indium clustering induced by phase separation was considered as another modifier, but it was found to have no significant influence on the band gap. Overall, this study provides important insights into the behavior of band-gap energy in strained superlattices, optimizing the performance of optoelectronic devices based on InGaN/GaN heterostructures.