Atomic-Scale Insights into the Growth of InGaN on Strained N-Polar GaN

N-polar InGaN provides an attractive route to long-wavelength optoelectronic devices. However, the growth of N-polar InGaN quantum wells with high In composition is still limited by the trade-off between In incorporation and crystalline quality. Although underlayer strain engineering has been widely used to address this trade-off in metal-polar InGaN, its role in N-polar InGaN growth remains insufficiently understood. In this work, first-principles calculations are employed to elucidate the effects of biaxial strain in the underlying N-polar GaN on In-related adsorption and incorporation during InGaN growth. Our calculations show that tensile strain stabilizes InGaN adsorption relative to GaN adsorption at both step terminations without altering their distinct step selectivities, thereby promoting In incorporation through a GaN-dominated step-flow pathway without aggravating alternating-step attachment asymmetry. After lattice incorporation, tensile strain generally weakens In segregation, with this tendency also modulated by surface reconstruction. A quantitative strain-composition relationship is further established for N-polar InGaN under MOCVD conditions based on a cooperative multi-In incorporation pathway. Importantly, this relationship reproduces the experimentally observed strain dependence of In composition. This work provides atomic-scale insights into strain-modulated N-polar InGaN growth and offers guidance for high-quality InGaN quantum wells with high In composition.