Thermodynamic Origin of High Efficiency in Long-Wavelength InGaN-Based LEDs on Si Substrates

The indium gallium nitride (InGaN)- based micro-LEDs are attractive for the next generation of displays. However, the low efficiency of InGaN-based red LEDs is the bottleneck for micro-LED development. For decades, tremendous efforts have been made to design and optimize different kinds of substrates to improve the quality of InGaN quantum wells. In this study, we evaluate the effect of substrate-induced biaxial strains on the behaviors of a single In atom on the GaN (0001) surface by employing first-principles calculations. We find that applying a slight tensile strain can further strengthen In adsorption compared with reducing the compressive strain, while the In atom exhibits relatively faster mobility under compressive strains. Additionally, the calculations of In incorporation in the GaN surface reproduced the composition-pulling effect and confirmed that tensile strain promotes the In incorporation. Furthermore, by comparing the thermodynamics of strained InGaN alloys, we conclude that applying the substrate with a larger lattice constant can stabilize the InGaN system and suppress the phase separation. This study not only clarifies the significant effect of the substrate-induced biaxial strain on InGaN quality but also establishes essential guidelines for optimizing growth conditions to improve the performance of high-In-content InGaN films.