First-principles based modeling for influence of epitaxy and packaging induced strains on emission properties of III-nitrides LED chips

Undesired residual strain always exists in the epitaxial film inevitably as a result of lattice mismatch and thermal expansion mismatch between the substrate and the epitaxial film. The strain affects crystalline quality as well as optical and electrical properties of LED epitaxial film. In this paper, we report on the effects of strain on the emission properties of III-nitrides based LEDs grown on various substrates. As results, the band-gap energy of III-nitrides shows blue shift with increasing compressive strain and increases in tensile strain results in a decrease of band-gap energy. A linear relation of the band-gap of III-nitride with the biaxial strain is observed. In addition, III-nitrides materials with larger band-gap energy show a larger shift of emission energy, which means purple and ultraviolet LEDs will be more non-uniform than blue and red LEDs under the same strain states.