Influence of strains on the optical properties of non-polar and semi-polar gallium nitride based LEDs

Currently, most gallium nitride based light emitting diodes (LEDs) are fabricated with polar c-plane [0001] direction. This orientation of gallium nitride has a large polarization electric field. Therefore, the device performance is adversely affected by strain induced piezoelectric polarization. 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 strains on the optical properties of non-polar and semi-polar gallium nitrides by means of first principle calculation. As results, the band-gap energies of non-polar (1-100) gallium nitride are smaller than that of non-polar (11-20) and that of semi-polar (11-22) gallium nitride under the same scale tensile strains. And it is shown that an opposite trend under compressive strains is observed. Besides, non-polar (1-100) gallium nitride based LED device will have more significant shift of emission wavelength than non-polar (11-20) and semi-polar (11-22) gallium nitride under the same strain states.