III-nitride ultraviolet, blue and green LEDs with SiO2 photonic crystals fabricated by UV-nanoimprint lithography

In this paper, we report the effect of the SiO2 photonic crystals (PhCs) on the enhancement of light-output power (LOP) in the UV, blue and green InGaN light-emitting diodes (LEDs). The SiO2 PhCs were fabricated by an UV-nanoimprint lithography technique. It is found that the LOP of the LEDs is effectively enhanced by the utilization of the SiO2 PhCs, and the enhancement of the LOP is strongly dependent on the emission wavelength of the active region. As compared to the LEDs without PhC structure, the LOP of the UV, blue and green LEDs with the SiO2 PhCs were enhanced by 27.7%, 14.6% and 40.5%, respectively. Moreover, the dependence of the light extraction efficiency on the emission wavelength was conducted through three-dimensional finite-difference time-domain (FDTD) simulation. The experimental observations were qualitatively consistent with the tendency of the FDTD simulation results.