3. III-Nitride Light-Emitting Diodes with Photonic Crystal Structures

In this chapter, four works involving the application of self-assembly NSL processes to GaN-based material are introduced, mainly to deal with the light extraction issues of GaN LEDs so as to suppress light confinement through reduction of total internal reflections at the GaN/air interfaces. Two electroluminescence devices incorporating nanosphere-patterned structure are first discussed; the self-assembled array of spheres with varying dimensions serves as a hard mask to form the close-packed PhCs onto the ITO film (Li and Choi, J Appl Phys 110 (5), 2011, [1]) and the intermediate layer of semiconductor (Li et al, Appl Phys Lett 102 (18), 2013, [2]). To extend the function of sphere-pattern array, dimension-adjusting procedure is employed to overcome the restrictions of close-packed patterning and realize photonic bandgap structures. With a well-defined periodic arrangement and with sufficiently large refractive index contrast between GaN and ambient, a wavelength-tunable PBG in the visible region can be opened up, which forbids the propagation of light within a specific range of frequencies and is extremely useful in molding the flow of emitted light from an LED. Two non-close-packed periodic patterns, namely air-spaced (Li and Choi, J Appl Phys 109 (2), 2011, [3]) and clover-shaped (Li et al, Appl Phys Lett 100 (14), 2013, [4]) PBG structures, are highlighted in this chapter.