No abstract

In this paper, we propose and demonstrate a convenient and flexible approach for preparation large-area of photonic crystals (PhCs) structures on the GaN-based LED chip. The highly-ordered porous anodic alumina (AAO) with pitch of wavelength scale was adopted as a selective dry etching mask for PhCs-pattern transfer. The PhCs with different pore depths were simultaneously formed on the entire surfaces of GaN-based LED chip including ITO, GaN surrounding contacts and the sidewall of the mesa by one-step reactive ion etching (RIE). The light output power improvement of PhCs-based GaN LED was achieved as high as 94% compared to that of the conventional GaN-based LED.

To improve light extraction from GaN-based light-emitting diodes (LEDs), we demonstrated an approach of modified laser lift-off (M-LLO) technique for patterning undoped GaN (u-GaN). The M-LLO consists in sequentially forming a two-dimensional triangular lattice pattern with a 4μm period on a polymer layer over a sapphire substrate backplane by UV imprint and delivering the pattern onto u-GaN accompanied with the removal of the sapphire substrate. The enhancement of light extraction from GaN-based M-LLO LED with a reflective Ag film on the 120nm deep u-GaN pattern was about 31% and 100% compared to that of a LLO-LED with a reflective film and a conventional LED with a sapphire substrate, respectively.

A ternary system, consisting of air, an air-core/dense-silica-shell core-shell particle, and liquids has been used to fabricate an inverse opal structure with low fill factor, high refractive index contrast, and reversible tuning capabilities of the bandgap spectral position. The original close-packed opal structure is a ternary self-assembled photonic crystal from monodisperse and spherical polystyrene-core/silica-shell colloidal particles with air as the void material. Calcination removed the polystyrene and converted the core-shell particles to hollow spheres with a dense shell. In a final step, liquid is infiltrated only in the voids between the hollow spheres, but does not penetrate in the shell. This allows facile and reversible tuning of the bandgap properties in an inverse opal structure.