Fabrication of two-dimensional InGaN/GaN photonic crystal structure using a modified nanosphere lithography technique

Abstract

By means of combining a very cost-effective lift-off process and a nanosphere lithography technique, we have fabricated two dimensional (2D) photonic crystal (PhC) structures on an InGaN/GaN multiple quantum well structure. Significant enhancement in photoluminescence (PL) intensity has been observed when the emission wavelength is within the photonic bandgap. Time-resolved PL measurements have shown that the spontaneous emission rate is strongly reduced by a factor of ∼4 due to the PhC effect. As a consequence, the emission intensity along 2D PhC slab-plane directions is effectively suppressed and redistributed to the direction normal to the 2D PhC slab-plane simultaneously. Temperature-dependent PL measurements have confirmed that the enhanced PL intensity is due to an increase in extraction efficiency as a result of the PhC effect.

Efficiency improvement and droop behavior in nanospherical-lens lithographically patterned bottom and top photonic crystal InGaN/GaN light-emitting diodes

“…As determined from the normalized polar plots, LEDs with bottom, top, and double PC structures possess much smaller view angles of 140.6°, 138.8°, and 136.9°, respectively, compared to that of 151.3°for LED without PC. For the PC LEDs, the light is effectively redirected to the top escape cone through SiO 2 arrays, resulting in the narrower beam profile [16]. Especially, double PC is found to produce the most significant focusing effect compared to planar LED, showing a view angle reduction of 14.4°.…”

“…One can observe that some threading dislocations (TDs) below the SiO 2 nanodisks are blocked and bent, while new TDs also appear during the regrowth, especially in the window regions. Here, most of the dislocations in the sample are edge type and mixed type, only visible along the [11][12][13][14][15][16][17][18][19][20] direction. According to the counting of TD lines in the plane-view micrograph, the TD density in the regrown n-GaN estimated below MQWs is about 1.5 × 10 8 cm −2 , which does not show a significant reduction compared to that in bottom n-GaN below the SiO 2 nanodisks.…”

Indium gallium nitride-based ultraviolet, blue, and green light-emitting diodes functionalized with shallow periodic hole patterns

“…To fabricate PHP on nanometer scale, nanoimprint lithography, direct holographic photodissolution, and laser interference lithography are commonly applied 252627282930. According to previous reports on LEDs with PHPs, research groups mainly investigated the photonic crystal effect on LEE improvement 31323334…”

Enhancing optical power of GaN-based light-emitting diodes by nanopatterning on indium tin oxide with tunable fill factor using multiple-exposure nanosphere-lens lithography

“…Nanosphere array in form of two-dimensional closed-packed hexagonal monolayer can be produced on a substrate directly by spin-coating or vertical deposition. 13 The self-assembled monolayer then serves as mask for pattern transfer to form periodic arrays of recessed air-holes, 9 protruding pillars, 10,11 or nanocone. 12 And the NSL has become more flexible since Wei Wu et al proposed nanosphere lens lithography (NSLL) technology.…”

“…1 However, the external light extraction efficiency of GaN-based LEDs is still highly limited by the total internal reflection (TIR) at the semiconductor/air interface. 2,3 Various nanopatterning techniques, including electron-beam lithography, 4 nanoimprint lithography, 5 holographic lithography, 6 and nanosphere lithography (NSL), [7][8][9][10][11][12] have been used to pattern onto LED structure, including layers of sapphire, p-GaN, n-GaN, and indium tin oxide (ITO), to suppress the TIR. Among those methods, NSL has been widely employed because of its advantages of easily operated, large-area and low-cost.…”