Improving Light Extraction Efficiency of GaN-Based LEDs by Al$_{\bm x}$Ga$_{{\bf 1}{\bm -}{\bm x}}$N Confining Layer and Embedded Photonic Crystals

Abstract

The interaction of low-order modes with photonic crystals (PhCs) has been a promising technique to increase light extraction efficiency (LEE) of LEDs. In this paper, numerical simulations based on the finite-difference time-domain method were carried out to explore different mechanisms that can effectively improve this interaction. The results showed that deeply etched PhCs have inefficient light extraction since they would decrease the effective thickness of the unetched layer and cut off some guided modes. By applying the Al x Ga 1 −x N confining layer, the distribution of guided modes was changed. The cap layer mode was isolated from the GaN buffer, and larger LEE was achieved. Furthermore, dramatic increments with oscillations were found in the LEE by using embedded PhCs. Resonances of the Bloch mode localized within these PhCs, which caused the oscillations, were further modified by a shallow Al x Ga 1 −x N confining layer. With the optimized parameters, over eightfold increment in LEE was achieved. In addition, dislocations caused by higher Al content and thicker Al x Ga 1 −x N layer were avoided. This proposed structure could be a very promising candidate for high extraction efficiency LEDs. Index Terms-Alx Ga 1 −x N confining layer, cap layer mode (CLM), embedded photonic crystals (PhCs), finite-difference timedomain (FDTD), LED, light extraction efficiency (LEE).

Study on Modulation Bandwidth and Light Extraction Efficiency of Flip-Chip Light-Emitting Diode with Photonic Crystals

“…As shown in Figure 4b, when the photonic crystal period is fixed at 400 nm, the LEE varies with the duty cycle and height of the photonic crystals. When the photonic crystals are deep into the active region, optical modes interact with the photonic crystals and are diffracted to escape, which increases the LEE [22]. When the photonic crystal height is 400 nm and the duty cycle is 0.3, the Purcell factor and LEE of PC-FCLED are 1.81 and 68%, which is 37% and 32.3% higher than those of a conventional planar FCLED, respectively.…”

Enhancing light extraction efficiency of GaN-based light-emitting diodes with reticulated photonic crystals

“…Figure 1(a) shows the schematic of reticulated PhCs structure LEDs applied in the simulation. Balancing the calculation time and accuracy, the simulation region was set to 4×4×3 μm3 for x,y, and z directions, respectively, since it has been shown that the observed extraction efficiencies did not vary significantly when the dimension increased further 16 . The LEDs structure was composed of a 1-μm thick substrate layer (sapphire), a 1.8-μm thick n-GaN layer, and a 200-nm p-GaN surface layer.…”

“…1(b)], were fabricated in the p-GaN layer. Between the n-GaN layer and the p-GaN layer was a conventional single dipole source with a Gaussian shape spectrum polarized in the in-plane direction 16 . The central wavelength of the spectrum was set to 465 nm, which has commonly been used in other reports 17 …”

“…Balancing the calculation time and accuracy, the simulation region was set to 4 × 4 × 3 μm 3 for x; y, and z directions, respectively, since it has been shown that the observed extraction efficiencies did not vary significantly when the dimension increased further. 16 The LEDs structure was composed of a 1-μm thick substrate layer (sapphire), a 1.8-μm thick n-GaN layer, and a 200-nm p-GaN surface layer. As the dry etching of multiple quantum wells (MQWs) could degrade the device performance, the reticulated PhCs, which consist of round holes and square holes [Fig.…”

“…Between the n-GaN layer and the p-GaN layer was a conventional single dipole source with a Gaussian shape spectrum polarized in the in-plane direction. 16 The central wavelength of the spectrum was set to 465 nm, which has commonly been used in other reports. 17 The power monitor for observing the amount of radiation power was placed 465 nm above the upper surface.…”