The InGaN-based light-emitting diode ͑LED͒ with an inclined undercut structure is fabricated through the photoelectrochemical two-step process to increase light extraction efficiency. In the first step the sidewall-undercut structure at the p-type and n-type GaN interface is created by selective wet oxidation on an n-type GaN surface in pure H 2 O solution. In the second step an inclined undercut structure through a crystallographic wet-etching process is formed by immersion in hot KOH solution. This crystallographic wet-etching process can remove the Ga 2 O 3 layer and form a ͕1011͖ p-type GaN stable plane, ͕1010͖ n-type GaN stable plane on the mesa sidewall. This inclined p-type GaN plane of LED structure can provide the higher overlap of incident light beam core and extraction core overlap on the mesa sidewall, and the total light output power of the treated LED is 2.10 times higher than the standard LED. Consequently, this inclined undercut LED structure is suitable for high-efficiency nitride-based LED application.Gallium nitride ͑GaN͒ has attracted considerable interest for application in light-emitting diodes ͑LEDs͒ and laser diodes. GaN has a lower refractive index than air ͑n Ϸ 2.5͒, 1 and the critical angle of the escape cone is about 23°and indicated about 4% of the total light extraction from the surface. The overall external quantum efficiency of InGaN-based LED is dependant on the internal quantum efficiency ͑ int ͒ and the light-extraction efficiency ͑ out ͒. 2 To increase the light-extraction ratio, the bottom pattern Al 2 O 3 substrate, 3,4 the top p-type GaN:Mg surface roughening process, 5,6 the n-type GaN:Si 7,8 surface roughening process using the laser-liftoff technique, and a selective oxidation on the mesa sidewall 9,10 through photoelectrochemical ͑PEC͒ wet oxidation were used to increase light extraction efficiency. In AlInGaP-based LEDs, a truncated inverted pyramid ͑TIP͒ and GaN-based LEDs ATON technique on a SiC substrate 11,12 shaping process can enhance the light extraction efficiency. The PEC process attempted on the selective etching process, 13,14 the oxidizing process, 15-17 and the selective oxidation on nitride-based semiconductors can affect the optical property of GaN-based materials. The crystallographic wet-chemicaletching stable planes of p-GaN are ͑0001͒, ͕1010͖, and ͕1012͖ 18 planes, and wet-chemical-etching stable planes of n-GaN are ͑0001͒, ͕1010͖, ͕1011͖, ͕1012͖, and ͕1013͖ 19 planes.In this paper, the inclined undercut LED structure is fabricated through the PEC wet oxidation process in deionized water ͑DI͒ and the following crystallographic wet etching process in hot KOH solution. This inclined undercut LED structure has a larger divergent angle and higher light extraction efficiency than standard LED. The forming mechanism of the PEC selective oxidation process on the n-type GaN layer and wet-etching stable plane on p-type GaN are discussed in detail in this paper. ExperimentalThe LED structures were grown by a metallorganic chemical vapor deposition system on C-f...

InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undopedGaN distributed Bragg reflectors (DBR) structure have been demonstrated. Si-heavily doped GaN epitaxial layers (n + -GaN) in the 12-period n + -GaN/u-GaN stack structure are transformed into low refractive index nanoporous GaN structure through the doping-selective electrochemical wet etching process. The central wavelength of the nanoporous DBR structure was located at 442.3 nm with a 57 nm linewidth and a 97.1% peak reflectivity. The effective cavity length (6.0λ), the effective penetration depth (278 nm) in the nanoporous DBR structure, and InGaN active layer matching to Fabry-Pérot mode order 12 were observed in the far-field photoluminescence radiative spectra. High electroluminescence emission intensity and line-width narrowing effect were measured in the DBR-LED compared with the non-treated LED structure. Non-linear emission intensity and line-width reducing effect, from 11.8 nm to 0.73 nm, were observed by increasing the laser excited power. Resonant cavity effect was observed in the InGaN LED with bottom nanoporous-DBR and top GaN/air interface.Gallium nitride (GaN) materials have considerable in optoelectronic devices such as light-emitting diodes (LEDs), laser diodes (LD) 1 , and vertical cavity surface emitting lasers (VCSEL) 2 . High reflectivity distributed Bragg reflectors (DBR) structure, short cavity thickness 3-5 , high transparence conductive layer, efficient transverse current spreading, small current confinement aperture, and resonant cavity controled in the nitride VCSEL need to be improved. Leonard et al. reported on violet nonpolar III-nitride VCSELs with a tunnel junction intracavity contact 6 and an Al ion implanted aperture 7 . The epitaxial AlGaN/GaN stack 8,9 and AlN/GaN stacks 10,11 structures had been reported for the bottom epitaxial DBRs in GaN-based VCSEL devices. Large lattice mismatch and low refractive index different of the stack structures are the challenges for the epitaxial DBR structures with long epitaxial growth time. The AlInN/GaN DBR structure 12,13 is lattice matched to GaN material, but the growth of AlInN layer remains a challenge in InGaN-based LED structures. To realize the high reflectivity with less pairs of stack structure, the air-gap/GaN DBR structures with large refractive index different had been fabricated through selectively anodized processe 14,15 , and thermal decomposition techniques [16][17][18] . But, the low mechanical strength and the tiny high reflective area remains a challenge for the photonic device fabrication. Plawsky et al. 19 . reported the nanoporous material for the photonics through the evaporation induced self-assembly process and oblique or glancing angle deposition. The resonant cavity effect of III-nitride thin-film flip-chip light-emitting diodes with anatase TiO 2 microsphere array were reported 20 . Nanoporous GaN material has been reported as an effective low refractive index for the DBR structure applications [21][22][23] .In this pa...

Epitaxial layers of InGaN light-emitting diodes (LED) were separated from undoped GaN/sapphire structures through a wet lift-off process. A 0.1-µm-thick Si-heavy-doped GaN:Si (n+-GaN) layer was inserted in the InGaN LED structure that acted as a sacrificial layer for a lateral wet etching process. The lateral etching rate of the n+-GaN sacrificial layer was 315 µm/h. The Fabry–Pérot interferences of the lift-off InGaN LED membranes were observed in the angle-resolved photoluminescence spectra that indicated that the lift-off InGaN membranes had a flat etched surface. High light extraction efficiency, narrow divergent angle, and flat wet-etched GaN surface were observed on the lift-off InGaN membrane

High-oriented Li-Al layered double hydroxide (LDH) films were grown on an InGaN light-emitting diode (LED) structures by immersing in an aqueous alkaline Al(3+)- and Li+-containing solution. The stand upward and adjacent Li-Al LDH platelet structure was formed on the LED structure as a textured film to increase the light extraction efficiency. The light output power of the LED structure with the Li-Al LDH platelet structure had a 31% enhancement compared with a conventional LED structure at 20 mA. The reverse leakage currents, at -5V, were measured at -2.3 × 10(-8) A and -1.0 × 10(-10)A for the LED structures without and with the LDH film that indicated the Li-Al LDH film had the insulated property acted a passivation layer that had potential to replace the conventional SiO2 and Si3N4 passivation layers. The Li-Al LDH layer had the textured platelet structure and the insulated property covering whole the LED surface that has potential for high efficiency InGaN LED applications.

Multiple-porous GaN structures were formed in InGaN light-emitting diodes (LEDs) structures through a selective photoelectrochemical (PEC) etching process. A 1.3 μm-thick PEC-treated n+-GaN:Si layer consisting of nanoporous, whisker, fiber-shaped, networking, and air-gap structures located at the bottom of the LED structure was fabricated. Multiple-porous GaN structures were formed caused by the non-uniformly lateral etching rate on the n+-GaN:Si layer under a high PEC-biased voltage. An 80 μm lateral etching width and a 70% bottom roughened area ratio were measured on the treated LED structure without affecting the electrical properties. The light output power of the treated LED had an approximate enhancement of 57% compared with the non-treated LED structure. Fabry–Pérot interferences of the treated LED structures were observed in angle-resolved electroluminescence spectra indicating that the effective optical refractive index of the bottom multiple-porous structure was reduced.