An epitaxial layer of an InGaN light-emitting diode (LED) structure was separated from a truncated-triangle-striped patterned-sapphire substrate through a chemical lift-off (CLO) process. A crystallographic stable and terminated V-shaped GaN grooved pattern was observed on the lift-off GaN surface. A peak wavelength blueshift phenomenon of the micro-photoluminescence spectrum was observed on the lift-off LED epitaxial layer (440.7 nm) compared with the LED/sapphire structure (445.8 nm). The free-standing LED epitaxial layer with a 453 nm electroluminescence emission spectrum was realized through a CLO process with the potential to replace the traditional laser lift-off process for vertical LED applications. (c) 2010 The Japan Society of Applied Physic

InGaN-based light-emitting diodes (LEDs) grown on triangle-shaped patterned sapphire substrates were separated through a chemical lift-off process by laterally etching an AlN sacrificial layer at the GaN/sapphire substrate interface. After the epitaxial growth, an air-void structure was observed at the patterned region on the sapphire substrate that provided an empty space to increase the lateral etching rate of the AlN buffer layer. The lateral etching rate of the AlN buffer layer was calculated at 10 mu m/min for the 100-mu m-width LED chip that was lifted off from the sapphire substrate. A triangular-shaped hole structure and a hexagonal-shaped air-void structure were observed on the lift-off GaN surface that was transferred from the patterned sapphire substrate. Comparing to the LED/sapphire structure, a peak wavelength blueshift phenomenon of the micro-photoluminescence spectra was observed on the lifted off LED chip caused by the release of a compressive strain at the GaN/sapphire substrate interface. The chemical lift-off process was achieved by using an AlN buffer layer as a sacrificial layer in a hot potassium hydroxide solution. (C) 2010 The Japan Society of Applied Physic

InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undoped-GaN 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.

In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga2O3 layers then formed around the GaN:Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga2O3-air layers, by a rough Ga2O3 surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications

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...