An AlN Sacrificial Buffer Layer Inserted into the GaN/Patterned Sapphire Substrate for a Chemical Lift-Off Process

Abstract

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

Analysis of threading dislocations in void shape controlled GaN re-grown on hexagonally patterned mask-less GaN

“…On the one hand it has been argued that the formation of voids plays a key role in stress relaxation, crack suppression and TDs reduction [22,23], while on the other hand voids can help in effectively diffracting light into the escape-cone and thus increasing the escape probability in light emitting structures [24]. Furthermore, the presence of voids can also assist in the lift-off process for the removal of substrates [25,26].…”

InGaN light-emitting diodes with embedded nanoporous GaN distributed Bragg reflectors

“…The laser scribing depth was 2.2 μ m to reach the as-grown 12-period n + -GaN/u-GaN stack structure by using a 355 nm laser. After the lateral wet etching process, the Si-heavy doped n + -GaN:Si layer was transformed into a nanoporous GaN layer through the doping-selective electrochemically etching process in a 0.5 M nitride acid solution at positive 8 V external bias voltage 24 . After the EC-etching process, a high refractive index n-type GaN:Si layer was transformed into a low refractive index nanoporous GaN layer.…”

Void Shapes Controlled by Using Interruption-Free Epitaxial Lateral Overgrowth of GaN Films on Patterned SiO2AlN/Sapphire Template

“…Recent studies have proposed several useful growth techniques to improve the crystal quality, such as epitaxial lateral overgrowth (ELOG) [4][5][6], pendeo-epitaxy (PE) [7], maskless PE [8], cantilever epitaxy [9], facet-controlled epitaxial lateral overgrowth (FACELO) [10,11], SiN x /GaN buffer layer [12], abbreviated growth mode [13][14][15], and freestanding GaN substrates [16][17][18]. Patterned sapphire substrate [19] and embedded air voids method [20,21] have been developed to further enhance the light extraction efficiency (LEE) of light-emitting diodes (LEDs).…”

“…In addition, embedded air voids play a key role in freestanding GaN substrate fabrication. Lin et al employed the GaN films grown on patterned sapphire substrate with large voids on the top region in the chemical lift-off process and found that the embedded voids can accelerate the wet etching process [17]. Bohyama et al acquired spontaneously separated freestanding GaN substrate by concentrating the compressive stress at the seeds because of the intentional formation of voids [18].…”