| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 99 === We use chemical lift-off technology to lift-off GaN epilayer grown on AlN sacrificial from two kinds of pattern sapphire.
The first type is InGaN-based light-emitting diodes (LEDs) grown on triangle-shaped patterned sapphire substrates. 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 10μm/min for the 100-μm-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 second type is an epitaxial layer of an InGaN light-emitting diode (LED) structure grown a truncated-triangle-striped patterned-sapphire substrate. A crystallographic stable and terminated V-shaped GaN grooved pattern was observed on the lift-off GaN surface. The peak wavelength blueshift phenomenon of the micro-photoluminescence spectrum was also 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 453nm electroluminescence emission spectrum was realized through a CLO process
The chemical lift-off process was achieved by using an AlN buffer layer as a sacrificial layer in a hot potassium hydroxide solution, which has the potential to replace the traditional laser lift-off process for vertical LED applications.
We also use this chemical etching technology to lateral etch InGaN light-emitting diodes (LED) which were grown on a truncated-triangle-striped patterned sapphire substrate. After growing a GaN layer on the patterned-sapphire substrate, it was observed that a higher lateral growth process formed a V-shaped-striped air-void structure. After a bottom-up N-face wet etching process on a GaN layer, the stable crystallographic etching planes were formed as the GaN {10(11) ¯} planes. We found out that treated LED structures had 65% light enhancements and smaller divergent angles. A rhombus-like air-void structure formed at GaN/patterned-sapphire interface provided a high light extraction process.
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