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Therese Karmstrand

Therese Karmstrand


Chalmers University of Technology


Applied Physics


Lesley Chan
Pavel Shapturenka
David Hwang

Faculty Sponsor(s): 

Michael Gordon

Faculty Sponsor's Department: 

Chemical Engineering

Project Title: 

Optimization of PEC etch parameters for lift-off of InGaN nanoLEDs

Project Description: 

Photoelectrochemical (PEC) etching is commonly used in the solid-state lighting industry to roughen InGaN/GaN light emitting diodes (LEDs) to enhance light extraction. Here, we adapt PEC etching to undercut nanoLED devices to remove them from their growth substrates, for subsequent transfer to flexible and transparent substrates for high density and near-eye displays. PEC etching of c-plane GaN devices is problematic, with low yield and surface roughness issues, often rendering devices inactive. To address this, we have investigated PEC etching of InGaN multi-quantum-wells (MQW) for lift-off of c-plane nanodevices, aiming to maximize lateral etch rates, while minimizing surface roughness. Metal organic chemical vapor deposition was used to grow n-GaN/InGaN MQW/n-GaN stacks on sapphire, where the InGaN serves as a model sacrificial etch and lift-off layer. PEC etching under different KOH electrolyte, temperature and UV exposure conditions was carried out with feedback from scanning electron and bright field optical microscopy. Results indicate that etch rates (~250-300 nm/min) and undercut roughness are similar for 0.1-1 M KOH at room temperature; extensive spatial variations were seen however, likely due to local material quality differences. Surface roughness was significantly reduced (320 à 80 nm) at lower etch temperature (3 °C) and in 0.05 M KOH, which we hypothesize is due to less etch facet formation at low T, without affecting KOH transport to the sacrificial InGaN layer and lateral etching rate. In future work, the number of quantum wells in the sacrificial layer and doping of regions near the MQW will be investigated to optimize the PEC process, ultimately leading to efficient lift-off of micro and nanoscale InGaN LED structures.