An Optimised Method for ZnO Sacrificial Layer Lift-Off on GaN Substrates

This study investigates the optimisation of the sacrificial layer epitaxial lift-off process using ZnO grown on GaN substrate. The aim of the study is to achieve efficient ZnO removal while preserving the integrity of the GaN layer. Previous studies [1] have identified two major challenges: the declining dissolution rate of ZnO in HCl solution without regular refreshment and the mechanical deformation of the GaN layer during the lift-off process (the GaN layer tends to crack and curve when directly transferred to glass substrate due to stress release during ZnO dissolution). This research establishes mathematical relationships between 0.1mol/mL to 2mol/mL concentration of HCl and ZnO dissolution rate, as well as between the thicknesses of GaN and ZnO layers. These relationships are crucial for preventing GaN layer defects during the ZnO stripping process