Lift-Off Mechanism of GaN Thin Films with Buried Nanocavities Investigated by SEM and TEM

Abstract

A process to slice and separate GaN layers with buried nanocavities was presented via an annealing process of nanoporous GaN (0002) thin films at 1050°C in an NH₃ ambient. We were able to separate and lift off GaN layers over a macroscopic area ($\ge$ cm²). The several growth stages of buried nanocavities were examined by scanning/transmission emission microscopy techniques. During the early stage of annealing, the annealing leads to variations in morphology from nanopores with rough sidewalls to columnar or hexagonal nanopores with smooth sidewalls. At the same time, amorphous gallium oxide and single crystal GaN with high dislocation density, which are formed by electrochemical etching, are converted into GaN with a perfect crystal lattice. Subsequently, the columnar or hexagonal nanopores are sealed, cut, and then spheroidized. Above a sufficiently high porosity (> 50%), the nanocavities will overlap one another and coalesce, allowing a stand-alone GaN thin film to be lifted off the original substrate.