TEM investigation of Tm implanted GaN, the influence of high temperature annealing

Abstract In this work we carry out characterization of GaN implanted with Tm ions by transmission electron microscopy. We have investigated samples implanted at room temperature with different energies (150–300 keV) and fluences (1 × 1014–4.9 × 1015 Tm/cm2). High temperature annealing was performed at 1000 °C and 1200 °C with the GaN surface protected by a 10 nm thick AlN cap grown by MOCVD prior to the implantation or by a proximity cap. The influence of fluence, energy, annealing temperature and AlN cap on the structural quality of the layers is discussed. Direct implantation in GaN, results in the formation of a nanocrystalline surface layer when a critical dose is exceeded. Moreover, there is a generation of basal stacking faults. Implanting through the AlN capping layer prevents the formation of the nanocrystalline layer even for high fluences but a high density of stacking faults is still observed after implantation. The AlN cap also protects the surface during high temperature annealing, showing no signs of surface dissociation after annealing at 1200 °C. At this temperature a significant reduction of the number of stacking faults is observed.