Compositional accuracy of atom probe tomography measurements in GaN: Impact of experimental parameters and multiple evaporation events

•The composition of GaN measured by atom probe is biased.•The main parameter influencing the compositional bias is the surface electric field.•The deficiency of Ga at high field is interpreted in terms of preferential evaporation.•The deficiency of N at low field is investigated through the study of multiple evaporation events.•The detected dissociation of molecular ions can produce neutral N, but in moderate quantities.•Further mechanisms of neutral N production are proposed. A systematic study of the biases occurring in the measurement of the composition of GaN by Atom Probe Tomography was carried out, in which the role of surface electric field and laser pulse intensity has been investigated. Our data confirm that the electric field is the main factor influencing the measured composition, which exhibits a deficiency of N at low field and a deficiency of Ga at high field. The deficiency of Ga at high field is interpreted in terms of preferential evaporation of Ga. The detailed analysis of multiple evaporation events reveals that the measured composition is not affected by pile-up phenomena occurring in detection system. The analysis of correlation histograms yields the signature of the production of neutral N2 due to the dissociation of GaN32+ ions. However, the amount of N2 neutral molecules that can be detected cannot account for the N deficiency found at low field. Therefore, we propose that further mechanisms of neutral N evaporation could be represented by dissociation reactions such as GaN+→ Ga++ N and GaN2+→ Ga2++ N.