Atom probe tomography evaporation behavior of C-axis GaN nanowires: Crystallographic, stoichiometric, and detection efficiency aspects

Abstract

The field evaporation behavior of c-axis GaN nanowires was explored in two different laser-pulsed atom probe tomography (APT) instruments. Transmission electron microscopy imaging before and after atom probe tomography analysis was used to assist in reconstructing the data and assess the observed evaporation behavior. It was found that the ionic species exhibited preferential locations for evaporation related to the underlying crystal structure of the GaN and that the species which evaporated from these locations was dependent on the pulsed laser energy. Additionally, the overall stoichiometry measured by APT was significantly correlated with the energy of the laser pulses. At the lowest laser energies, the apparent composition was nitrogen-rich, while higher laser energies resulted in measurements of predominantly gallium compositions. The percent of ions detected (detection efficiency) for these specimens was found to be considerably below that shown for other materials, even for laser energies which produced the expected Ga:N ratio. The apparent stoichiometry variation and low detection efficiency appear to be a result of evaporation of Ga ions between laser pulses at the lowest laser energies and evaporation of neutral N2 species at higher laser energies. All of these behaviors are tied to the formation of nitrogen-nitrogen bonds on the tip surface, which occurred under all analysis conditions. Similar field evaporation behaviors are therefore expected for other materials where the anionic species readily form a strong diatomic bond.

Laser-assisted atom probe tomography of 15N-enriched nitride thin films for analysis of nitrogen distribution in silicon-based structure

“…2 and 3 was due to molecular ion N 2 + . This tendency is similar to that seen in previously reported results of films including nitrogen, such as SiON [4], GaN [8][9][10][11] and TiAlN [12], whereas O + , not O 2 + , was the largest contribution to oxygen counts of SiO 2 [5]. Fig.…”

A Brief Comment on Atom Probe Tomography Applications

“…For example, in the case of GaN, at the lowest laser energies, the apparent composition is nitrogen-rich, while higher laser energies results in gallium-rich (i.e., nitrogen-deficient) (Gu et al, 2013;Riley et al, 2014;Sanford et al, 2014). The origin of this trend is controversial until now, but one widely proposed interpretation is the formation of a significant amount of neutral N 2 gas molecules at low electric field (high laser energy) (Diercks et al, 2013;Gault et al, 2016). In addition to oxide and nitride, laser-dependent APT measured stoichiometry have been demonstrated for other compound semiconductors such as Cu(In,Ga)Se 2 , CdTe, Ge 2 Sb 2 Te 5 (Chae et al, 2016;Choi et al, 2011;Larson et al, 2012).…”

Atomic-scale tomography of semiconductor nanowires

“…15. Diercks studied evaporation behavior of GaN associated with laser energy [77]. In addition, Dawahre [78] first mapped the unintentional impurities N atom along ZnO nanowires from APT dataset and concluded that there was no big difference on the two ZnO nanowire with different precursors apart from tiny N impurities induced by O/N precursor which was only identifiable by APT as shown in Fig.…”