Field-Dependent Measurement of GaAs Composition by Atom Probe Tomography

Abstract

The composition of GaAs measured by laser-assisted atom probe tomography may be inaccurate depending on the experimental conditions. In this work, we assess the role of the DC field and the impinging laser energy on such compositional bias. The DC field is found to have a major influence, while the laser energy has a weaker one within the range of parameters explored. The atomic fraction of Ga may vary from 0.55 at low-field conditions to 0.35 at high field. These results have been interpreted in terms of preferential evaporation of Ga at high field. The deficit of As is most likely explained by the formation of neutral As complexes either by direct ejection from the tip surface or upon the dissociation of large clusters. The study of multiple detection events supports this interpretation.

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

“…For this reason, these tails do not present an exponential form. Similar behaviors were recently reported in GaAs atom probe measurements [8] . Parasitic species such as hydrogen-, carbon-, nitrogen-and oxygenrelated peaks and hydrides were also detected, most likely supplied by the environment during the specimen preparation procedure.…”

“…These are general features which have been systematically observed also for other materials. Atom probe mass spectra are known to be strongly affected by the electric field conditions at which measurements were carried out [1,8] . The so-called effective electric field F eff can be calculated through the Kingham's post-ionization model [20] .…”

“…Finally, recent observations indicate that the formation of molecular ions and their field dissociation can affect composition measurements [5,7] . The mechanisms that promote both formation and dissociation of molecular ions are not well understood: experiments show at least that non-dissociated group-V molecular ions are more abundant at low field conditions [1,8] . Furthermore, theory shows that dissociation can be promoted by the high electric field surrounding the tip and/or by the fact that molecules can leave the tip in an excited state [9,10] .…”

“…Furthermore, theory shows that dissociation can be promoted by the high electric field surrounding the tip and/or by the fact that molecules can leave the tip in an excited state [9,10] . Moreover, dissociation processes and correlated evaporation can lead to intrinsic detection issues (pile-up effect), which reduce the probability of detecting certain ions [8,11] . In this article, a quantitative analysis of multiple events allows us to determine the impact of these phenomena on the accuracy of composition measurements in atom probe tomography, and to suggest an alternative mechanism of N loss that should be ascertained with theoretical means.…”

Preferential Evaporation in Atom Probe Tomography: An Analytical Approach

“…FeCu (Takahashi et al, 2017), cemented tungsten carbide (Peng et al, 2017), GaAs (Russo et al, 2017), ODS steel (Hatzoglou et al, 2017) or ZnO (Amirifar et al, 2015). It has been determined that the measured elemental composition depends on the APT analysis conditions.…”