Composition of Wide Bandgap Semiconductor Materials and Nanostructures Measured by Atom Probe Tomography and Its Dependence on the Surface Electric Field

Abstract

Atom probe tomography allows for three-dimensional reconstruction of the elemental distribution in materials at the nanoscale. However, the measurement of the chemical composition of compound semiconductors may exhibit strong biases depending on the experimental parameters used. This article reports on a systematic analysis of the composition measurement of III–N binary (AlN, GaN) and ternary compounds (InGaN, InAlN), MgO, and ZnO by laser-assisted tomographic atom probe as a function of laser power and applied DC bias. We performed separate series of measurements at constant bias, constant laser pulse energy, and constant detection rate and a spatial analysis of the surface field through detector hitmap ratios of elemental charge states. As a result, (i) we can determine the separate roles of laser energy and surface field—the latter being the dominant factor under standard conditions of analysis; (ii) we compare the behavior of different samples and (iii) different materials; and (iv) we critically discuss the reliability of the measurement of InxGa1–xN and InxAl1–xN alloy fractions and of the Tb concentration in rare-earth-doped ZnO.