Composition profiling of GaAs/AIGaAs quantum dots grown by droplet epitaxy

Droplet epitaxy (DE) is a growth method which can create III-V quantum dots (QDs) whose optoelectronic properties can be accurately controlled through the crystallisation conditions. In this work, GaAs/AlGaAs DE-QDs have been analyzed with the complimentary techniques of crosssectional scanning tunneling microscopy and atom probe tomography. Structural details and a quantitative chemical analysis of QDs of different sizes are obtained. Most QDs were found to be pure GaAs, while a small proportion exhibited high intermixing caused by a local etching process. Large QDs with a high aspect ratio were observed to have an Al-rich crown above the GaAs QD. This structure is attributed to differences in mobility of the cations during the capping phase of the DE growth

Industrial application of atom probe tomography to semiconductor devices

\u3cp\u3eAdvanced semiconductor devices offer a metrology challenge due to their small feature size, diverse composition and intricate structure. Atom probe tomography (APT) is an emerging technique that provides 3D compositional analysis at the atomic-scale; as such, it seems uniquely suited to meet these challenges. However, the semiconductor industry has demanding requirements against which the techniques in use are evaluated. This article explores the use of APT in the semiconductor industry, showing the potential of the technique, the obstacles that occur in practise, and possible future developments.\u3c/p\u3

Dopant distribution in atomic layer deposited ZnO:Al films visualized by transmission electron microscopy and atom probe tomography

\u3cp\u3eThe maximum conductivity achievable in Al-doped ZnO thin films prepared by atomic layer deposition (ALD) is limited by the low doping efficiency of Al. To better understand the limiting factors for the doping efficiency, the three-dimensional distribution of Al atoms in the ZnO host material matrix has been examined on the atomic scale using a combination of high-resolution transmission electron microscopy (TEM) and atom probe tomography (APT). Although the Al distribution in ZnO films prepared by so-called ALD supercycles is often presented as atomically flat δ-doped layers, in reality a broadening of the Al-dopant layers is observed with a full-width-half-maximum of ∼2 nm. In addition, an enrichment of the Al at grain boundaries is observed. The low doping efficiency for local Al densities > ∼1 nm\u3csup\u3e-3\u3c/sup\u3e can be ascribed to the Al solubility limit in ZnO and to the suppression of the ionization of Al dopants from adjacent Al donors.\u3c/p\u3