Atom Probe Tomography Analysis of Low-Dimensional Electronic Materials and Heterostructure

Atom probe tomography (APT) was used to analyze doping and alloying in low-dimensional electronic materials including thin film heterostructures, van der Waals materials, and colloidal quantum dots (QDs).;Firstly, APT was used to reveal structure-property relationship for low-dimensional thin film semiconductors used in electronic and opto-electronic devices. APT was shown to be capable of revealing buried interfaces, evaluating alloying distribution, and determining spatial correlations between dopants. APT, correlated with high-resolution X-ray diffraction (XRD) and micro-photoluminescence (micro-PL), was used to analyze indium distribution in continuous and discontinuous InGaN quantum wells (QWs) to identify factors contributing to the increase in internal quantum efficiency (IQE). Relative to the control growth, hydrogen dosing leads to narrower and discontinuous quantum wells of lower indium content with more abrupt interfaces, which contributes to an increased radiative recombination rate by increasing the electron-hole wavefunction overlap, as revealed by simulations. Hydrogen dosing also selectively etches QWs near defects, which contributes to higher IQE by keeping carriers away from defects and thus reducing non-radiative recombination. APT analysis was also used to determine the Ag dopant distribution in a Ta2O5-based low energy switching memristor devices. By manually tuning the laser energy to avoid fracture caused by different evaporation fields, the Ta2O5:Ag layer was analyzed and the distribution of Ag atoms evaluated. Based on the APT results and electrical performance data, a switching mechanism based on conductive tunneling paths instead of the continuous traditional conductive filaments was proposed for the memristor device. This research indicates the potential for APT analysis used in memristor devices.;A proof-of-principle application of APT analysis of doping in 2D materials was demonstrated for the first time by analyzing Ag doping in (PbSe) 5(Bi2Se3)3 and Cu doping in Bi2Se 3. APT analysis shows that Ag dopes both Bi2Se3 and PbSe layers in (PbSe)5(Bi2Se3)3 , and correlations in the position of Ag atoms suggest a pairing across neighboring Bi2Se3 and PbSe layers. Density functional theory (DFT) calculations confirm the favorability of substitutional doping for both Pb and Bi and provide insights into the observed spatial correlations in dopant locations. APT analysis also shows that Cu exists within the layer and between layers in Bi2Se3. Results suggest that van der Waals interactions are strong enough to hold layers together during field evaporation, at least for (PbSe)5(Bi2Se3)3 and Bi2Se3; however, van der Waals interactions make atoms in the same monolayer tend to be evaporated together, limiting the spatial resolution of resolving atomic layers. This work revealed the influence of bonding anisotropy on field evaporation. (Abstract shortened by ProQuest.).