Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO(3). The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features.

Temperature dependent thermopower and Hall effect measurements, combined with model calculations including all of the relevant elastic and inelastic scattering mechanisms, are used to quantify the role of charged line defects on electron transport in n-type InN films grown by molecular beam epitaxy. Films with electron concentrations between 4 × 10 17 to 5 × 10 19 cm −3 were investigated. Charged point and line defect scattering produce qualitatively different temperature dependences of the thermopower and mobility, allowing their relative contribution to the scattering to be evaluated using charge neutrality at the measured electron concentration. Both charge state possibilities for the dislocations, that is, positively charged (donors) or negatively charged (acceptors), were considered. The 100-300 K temperature dependence of the mobility and the 200-320 K temperature dependence of the thermopower can be modeled well with either assumption. The dislocation density was independently measured by plan-view and cross-sectional transmission electron microscopy and corresponds well with the values obtained from transport modeling.

High quality Bi2Te3 and Sb2Te3 topological insulators films were epitaxially grown on GaAs (111) substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111) substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111) substrate is better than a vicinal substrate to provide high quality Bi2Te3 and Sb2Te3 films. Hall and magnetoresistance measurements indicate that p type Sb2Te3 and n type Bi2Te3 topological insulator films can be directly grown on a GaAs (111) substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.