Charge writing at the LaAlO3/SrTiO3 surface

Biased conducting-tip atomic force microscopy (AFM) has been shown to write and erase nanoscale metallic lines at the LaAlO3/SrTiO3 interface. Using various AFM modes, we show the mechanism of conductivity switching is the writing of surface charge. These charges are stably deposited on a wide range of LaAlO3 thicknesses, including bulk crystals. A strong asymmetry with writing polarity was found for 1 and 2 unit cells of LaAlO3, providing experimental evidence for a theoretically predicted built-in potential.Comment: 12 pages, 4 figures, plus supplementary information, submitted to Nano Letter

Termination Control of the Interface Dipole in La0.7_{0.7}Sr0.3_{0.3}MnO3_3/Nb:SrTiO3_3 (001) Schottky Junctions

In order to investigate the interface termination dependence of perovskite band alignments, we have studied the Schottky barrier height at La$_{0.7}$Sr$_{0.3}$MnO$_3$/Nb:SrTiO$_3$ (001) heterointerfaces. As the Nb:SrTiO$_3$ semiconductor was varied from TiO$_2$ termination to SrO termination by variable insertion of a SrMnO$_3$ layer, a large systematic increase in the Schottky barrier height was observed. This can be ascribed to the evolution of the interface dipole induced to screen the polar discontinuity at the interface, which gives a large internal degree of freedom for tuning band diagrams in oxides.Comment: 10 pages, 5 figure

A heteroepitaxial perovskite metal-base transistor

'More than Moore' captures a concept for overcoming limitations in silicon electronics by incorporating new functionalities in the constituent materials. Perovskite oxides are candidates because of their vast array of physical properties in a common structure. They also enable new electronic devices based on strongly-correlated electrons. The field effect transistor and its derivatives have been the principal oxide devices investigated thus far, but another option is available in a different geometry: if the current is perpendicular to the interface, the strong internal electric fields generated at back-to-back heterojunctions can be used for oxide electronics, analogous to bipolar transistors. Here we demonstrate a perovskite heteroepitaxial metal-base transistor operating at room temperature, enabled by interface dipole engineering. Analysis of many devices quantifies the evolution from hot-electron to permeable-base behaviour. This device provides a platform for incorporating the exotic ground states of perovskite oxides, as well as novel electronic phases at their interfaces

Experimental evidence of zone-center optical phonon softening by accumulating holes in thin Ge

We discuss the impact of free carriers on the zone-center optical phonon frequency in germanium (Ge). By taking advantage of the Ge-on-insulator structure, we measured the Raman spectroscopy by applying back-gate bias. Phonon softening by accumulating holes in Ge film was clearly observed. This fact strongly suggests that the phonon softening in heavily-doped Ge is mainly attributed to the free carrier effect rather than the dopant atom counterpart. Furthermore, we propose that the free carrier effect on phonon softening is simply understandable from the viewpoint of covalent bonding modification by free carriers