High-mobility perovskite BaSnO3 films are of significant interest as new wide bandgap semiconductors for power electronics, transparent conductors, and as high mobility channels for epitaxial integration with functional perovskites. Despite promising results for single crystals, high-mobility BaSnO3 films have been challenging to grow. Here, we demonstrate a modified oxide molecular beam epitaxy (MBE) approach, which supplies pre-oxidized SnOx. This technique addresses issues in the MBE of ternary stannates related to volatile SnO formation and enables growth of epitaxial, stoichiometric BaSnO3. We demonstrate room temperature electron mobilities of 150 cm2 V−1 s−1 in films grown on PrScO3. The results open up a wide range of opportunities for future electronic devices.

Using time-domain thermoreflectance, the thermal conductivity and elastic properties of a sputter deposited LiCoO 2 film, a common lithium-ion cathode material, are measured as a function of the degree of lithiation. Here we report that via in situ measurements during cycling, the thermal conductivity of a LiCoO 2 cathode reversibly decreases from B5.4 to 3.7 W m À 1 K À 1 , and its elastic modulus decreases from 325 to 225 GPa, as it is delithiated from Li 1.0 CoO 2 to Li 0.6 CoO 2 . The dependence of the thermal conductivity on lithiation appears correlated with the lithiation-dependent phase behaviour. The oxidation-statedependent thermal conductivity of electrolytically active transition metal oxides provides opportunities for dynamic control of thermal conductivity and is important to understand for thermal management in electrochemical energy storage devices.

The magnetotransport properties of epitaxial films of Cd_{3}As_{2}, a paradigm three-dimensional Dirac semimetal, are investigated. We show that an energy gap opens in the bulk electronic states of sufficiently thin films and, at low temperatures, carriers residing in surface states dominate the electrical transport. The carriers in these states are sufficiently mobile to give rise to a quantized Hall effect. The sharp quantization demonstrates surface transport that is virtually free of parasitic bulk conduction and paves the way for novel quantum transport studies in this class of topological materials. Our results also demonstrate that heterostructuring approaches can be used to study and engineer quantum states in topological semimetals.

Epitaxial, strain-engineered Dirac semimetal heterostructures promise tuning of the unique properties of these materials. In this study, we investigate the growth of thin films of the recently discovered Dirac semimetal Cd3As2 by molecular beam epitaxy. We show that epitaxial Cd3As2 layers can be grown at low temperatures (110 °C–220 °C), in situ, on (111) GaSb buffer layers deposited on (111) GaAs substrates. The orientation relationship is described by (112)Cd3As2 || (111) GaSb and [11¯0]Cd3As2 || [1¯01]GaSb. The films are shown to grow in the low-temperature, vacancy ordered, tetragonal Dirac semimetal phase. They exhibit high room temperature mobilities of up to 19300 cm2/Vs, despite a three-dimensional surface morphology indicative of island growth and the presence of twin variants. The results indicate that epitaxial growth on more closely lattice matched buffer layers, such as InGaSb or InAlSb, which allow for imposing different degrees of epitaxial coherency strains, should be possible.

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Controlling the interaction of a single quantum emitter with its environment is a key challenge in quantum optics. Here, we demonstrate deterministic coupling of single nitrogen-vacancy ͑NV͒ centers to high-quality photonic crystal cavities. We preselect single NV centers and position their 50-nm-sized host nanocrystals into the mode maximum of photonic crystal S1 cavities with few-nanometer accuracy. The coupling results in a strong enhancement of NV center emission at the cavity wavelength. © 2011 American Institute of Physics. ͓doi:10.1063/1.3571437͔Spontaneous light emission can be controlled by enhancing or suppressing the vacuum fluctuations of the electromagnetic field at the location of the light source. 1 When placed into highly confined optical fields, such as those created in optical cavities or plasmonic structures, the optical properties of single quantum emitters can change drastically. [2][3][4][5] In particular, photonic crystal ͑PC͒ cavities show high quality factors combined with an extremely small mode volume. 6 It is challenging however to efficiently couple single photon sources to a PC cavity because the emitter has to be positioned in the localized optical mode, which is confined to an extremely small volume with a size of about a wavelength. [7][8][9] Nitrogen-vacancy ͑NV͒ centers in diamond are promising candidates for application as solid state quantum bits. [10][11][12] Long distance entanglement between NV centers enabling quantum repeater protocols may be achieved by two-photon quantum interference, 13,14 but is hindered by the NV centers' weak coherent photon emission rate. Being able to control and reshape the emission spectrum of a single NV center is therefore not only of fundamental interest but could also have potential applications in solid state quantum information processing. 15 Fabrication of high-quality PC cavities in diamond would be a natural way to control the emission properties of embedded NV centers but this is challenging because of the difficulties in growing and etching diamond single-crystal thin films. 16,17 An alternative, hybrid approach is to position a diamond nanocrystal with a single NV center near a PC cavity of a different material. [18][19][20][21] Because of the small size of such a crystal, the NV center can be placed in the highly confined optical mode where coupling can be efficient.Here, we demonstrate the deterministic nanoassembly of coupled single NV center-PC cavity systems by positioning ϳ50 nm sized diamond nanocrystals into gallium phosphide S1 cavities located on a different chip. The S1 cavity offers unique advantages over the well-studied L3 cavity. 19,20 Whereas in the L3 cavity the mode maximum is confined within the dielectric material, the mode maximum of the S1 cavity is localized in the air holes surrounding the cavity, making it accessible for coupling to external emitters. We are able to pick up and place a preselected diamond nanocrystal exactly into the mode maximum of a PC cavity, due to the versatility of our nanopositioning ...

The quality factors of modes in nearly identical GaAs and Al 0.18 Ga 0.82 As microdisks are tracked over three wavelength ranges centered at 980, 1460, and 1600 nm, with quality factors measured as high as 6.62ϫ 10 5 in the 1600 nm band. After accounting for surface scattering, the remaining loss is due to sub-band-gap absorption in the bulk and on the surfaces. The observed absorption is, on average, 80% greater in AlGaAs than in GaAs and is 540% higher in both materials at 980 nm than at 1600 nm. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2435608͔In recent semiconductor cavity quantum electrodynamics experiments involving self-assembled III-V quantum dots ͑QDs͒, Rabi splitting of the spontaneous emission line from individual QD excitonic states has been measured for the first time.

Vertical heterojunction NiO/β n-Ga2O/n+ Ga2O3 rectifiers employing NiO layer extension beyond the rectifying contact for edge termination exhibit breakdown voltages (VB) up to 4.7 kV with a power figure-of-merits, VB2/RON of 2 GW·cm−2, where RON is the on-state resistance (11.3 mΩ cm2). Conventional rectifiers fabricated on the same wafers without NiO showed VB values of 840 V and a power figure-of-merit of 0.11 GW cm−2. Optimization of the design of the two-layer NiO doping and thickness and also the extension beyond the rectifying contact by TCAD showed that the peak electric field at the edge of the rectifying contact could be significantly reduced. The leakage current density before breakdown was 144 mA/cm2, the forward current density was 0.8 kA/cm2 at 12 V, and the turn-on voltage was in the range of 2.2–2.4 V compared to 0.8 V without NiO. Transmission electron microscopy showed sharp interfaces between NiO and epitaxial Ga2O3 and a small amount of disorder from the sputtering process.