Explore the vast range of titles available.

We report on the intrinsic optoelectronic response of high-quality dual-gated monolayer and bilayer graphene p-n junction devices. Local laser excitation (of wavelength 850 nanometers) at the p-n interface leads to striking six-fold photovoltage patterns as a function of bottom-and top-gate voltages. These patterns, together with the measured spatial and density dependence of the photoresponse, provide strong evidence that nonlocal hot carrier transport, rather than the photovoltaic effect, dominates the intrinsic photoresponse in graphene. This regime, which features a long-lived and spatially distributed hot carrier population, may offer a path to hot carrier-assisted thermoelectric technologies for efficient solar energy harvesting.

Introducing an extremely thin layer of boron nitride between a sapphire substrate and the gallium nitride semiconductor grown on it is shown to facilitate the transfer of the resulting nitride structures to more flexible and affordable substrates. Lift-off for nitride semiconductors Nitride semiconductors are renowned for their excellent electronic and optical properties and are the materials of choice for many optical devices, including BluRay players. But they have an important practical drawback: they are very particular about the substrates (typically sapphire) on which they can be grown. This has stimulated the search for new ways of transferring such materials from one substrate to another. Here Kobayashi et al . demonstrate, using a gallium nitride-based device, that the addition of an extremely thin layer of hexagonal boron nitride to the initial growth surface facilitates the straightforward mechanical release of the resulting nitride structures, as well as subsequent transfer to any suitable substrate, including metals, glass and transparent plastics. Nitride semiconductors are the materials of choice for a variety of device applications, notably optoelectronics 1 , 2 and high-frequency/high-power electronics 3 . One important practical goal is to realize such devices on large, flexible and affordable substrates, on which direct growth of nitride semiconductors of sufficient quality is problematic. Several techniques—such as laser lift-off 4 , 5 —have been investigated to enable the transfer of nitride devices from one substrate to another, but existing methods still have some important disadvantages. Here we demonstrate that hexagonal boron nitride (h-BN) can form a release layer that enables the mechanical transfer of gallium nitride (GaN)-based device structures onto foreign substrates. The h-BN layer serves two purposes: it acts as a buffer layer for the growth of high-quality GaN-based semiconductors, and provides a shear plane that makes it straightforward to release the resulting devices. We illustrate the potential versatility of this approach by using h-BN-buffered sapphire substrates to grow an AlGaN/GaN heterostructure with electron mobility of 1,100 cm 2  V −1  s −1 , an InGaN/GaN multiple-quantum-well structure, and a multiple-quantum-well light-emitting diode. These device structures, ranging in area from five millimetres square to two centimetres square, are then mechanically released from the sapphire substrates and successfully transferred onto other substrates.

One-dimensionally connected organic nanostructures with dissimilar semiconducting properties are expected to provide a reliable platform in understanding the behaviors of photocarriers, which are important for the development of efficient photon-to-electrical energy conversion systems. Although bottom-up supramolecular approaches are considered promising for the realization of such nanoscale heterojunctions, the dynamic nature of molecular assembly is problematic. We report a semiconducting nanoscale organic heterojunction, demonstrated by stepwise nanotubular coassembly of two strategically designed molecular graphenes. The dissimilar nanotubular segments, thus connected noncovalently, were electronically communicable with one another over the heterojunction interface and displayed characteristic excitation energy transfer and charge transport properties not present in a mixture of the corresponding homotropically assembled nanotubes.

Spintronics increases the functionality of information processing while seeking to overcome some of the limitations of conventional electronics. The spin-injected field effect transistor, a lateral semiconducting channel with two ferromagnetic electrodes, lies at the foundation of spintronics research. We demonstrated a spin-injected field effect transistor in a high-mobility InAs heterostructure with empirically calibrated electrical injection and detection of ballistic spin-polarized electrons. We observed and fit to theory an oscillatory channel conductance as a function of monotonically increasing gate voltage.

By trapping molecules between two gold electrodes with a temperature difference across them, the junction Seebeck coefficients of 1,4-benzenedithiol (BDT), 4,4′-dibenzenedithiol, and 4,4\"-tribenzenedithiol in contact with gold were measured at room temperature to be +8.7 ± 2.1 microvolts per kelvin (μV/K), +12.9 ± 2.2 μV/K, and +14.2 ± 3.2 μV/K, respectively (where the error is the full width half maximum of the statistical distributions). The positive sign unambiguously indicates p-type (hole) conduction in these heterojunctions, whereas the Au Fermi level position for Au-BDT-Au junctions was identified to be 1.2 eV above the highest occupied molecular orbital level of BDT. The ability to study thermoelectricity in molecular junctions provides the opportunity to address these fundamental unanswered questions about their electronic structure and to begin exploring molecular thermoelectric energy conversion.

Solid-sate physics: Practical polaritronics A tight control over light–matter interactions can be achieved at a nanometre scale in a semiconductor microcavity. The strong coupling between excitons in the semiconductor material and photons resonating in the cavity gives rise to new hybrid half-light/half-matter quasiparticles called polaritons. The unique properties of polaritons, giving rise to exotic lasing and quantum condensation effects, have the potential to spawn a new generation of particle emitters and semiconductor lasers. Polariton lasing and nonlinearities have been demonstrated in optical experiments, but it would be of considerable technological interest to demonstrate electrically driven polariton light-emitting devices. This has now been accomplished in a gallium arsenide diode that emits light directly from polariton states held at the relatively high temperature of 235 K (−38° C). The authors believe that the findings represent a significant step towards the realization of a new class of ultra-efficient polaritronic devices with unprecedented characteristics. The increasing ability to control light–matter interactions at the nanometre scale has improved the performance of semiconductor lasers in the past decade. The ultimate optimization is realized in semiconductor microcavities, in which strong coupling between quantum-well excitons and cavity photons gives rise to hybrid half-light/half-matter polariton quasiparticles 1 . The unique properties of polaritons—such as stimulated scattering 2 , 3 , parametric amplification 4 , 5 , 6 , lasing 7 , 8 , 9 , 10 , condensation 11 , 12 , 13 and superfluidity 14 , 15 —are believed to provide the basis for a new generation of polariton emitters and semiconductor lasers. Until now, polariton lasing and nonlinearities have only been demonstrated in optical experiments, which have shown the potential to reduce lasing thresholds by two orders of magnitude compared to conventional semiconductor lasers 16 . Here we report an experimental realization of an electrically pumped semiconductor polariton light-emitting device, which emits directly from polariton states at a temperature of 235 K. Polariton electroluminescence data reveal characteristic anticrossing between exciton and cavity modes, a clear signature of the strong coupling regime. These findings represent a substantial step towards the realization of ultra-efficient polaritonic devices with unprecedented characteristics.