ABSTRACT
GaAs core-shell p-n junction tunnel diodes were demonstrated by combining vapor-liquid-solid growth with gallium oxide deposition by atomic layer deposition for electrical isolation. The characterization of an ensemble of core-shell structures was enabled by the use of a tungsten probe in a scanning electron microscope without the need for lithographic processing. Radial tunneling transport was observed, exhibiting negative differential resistance behavior with peak-to-valley current ratios of up to 3.1. Peak current densities of up to 2.1 kA/cm(2) point the way to applications in core-shell photovoltaics and tunnel field effect transistors.
ABSTRACT
Carbon is a commonly used p-type dopant in planar III-V semiconductors, however its use in nanowire (NW) growth has been much less reported. In this work we show that the morphology of gold assisted GaAs NWs can be strongly modified by the presence of CBr(4) vapor during growth by metalorganic vapor phase epitaxy. GaAs NWs were grown under conditions which result in strong tapering and lateral growth at low growth temperatures by the use of triethylgallium (TEGa) instead of the more usual precursor, trimethylgallium (TMGa). Under these conditions, NWs grown in the presence of CBr(4) exhibit higher axial and lower radial growth rates, and negligible tapering compared with NWs grown in the absence of CBr(4) under the same conditions. We attribute this primarily to the suppression of the 2d growth rate by CBr(4), which enhances the axial growth rate of the nanowires. NWs grown with CBr(4) show stacking-fault-free zincblende structure, while the NWs grown without CBr(4) show a high density of stacking faults. This work underlines the striking effects which precursor chemistry can have on nanowire morphology.
Subject(s)
Arsenicals/chemistry , Gallium/chemistry , Hydrocarbons, Brominated/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
We demonstrate the use of Fourier transform infrared (IR) spectroscopy for midinfrared emission measurements following x-ray or electron excitation. Spectra from an InAs low band-gap semiconductor film, which emits in the IR from 3000 to 3400 cm(-1), are presented. There is good agreement between the present results and previously published laser-excited spectra. Using focused beams, it should be possible to perform sub-diffraction-limited IR imaging. In addition, simultaneous structural and electronic analysis could be performed using the x-ray or electron excitation probes.
Subject(s)
Calcinosis/prevention & control , Coronary Artery Disease/prevention & control , Mass Screening , Tomography, X-Ray Computed , Adult , Calcinosis/diagnostic imaging , Coronary Artery Disease/diagnostic imaging , Female , Humans , Male , Middle Aged , Practice Guidelines as Topic , Risk Factors , TexasABSTRACT
1. The polymerase chain reaction has been used to amplify specifically the cDNA coding for the secreted form of ovine trophoblast protein-one from a preparation of total cellular RNA extracted from sheep embryos removed from ewes 16 days after mating. 2. Cloning and sequencing of the amplified cDNA revealed two new sequence variants: SPW49 having 93% similarity with deduced amino acid sequences from published cDNA data, and SPW27 a variant coding for a deleted form of ovine trophoblast protein-one. 3. The gene for ovine trophoblast protein-one is intronless. 4. This study provides further evidence for the existence of an ovine trophoblast protein-one gene family. 5. Both variants contain a potential N-glycosylation site not apparent in published sequences for ovine trophoblast protein-one.
