Selvakumar V. Nair

High-temperature ferromagnetism in Mn-doped ZnO nanowires

We have observed ferromagnetism in dilute (∼1–4at.%) Mn-doped crystalline ZnO nanowires at temperatures up to 400K. Arrays of freestanding single crystal ZnO:Mn nanowires were fabricated by Au-catalyzed vapor-liquid-solid growth. Structure and compositional analyses revealed that Mn was incorporated into the ZnO lattice. From the observed saturation magnetization, the magnetic moment per Mn atom is estimated to be between 0.3μB and 1.2μB. Photoluminescence measurements show a strong suppression of defect related midgap emission, indicative of an interplay between Mn doping and native point defects.

Biexciton recombination rates in self-assembled quantum dots

The radiative recombination rates of interacting electron-hole pairs in a quantum dot are strongly affected by quantum correlations among electrons and holes in the dot. Recent measurements of the biexciton recombination rate in single self-assembled quantum dots have found values spanning from two times the single exciton recombination rate to values well below the exciton decay rate. In this paper, a Feynman path-integral formulation is developed to calculate recombination rates including thermal and many-body effects. Using real-space Monte Carlo integration, the path-integral expressions for realistic three-dimensional models of

Room temperature single nanowire ZnTe photoconductors grown by metal-organic chemical vapor deposition

\mathrm{In}\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{As}

Direct observation of single-charge-detection capability of nanowire field-effect transistors

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Electron transport in degenerate Mn-doped ZnO nanowires

\mathrm{Cd}\mathrm{Se}∕\mathrm{Zn}\mathrm{Se}

Two-exciton state in GaSb∕GaAs type II quantum dots studied using near-field photoluminescence spectroscopy

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Imaging and single dot spectroscopy of InP self-assembled quantum dots

\mathrm{In}\mathrm{P}∕\mathrm{In}\mathrm{Ga}\mathrm{P}

Probing the gate--voltage-dependent surface potential of individual InAs nanowires using random telegraph signals.

dots are evaluated, including anisotropic effective masses. Depending on size, radiative rates of typical dots lie in the regime between strong and intermediate confinement. The results compare favorably to recent experiments and calculations on related dot systems. Configuration interaction calculations using uncorrelated basis sets are found to be severely limited in calculating decay rates.

Highly confined mode above the light line in a two-dimensional photonic crystal slab

Single nanowire ZnTe photoconductors prepared by metal-organic chemical vapor deposition are presented. These photodetectors exhibit the highest reported visible responsivity of 360 A/W (at 530 nm) and gain of 8640 (at 3 V bias). The high gain reflects a long carrier lifetime (i.e., ∼1 μs) and the role of fast selective trapping of one carrier is presented to explain this. These results reveal that such single ZnTe nanowires are excellent candidates for applications requiring high performance visible nanoscale photoconductive detectors.

Many carrier effects in self-assembled InP quantum dots

A single localized charge can quench the luminescence of a semiconductor nanowire, but relatively little is known about the effect of single charges on the conductance of the nanowire. In one-dimensional nanostructures embedded in a material with a low dielectric permittivity, the Coulomb interaction and excitonic binding energy are much larger than the corresponding values when embedded in a material with the same dielectric permittivity. The stronger Coulomb interaction is also predicted to limit the carrier mobility in nanowires. Here, we experimentally isolate and study the effect of individual localized electrons on carrier transport in InAs nanowire field-effect transistors, and extract the equivalent charge sensitivity. In the low carrier density regime, the electrostatic potential produced by one electron can create an insulating weak link in an otherwise conducting nanowire field-effect transistor, modulating its conductance by as much as 4,200% at 31 K. The equivalent charge sensitivity, 4 × 10(-5) e Hz(-1/2) at 25 K and 6 × 10(-5) e Hz(-1/2) at 198 K, is orders of magnitude better than conventional field-effect transistors and nanoelectromechanical systems, and is just a factor of 20-30 away from the record sensitivity for state-of-the-art single-electron transistors operating below 4 K (ref. 8). This work demonstrates the feasibility of nanowire-based single-electron memories and illustrates a physical process of potential relevance for high performance chemical sensors. The charge-state-detection capability we demonstrate also makes the nanowire field-effect transistor a promising host system for impurities (which may be introduced intentionally or unintentionally) with potentially long spin lifetimes, because such transistors offer more sensitive spin-to-charge conversion readout than schemes based on conventional field-effect transistors.