Photon-triggered nanowire transistors.

Photon-triggered electronic circuits have been a long-standing goal of photonics. Recent demonstrations include either all-optical transistors in which photons control other photons or phototransistors with the gate response tuned or enhanced by photons. However, only a few studies report on devices in which electronic currents are optically switched and amplified without an electrical gate.

Nonlinear mixing in nanowire subwavelength waveguides.

The realization of nonlinear photonic circuits to achieve the control of light-by-light is contingent upon a strong nonlinear response that can be captured in a guided-wave geometry. There remains a need to further scale down waveguides while maintaining a strong nonlinear response. In this study, we report second-harmonic generation and optical parametric generation using the second-order nonlinear response in an 80 nm thick CdS nanowire subwavelength waveguide.

Single p-type/intrinsic/n-type silicon nanowires as nanoscale avalanche photodetectors.

We report the controlled synthesis of axial modulation-doped p-type/intrinsic/n-type (p-i-n) silicon nanowires with uniform diameters and single-crystal structures. The p-i-n nanowires were grown in three sequential steps: in the presence of diborane for the p-type region, in the absence of chemical dopant sources for the middle segment, and in the presence of phosphine for the n-type region. The p-i-n nanowires were structurally characterized by transmission electron microscopy, and the spatially resolved electrical properties of individual nanowires were determined by electrostatic force and scanning gate microscopies.

Hybrid single-nanowire photonic crystal and microresonator structures.

We report a hybrid approach for photonic systems that combines chemically synthesized single nanowire emitters with lithographically defined photonic crystal and racetrack microresonator structures. Finite-difference time-domain calculations were used to design nanowire photonic crystal structures where the photonic band gap overlaps the electronic band gap of the nanowire. Photoluminescence (PL) images of cadmium sulfide (CdS) nanowire photonic crystal structures designed in this way demonstrate localized emission from engineered defects and light suppression in regions of the photonic crystal.

General synthesis of manganese-doped II-VI and III-V semiconductor nanowires.

A general approach for the synthesis of manganese-doped II-VI and III-V nanowires based on metal nanocluster-catalyzed chemical vapor deposition has been developed. High-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy studies of Mn-doped CdS, ZnS, and GaN nanowires demonstrate that the nanowires are single-crystal structures and homogeneously doped with controllable concentrations of manganese ions. Photoluminescence measurements of individual Mn-doped CdS and ZnS nanowires show characteristic pseudo-tetrahedral Mn2+ ((4)T1-->(6)A1) transitions that match the corresponding transitions in bulk single-crystal materials well.

Lasing in single cadmium sulfide nanowire optical cavities.

The mechanism of lasing in single cadmium sulfide (CdS) nanowire cavities was elucidated by temperature-dependent and time-resolved photoluminescence (PL) measurements. Temperature-dependent PL studies reveal rich spectral features and show that an exciton-exciton interaction is critical to lasing up to 75 K, while an exciton-phonon process dominates at higher temperatures. These measurements together with temperature and intensity dependent lifetime and threshold studies show that lasing is due to formation of excitons and, moreover, have implications for the design of efficient, low threshold nanowire lasers.

Imaging and analysis of nanowires.

We used vapor-liquid-solid (VLS) methods to synthesize discrete single-element semiconductor nanowires and multicomposition nanowire heterostructures, and then characterized their structure and composition using high-resolution electron microscopy (HRTEM) and analytical electron microscopy techniques. Imaging nanowires requires the modification of the established HRTEM imaging procedures for bulk material to take into consideration the effects of finite nanowire width and thickness. We show that high-resolution atomic structure images of nanowires less than 6 nm in thickness have lattice "streaking" due to the finite crystal lattice in two dimensions of the nanowire structure.

Synthesis of CdS and ZnS nanowires using single-source molecular precursors.

Single-source molecular precursors were used to synthesize II-VI compound semiconductor nanowires for the first time. Cadmium sulfide and zinc sulfide nanowires were prepared using cadmium diethyldithiocarbamate, Cd(S2CNEt2)2, and zinc diethyldithiocarbamate, Zn(S2CNEt2)2, respectively, as precursors in a gold nanocluster-catalyzed vapor-liquid-solid growth process. High-resolution transmission electron microscopy studies show that the CdS and ZnS nanowires are single-crystal wurtzite structures with stoichiometric compositions.