Carl J. Barrelet

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.

Semiconductor nanowire laser and nanowire waveguide electro-optic modulators

Electric field modulation of visible and ultraviolet nanoscale lasers consisting of single CdS or GaN nanowires has been achieved using integrated, microfabricated electrodes. Modulation of laser emission intensity is achieved with no detectable change in the laser wavelength. The devices can also be operated below the lasing threshold to modulate the intensity of light propagating within the nanowire waveguide. Studies of the electric field dependence in devices of varied geometry indicate that modulation is due to an electroabsorption mechanism. These findings expand opportunities for multicolor, nanowire-based photonic devices and circuits.

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. Moreover, our three-dimensional finite-difference time-domain (FDTD) simulations demonstrate that it is possible to enhance the coherence length due to the very nature of the subwavelength geometry. Nonlinear mixing in a nanowire subwavelength waveguide represents an advance toward all-optical processing and all-optical switching in integrated photonic circuits.

Microstadium single-nanowire laser

We report room-temperature lasing in an optically pumped single-nanowire stadium microresonator. The photoluminescence from a chemically synthesized GaN nanowire is coupled and confined in a silicon-nitride stadium microcavity. Photoluminescence spectroscopy exhibits lasing at 372nm with a lasing threshold of 1536kW∕cm2. We compute a Q factor of ∼3500 for the microstadium single-nanowire structure using finite-difference time-domain simulation. The successful demonstration of this hybrid structure using bottom-up and top-down approaches represents a significant step toward high-density integration of functional building blocks for an ultracompact nanophotonic circuit.

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. Here we show photon-triggered nanowire (NW) transistors, photon-triggered NW logic gates and a single NW photodetection system. NWs are synthesized with long crystalline silicon (CSi) segments connected by short porous silicon (PSi) segments. In a fabricated device, the electrical contacts on both ends of the NW are connected to a single PSi segment in the middle. Exposing the PSi segment to light triggers a current in the NW with a high on/off ratio of >8 × 106. A device that contains two PSi segments along the NW can be triggered using two independent optical input signals. Using localized pump lasers, we demonstrate photon-triggered logic gates including AND, OR and NAND gates. A photon-triggered NW transistor of diameter 25 nm with a single 100 nm PSi segment requires less than 300 pW of power. Furthermore, we take advantage of the high photosensitivity and fabricate a submicrometre-resolution photodetection system. Photon-triggered transistors offer a new venue towards multifunctional device applications such as programmable logic elements and ultrasensitive photodetectors.

Semiconductor nanowires embedded in optical microcavities

Optical loss of a chemically-synthesized light-emitting nanowire can be reduced by embedding the nanowire in an optical microcavity. Design of nanowire/photonic crystal platform as well as characterization of nanowire embedded in race-track microresonator are presented.

Hybrid single nanowire photonic crystal structure

We combine chemically-synthesized single nanowire emitters with lithographically-defined photonic crystal structures. Localized emission from engineered defects and light suppression in regions of the photonic crystal are demonstrated by photoluminescence imaging and spectroscopy measurements.