Xiuping Wang

High-performance surface-enhanced Raman scattering sensors based on Ag nanoparticles-coated Si nanowire arrays for quantitative detection of pesticides

A surface-enhanced Raman scattering (SERS) sensor made of Ag nanoparticles-coated Si nanowire (SiNW) arrays was fabricated for the quantitative detection of Carbaryl (an important nitrogen pesticide). H-terminated SiNWs were capable of reducing silver ions, leading to uniform deposition of silver nanoparticles on SiNW arrays. Such wire arrays exhibited a superior detection sensitivity of 10−17u2002M Rodamine 6G with high reproducibility. The sensor also enabled high sensitivity, reproducibility, and stability detection of Carbaryl. Significantly, the linear relation between the logarithmic concentrations and Raman peak intensities provided quantitative detection of Carbaryl.

Strongly coupled single quantum dot in a photonic crystal waveguide cavity

Cavities embedded in photonic crystal waveguides offer a promising route toward large scale integration of coupled resonators for quantum electrodynamics applications. In this letter, we demonstrate a strongly coupled system formed by a single quantum dot and such a photonic crystal cavity. The resonance originating from the cavity is clearly identified from the photoluminescence mapping of the out-of-plane scattered signal along the photonic crystal waveguide. The quantum dot exciton is tuned toward the cavity mode by temperature control. A vacuum Rabi splitting of ∼140u2002μeV is observed at resonance.

Ultra Low Dark Current, High Responsivity and Thin Multiplication Region in InGaAs/InP Avalanche Photodiodes

A separate absorption, grading, charge and multiplication InGaAs/InP avalanche photodiode with ultra low dark current and high responsivity is demonstrated. It has a thin multiplication layer and a planar structure. Through the use of a well and a single floating guard ring to suppress edge breakdown, the device can easily be fabricated by one step epitaxial growth and one step diffusion. The dark current of a 30 μm diameter device is as low as 0.028 nA at punch-through and 0.1 nA at 90% of the breakdown voltage. The responsivity at 1.55 μm is 0.93 A/W at unity gain and the multiplication layer is estimated to be less than 300 nm.

Optically controlled quantum dot gated transistors with high on/off ratio

We report the design and fabrication of InAs quantum dot gated transistors, which are normally-on, where the channel current can be switched off by laser illumination. Laser light at 650 nm with a power of 850 pW switches the channel current from 5u2002μA to 2 pA, resulting in an on/off ratio of more than 60 dB. The switch-off mechanism and carrier dynamics are analyzed with simulated band structure.