Search

A self-powered photodetector with ultrahigh sensitivity, fast photoresponse, and wide spectral detectivity covering from 1000 nm to 400 nm based on graphene/ZnO/Si triple junctions has been designed, fabricated, and demonstrated. In this device, graphene serves as a transparent electrode as well as an efficient collection layer for photogenerated carriers due to its excellent tunability of Fermi energy. The ZnO layer acts as an antireflection layer to trap the incident light and enhance the light absorption. Furthermore, the insertion of the ZnO layer in between graphene and Si layers can create build-in electric field at both graphene/ZnO and ZnO/Si interfaces, which can greatly enhance the charge separation of photogenerated electron and hole pairs. As a result, the sensitivity and response time can be significantly improved. It is believed that our methodology for achieving a high-performance self-powered photodetector based on an appropriate design of band alignment and optical parameters can be implemented to many other material systems, which can be used to generate unique optoelectronic devices for practical applications. [ABSTRACT FROM AUTHOR]

Graphene's advantages for sensor applications are offset by its low electric impedance and consequently low signal-to-noise ratio. We have improved the sensitivity of graphene based photosensors by integrating an energy filtering barrier as an amplifying element. The resulting graphene devices exhibit the highest reported photosensitivity (Ion/Ioff∼4000, gain∼10 A/W) while retaining broad band detection and high speed response. In addition to this unprecedented photosensitivity, the proposed device structure renders the complete graphene photosensitive which enables large scale and flexible photodetectors. The presented approach represents a universal route to enhancing the performance of graphene sensors. [ABSTRACT FROM AUTHOR]

Profile transformation of sidewalls and roughness reduction by KrF excimer laser reformation at different illumination conditions are presented. The effective energy density derived from a finite element model of heat transfer is used to characterize the molten depth of Si during high energy laser illumination at normal and oblique incidence. The operation range of laser reformation as a sidewall smoothing technique, including incident angles and energy densities, is determined by the effective energy density. Using an energy density higher than 1.4 J/cm2 at the incident angle of 75° is recommended for a minimal residual roughness, acceptable sidewall profile transformation, and a practical interval-height ratio. The upper bound of scattering loss after laser reformation at different effective energy densities is also calculated. [ABSTRACT FROM AUTHOR]

Raman spectra of isolated single-walled carbon nanotubes (SWNTs) were obtained for a wide range of laser excitation energies to study the resonance excitation window of the radial breathing mode feature for members of (2n+m) families. A chiral angle (θ) dependence of the resonance window width (Γ) was observed, which is much stronger than the diameter dependence. The implications of this work on nanotube metrology are discussed. [ABSTRACT FROM AUTHOR]