63 research outputs found
Electronic properties of GaAs surfaces etched in an electron cyclotron resonance source and chemically passivated using P2S5P2S5
Photoreflectance has been used to study the electronic properties of (100) GaAs surfaces exposed to a Cl2/ArCl2/Ar plasma generated by an electron cyclotron resonance source and subsequently passivated by P2S5.P2S5. The plasma etch shifts the Fermi level of p-GaAsp-GaAs from near the valence band to midgap, but has no effect on n-GaAs.n-GaAs. For ion energies below 250 eV, post-etch P2S5P2S5 chemical passivation removes the surface etch damage and restores the electronic properties to pre-etch conditions. Above 250 eV, the etch produces subsurface defects which cannot be chemically passivated. Auger electron spectroscopy shows that etching increases As at the GaAs/oxide interface, while passivation reduces it. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69373/2/APPLAB-73-1-114-1.pd
Fowler-Nordheim-like local injection of photoelectrons from a silicon tip
Tunneling between a photo-excited p-type silicon tip and a gold surface is
studied as a function of tip bias, tip/sample distance and light intensity. In
order to extend the range of application of future spin injection experiments,
the measurements are carried out under nitrogen gas at room temperature. It is
found that while tunneling of valence band electrons is described by a standard
process between the semiconductor valence band and the metal, the tunneling of
photoelectrons obeys a Fowler-Nordheim-like process directly from the
conduction band. In the latter case, the bias dependence of the photocurrent as
a function of distance is in agreement with theoretical predictions which
include image charge effects. Quantitative analysis of the bias dependence of
the dark and photocurrent spectra gives reasonable values for the distance, and
for the tip and metal work functions. For small distances image charge effects
induce a vanishing of the barrier and the bias dependence of the photocurrent
is exponential. In common with many works on field emission, fluctuations in
the tunneling currents are observed. These are mainly attributed to changes in
the prefactor for the tunneling photocurrent, which we suggest is caused by an
electric-field-induced modification of the thickness of the natural oxide layer
covering the tip apex.Comment: 12 pages, 11 figures. Submitted to Phys. Rev.
Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry
Modulated electroreflectance spectroscopy of semiconductor
self-assembled quantum dots is investigated. The structure is modeled as dots
with lens shape geometry and circular cross section. A microscopic description
of the electroreflectance spectrum and optical response in terms of an external
electric field () and lens geometry have been considered. The field
and lens symmetry dependence of all experimental parameters involved in the
spectrum have been considered. Using the effective mass formalism
the energies and the electronic states as a function of and dot
parameters are calculated. Also, in the framework of the strongly confined
regime general expressions for the excitonic binding energies are reported.
Optical selection rules are derived in the cases of the light wave vector
perpendicular and parallel to . Detailed calculation of the Seraphin
coefficients and electroreflectance spectrum are performed for the InAs and
CdSe nanostructures. Calculations show good agreement with measurements
recently performed on CdSe/ZnSe when statistical distribution on size is
considered, explaining the main observed characteristic in the
electroreflectance spectra
Optical Properties of Gallium-Doped Zinc Oxide-A Low-Loss Plasmonic Material: First-Principles Theory and Experiment
Searching for better materials for plasmonic and metamaterial applications is an inverse design problem where theoretical studies are necessary. Using basic models of impurity doping in semiconductors, transparent conducting oxides (TCOs) are identified as low-loss plasmonic materials in the near-infrared wavelength range. A more sophisticated theoretical study would help not only to improve the properties of TCOs but also to design further lower-loss materials. In this study, optical functions of one such TCO, gallium-doped zinc oxide (GZO), are studied both experimentally and by first-principles density-functional calculations. Pulsed-laser-deposited GZO films are studied by the x-ray diffraction and generalized spectroscopic ellipsometry. Theoretical studies are performed by the total-energy-minimization method for the equilibrium atomic structure of GZO and random phase approximation with the quasiparticle gap correction. Plasma excitation effects are also included for optical functions. This study identifies mechanisms other than doping, such as alloying effects, that significantly influence the optical properties of GZO films. It also indicates that ultraheavy Ga doping of ZnO results in a new alloy material, rather than just degenerately doped ZnO. This work is the first step to achieve a fundamental understanding of the connection between material, structural, and optical properties of highly doped TCOs to tailor those materials for various plasmonic applications
Plasmonic Properties of Vertically Aligned Nanowire Arrays
Nanowires (NWs)/Ag sheath composites were produced to investigate plasmonic coupling between vertically aligned NWs for surface-enhanced Raman scattering (SERS) applications. In this investigation, two types of vertical NW arrays were studied; those of ZnO NWs grown on nanosphere lithography patterned sapphire substrate via vapor-liquid-solid (VLS) mechanism and Si NW arrays produced by wet chemical etching. Both types of vertical NW arrays were coated with a thin layer of silver by electroless silver plating for SERS enhancement studies. The experimental results show extremely strong SERS signals due to plasmonic coupling between the NWs, which was verified by COMSOL electric field simulations. We also compared the SERS enhancement intensity of aligned and random ZnO NWs, indicating that the aligned NWs show much stronger and repeatable SERS signal than those grown in nonaligned geometries
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