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Al-doped ZnO (AZO) films with high transmittance and low resistivity were achieved on low temperature substrates by radio frequency magnetron sputtering using a high temperature target. By investigating the effect of target temperature (TG) on electrical and optical properties, the origin of electrical conduction is verified as the effect of the high TG, which enhances crystal quality that provides higher mobility of electrons as well as more effective activation for the Al dopants. The optical bandgap increases from 3.30 eV for insulating ZnO to 3.77 eV for conducting AZO grown at high TG, and is associated with conduction-band filling up to 1.13 eV due to the Burstein-Moss effect. [ABSTRACT FROM AUTHOR]

We report time-dependent photocurrent and transport measurements of sub-bandgap photoexcited carriers in nitrogen-rich (type Ib), single-crystal diamond. Transient carrier dynamics are characteristic of trapping conduction with long charge storage lifetimes of ∼3 hours. By measuring the photoexcited Hall effect, we confirm that the charge carriers are electrons and by varying the excitation energy we observe a strong turn-on in the photoconduction at ∼1.9 eV. These findings shed light on sub-bandgap states in nitrogen-doped single-crystal diamond. [ABSTRACT FROM AUTHOR]

Diamond-based photonic devices offer exceptional opportunity to study cavity quantum electrodynamics at room temperature. Here we report fabrication and optical characterization of high quality photonic crystal microcavities based on nanocrystalline diamond. Fundamental modes near the emission wavelength of negatively charged nitrogen-vacancy centers (637 nm) with quality factors as high as 585 were observed. Three-dimensional finite-difference time-domain simulations were carried out, having excellent agreement with the experimental results in the values of the mode frequencies. Polarization of the modes was measured; their anomalous behavior provides important insights to scattering loss in these structures. [ABSTRACT FROM AUTHOR]

The authors report on the dispersive phase response of light traversing a tapered optical fiber coupled to the whispering-gallery modes (WGMs) of GaAs microdisks with cavity Q factors of up to 3×105 at wavelengths of around 1.5 μm. The group delay of the coupled light, that is, a derivative of the phase shift, becomes positive (+10 ps) and then negative (-55 ps) near the high-Q WGM resonances, as compared with a reference group delay without evanescent-wave coupling. The chromatic dispersion becomes as high as ±8 ns/nm near WGM wavelengths. [ABSTRACT FROM AUTHOR]

Nanocrystalline diamond microdisks have been fabricated and characterized. The process conditions were chosen to ensure smooth and vertical sidewalls. Focused ion beam milling was used to create ultrasmooth sidewalls. Whispering gallery modes were observed near the nitrogen-vacancy center emission wavelength (637 nm) by photoluminescence and near ∼1550 nm by evanescent fiber coupling. The cavity quality factors (Q) are about 100 in both experiments. The Q’s for these disks were calculated to be as high as 105 by three-dimensional finite-difference time-domain simulations. The authors believe the Q’s to be limited by absorption and scattering within the nanocrystalline cavity material. [ABSTRACT FROM AUTHOR]

We have observed optical emission from self-assembled InAs/GaAs quantum dots (QDs) embedded within the single-hole-defect, square-lattice (S1) photonic crystal microcavity. Cavities were measured to have quality factors as high as 4000. Finite-difference time-domain (FDTD) calculations were used to determine the specific S1 geometry that is resonant at the center of our ensemble QD spectrum. Extensive, systematic measurements fully confirmed the FDTD simulations and mapped resonant wavelengths as a function of varying lattice constant and hole radius of the photonic crystal structures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]