The optical properties of single InAs∕GaAs quantum dots (QDs) were studied as a function of their distance from the air∕GaAs interface. A short-period superlattice structure allows us to controllably shorten the distance between the QDs and the surface in 6-nm steps. The QD luminescence intensity and lifetime measurements show that quantum tunneling effect results in a sharp reduction in fluorescence efficiency and lifetime when the wetting-layer–surface distance is within 9 nm. For distances between 15 and 40 nm, broadening of the photoluminescence linewidths of single QDs was observed. Since exciton recombination time and efficiency are in this case unchanged with respect to bulk QDs, the observed line broadening is most likely due to dephasing or spectral diffusion processes.
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 (637nm) by photoluminescence and near ∼1550nm 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.
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.
Freestanding and suspended single crystal diamond devices, micro disks and beam structures, have been fabricated on single crystal diamond substrates using a lift-off process employing ion implantation followed by electrochemical etching. The ion implantation created subsurface damage in the diamond while the top surface was sufficiently undamaged that a subsequent homo-epitaxial diamond layer could be grown by chemical vapor deposition (CVD). After the CVD growth and patterning by lithography and reactive ion etching, the underlying damage layer was etched/removed by an electrochemical etch. Different implant ions and energies were simulated and tested to optimize the process. The electrochemical etching process was monitored by an optical video technique. The electrochemical etching process used both ac and dc applied electrical potentials. Photoluminescence (PL), Raman spectra, and polarized light transmission microscopy have been used to characterize the implanted substrate and liftoff films. AFM has been used to monitor the surface changes after mechanical polishing, ion implantation, CVD growth and the lift-off process. This research has revealed that the parameters of ion implantation (implant species, dose and energy) dramatically affect the lift-off process. The etching mechanism and critical parameters are discussed in this work. PL spectroscopy indicated differences between the uppermost layers of the homoepitaxial film and the lift-off interface. Three principal classes of defects have been observed: growth defects inherent in the diamond substrates (type Ib, HPHT), defects induced by the polishing process and associated stress, and point defects.Mater. Res. Soc. Symp. Proc. Vol. 956
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