GaN/AlN quantum dots (QDs) have been observed to emit in deep ultra violet (UV) regime. The emission wavelength
can be tuned from 270 nm to 238 nm using GaN growth time and Ga flux. In this work, tunnel injection GaN/AlN QD
UV LEDs have been fabricated utilizing polarization doped p-n junctions grown on AlN templates on sapphire. The QD
EL emission is obtained at 250 nm whereas a second peak emission is observed at 290 nm from the p-type AlGaN.
However, the enhanced doping and carrier injection in polarization doped structure boosts the deep-UV emission
intensity by 26 times compared to non-polarization doped UV LED.
KEYWORDS: Luminescence, Objectives, Atomic force microscopy, Polarization, Near field scanning optical microscopy, Glasses, Confocal microscopy, Silicon, Near field optics, Quantum dots
We have studied the influence of Si atomic force microscope (AFM) probes on fluorescence of ZnS overcoated CdSe quantum dots (QDs) in an apertureless near-field scanning optical microscope (ANSOM). In these ANSOM measurements, the excitation light polarization and probe preparation procedure strongly affect the QD fluorescence. When the excitation light polarization is orthogonal to the probe axis (and parallel to the substrate surface), we detect 50 to 80% fluorescence quenching, with a HF-etched Si probe scanning ~10 nm above the sample. With polarization of the excitation collinear with the probe axis, the optical field is amplified many times in the near-field zone, and the net result is a 2-4 times fluorescence enhancement. In this work we utilize a home-built, non-contact AFM and confocal ANSOM microscope under total internal reflection of Ar+ laser beam excitation.
KEYWORDS: Luminescence, Optical spheres, Near field optics, Atomic force microscopy, Molecules, Near field scanning optical microscopy, Prisms, Picosecond phenomena, Silicon, Zinc
The fluorescence of single ZnS overcoated CdSe quantum dots (QDs) and dye doped polystyrene spheres (PSs) embedded in the evanescent optical field has been studied using an apertureless near-field scanning optical microscope (ANSOM) operating in non-contact and dynamic-force modes. The fluorescence intensity of an individual QD can be enhanced 5 times when an HF etch-cleaned silicon probe is located over the QD and spatially resolved with ~30 nm full width at half maximum when the ANSOM is operating in non-contact mode. Furthermore, we show that the fluorescence contrast in ANSOM is typically 5 times greater than the above enhancement coefficient. In the case of ANSOM dynamic-force mode, the fluorescence of QDs and PSs depends on the pressure applied by the probe to the sample.
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