Faculty Recital

Program listing performers and works performe

Influence of air pollutants on the lifetime of LEDs and analysis of degradation effects

Compared to traditional light sources light emitting diodes (LEDs) provide an increased efficiency and long lifetime, making them the primary choice for many applications. However, these lifetimes are highly dependent on operational conditions like junction temperature, drive current and environmental conditions like the exposure to humidity or air pollutants. This work studies the effects of common air pollutants in different concentrations on the lifetime of commercial LEDs with different packages and analyses the observed degradation mechanisms on the AlGaInN LED chips, the metallization and the package components. A special focus is put on the effects of hydrogen sulfide

LUZIOLA SUBINTEGRA (POACEAE: ORYZEAE), NEW TO FLORIDA AND THE UNITED STATES

Volume: 2Start Page: 633End Page: 63

Ultraviolet laser ablation as technique for defect repair of GaN-based light-emitting diodes

Defect repair of GaN-based light-emitting diodes (LEDs) by ultraviolet laser micromachining is reported. Percussion and helical drilling in GaN by laser ablation were investigated using 248 nm nanosecond and 355 nm picosecond pulses. The influence of laser ablation including different laser parameters on electrical and optical properties of GaN-based LED chips was evaluated. The results for LEDs on sapphire with transparent conductive oxide p-type contact on top as well as for thin-film LEDs are reported. A reduction of leakage current by up to six orders in magnitude and homogeneous luminance distribution after proper laser defect treatment were achieved

Verfahren und Vorrichtung zur Herstellung eines Halbleiterbauelements

The method comprises depositing a semiconductor layer structure on a substrate, where the structure comprises a gallium nitride (GaN)-based semiconductor layer, and partially removing the semiconductor layer in local areas by laser machining. The laser treatment is carried out by: exposing the semiconductor layer to a projection mask (4), which is illuminated with laser radiation of an ablation laser (1) such that exposure areas of the semiconductor layer is exposed through recesses in the projection mask; and occulting the GaN-based semiconductor layer shaded by the projection mask. The method comprises depositing a semiconductor layer structure on a substrate, where the semiconductor layer structure comprises a gallium nitride (GaN)-based semiconductor layer, and partially removing the GaN-based semiconductor layer in local areas by laser machining. The laser treatment is carried out by: exposing the GaN-based semiconductor layer to a projection mask (4), which is illuminated with laser radiation of an ablation laser (1) such that exposure areas of the GaN-based semiconductor layer is exposed through recesses in the projection mask; and occulting the GaN-based semiconductor layer shaded by the projection mask. A laser fluence of the ablation laser is above an ablation threshold of the GaN-based semiconductor layer. An excimer laser is used as the ablation laser, and has a wavelength of = 351 nm and a pulse length of = 40 nanoseconds. The semiconductor layer structure comprises an active region in the exposure areas. A luminous area of a semiconductor device is effected by removing the active region in the exposure areas by mechanical separation and electrical isolation. The exposure areas of the semiconductor layer structure are completely removed. A set of semiconductor devices is formed on a wafer that is perpendicular to the laser radiation. The removing step is repeated for five times. The method further comprises displacing the wafer such that the displacement of the wafer is perpendicular to the laser radiation, and etching step. The displacing step is carried out simultaneously with the removing step. An independent claim is included for an apparatus for processing a semiconductor device. USE: The method is useful for manufacturing a semiconductor device such as GaN-based LED (all claimed). ADVANTAGE: The method is capable of accurately controlling the laser ablation depth thus economically and time-effectively manufacturing the semiconductor device with good quality and without damaging the semiconductor material during the laser processing. The diagram shows a schematic view of an apparatus for processing a semiconductor device. 1 : Ablation laser 3 : Beam homogenizer 4 : Projection mask 5 : Focusing lens 7 : Holde

Adaptive camouflage panel in the visible spectral range

In this work an adaptive panel in the visible spectral range is presented. Principal possibilities and basic aspects of adaptive camouflage in the VIS are considered and some details are discussed. The panel consists of modular tiles, each containing several high power four-color-LEDs controlled by a microcontroller and high current power supply and each tile designed to operate autonomously. To control the color and the intensity several color sensors were integrated into the system. The purpose of the panel is to take on a uniform color to best match its appearance to a given reference color, where both the panel and the reference color are subject to the same environmental conditions. The panel was not designed, however, to produce different camouflage patterns. The tiles on the surface were covered by a dark plastic plate in order to provide dark and saturated colors and to guarantee a dark appearance in the passive state of the system. As was to be expected, extreme situations like high ambient brightness and direct solar illumination turned out to be particularly challenging. Substantial tests and some modifications were performed to achieve a satisfactorily uniform color reproduction of a given reference color. Physical measurements as well as observer tests have been performed to demonstrate the capability of the adaptive system

Microstructural and optical emission properties of diamond multiply twinned particles

Multiply twinned particles (MTPs) are fascinating crystallographic entities with a number of controllable properties originating from their symmetry and cyclic structure. In the focus of our studies are diamond MTPs hosting optically active defects—objects demonstrating high application potential for emerging optoelectronic and quantum devices. In this work, we discuss the growth mechanisms along with the microstructural and optical properties of the MTPs aggregating a high-density of “silicon-vacancy” complexes on the specific crystal irregularities. It is demonstrated that the silicon impurities incite a rapid growth of MTPs via intensive formation of penetration twins on {100} facets of regular octahedral grains. We also show that the zero-phonon-line emission from the Si color centers embedded in the twin boundaries dominates in photo- and electroluminescence spectra of the MTP-based light-emitting devices defining their steady-state optical properties

Design, fabrication and characterization of near milliwatt power RCLEDs emitting at 390 nm

International audienceWe report on the realization and first demonstration of CW near-milliwatt-power emission at λ = 390 nm from resonant-cavity light-emitting diode (RCLED) on GaN templates. The vertical cavity consists of a bottom AlGaN/GaN distributed Bragg reflector and a top dielectric SiO2/ZrO2 mirror enclosing a GaInN/GaN multiple-quantum-well active layer. RCLEDs with total optical output of about 600 μW at an injection current of 20 mA were achieved before packaging, taking account of current growth and processing considerations. Dislocations generated during the growth of the RCLED structure seem to be affecting the mean light output. This can be further improved by the use of high-quality low-dislocation-density GaN templates or freestanding GaN substrates