This work comprises different approaches for the efficiency enhancement of white organic light-emitting diodes (OLEDs). In particular, diffusion and transfer processes of excited singlet and triplet states are investigated. Generation of white light is realized by using the so-called triplet harvesting method where the otherwise nonradiatively decaying triplets of a blue fluorescent emitter are transferred to a highly efficient phosphorescent emitter and result in additional emission at lower energies. Triplet harvesting significantly increases the internal quantum efficiency in OLEDs. First, the well-known blue emitter 4P-NPD is investigated as model case. Using time-resolved spectroscopy, triplet harvesting by a yellow and red phosphorescent emitter, respectively is directly proven. However, triplet harvesting by a green emitter is not possible due to the low triplet energy of 4P-NPD. Using quantum chemical calculations, two new emitter molecules, 8M-4P-NPD and 8M-4P-FPD, are synthesized with the aim to rise the triplet energy. Their properties and their ability to facilitate triplet harvesting by a green emitter are studied. For the first time, a white triplet harvesting OLED is demonstrated where triplet harvesting occurs directly from a blue emitter to a green and a red emitter. Furthermore, an additional singlet transfer is observed in the triplet harvesting OLEDs under investigation. Using the phosphorescent emitter as singlet sensor, this effect allows the determination of the singlet diffusion length in 4P-NPD. By varying the distance between singlet generation zone and singlet sensor, a singlet diffusion length of 4.6 nm is found. One further approach to increase the efficiency is the optimization of a tandem OLED which comprises two single OLED units stacked on top of each other. At a luminance of 1,000 cd/m², the white tandem OLED shows an external quantum efficiency of 25%, a luminous efficacy of 33 lm/W, a color rendering index (CRI) of 62, and Commission Internationale de l’Eclairage (CIE) color coordinates of (0.53/0.43). These efficiencies are comparable to state-of-the-art efficiencies of white OLEDs. Finally, the highly efficient white tandem structure is applied on an alternative electrode consisting of flattened silver nanowires. In comparison to the conventional OLED with indium-tin oxide (ITO) electrode, this OLED shows similarly high efficiencies as well as a superior color stability in terms of viewing angles. The color stability can be assigned to the light scattering properties of the nanowires. The OLED with silver nanowire electrode shows efficiencies of 24% and 30 lm/W at 1,000 cd/m² with a CRI of 69 and CIE coordinates of (0.49/0.47). / In dieser Arbeit werden verschiedene Ansätze zur Effizienzsteigerung in weißen organischen lichtemittierenden Dioden (OLEDs) erforscht. Hierfür werden im Besonderen Diffusions- und Transferprozesse von angeregten Singulett- und Triplettzuständen untersucht. Zur Erzeugung von weißem Licht wird die sogenannte “triplet harvesting” Methode verwendet, bei der die sonst nicht zur Emission beitragenden Triplettzustände eines fluoreszenten blauen Emitters auf einen hocheffizienten phosphoreszenten Emitter übertragen werden. Dieser liefert dann zusätzliche Emission im niederenergetischen Spektralbereich. Durch triplet harvesting kann die interne Quantenausbeute in OLEDs beträchtlich gesteigert werden. Zunächst wird der bekannte blaue Emitter 4P-NPD als Modellbeispiel untersucht. Mittels zeitlich aufgelöster Spektroskopie kann triplet harvesting auf einen gelben bzw. roten Emitter direkt nachgewiesen werden. Allerdings ist auf Grund der niedrigen Triplettenergie triplet harvesting auf einen grünen Emitter nicht möglich. In Anbetracht dieser Tatsache werden unter Zuhilfenahme quantenchemischer Betrachtungen zwei neue Emittermoleküle, 8M-4P-NPD und 8M-4P-FPD, synthetisiert und auf ihre Eigenschaften und ihre Eignung für triplet harvesting untersucht. Dabei wird zum ersten Mal eine weiße OLED realisiert, in der triplet harvesting von einem blauen Emitter direkt auf einen grünen und einen roten Emitter erfolgt. Des Weiteren wird bei den untersuchten triplet harvesting OLEDs ein zusätzlicher Singulettübertrag auf den phosphoreszenten Emitter beobachtet. Dieser Effekt wird zur Bestimmung der Singulettdiffusionslänge in 4P-NPD genutzt. Der phosphoreszente Emitter dient dabei als Singulettsensor. Über eine Variation des Abstands zwischen Singulettgenerationszone und Sensor wird eine Singulettdiffusionslänge von 4,6 nm bestimmt. Ein weiterer Ansatz zur Effizienzsteigerung besteht in der Optimierung einer aus zwei OLEDs zusammengesetzten Tandem OLED. Bei einer Leuchtdichte von 1000 cd/m² erzielt diese weiße Tandem OLED eine externe Quanteneffizienz von 25% und eine Leistungseffizienz von 33 lm/W mit einem Farbwiedergabeindex (CRI) von 62 und Commission Internationale de l’Eclairage (CIE) Farbkoordinaten von (0,53/0,43). Diese Effizienzen sind vergleichbar mit dem aktuellen Forschungsstand weißer OLEDs. Schließlich wird diese hocheffiziente weiße Tandemstruktur auf eine alternative Elektrode bestehend aus flachgedrückten Silbernanodrähten aufgebracht. Im Vergleich zur konventionellen OLED mit Indiumzinnoxid (ITO) Elektrode erreicht diese ähnlich hohe Effizienzen sowie eine verbesserte Farbstabilität bezüglich des Betrachtungswinkels, was auf die Streueigenschaften der Nanodrähte zurückgeführt werden kann. Bei einer Leuchtdichte von 1000 cd/m² zeigt die OLED mit Silbernanodrahtelektrode Effizienzen von 24% und 30 lm/W bei einem CRI von 69 und CIE Koordinaten von (0,49/0,47).

This thesis details an innovative laser diode packaging method to improve the accuracy of the laser locator by modifying the location method and packaging process. This method features its simplicity in the packaging process, the capability in tweaking the rotary angle of the laser diode, and an effective solution to the scaling effect as well as the enhancement in yield. The gripping micro-unit,consisting of a refined micro gripper together with the piezoelectric actuator and coupler,integrates a self-designed rotary adjustment and release unit to enable the micro-rectangle unit such as a laser unit to fine tune the location of the object. It works with the linear stage, platform, and image acquisition system to become the core of the proposed location system. A series of experiments are designed to verify the functionality. A precise linear stage without the rotary axis is applied to control the locator,adjust the location of the laser, and minimize the error from equipment. The result demonstrates its feasibility.

In last decade, white light emitting diodes(LEDs) have become used widely from traditional indicator to general illumination. The increase of its power is the key improving issue. The current light efficiency of white LED about 30%. In other words ,more than 70% of the input electrical energy will be generated in the form of heat. So, how to get rid of the heat damage in high power LED is a severe problem. The finite element analysis is employed to simulate high power white LEDs temperature distribution and thermal stress distributions caused by the dissipated heat. The effects of package parameters, i.e. die attach, solder material, solder thickness, and chip substrate, on the temperature and thermal stress distributions on high power LED packages are simulated and studied in this thesis. A comparison between the 40mil single chip package and the chip on board(CoB) package has also been executed in this study. Simulated results indicate that the highest power of a single 40mil chip package is 7watt. The thermal stress distribution , i.e. the peak value of local thermal stress is over its yield strength, is occurred as the power up to 7watt. Numerical results also reveal that the appropriate fin design can improve the heat dissipation significantly in high power LED package.

In the literatures of investigating the coupling mechanism between laser diodes and fibers, Gaussian beam profile was used to describe the propagation of laser beams. But the real laser diode beams exist astigmatism. In order to understand the distributions of real laser diode beams, we used single-mode fiber interferometer to measure the near-field intensity and phase distributions of laser diodes. The nanometer aperture of taper fiber was used to scan through the horizontal and vertical directions across the maximal intensity point of the planes which were perpendicular to propagation axis to measure the intensity and phase distributions of laser diodes. In the measurement of phase distributions, these two single-mode fibers produced interference fringes through accepting laser beams. When the taper fiber scanned the optical field and the reference fiber kept a fixed distance from a laser diode for a stationary phase, the interference fringes shifted because of the phase difference of laser diodes change. In the measurement, in order to improve the stability of interference fringes and consider the aperture of taper fiber, we altered some experiment frameworks. There were four types of experimental framework. According to the experiment results of the near-field measurements, the measured beam widths along the horizontal and vertical directions at the laser diode facet were 4.11 £gm and 1.57 £gm respectively. The measured wavefront radius curvature were 6.59 £gm and 2.96 £gm in horizontal axis and vertical axis respectively. After Gaussian beam fitting, the beam widths along the horizontal and vertical directions at the laser diode facet were 4.04 £gm and 0.83 £gm respectively. The difference in beam widths between measured values and Gaussian fitting were 0.07 £gm and 0.74 £gm. The measured beam widths and the Gaussian beam curve fitting had similar results. We could see that the beam spread tendency in the z-axis for the laser beam which propagated in the z direction. In the phase distribution measurement, the measured wavefront radius curvatures and the theoretically calculated Gaussian beam values had a slight difference. The calculated wavefront radius curvatures at the laser diode facet were 11921.51 £gm and 3.48 £gm in horizontal axis and vertical axis respectively. They were 1809 times and 1.2 times of the measured values. The aperture of taper fiber was expanded because of the energy of laser beams, which also caused the spatial resolution degeneration. Moreover, the wavefront radius curvature in horizontal direction was biggish so the measurement framework also limited the ability of the phase distribution measurement. The above points were the reasons to cause the error of the phase distribution measurement. Furthermore, the measurement of the laser diode facet is under investigation.

In this thesis, with external cavity semiconductor laser, a high lateral resolution thickness measurement is proposed and demonstrated. The approach is typical an intra-cavity measurement of focused cell thickness by wavelength tuning of an external cavity laser diode. In addition, using blue light of 406nm as laser diode, higher lateral resolution is also observed. Using the proposed thickness method, the lateral resolution and longitudinal resolution have been demonstrated with 20£gm and 0.15£gm, respectively. We also discuss the feasibility of £gm scaled lateral resolution through improvement of laser diode, such as M^2~1.

In this thesis, we design electrode shape of light emitter diode (LED) to help the current diffusing uniformly. The purpose of the uniform current is to avoid the waste heat from the devices and enhance the efficiency of active region. The LED samples adopted in this study are GaN base materials grown on sapphire. The P-N electrodes must be processed on the same side since the poor conductivity of sapphire. The same side P-N electrode will results in current crowding phenomena. We design special electrode shapes to make the current diffuse uniformly and reduce the current crowding phenomena. First, we use COMSOL simulation software to simulate the current spreading between the electrodes. We adopt the same parameters from the reference papers to confirm the reliabilities of the simulation. Then we simulate several electrode shapes with highly uniform current spreading. Second, we use the simulation results to fabricate electrode on chips. The first set is LED without transparent conductive layer. This set is to confirm whether the fabrication processes is feasible and adjust the simulation parameters at the same time. The second set is LED with transparent conductive layer. The experimental emission intensity has deviation from the simulation results. We deduce the emission intensities from smaller LED chip size will have great influence on illumination surface. The third set is electrodes fabricated on large size LED chip. The electrode patterns successfully enhance the uniformity of current spreading, and enhance the output light intensity of 21%. The current density distribution trend from simulation is matched with the illumination intensities.

This research plans the power capacities of the obstacle lighting on the power transmission towers, which are located in the areas where the utility cannot reach. The obstacle lighting is formed by light emitting diodes (LEDs), which are powered mainly by solar cells and subordinately by rechargeable batteries. The solar cells charge the batteries during the sunny daytime with plenty sunlight. When the sunlight is insufficient and the obstacle lamp is turned on, batteries and solar cells supply the obstacle lighting simultaneously. The power capacities of the solar cells and batteries are designated to keep the obstacle lighting system uninterruptible either under the drastic weather variation or a long period of insufficient sunlight. Under the specified operation rules of the obstacle lighting, a more economical and precise method is proposed for planning the power capacities of solar cells and batteries based on the weather data from Central Weather Bureau in recent 6 years following. The power planning method is implemented in the areas of Kaohsiung, Chiayi and Ali mountain to demonstrate the feasibility and the accuracy in reality.

In this thesis, we use self-assembled nano metal particles as a dry etching mask to from nanopillars. The nanopillars integrated with traditional light-emitting diode (LED) p-type GaN surface is designed to increase the light extraction efficiency. The initial fabrication process adopted in this study is using 100nm SiO2 as thermal aggregation layer. The poor thermal conductivity of SiO2 material will help to accumulate heat on the surface. Then, 10nm Ni thin film is deposited on the SiO2, and rapid annealed at 900oC (working pressure of 1~3¡Ñ10-6 Torr). The Ni nanospheres are prepared to integrate with LED chip processes. We use the etching times (pillar heights) as experimental parameters to study the degree of light extraction efficiency. Traditional right angle branch electrode samples of as grown, 20, 30, 40 sec etching time are analyzed by LI curve measurement. Under 20mA injection current, samples with 20, 30, 40 sec etching times have better light extraction than as grown, an increase of 6.54%, 3.27%, 1.63%, respectively. The experimental results reveal that self-assembled nano metal particles as a dry etching mask on the p-type GaN LED surface can increase the light extraction efficiency.

This thesis investigates the effects of varying the crystallographic orientations of epitaxial ZnO thin films to produce functional ZnO P-N diodes. First, with the atomic layer deposition (ALD), a p-type m-oriented ZnO epitaxial layer is deposited onto an also m-oriented Al2O3 substrate. Then an n-type ZnO layer, mostly textured along the c-axis, is grown atop to form a P-N diode by RF sputtering method. The Hall Effect of the m-ZnO thin film is measured separately at various temperatures and magnetic fields in Quantum Design¡¦s Physical Property Measurement System (PPMS) to determine the nature of the charge carriers. The m-oriented ZnO films are found to be p-type semiconductors, with carrier concentration approximately ~ 1021 1/cm3, which falls in the category of highly-doped degenerate semiconductor. In order to further prove that these films are indeed p-type, naturally n-type c-textured ZnO films are put on the m-films at room temperature by magnetron sputtering to see if the current-voltage (I-V) curves do follow the P-N junction characteristics. In optimizing the c-ZnO film quality and reducing the effects of the junction defects, the gas-mixture ratio between argon and oxygen was varied to compare for the changes in the performance of the resulted materials and devices. X-ray diffraction was used to characterize the crystallographic orientations and the general qualities of the samples by 2£c-£s scan, rocking scan, £p-scan and pole figure measurement. Understanding of the P-N diode is acquired through the analysis of the leakage current and the quantum tunneling phenomena as manifested in the I-V characteristics.

A simulation algorithm is proposed in this thesis to investigate the effects of lensed fiber parameters on the variation of radius of curvature of the melted lens and the coupling efficiency of butterfly type laser diode transiver module. Two different endface shapes, i.e. the taper and the conical-wedge type lensed fibers, will be studied. The effect of endface shapes, sizes, and the melting zone volume on the coupling efficiency of lensed fibers are simulated and discussed. In the study on the conical type lensed fiber, the MARC¡¦s elastic-plastic-thermal finite element model is employed to simulate the melting and the solidification processes at the fiber tip endface with different conical angles. The temperature dependent material properties are used to calculate the melting zone and the post-melten deformation during the heating process. The Surface Evolver Software has also been employed to simulate the solidified lens shapes. The variation of radius of curvature of the tip lens is analyzed. The ZEMAX optical analysis software is applied to explore the relation between the coupling efficiency and the distribution of the radius of curvature. The variation of laser signal coupling efficiency introduced from different conical lensed fibers is simulated numerically. A good agreement between the published measured data and the simulated results indicate the proposed simulation model is feasible. The effect of endface shape and molten zone size on the conical wedge type lensed fiber has been studied in a similar way. The coherence between the shape of solidified elliptical lens at fiber tip and the coupling efficiency for the 980nm LD will be explored. Different endface shapes will also be investigated by using the simulation model proposed previously. Different aspect ratio of the conical-wedge type tip will be introduced to compensate the elliptical LD ray model and to recover the coupling efficiency loss. The agreement between the results simulated using the proposed model and the measured data is examined. The simulated results indicate that the coupling efficiency of a butterfly type laser diode transever can be improved significantly by controlling the shape of the lens introduced in this type lensed fiber. The optimal grinding parameters and the melting parameters used to fabricate the lensed fibers will also be studied. The effects of the shape parameters, i.e. the conical taper angle, the wedge angle and the size of molten zones on the curvature variation of the lens will also be studied. A better understanding about the design and fabrication of the lensed fiber of a laser diode based transever module is expected from the results presented in this thesis.