Oxide nanowire arrays are playing an important role in energy sciences nowadays, including energy harvesting, energy storage, and power management. By utilizing a wet chemical growth method, we demonstrated the capabilities of synthesizing density controlled vertical ZnO nanowire arrays on a general substrate, optimizing the aspect ratio of the vertical ZnO nanowire arrays guided by a statistical method, epitaxially growing patterned vertical ZnO nanowire arrays on inorganic substrates, epitaxially growing patterned horizontal ZnO nanowire arrays on non-polar ZnO substrates, and the lift-off of the horizontal ZnO nanowire arrays onto general flexible substrates. In addition, single crystalline PbZrxTi1-xO3 (PZT) nanowire arrays were epitaxially grown on conductive and nonconductive substrates by hydrothermal decomposition. Beyond that, based on the as-synthesized ZnO nanowire arrays, we demonstrated multilayered three dimensionally integrated direct current and alternating current nanogenerators. By integrating a ZnO nanowire based nanogenerator with a ZnO nanowire based nanosensor, we demonstrated solely ZnO nanowire based self-powered nanosystems. Also, utilizing a commercial full-wave bridge rectifier, we rectified the alternating output charges of the nanogenerator based on PZT nanowire arrays, and the rectified charges were stored into capacitors, which were later discharged to light up a laser diode (LD). In addition, blue/near-ultraviolet (UV) light emitting diodes (LED) composed of ordered ZnO nanowire arrays on p-GaN wafers were presented.

The greenhouse industry is interested in light emitting diodes (LEDs) as a light source supplement to solar light to improve plant growth and development. Before LEDs can be adopted as supplemental light for greenhouse crops, plant responses to LED spectral quality need to be investigated. Tomato and cucumber seedlings were grown under different supplemental blue and red photon flux ratios (B:R ratios) under high (16-19 mol m⁻² d⁻¹) and low (5-9 mol m⁻² d⁻¹) solar daily light integrals (DLIs). The supplemental daily light integral was 3.6 mol m⁻² d⁻¹. A treatment without supplemental light served as a control. Both tomato and cucumber seedlings had increased growth rate and improved morphology when grown under the supplemental LED light compared to the control. However, no significant differences were observed for any growth and morphological parameters measured in this study between the different B:R ratios for both cucumber and tomato transplants under high DLI conditions. Cucumber seedlings showed a tendency to decrease dry mass, leaf number and leaf area under low DLI conditions with increasing B:R ratio. Tomato seedlings did not show any differences between the different B:R ratios under low DLI conditions. Seedlings growth and morphology under supplemental LED light were compared to those under supplemental high pressure sodium (HPS) light. Cucumber seedlings under supplemental HPS light had greater shoot dry mass than those under the supplemental red LED light. Tomato shoot dry mass showed no differences between the HPS and red LED supplemental light treatments. Cucumber seedlings were also grown under supplemental LED pulsed lighting and supplemental LED continuous lighting. Cucumber seedlings showed no differences in shoot dry mass and net photosynthetic rate between the treatments. Collectively, these studies concluded that red LED is preferred for supplemental lighting and the increase of blue light does not offer any benefits unless the efficiency of blue LEDs largely exceeds the red LEDs. The results of this research can be used for fixture development by LED manufactures and as a decision making tool for the adoption of supplemental LED lighting by greenhouse growers.

Increasing the rate of orthodontic tooth movement (OTM) can reduce risks such as periodontal disease and caries. This study investigated whether light emitting diode (LED) phototherapy could accelerate the rate of OTM. Orthodontic patients with bilaterally symmetric extraction of premolars were recruited. During space closure, LED phototherapy was applied to one side of the dental arch for a specified time and the contralateral side acted as the control. Space closure was measured immediately prior to, during and later in space closure. All 11 patients were compliant with LED application. The results revealed no significant changes in the rate of OTM with LED phototherapy over 3 months of extraction space closure. The findings were contrary to previous findings with laser phototherapy and could be related to the dosage or method of LED phototherapy delivery. Further investigations are needed to determine whether LED phototherapy application can influence the rate of OTM.

Increasing the rate of orthodontic tooth movement (OTM) can reduce risks such as periodontal disease and caries. This study investigated whether light emitting diode (LED) phototherapy could accelerate the rate of OTM. Orthodontic patients with bilaterally symmetric extraction of premolars were recruited. During space closure, LED phototherapy was applied to one side of the dental arch for a specified time and the contralateral side acted as the control. Space closure was measured immediately prior to, during and later in space closure. All 11 patients were compliant with LED application. The results revealed no significant changes in the rate of OTM with LED phototherapy over 3 months of extraction space closure. The findings were contrary to previous findings with laser phototherapy and could be related to the dosage or method of LED phototherapy delivery. Further investigations are needed to determine whether LED phototherapy application can influence the rate of OTM.

ZnO material based hetero-junctions are a potential candidate for the design andrealization of intrinsic white light emitting devices (WLEDs) due to several advantages overthe nitride based material system. During the last few years the lack of a reliable andreproducible p-type doping in ZnO material with sufficiently high conductivity and carrierconcentration has initiated an alternative approach to grow n-ZnO nanorods (NRs) on other ptypeinorganic and organic substrates. This thesis deals with ZnO NRs-hetero-junctions basedintrinsic WLEDs grown on p-SiC, n-SiC and p-type polymers. The NRs were grown by thelow temperature aqueous chemical growth (ACG) and the high temperature vapor liquid solid(VLS) method. The structural, electrical and optical properties of these WLEDs wereinvestigated and analyzed by means of scanning electron microscope (SEM), current voltage(I-V), photoluminescence (PL), cathodoluminescence (CL), electroluminescence (EL) anddeep level transient spectroscopy (DLTS). Room temperature (RT) PL spectra of ZnOtypically exhibit one sharp UV peak and possibly one or two broad deep level emissions(DLE) due to deep level defects in the bandgap. For obtaining detailed information about thephysical origin, growth dependence of optically active defects and their spatial distribution,especially to study the re-absorption of the UV in hetero-junction WLEDs structure depthresolved CL spectroscopy, is performed. At room temperature the CL intensity of the DLEband is increased with the increase of the electron beam penetration depth due to the increaseof the defect concentration at the ZnO NRs/substrate interface. The intensity ratio of the DLEto the UV emission, which is very useful in exploring the origin of the deep level emissionand the distribution of the recombination centers, is monitored. It was found that the deepcenters are distributed exponentially along the ZnO NRs and that there are more deep defectsat the root of ZnO NRs compared to the upper part. The RT-EL spectra of WLEDs illustrateemission band covering the whole visible range from 420 nm and up to 800 nm. The whitelightcomponents are distinguished using a Gaussian function and the components were foundto be violet, blue, green, orange and red emission lines. The origin of these emission lines wasfurther identified. Color coordinates measurement of the WLEDs reveals that the emitted lighthas a white impression. The color rendering index (CRI) and the correlated color temperature(CCT) of the fabricated WLEDs were calculated to be 80-92 and 3300-4200 K, respectively.

In the last decades, investigations of organic light-emitting diodes (OLEDs) have tackled several key challenges of this lighting technology and have brought the electron to photon conversion efficiency close to unity. However, currently only 20% to 30% of the photons can typically be extracted from OLED structures, as total internal reflection traps the major amount of the generated light inside the devices. This work focuses on the optimization of the optical properties of top-emitting OLEDs, in which the emission is directed away from the substrate. In this case, opaque materials, e.g. a metal foil or a display backplane can be used as substrate as well. Even though top-emitting OLEDs are often preferred for applications such as displays, two main challenges remain: the application of light extraction structures and the deposition of highly transparent materials as top electrode, without harming the organic layers below. Both issues are addressed in this work. First, top-emitting OLEDs are deposited on top of periodically corrugated light outcoupling structures, in order to extract internally trapped light modes by Bragg scattering and to investigate the basic scattering mechanisms in these devices. It is shown for the first time that the electrical performance is maintained in corrugated top-emitting OLEDs deposited on top of light extraction structures. Furthermore, as no adverse effects to the internal quantum efficiency have been observed, the additional emission from previously trapped light modes directly increases the device efficiency. It has been proven that the spectral emission of corrugated OLEDs is determined by the interference of all light modes inside the air light-cone, including the observation of destructive interference and anti-crossing phenomena. The formation of a coherently coupled mode pair of the initial radiative cavity mode and a Bragg scattered mode has been first observed, when grating structures with an aspect ratio > 0.2 are applied. There, the radiative cavity mode partially vanishes. The observation and analysis of such new emission phenomena in corrugated top-emitting OLEDs has been essential in obtaining a detailed insight on fundamental scattering processes as well as for the optimization and control of the spectral emission by light extraction structures. Second, the adverse impact of using only moderately transparent silver electrodes in white top-emitting OLEDs has been compensated improving the metal film morphology, as the organic materials often prevent a replacement by state-of-the-art electrodes, like Indium-tin-oxide (ITO). A high surface energy Au wetting layer, also in combination with MoO3, deposited underneath the Ag leads to smooth, homogeneous, and closed films. This allows to decrease the silver thickness from the state-of-the-art 15 nm to 3 nm, which has the advantage of increasing the transmittance significantly while maintaining a high conductivity. Thereby, a transmittance comparable to the ITO benchmark has been reached in the wavelength regime of the emitters. White top-emitting OLEDs using the wetting layer electrodes outperform state-of-the art top-emitting devices with neat Ag top electrodes, by improving the angular colorstability, the color rendering, and the device efficiency, further reaching sightly improved characteristics compared to references with ITO bottom electrode. The enormous potential of wetting layer metal electrodes in improving the performance of OLEDs has been further validated in inverted top-emitting devices, which are preferred for display applications, as well as transparent OLEDs, in which the brittle ITO electrode is replaced by a wetting layer electrode. Combining both concepts, wetting layer electrodes and light extraction structures, allows for the optimization of the grating-OLED system. The impact of destructive mode interference has been reduced and thus the efficiency increased by a decrease of the top electrode thickness, which would have not been achieved without a wetting layer. The optimization of corrugated white top-emitting OLEDs with a top electrode of only 2 nm gold and 7 nm silver on top of a grating with depth of 150 nm and period of 0.8 µm have yielded a reliable device performance and increased efficiency by a factor of 1.85 compared to a planar reference (5.0% to 9.1% EQE at 1000 cd/m2). This enhancement is comparable to common light extraction structures, such as half-sphere lenses or microlens foils, which are typically restricted to bottom-emitting devices. Overall, the deposition of top-emitting OLEDs on top of light extraction structures finally allow for an efficient extraction of internally trapped light modes from these devices, while maintaining a high device yield. Finally, the investigations have resulted in a significant efficiency improvement of top-emitting OLEDs and the compensation of drawbacks (optimization of the white light emission and the extraction of internal light modes) in comparison to the bottom-emitting devices. The investigated concepts are beneficial for OLEDs in general, since the replacement of the brittle ITO electrodes and the fabrication of roll-to-roll processing compatible light extraction structures are also desirable for bottom-emitting, or transparent OLEDs.

Cette thèse porte sur l'élaboration de dispositifs d'émission et de photodétection à base de nanocristaux colloïdaux dans le visible et le proche infrarouge. Dans un premier temps, nous avons développé des dispositifs lumineux à base de nanocristaux de CdSe/ZnS émettant dans le rouge-orange. Pour cela, nous avons tout d'abord travaillé en déposant des polymères par voie liquide, des nanocristaux par différentes techniques humides ou sèches et enfin des petites molécules par évaporation. Ensuite, dans un but d'optimisation des performances de nos dispositifs, nous avons développé une technique originale de dépôt des QDs, que nous avons appelée Langmuir Schaeffer Stamping (LSS). Cette technique de dépôt économique en matériaux et homogène permet de travailler uniquement avec un empilement de films minces déposés par évaporation des petites molécules, et permet une nette augmentation de l'efficacité des composants. Nous avons étudié les mécanismes à l'origine de l'électroluminescence, dans nos dispositifs c'est l'injection directe qui prédomine. Enfin, en travaillant à l'aide de nanocristaux de PbS, nous avons développé des photodétecteurs pour le proche infrarouge de détectivité 109Jones. Des sources QDLEDs infrarouges à base de nanocristaux de PbS ont également été élaborées. / This work is devoted to the development of Visible and Near-Infrared Light Emitting Diodes and photodetectors based on colloidal nanocrystals. First, we report a wet strategy for solution processed QDLEDs. Using spin coated and inkjet printed polymers, we have developed our first devices. Unfortunately, their efficiencies were quite low. To overcome these issues, we have developed an original QDs deposition method based on stamping and Langmuir processes, called Langmuir-Schaeffer Stamping (LSS). LSS is a very cost-efficient, dry, simple and homogeneous method to deposit nanocrystals on any substrate, even on small molecules deposited layers. Using LSS, we have developed efficient devices whose specifications are reported here. Direct injection and Förster mechanisms are studied. Furthermore we have fabricated infrared devices with PbS nanocrystals. Performances of our 109 Jones NIR photo-detectors and NIR-QDLEDs are presented in this thesis.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15612号 / 工博第3301号 / 新制||工||1498(附属図書館) / 28139 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 藤田 静雄, 准教授 山田 啓文 / 学位規則第4条第1項該当

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22463号 / 工博第4724号 / 新制||工||1738(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 梶 弘典, 教授 佐藤 啓文, 教授 関 修平 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18288号 / 工博第3880号 / 新制||工||1595(附属図書館) / 31146 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 田中 一義, 教授 田中 庸裕, 教授 佐藤 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM