For the shortage of energy and the environmental issues, the development of solar cells has become an important technology. However, solar cells have low efficiency of energy conversion due to their high surface reflection on a flat Si substrate which is 38 %. To decrease the surface reflectance of the silicon solar cells, anti-reflection coatings (ARCs) are proposed on the solar cells. We use Lighttools software to investigate several kinds of ARCs to decrease the surface reflectance. We first consider the reflectance of the single-layer ARC with quarter wavelength. It can effectively decrease about 30 % surface reflection as compared with a flat Si substrate. The half-cylinder texture and the wave texture are designed on a PMMA single-layer coating. It is found that the half-cylinder ARC and the wave ARC can usefully diminish the surface reflectance for perpendicular light. Low reflectance can be achieved in the hemispherical microlens ARCs over an extended spectral region for omnidirectional incident light. The impact of the microlens sizes, periods, and arrangements are investigated. The lowest normal reflectance of the closely-packed triangular-lattice hemispherical microlens ARC is 4.8%. By adding smaller hemispherical microlenses, the surface reflectance of the hemispherical microlens ARC can be as low as 1.86 %. To obtain the lowest average surface reflectance, both-sided patterned surface texture ARCs are designed. Their lowest average surface reflectance is 2.24%. Finally, we simulate the reflectance of the nanowire ARCs. The influence of the wire length and the angle of inclination are discussed for high-efficiency and low-cost solar cells.

The thesis consists of two aspects: (1) Research on regrowth by molecular beam epitaxy, and (2) Silicon monoxide coating. In part one, we used (NH4)2Sx to passivate the InAlGaAs/InP surface. From the X-ray photoelectron spectroscopy (XPS), the passivated surface shows a dramatic reduce of oxidation. A preparation chamber for the regrowth has been setup to proceed the sulfur passivation method. We can obtain a clean surface for regrowth after heating and putting samples in the high vacuum chamber. In the design of regrowth layers, we have found the best waveguide structure by regrowth. When the ridge width is 2.5 mm with etching depth 1.4 mm, a circular mode profile can be obtained by Fimmwave simulation. In the integration between devices, we have designed the best waveguide structure after regrowth by BeamProp 3D. The best design will make the propagation loss smaller than 0.21%. The second part is anti-reflection (AR) coating by silicon monoxide (SiO) deposition. The SiO refractive index of 1.8837 was obtained by transmission, and ellipsometer measurements. The corresponding AR coating thickness for InP substrate is 2057 &#x00C5;. In order to make AR coating on lasers of different effective index, we design the double-layer coating. For Beam Expander Semiconductor Optical Amplifier (BESOA), SiO2 / SiO and Si3NX / SiO double-layer coatings were compared with SiO single layer. The reflectance (R) was reduced 16.86 % and 25.12 %, respectively, and the R < 1% bandwidth extends 200 &#x00C5;.

Light reflection from the glass surface of a photovoltaic (PV) module is a significant source of energy loss for all types of PV devices. The reflection at the glass and air interface accounts for ~4% of the total energy. Single layer anti-reflection coatings with sufficiently low refractive index have been used, such as those using magnesium fluoride or porous silica, but these are only effective over a narrow range of wavelengths. Multilayer-antireflection coatings reduce the weighted average reflection over the wavelength range used by solar technologies more effectively by utilising interference effects. Multilayer stacks consisting of silica and zirconia layers deposited using reactive magnetron sputtering and single layer porous silica coatings were compared in terms of effectiveness and durability. Details of the stack design, sputter deposition process parameters, and the optical and micro-structural properties of the layers of the multilayer coating are provided and similar properties where applicable for the single layer coatings. Anti-reflection coatings on glass exposed to the outdoors must not degrade over the lifetime of the module. A comprehensive set of accelerated environmental durability tests has been carried out in accordance with IEC 61646 PV qualification tests. The durability tests confirmed no damage to the coatings or performance drop as a result of thermal cycling or damp heat. All attempts to perform pull tests on either coating resulted in either adhesive or substrate failure, with no damage to the coating itself. Scratch resistance, abrasion resistance, and adhesion tests have also been conducted. The optical performance of the coatings was monitored during these tests and the coatings were visually inspected for any sign of mechanical failure. These tests provide confidence that broadband anti-reflection coatings are highly durable and will maintain their performance over the lifetime of the solar module. Additionally heat treatment experiments demonstrated both coatings can withstand up to 600°C temperatures and can thereby withstand CdTe manufacturing processes allowing for pre-coated glass. Additionally experiments demonstrated that multi-layer coatings are resistant to acid attack. Thin film photovoltaic devices are multilayer opto-electrical structures in which light interference occurs. Light reflection at the interfaces and absorption within the window layers reduces transmission and, ultimately, the conversion efficiency of photovoltaic devices. Optical reflection losses can be reduced by adjusting the layer thicknesses to achieve destructive interference within the structure of the cell. The light transmission to the CdTe absorber of a CdS/CdTe cell on a fluorine doped tin oxide transparent conductor has been modelled using the transfer matrix method. The interference effect in the CdS layer and high resistance transparent buffer layers (SnO2 and ZnO) has been investigated. The modelling shows that due to relatively high absorption within the SnO2 layer, there are modest benefits to engineering anti-reflection interference in the stack. However, a ZnO buffer layer has limited absorption and interference can be exploited to provide useful anti-reflection effects. Additionally the light transmission to the perovskite absorber of a thin film solar cell using fluorine doped tin oxide (FTO) transparent conductor has been modelled. Alternative transparent conductor materials have also been investigated including aluminium doped zinc oxide (AZO) and indium tin oxide (ITO) and shown to be beneficial to transmission.

Optical tweezers are a sensitive position and force transducer widely employed in physics and biology. In a focussed laser, forces due to radiation pressure enable to trap and manipulate small dielectric particles used as probes for various experiments. For sensitive biophysical measurements, microspheres are often used as a handle for the molecule of interest. The force range of optical traps well covers the piconewton forces generated by individual biomolecules such as kinesin molecular motors. However, cellular processes are often driven by ensembles of molecular machines generating forces exceeding a nanonewton and thus the capabilities of optical tweezers. In this thesis I focused, fifirst, on extending the force range of optical tweezers by improving the trapping e fficiency of the probes and, second, on applying the optical tweezers technology to understand the mechanics of molecular motors. I designed and fabricated photonically-structured probes: Anti-reflection-coated, high-refractive-index, core-shell particles composed of titania. With these probes, I significantly increased the maximum optical force beyond a nanonewton. These particles open up new research possibilities in both biology and physics, for example, to measure hydrodynamic resonances associated with the colored nature of the noise of Brownian motion. With respect to biophysical applications, I used the optical tweezers to study the mechanics of single kinesin-8. Kinesin-8 has been shown to be a very processive, plus-end directed microtubule depolymerase. The underlying mechanism for the high processivity and how stepping is affected by force is unclear. Therefore, I tracked the motion of yeast (Kip3) and human (Kif18A) kinesin-8s with high precision under varying loads. We found that kinesin-8 is a low-force motor protein, which stalled at loads of only 1 pN. In addition, we discovered a force-induced stick-slip motion, which may be an adaptation for the high processivity. Further improvement in optical tweezers probes and the instrument will broaden the scope of feasible optical trapping experiments in the future.

Optical tweezers are a sensitive position and force transducer widely employed in physics and biology. In a focussed laser, forces due to radiation pressure enable to trap and manipulate small dielectric particles used as probes for various experiments. For sensitive biophysical measurements, microspheres are often used as a handle for the molecule of interest. The force range of optical traps well covers the piconewton forces generated by individual biomolecules such as kinesin molecular motors. However, cellular processes are often driven by ensembles of molecular machines generating forces exceeding a nanonewton and thus the capabilities of optical tweezers. In this thesis I focused, fifirst, on extending the force range of optical tweezers by improving the trapping e fficiency of the probes and, second, on applying the optical tweezers technology to understand the mechanics of molecular motors. I designed and fabricated photonically-structured probes: Anti-reflection-coated, high-refractive-index, core-shell particles composed of titania. With these probes, I significantly increased the maximum optical force beyond a nanonewton. These particles open up new research possibilities in both biology and physics, for example, to measure hydrodynamic resonances associated with the colored nature of the noise of Brownian motion. With respect to biophysical applications, I used the optical tweezers to study the mechanics of single kinesin-8. Kinesin-8 has been shown to be a very processive, plus-end directed microtubule depolymerase. The underlying mechanism for the high processivity and how stepping is affected by force is unclear. Therefore, I tracked the motion of yeast (Kip3) and human (Kif18A) kinesin-8s with high precision under varying loads. We found that kinesin-8 is a low-force motor protein, which stalled at loads of only 1 pN. In addition, we discovered a force-induced stick-slip motion, which may be an adaptation for the high processivity. Further improvement in optical tweezers probes and the instrument will broaden the scope of feasible optical trapping experiments in the future.

An enhanced thermal imaging concept made possible through the development of a gradient-indexed metamaterial infrared detector that offers broadband transmission and reflection in THz waves. This thesis proposes a proof of feasibility for a metamaterial infrared detector containing an anti-reflective coating with various geometrically varying periodic metasurfaces, a gradient-indexed dielectric multilayer for near-perfect longpass filtering, and a gradient index of refraction (GRIN) metalens for enhanced focal plane thermal imaging. 2D Rigorous Coupled-Wave Analysis (RCWA) is used for understanding the photonic gratings performance based on material selection and varying geometric structure. Finite Difference Time Domain (FDTD) is used to characterize performance for a diffractive metalens by optimizing the radius and arrangement of cylindrical nanorods to create a desired phase profile that can achieve a desired focal distance for projections on a detector for near- to far-infrared thermal imaging. Through combining a micromachined anti-reflective coating, a near-perfect longpass filter, and metamaterial GRIN metalens, infrared/THz focal plane thermal imaging can obtain faster photo-response and image quality at targeted wavelengths, which allows for scientific advancements in electro-optical devices for the Department of Defense, aerospace, and biochemical detection applications.

Diese Arbeit untersucht den Einfluss verschiedener physikalischer Parameter auf das Verhalten von Frequenz-abstimmbaren External-Cavity Quantenkaskadenlasern (EC-QCLs) theoretisch und experimentell. Diese beinhalten unter anderen die Antireflexschicht, die Art der Optiken, die geometrischen und die mechanisch/strukturellen Eigenschaften. Dies wurde erreicht durch Aufbau dreier sehr unterschiedlicher EC-Konfigurationen, der Diskussion und dem Vergleich ihrer Leistungsmerkmale und ihrer Vor- und Nachteile für verschiedene Anwendungen unter hauptsächlicher Verwendung von QCLs desselben Wafers der Vergleichbarkeit wegen. Für den letzten Teil dieser Arbeit wurde ein neuer Typus EC-QCL mit vielversprechenden Eigenschaften entwickelt, sodass wir glauben er hat das Potential das Littrow Design langfristig abzulösen. Dieses selbststabilisierende Design verwendet einen Retroreflektor als externen Reflektor. Für die Demonstration dieses Konzepts war die Entwicklung eines Tuning-Elements in Form eines Winkel-verstimmbaren Mittinfrarot-Bandpass-Interferenzfilters mit sehr hohem Gütefaktor vonnöten. Für das Design des Filters wurden Materialien mit sehr strengen Toleranzen bezüglich ihrer physikalischen und optischen Eigenschaften auf Basis von theoretischen Überlegungen ausgewählt und eine Fabrikationsmethode mit hochoptimierten Prozessparametern entwickelt. Die ersten Filter auf Basis von Yttriumfluorid/Yttriumoxid/Germanium/Silizium haben eine Transmissionsbandbreite von 0.14% der Zentralwellenlänge und eine maximale Transmission von etwa 60%. Die EC Konfiguration resultierte in verminderter Empfindlichkeit gegenüber Mechanischen Störungen des Reflektors um zwei Größenordnungen. Das Design behebt die grundsätzliche Limitierung des Littrow Designs bezüglich Miniaturisierung, da kein großer Strahldurchmesser vonnöten ist um kleine Bandbreiten des Littrowgitters zu erreichen. / This thesis thoroughly investigates theoretically and experimentally the effects many physical parameters have on the performance of Tunable External-Cavity Quantum-Cascade Lasers (EC-QCLs). These include, among others, the anti-reflection coating, the type of optics, and the geometrical as well as mechanical and structural properties of the EC setup. This was done by assembling three very different EC setups and comparing and discussing their performance, as well as advantages and disadvantages for different purposes using mainly QCLs from the same original wafer for better comparability. For the last part of this thesis, a new type of EC-QCL configuration was developed with properties so promising that we believe it has the potential to replace the Littrow Cavity in the long term. This is an alignment-stabilized and interference filter-tuned design using a retroreflector as the external reflector. For the demonstration of this concept, development of the tuning element in the form of an angle-tunable high-Q mid-infrared bandpass filter was necessary. For the design of the filter, materials with very strict tolerances on the physical and optical properties were selected from theoretical considerations and a fabrication method with highly optimized process parameters was developed. The first filters on the basis of yttrium fluoride/yttrium oxide/germanium/silicon have a transmission bandwidth of 0.14% of the central wavelength and a peak transmission of approximately 60%. The EC configuration resulted in a sensitivity reduction to mechanical perturbations of the reflector by two orders of magnitude, with a calculated potential for three orders of magnitude using optimized optics. This design lifts the fundamental constraint on miniaturization imposed on the Littrow design that requires large beam diameters to ensure a small bandwidth of the Littrow grating.

Porous metal oxides formed by supercritical carbon dioxide (SCCO2) treatments at low temperature were used for displays, solar cells, and light emitting diodes (LEDs) applications. The SCCO2 fluid, also known as green solvents, exhibits low viscosity, low surface tension and high diffusivity as gases, and high density and solubility same with liquids. In this thesis, we successfully fabricated porous antimony-doped tin oxide (ATO) and porous indium tin oxide (ITO) by the SCCO2 treatments. In addition, the treatment can also be used to improve the work function and surface energy of ITO anode of an organic LED (OLED). The performance of the OLEDs was drastically enhanced in comparison with that of the devices without any ITO surface treatments. First, the porous ATO films were formed by the SCCO2 treatment for absorption of silver molecules in silver electro deposition devices. The porosity, resistivity and average optical transmittance of the porous ATO film in visible wavelength were 43.1%, 3 £[-cm and 90.4%, respectively. For the silver electro deposition devices with the porous ATO film, the transmittance contrast ratio of larger than 12 in visible spectrum was obtained at an operating voltage of 1.5 V. Furthermore, for the 0.25 cm2 device, the switching time of 4.5 seconds was achieved by applying a square-wave voltage ranging from 1.5 to -0.2 V between the electrodes. On the other hand, the porous ITO with low refractive index was prepared by SCCO2/IPA treatment on gel-coated ITO thin films. The high refractive index of the ITO film was achieved by long-throw radio-frequency magnetron sputtering technique at room temperature. The index contrast (£Gn) was higher than 0.6 between porous ITO and sputtered ITO films. The large £Gn is useful for fabricating conductive anti-reflection (AR) and high reflection (HR) structures using the porous ITO on sputtered ITO bilayers. The weighted average reflectance and transmittance of 4.3% and 83.1% were achieved for the double-layer ITO AR electrode with a sheet resistance of 1.1 K£[/¡E. For HR structures, the reflectance and sheet resistance were 87.9% and 35 £[/¡E with 4 periods ITO bilayers. Finally, the SCCO2 treatments with strong oxidizer H2O2 were proposed to modify surface property of ITO anode of a fluorescent OLED. The highest work function and surface energy of 5.5 eV and 74.8 mJ/m2 was achieved by the SCCO2/H2O2 treatment. For the OLED with 15 min SCCO2 treatment at 4000 psi, the turn-on voltage and maximum power efficiency of 6.5 V and 1.94 lm/W were obtained. The power efficiency was 19.3% and 33.8% higher than those of the OLEDs with oxygen plasma treated and as-cleaned ITO anodes.

Mitt-Infrarot-Technologie (mid-IR) ist ein äußerst leistungsfähiges Werkzeug für die Anwendung in der Molekülspektroskopie, da die Schwingungsmoden vieler Moleküle in diesem Wellenlängenbereich liegen. Der Quantenkaskadenlaser mit externem Resonator (EC-QCL) kann alle Bereiche dieses Spektrums abdecken. Das Hauptanliegen dieser Arbeit ist die Verbesserung der Leistung des EC-QCL im Hinblick auf die Breite des Wellenlängen-Durchstimmbereichs und die Laserleistung. Theoretische Untersuchungen bestätigen zunächst, dass der QCL die Schlüsselrolle bei EC-Systemen einnimmt: Die Effizienz des EC wird bestimmt durch die Effizienz des QCL und die Güte der Antireflex-Schicht (ARC) der Laserfacette. Die Breite des Durchstimmbereichs wird bestimmt durch das Gain-Spektrum des QCL. Im Rahmen dieser Arbeit wurden die QCL in unserer Gruppe hergestellt und vom QCL-Wachstum selbst bis hin zur Facettenbeschichtung optimiert. Eine der größten Herausforderungen in der Herstellung des EC-Systems ist die Reduktion des Reflexionsvermögens innerhalb der Facetten des Laserchips. Dafür haben wir ein neues ARC-Konzept entwickelt und auf dem beschichteten Substrat demonstriert, dass innerhalb des gesamten, sehr breiten Wellenlängenbereichs von 7–12 μm die Reflexion auf unter 1% reduziert wird. Das Beschichtungsmodell wurde außerdem auf „broad-gain“-QCL-Facetten angewendet, wodurch die Reflexion auf 0,75% über den gesamten Emissions-Wellenlängenbereich reduziert werden konnte. Ein weiterer Schwerpunkt dieser Arbeit ist die Entwicklung und Konstruktion von EC-Lasersystemen. Es wurden zwei kompakte Laser vom Littrow-Typ entwickelt, die von 920 cm-1 bis 1190 cm-1 durchstimmbar sind und die eine Pulsleitung von 0.45 W erreichen. Außerdem wurde eine neue optische Konfiguration des EC-Systems vorgeschlagen um eine höhere Ausgangsleistung zu erzielen. Dieser „Intra-cavity Out-coupling Laser“ erreicht eine Pulsleistung von 1 W und den gleichen Emissionbereich wie die beiden Littrow-Laser. / Mid-infrared (mid-IR) technology is a very powerful tool for molecular spectroscopy since vibration modes of many molecules lie in this wavelength range. The External-Cavity Quantum Cascade Laser (EC-QCL) can cover any part of this spectral range. The main goal of this study is to improve EC-QCL performance in terms of wavelength tunability and laser power. The theoretical study about Quantum Cascade Laser (QCL) and EC systems has confirmed that the QCL plays the core role of EC-QCL systems; the power efficiency of an EC system is determined by the combination of the power efficiency of QCL and AR-coating of the laser facet. The width of the tuning range is determined by the gain spectrum of QCL. During this work, QCLs have been fabricated in our group and the optimization of these factors were carried out with various approaches, from QCL growth to facet coatings. One of the major challenges in making EC systems is to reduce the intra-facet reflectivity of the laser chip, and we first proposed a new anti-reflection (AR) coating concept and demonstrated its performance for the first time to the community, achieving good reduction of reflection of the AR-coated substrate over 7-12 μm range, keeping below R < 1% reflection over the entire spectrum. The coating model was applied on broad-gain QCL facets, and the reflection was reduced to 0.75% over the entire emission wavelength range. Furthermore, this work focused on the development and engineering of laser systems, and two compact Littrow-type lasers and an EC system with a new optical configuration have been developed, achieving good performances; tunable from 920 cm-1 to 1190 cm-1 and 0.45 W pulse power. The new type of laser, an Intra-cavity out-coupling EC laser, was also proposed to enhance the power output and achieved over 1 W pulse power with keeping the same tuning range as the Littrow-type. / 中赤外分光の技術は非常に有用である。これはとりわけ多くの分子振動モードがこの波長帯域に存在しているためである。可変長レーザーである外部共振器量子カスケードレーザー(External cavity quantum cascade laser, EC-QCL)は、これらスペクトル領域を網羅することが可能で、したがって、EC-QCLは産業スケールを含めた、標準的な光源として非常に潜在的である。商品化のフェーズをさらに推し進めるため、このレーザー性能におけるボトムアップの技術が求められてる。 多くの中赤外光のアプリケーションには広帯域の光源が求められている。この研究はおもにそうした性能を最大化することを背景としている。具体的な目的としては、波長の変調性および光源の強度の向上である。これらの目的に取り組むため、我々はいくつかの段階にステージ化して研究を進めてきた。まず初めに、QCLおよびEC-QCLの基本的な特性の追求から始めた。QCLおよびEC-QCLの物理機構の理論的な考察を行い、これらからEC-QCL形態における要素の最適条件もしくは要請を求めた。QCL素子が、その主要な部位であり、EC系におけるほとんどの性能特性である量子効率、変調領域幅、増幅器の光学損失を決定する。 さまざまなアプローチによりこれら緒特性の最適化が行われた。 この研究のなかで、我々グループ内でシステムの心臓となるQCL素子の全製造プロセス(結晶成長から素子コーティングに至るまで)をおこなった。これら製造手順および性能特性の詳細もまた本論文に記す。 ECレーザーにおける要請特性の中で特に困難な課題として、レーザー素子の内部断面(intra-facet)の反射率の低減があげられる。これに応じるものとして、我々は新たな反射防止膜のコンセプトで、特に中赤外光領域に有益なものを提案した。この実現のために、様々な誘電体物質の光学特性を調べ、中赤外光の応用に最適なものを選択し、実際のコーティングに応用した。ここで提案されたモデル``quasi-Lockhart'' (疑ロックハート)のコーティングは、実験によりその高い性能が実証された。波長7–12 μmの領域をカバーし、かつその全領域内で反射率を1%以下に抑えることができた。またこのコーティングは広帯域ゲインのチップにも施され、その反射率を全体域をカバーしながら、0.75%まで低減させた。この成果はEC-QCLだけでなく、一般の中赤外光の光学コーティングにおいても大いに有用であろう。 さらに、我々は本研究の中でレーザーシステムの構築にも取り組んだ。この研究のなかで、二台のLittrow型レーザーと、新たな光学系をもつECレーザーを構築し、その高性能性を実証した。Littrow型では920 cm-1-1190 cm-1の帯域とパルス強0.45 Wを達成。新たなレーザーシステムであるIntra-cavity out-coupling系は従来の系にくらべ高出力することを目的とされ、その帯域を維持しながら、パルス強1~Wの出力を達成した。またこれら新たなシステムを用いて、またプロジェクトバートナーとの食道癌の細胞イメージングも試験、およびグループにおいてアンモニアの吸光度測定を実施した。