Growth and characterisation of sputtered transparent conducting oxides targeting improved solar cell efficiency

Transparent conducting oxides (TCO) are used to improve lateral current collection in thin film solar cells while allowing light into the absorber layers. Sputtering, an industrially mature coating technology, is potentially useful for low cost production of high quality TCO films. ZnO:Al films were grown by reactive MF (mid frequency) dual cathode magnetron sputtering from Zn:Al targets on glass with dynamic deposition rates up to 115 nm.m.minˉ¹ compared to 6 nm.m.minˉ¹ by RF sputtering from a single ceramic target. Adjusting the distribution of the oxygen influx improved the uniformity of the thickness and resistivity of ZnO:Al films grown on substrates measuring 30 cm × 30 cm. The ZnO:Al films were texture-etched for light trapping in micro-crystalline silicon (μc-Si:H) solar cells. Optimally textured ZnO:Al films were used as front contacts in 1 cm² single junction μc-Si:H solar cells yielding an initial efficiency of 8.4 % which is comparable to cells on textured RF sputtered ZnO:Al films, despite the much higher deposition rate. [Continues.

Growth optimisation and laser processing of thin film phosphors for electroluminescent displays

This thesis presents results of a study of ZnS:Mn thin film phosphors used in Thin Film ELectroluminescent (TFEL) and Laterally Emitting TFEL (LETFEL) devices, examining techniques for phosphor growth optimisation and post deposition processing in order to strengthen development of novel TFEL devices. To achieve this, thin films of phosphor were deposited using RF magnetron sputtering to investigate the use of co-sputtering in order to optimise dopant concentration. 800 nm films of ZnS:Mn were simultaneously co-sputtered from ZnS and ZnS:Mn (1 wt.%) solid targets. The thin films were deposited at different manganese concentrations by varying the relative RF power applied to each target. The films were deposited directly onto 100 mm diameter (100) n-type silicon substrates, or onto a layer of 300 nm of Y2O3 to fabricate electroluminescent test devices. Luminescence from the phosphor films was characterised via photoluminescent excitation using a 337 nm pulsed N2 laser, with the photoluminescence (PL) optimum obtained at 0.38 ZnS:Mn power ratio. Electroluminescence (EL) from TFEL devices were excited by applying a sinusoidal waveform voltage at a frequency of 1 kHz with maximum luminance obtained at 0.36 ZnS:Mn power ratio

Micro-Nano Surface Functionalization of Materials and Thin Films for Optical Applications

This book contains the articles collected for the Special Issue entitled "Micro-nano Surface Functionalization of Materials and Thin Films for Optical Applications" in the journal Coatings (ISSN 2079-6412). These selected articles provide a meaningful overview of recent advances and concepts beyond the state-of-the-art regarding surface functionalization of materials and deposition of thin films to be used in optical applications. The aim was to cover all relevant aspects of the topic (simulation, design, fabrication, characterization and applications) with a special emphasis on non-conventional methods for surface modification of materials, combinations of mature fabrication routes with emerging technologies (i.e., additive manufacturing) and large-area fabrication concepts to pave the way to an industrial utilization of the developed materials. This overview comprises the recent work of reputed scientists from Germany, Austria, Spain and India on: - New developments on the scale-up deposition of transparent conductive materials by magnetron sputtering,- Design of hierarchical surface structures at different scale lengths for nanoimprinting of optical nano- and micro-structures, - Non-conventional preparation of rutile-type TiO2 films at room temperature for optical applications on heat-sensitive substrates, - Design of spectrally selective solar absorber coatings based on computational simulation and ellipsometry measurements

Work Function Extraction of Indium Tin Oxide Used As Transparent Gate Electrode For MOSFET.

Recent commercialization has peaked interest in transparent conducting oxides being implemented in display technology. Indium Tin Oxide (ITO) is a popular transparent conducting oxide which has been utilized as high work function electrode in liquid crystal displays, solar cells, gas sensors and heat reflecting films. Indium Tin Oxide films exhibit excellent transmission characteristics in the visible and infrared spectrum while maintaining high electrical conductivity. High work function electrodes are used to inject holes into organic materials. In majority applications the ITO work function has an impact on the device performance as it affects the energy barrier height at the hetero-junction interface. Hence, the work function of ITO is of critical importance. In this thesis, the work function of ITO is extracted successfully from a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) device for the first time. Two MOSFET devices are fabricated using a four level mask under exact same conditions. Aluminum metal is used as a drain and source contact for both MOSFETs. One of the MOSFET has aluminum gate contact and transparent conducting ITO is used as gate contact for the second MOSFET. From the threshold voltage equation of both the fabricated MOSFETs, work function of ITO is extracted. Further optical transmission studies of ITO performed in the visible spectra are also reported in this study

Applications of transparent conductive indium tin oxide films in automotive and vitrifications industries

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2009Includes bibliographical references (leaves: 76-79)Text in English; Abstract:Turkish and Englishxii, 79 leavesDue to its unique electrical and optical properties, highly doped n-type Indium tin oxide used for various applications such as smart glass, LCDs, OLEDs, solar cells and car windows. In this study Indium Tin Oxide (ITO) thin films were grown by both DC and RF magnetron sputtering techniques. To know deposition rate of ITO, system was calibrated for both DCMS and RFMS and then ITO were grown on glass substrate with the thickness of 70 nm and 40 nm by changing substrate temperature. The effect of substrate temperature, film thickness and sputtering method on structural, electrical and optical properties were investigated. Wan der Pauw method was used for electrical characterization and to use this method properly, we patterned ITO thin films by photolithography and Ion beam etching techniques. The results show that substrate temperature and film thickness substantially affects the film properties, especially crystallization and resistivity. The thin films grown at the lower than 150 oC showed amorphous structure. However, crystallization was detected with the further increase of substrate temperature. Substrate temperature and film thickness increment were lead to increase band gap of ITO which can be explained by BMS. Band gap of ITO was calculated to be about 3.64 eV at the substrate temperature of 150 oC, and it widened with substrate temperature increment. From electrical measurements the resistivity at room temperature was obtained 1.28*10 and 1.29*10 cm, for DC and RF sputtered films, respectively. We also measured temperature dependence resistivity and the Hall coefficient of the films, and we calculated carrier concentration and Hall mobility

Engineering Si-compatible materials based on transparent nitrides and conductive oxides (TNCOs) for broadband active plasmonic and metamaterials applications

Alternative plasmonic materials of Transparent Nitrides and Conductive Oxides (TNCOs) including Indium Tin Oxide (ITO), Al-doped ZnO (AZO) and Titanium Nitride (TiN), have been proposed as novel material platforms for Si-compatible plasmonics and metamaterials, showing enhanced light-matter interaction over a broad spectral range. It has been recently shown that these materials feature reduced optical losses compared with conventional noble metals such as Au and Ag in the visible and near-infrared spectral range. However, it is still an open challenge to tailor the structural and optical properties of these materials, and to further reduce their optical losses, in order to effectively utilize them in photonic devices. In this thesis work, I demonstrate wide tunability of the optical and structural properties of ITO, AZO and TiN thin films, by using post-deposition annealing treatments, enabling significant reduction of their optical losses. By measuring the optical bandgaps of the investigated materials, I show that the tunability of the optical properties originates from the modulation of the free carrier concentration induced by the annealing treatment. Moreover, I perform XRD characterization of the fabricated films, indicating that the annealing also effectively tunes the grain size, which is consistent with the change of the optical properties. Eventually, I investigate the role of the annealing gases for ITO and AZO, demonstrating that free-carrier modulation in ITO and AZO is due to the change in the density of oxygen vacancies after post-deposition annealing. In particular, TNCOs possess epsilon-near-zero (ENZ) condition in near-infrared range with optical loss ε^"<1, thus providing enhanced internal fields in the medium at the ENZ condition. In collaboration with Prof. Nader Engheta and the previous post-doc in our group Dr. Antonio Capretti, we demonstrate enhanced second-harmonic generation (SHG) and third-harmonic generation (THG) from ITO thin films driven by ENZ condition. It results that the SHG generation efficiency is comparable with that of a crystalline quartz plate of thickness 0.5 mm, and that the THG generation efficiency is ∼600 times larger than crystalline silicon. As an application for the fabricated TiN material, I investigate PL intensity and lifetime in Hyperbolic Metamaterials (HMMs) coupled with emitting Si Quantum Dots (QDs). In collaboration with Hiroshi Sugimoto in Prof. Minoru Fujii’s group and the previous post-doc in our group Dr. Sandeep Inampudi, we demonstrate up to 1.6-times enhanced decay rate of QDs emission. Photonic devices based on TNCO plasmonic materials offer an effective approach for the engineering of novel Si-based photonic devices with enhanced light-matter coupling over a broad spectral range. As an application for the fabricated ITO, in collaboration with Hongwei Zhao in Prof. Jonathan Klamkin’s group, electro-absorption modulators are numerically investigated to show high extinction ration of greater than 6dB, while insertion loss is less than 1.3dB for wavelength range from 1.25 µm to 1.42 µm. Additionally, we demonstrate tunable optical properties of ITO thin films in mid-infrared spectrum by thermal annealing of ITO in oxygen environment. In collaboration with Sajan Shrestha and Adam Overvig in Prof. NanFang Yu’s group, we fabricate 2D periodic arrays of ITO and show wide tuning of plasmonic resonances of ITO nanostructure from 4 µm to 10 µm. Combining with the tunability of ITO thin films in near-infrared, the ITO material platform provides a promising method for the control and engineering of Si-based tunable plasmonic and metamaterial devices in the infrared spectrum. Finally, in collaboration with my colleague Ren Wang, we experimentally demonstrate silicon nanodisk arrays with tunable anapole mode excitation in the visible spectrum. The proposed high index nanostructures can be used to enhance absorption rate for applications in semiconductor photodetector

Study of Thermoelectric Properties of Indium Silicon Oxide Thin Films

Thermoelectric devices, which convert heat into electricity, are regarded as an environmentally friendly alternative to fossil fuels used as the main resource for energy production. In the last few decades, transparent oxide semiconductors and conductors, namely Indium oxide-based materials, have been studied and applied in thin film transistors and solar cells. Nevertheless, this group of materials has also been studied for thermoelectric applications. In this dissertation, amorphous Indium silicon oxide (ISO) thin films were sputtered at room temperature on glass substrate, under different oxygen contents in the argon and oxygen mixture. The thermoelectric properties were evaluated as a function of deposition conditions and post-deposition annealing parameters (temperature and time). These properties were analysed and correlated with respective structural, morphological, optical, and electrical properties. For films deposited with no oxygen and annealed at 300 ºC for 24 h, the Seebeck coefficient and electrical resistivity at room temperature were 68:6 VK1 and 4:7 102 cm, respectively. Thin films deposited at higher oxygen percentages showed, in turn, very low conductivity values not being possible to measure the Seebeck coefficient. The maximum power factor achieved was 10 Wm1K2 for the aforementioned annealing conditions. A simultaneous increase of the Seebeck coefficient and electrical conductivity was also observed, mainly due to scattering mechanisms which enhanced the Seebeck coefficient. Although ISO thin films properties present a good stability when submitted to different post-deposition conditions, further studies need to be performed in order to optimise the thermoelectric properties and hence the power factor