Exploration of Transparent Electronic Devices (original) (raw)
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Transparent Electronics: An Emerging Field in Technology
International Journal of Research in Engineering and Technology, 2018
Transparent Electronics, as a field of science and technology, has come into view and is increasing with huge leaps and bounds. It is trying to produce an entirely invisible electronic circuitry and opto-electronic devices. The first example of transparent electronics was reported by researchers at Oregon State University and Hewlett Packard to make transparent transistors that are inexpensive, stable and environment friendly. The Swiss Federal Institute of Technology made a transistor so thin that it can wrap around a human hair. Transparent electronics could be applied in various consumer electronics, new energy sources and transportation. For example, windshields of automobile which could transmit visual information to the driver, flexible electronics that could be folded up for ease of transport. When deposited onto glass, could double as an electronic device, possibly improving security systems or offering transparent displays. In the similar way, windows could be used to produce electrical power. The key component in these applications are wide band gap semiconductors, where oxides of different origin play an important role, not only as passive component but also as an active component similar to what we observe in conventional semiconductors with crystalline or amorphous like structure. The first scientific goal of this technology must be to discover, understand, and implement transparent high-performance electronic materials. Consequently, in order to enable this revolutionary technology requires bringing together expertise from various pure and applied sciences, including material science, chemistry, physics, electrical/electronic engineering, and display science.
Transparent electronics is the next level of technology that the world requires. It is a technology which helps in producing invisible electronic circuits and optoelectronic devices. Numerous applications can be built upon transparent electronics which would change the style of the world we are living in today. The applications contain consumer electronics such as transparent windows which would sense the trespassing and would send a message to the owner of the house regarding the intruding action of someone, transparent windshields, electronic spectacles similar to Google glass, e-Wear or e-Skin etc. However the materials for such type of technology must be transparent and also possess the conductivity characteristics which are quite contradictory. Transparent conductors are neither 100% optically transparent nor metallically conductive. But some of the compounds have been discovered which possess these two properties to a satisfactory extent. And the research of such materials is still going on. The key performance metrics of transparent thin film transistors would be high device mobility and low temperature fabrication. Generally high device mobility enables fast device operation and low power consumption, which broadens the application area of TTFTs. On the other hand, low temperature fabrication is essential for transparent devices made on flexible substrates which would enable novel applications. Low temperature fabrication also lowers the fabrication expense significantly. Despite the above mentioned success, the reported mobility values are still low compared to those of non-transparent devices indicating further room for improvement.
Transparent conducting materials: Overview and recent results
2012
Low temperature plasma processes provide a toolbox for etching, texturing and deposition of a wide range of materials. Here we present a bottom up approach to grow epitaxial crystalline silicon films (epi-Si) by standard RF-PECVD at temperatures below 200°C. Booth structural and electronic properties of the epitaxial layers are investigated. Proof of high crystalline quality is deduced from spectroscopic ellipsometry and HRTEM measurements. Moreover, we build heterojunction solar cells with intrinsic epitaxial absorber thickness in the range of a few microns, grown at 175 °C on highly doped (100) substrates, in the wafer equivalent approach. Achievement of a fill factor as high as 80 % is a proof that excellent quality of epitaxial layers can be produced at such low temperatures. While 8.5 % conversion efficiency has already been achieved for a 3.4 µm epitaxial silicon absorber, the possibility of reaching 15 % conversion efficiency with few microns epi-Si is discussed based on a detailed opto-electrical modeling of current devices.
Unconventional approaches to combine optical transparency with electrical conductivity
Applied Physics A, 2007
The combination of electrical conductivity and optical transparency in the same material-known to be a prerogative of only a few oxides of post-transition metals, such as In, Sn, Zn and Cd-manifests itself in a distinctive band structure of the transparent conductor host. While the oxides of other elements with s 2 electronic configuration, for example, Mg, Ca, Sc and Al, also exhibit the desired optical and electronic features, they have not been considered as candidates for achieving good electrical conductivity because of the challenges of efficient carrier generation in these wide-bandgap materials. Here we demonstrate that alternative approaches to the problem not only allow for attaining the transport and optical properties which compete with those in currently utilized transparent conducting oxides (TCO), but also significantly broaden the range of materials with a potential of being developed into novel functional transparent conductors.
International Journal of Engineering and Advanced Technology, 2019
This work discusses the development of innovative transistor from intelligent thin film. A developed semiconductor junction that constitutes the core of concepted transistor is being studied. Each technology of semiconductors has shortage of some performances. The recent work is an alternative by exploiting intelligent materials to build a transistor with transparency and flexibility characteristics. Many processes are encountered during preparation of the film especially chemical deposition and exposition to laser beam to ensure dopants integration. The physical phase is a challenge for newest technology like the plasma. Thereon, we give a real example of smart thin film. The band gap is also a defiance that we are reducing to ameliorate precisely the impedance and thickness and keep at order of nanotechnology. The fabricated junctions are tested by studying their operation in ordinal conditions. We judge the quality of junctions and transistor from their optical properties and ele...
Intrinsic Transparent Conductors without Doping
Transparent conductors (TCs) combine the usually contraindicated properties of electrical conductivity with optical transparency and are generally made by starting with a transparent insulator and making it conductive via heavy doping, an approach that generally faces severe "doping bottlenecks." We propose a different idea for TC design-starting with a metallic conductor and designing transparency by control of intrinsic interband transitions and intraband plasmonic frequency. We identify the specific design principles for three such prototypical intrinsic TC classes and then search computationally for materials that satisfy them. Remarkably, one of the intrinsic TC, Ag 3 Al 22 O 34 , is predicted also to be a prototype 3D compounds that manifest natural 2D electron gas regions with very high electron density and conductivity. The functionality of transparency plus conductivity [1,2] lies at the center of many technological applications such as solar cells, touch-screen sensors, light emitting diodes, electronic papers, infrared or ultraviolet photo detectors, smart windows, and flat panel display [1-9], yet materials with such seemingly contraindicated properties are difficult to come by. The traditional strategy for searching for TCs has followed the path illustrated by the arrow in Fig. 1(a): start from a transparent insulator and find ways to make it conductive by doping it extensively without affecting its optical transparency [1-9]. Successful examples are very few and include electron doped ZnO, Sn-doped In 2 O 3 , and La-doped SrGeO 3 for electron-conducting (n-type) TCs [3,4,7,8], as well as hole-doped CuAlO 2 and K-doped SrCu 2 O 2 for hole-conducting (p-type) TCs [5,9]. The limiting factors are rooted in defect physics [10-12] and include difficult to fulfill requirements such as finding wide-gap insulators that can be amply doped without promoting carrier compensation or structural deformations. In this Letter, we revisit the basic-physics design principles needed for transparent conductivity and find that a different, previously overlooked route, illustrated by the arrow in Fig. 1(b), may be possible-start from an opaque conductor that already has plenty of free carriers, then design optical transparency to realize an intrinsic (i.e., without intentional chemical doping) TC. However, not all bulk conductors will do; one needs to search for bulk metals that (a) have a sufficiently broad energy window in their electronic structure either below the Fermi energy E F (for an n-type TC) or above E F (for a p-type TC), so the interband transitions across the "energy window" will not obscure optical transparency, and (b) do not have a high plasma frequency (ω p) [13] (such as ∼15 eV=ℏ for Al [13]) so the free carrier reflection will not limit transparency. If one can find metals that satisfy such conditions this would result in the interesting case of metallic conductivity in a transparent and pristine (undoped) crystal. This approach is applicable to bulk compounds and, thus, is different from the approach of using ultrathin films of metallic materials that are transparent only when they are kept ultra thin [14-17]. The two conditions noted above can appear unusual and indeed materials satisfying them have, to our knowledge, not been deliberately searched before. Here, we illustrate the concept of intrinsic TC by discussing first simple, hypothetical structures of RbTe in the zinc blende structure and highly compressed crystalline silicon in the diamond structure, followed by realistic but more complex metallic ceramics reported as having been previously synthesized (but not characterized for conductivity or transparency) in the ICSD compilation of inorganic structures [18] as well as Transparent Opaque Conductor Insulator Transparent Opaque Conductor Insulator TC (b) (a) TC FIG. 1 (color online). (a) The traditional strategy for designing bulk transparent conductors that starts from a wide-gap insulator and finds ways to make it conductive by extensive doping without affecting its crystal structure or optical transparency. (b) The new strategy that starts from a metal that already has plenty of free carriers and designs optical transparency to realize an intrinsic (i.e., without intentional chemical doping) TC. This approach requires a technique for controlling the plasma frequency via the control of carrier density and band dispersion so the free carrier reflection will not limit transparency.
Transparent conductors--a status review
Thin solid films, 1983
Non-stoichiometric and doped films of oxides of tin, indium, cadmium, zinc and their various alloys, deposited by numerous techniques, exhibit high transmittance in the visible spectral region, high reflectance in the IR region and nearly metallic conductivity. The electrical as ...
Recent Progress in Transparent Conductive Materials for Photovoltaics
Energies
Transparent conducting materials (TCMs) are essential components for a variety of optoelectronic devices, such as photovoltaics, displays and touch screens. In recent years, extensive efforts have been made to develop TCMs with both high electrical conductivity and optical transmittance. Based on material types, they can be mainly categorized into the following classes: metal oxides, metal nanowire networks, carbon-material-based TCMs (graphene and carbon nanotube networks) and conjugated conductive polymers (PEDOT:PSS). This review will discuss the fundamental electrical and optical properties, typical fabrication methods and the applications in solar cells for each class of TCMs and highlight the current challenges and potential future research directions.
Advanced Materials Interfaces
strategy for conventional transparent conducting oxides (TCOs) is to resort to degenerately dope wide-bandgap semiconductors to achieve the two key properties: electrical conductivity and optical transparency. Wide bandgap semiconductors are selected as host materials, which have the interband transitions above the visible spectrum, whereas dopants increase carrier density and thus electrical conductivity. Tin-doped indium oxides (ITOs) have been widely used because of its best balance of high electrical conductivity and optical transparency in the visible spectrum. [3] However, the increasing use of ITO as TCOs has resulted in the increase in the cost of ITO due to the limited availability of indium ore. [4] Meanwhile, many other applications, such as solar blind detection, ultraviolet (UV) lithography, UV light-emitting diodes, and UV curing, require transparent conductors in the UV spectrum. [5-8] However, conventional TCOs with high conductivity present low transmittance on the UV side of the spectrum. [1] Recently, an alternative design strategy has been proposed to use correlated metals with the intrinsic high carrier density exhibiting strong electron correlations to achieve both high electrical conductivity, thus low resistivity, and optical transparency in the UV-visible spectral range, overcoming the limitations of conventional TCOs. [9-19] It has been shown that as correlated metal films on single crystal substrates get thin, they maintain low resistivity and thus low sheet resistance at room temperature (RT) whereas their optical transmittance is comparable to (or higher than) conventional TCOs in the visible (or UV) spectrum. [9,10,17] However, the epitaxy so far required expensive and size-limited single crystal substrates, which impedes the application of correlated metals as TCOs. Meanwhile, oxide nanosheets drew attention because they can be used as buffer layers to promote the growth of highquality and thus high-performance transition metal oxide films regardless the supporting substrates. [20-26] Almost full coverage of oxide nanosheets can be obtained on virtually any flat substrates without the limitation of the substrate size by using Langmuir-Blodgett method. [21,24,25] Boileau et al. showed that correlated CaVO 3 and SrVO 3 (SVO) films with a thickness of 40 nm on Ca 2 Nb 3 O 10 (CNO) nanosheets on glass had the RT Correlated metals with high carrier density and strongly correlated electron effects provide an alternative route to achieve transparent conducting materials, different from the conventional degenerately doped wide-bandgap transparent conducting oxides (TCO). The extremely low electrical resistivity and high optical transparency in the ultraviolet-visible spectral range shown in 4d correlated metals present an advantage over conventional TCOs. However, most of the 4d correlated metals are grown epitaxially on single crystal substrates. Here, it has been shown that Ca 2 Nb 3 O 10 nanosheets with different buffer layers promote the growth of high-quality 4d 2 SrMoO 3 films on fused silica substrates, overcoming the use of expensive and size-limited singlecrystal substrates. The room temperature electrical resistivity of SrMoO 3 is as low as 61 µΩ cm, the lowest reported value on amorphous transparent substrates to date, without compromising its high optical transmittance. 4d 1 correlated metal SrNbO 3 on Ca 2 Nb 3 O 10 nanosheets also exhibits similarly high optical transmittance but a higher room temperature resistivity of 174 µΩ cm. These findings facilitate the use of highly conducting and transparent 4d correlated metals not only as TCOs on technologically relevant substrates for the applications in the ultraviolet-visible spectral range but also as electrodes for other oxide-based thin film technologies.