Transparent Conducting Oxide

(Received 10 October 2014; revised manuscript received 4 February 2015; published 2 March 2015) Epitaxial p-type transparent conducting oxide (TCO) Cr 2 O 3 :Mg was grown by electron-beam evaporation in a molecular beam epitaxy system on c-plane sapphire. The influence of Mg dopants and the oxygen partial pressure were investigated by thermoelectric and electrical measurements. The conduction mechanism is analyzed using the small-polaron hopping model, and hopping activation energies have been determined, which vary with doping concentration in the range of 210–300 ± 5 meV. Films with better conductivity were obtained by postannealing.

Associate Professor, Department of Applied Physics, School for Physical Sciences, Babasaheb Bhimrao Ambedkar University, Lucknow, U.P., India 3 ABSTRACT: Present review reports the properties and applications of transparent conducting oxides (TCOs) thin films. Particular deposition techniques for TCO’s manufacturing are important for several reasons as thickness uniformity and low production costs. In day to day life, transparent conducting oxide materials are used in various devices and mostly found in display technology, organic light-emitting-diodes, thin-film solar photovoltaics and smart windows. Also, they play a leading role in solid state gas sensors. Different types of oxides exhibit different response towards oxidising and reducing gases by the variation of their electrical properties. Detail discussion of electronic and optical properties of TCOs have also been carried out.

and shown that Gd can be incorporated into BSO. The result is a good transparent conducting oxide, with high room- temperature electron mobility values. The addition of a mag- netic moment while preserving metallicity as well as optical transparency can be useful in the fabrication of functional devices, with the ability to further tailor functionality via the Gd concentration.

Thin film solar cells, if film thickness is thinner than the optical absorption length, typically give lower cell performance. For the thinner structure, electric current loss due to light penetration can offset the electric current gain obtained from higher built-in electric field. Light trapping schemes can increase the effective optical absorption length and thus enhance the electric current for thinner solar cells. Here a new light trapping scheme based on light trapping transparent conducting oxide layer (LT- TCO) is proposed to enhance the performance of thin film solar cells. Three different configurations of integrating the LT-TCO layer in solar cells are proposed and evaluated.

Telp (031) 5924448, e-mail: widi@chem-eng.its.ac.id Abstract ZnO:Al particles are widely used as semiconductor material in various fields of technology, such as transparent conducting oxide (TCO). Synthesis of ZnO:Al particles using spray pyrolysis method has many advantages. The generated particles are relatively homogenous size distribution, spherical, and easily adjusted the particle size in range nano-submicrometer. Here, we studied the effect of doping concentration (1-4 at.%), operation temperature (500-900°C) and carrier gas flow rate (2-4 L/min) on the characteristics of the generated particles including morphology, crystallinity, and transparancy. In order to analyse the morphology, crystallinity, and transparancy of the generated particles, we used Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), dan UV-Vis spectrophotometer, respectively. The optimum condition for the highest crystallinity and transparancy was obtained by partices synthesized using doping concentration of 2 at.%, furnace of 900°C and carrier gas flow rate of 2 liter/minute

10 Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, United States (Received 29 July 2015; revised manuscript received 21 October 2015; published 15 January 2016) We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO 3 , using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La-BaSnO 3 is driven purely by electrostatic interactions.

Leicestershire, LE11 3TU, United Kingdom Abstract — a combinatorial study of transparent conducting oxide thin films based on SnO 2 –TiO 2 -WO 3 phase space is reported. These multinary oxide films were fabricated by magnetron reactive co-sputtering of tin monoxide (SnO), titanium (Ti) and tungsten (W) targets. SnO 2 –TiO 2 -WO 3 film compositions with Ti/Sn ratio (0.02 – 0.12) and W/(Ti+Sn) ratio (0.02 – 0.25) were explored. The effect of oxygen partial pressure on composition, structure and optical properties was evaluated.

Po Kai Chiu 1,2* , Wen Hao Cho 1 , Hung Ping Chen 1 , Chien Nan Hsiao 1 and Jer Ren Yang 2 Abstract Transparent conducting ZnO/Ag/ZnO multilayer electrodes having electrical resistance much lower than that of widely used transparent electrodes were prepared by ion-beam-assisted deposition (IAD) under oxygen atmosphere. The optical parameters were optimized by admittance loci analysis to show that the transparent conducting oxide (TCO) film can achieve an average transmittance of 93%. The optimum thickness for high optical transmittance and good electrical conductivity was found to be 11 nm for Ag thin films and 40 nm for ZnO films, based on the admittance diagram. By designing the optical thickness of each ZnO layer and controlling process parameters such as IAD power when fabricating dielectric-metal-dielectric films at room temperature, we can obtain an average transmittance of 90% in the visible region and a bulk resistivity of 5 × 10 −5 Ω -cm. These values suggest that the transparent ZnO/Ag/ZnO electrodes are suitable for use in dye-sensitized solar cells.

In summary, well-aligned ZnO/ZnTe core/shell nano- wire arrays were successfully fabricated on transparent conducting oxide glass substrates by CVD and MOCVD. The structures' properties were investigated in detail by SEM, TEM, and XRD studies; the results showed the core/shell structure that the ZnTe shell deposited dir- ectly in the radial direction from the surface of the ZnO nanowire. The ZnO core was consisted of the (002) plane of wurtzite structure; the ZnTe shell was con- sisted of the (111) plane of zincblende structure. The optical properties were investigated by PL and trans- mission studies. The results showed that the ZnO/ZnTe core/shell nanowires have desirable optical properties.

Abstract CdS/CdTe/Au thin film solar cells have been fabricated on different transparent conducting oxide (TCO) substrates/front contacts to study the influence of these different TCOs on the performance of the devices. The TCOs used were ZnO, ZnO:Al and SnO 2 :F. Under dark condition, all three device structures of the type glass/TCO/n-CdS/n-CdTe/Au n-n heterojunction+Schottky barrier, show interesting rectifying behaviors with rectification factors (RF) in the range (10 2.5 – 10 5.0 ), Schottky barrier heights (Φ B ) greater than (0.69 – 0.81) eV, diode ideality factors (n) in the range (1.85 – 2.12), reverse saturation current densities (J 0 ) in the range (3.18×10 -6 – 3.18×10 -8 ) Acm -2 , series resistances (R s ) in the range (507 – 1114) Ω and shunt resistances (R sh ) in the range (0.84 – 271) MΩ. The device structures glass/SnO 2 :F/n- CdS/n-CdTe/Au and glass/FTO/ZnO:Al/n-CdS/n-CdTe/Au show the best performance with equal J 0 of 3.18×10 -8 Acm -2 , equal Φ B > 0.81 eV, RF of 10 4.9 and 10 5.0 , n value of 2.01 and 2.12, R s of 615 Ω and 507 Ω and R sh of 197 and 271 MΩ respectively. The device structure with ZnO shows the least performance. Under AM1.5 illumination, the device structure glass/SnO 2 :F/n- CdS/n-CdTe/Au shows the best solar cell performance with open-circuit voltage of 630 mV, short-circuit current density of 23.5 mAcm -2 , fill factor of 0.44 and conversion efficiency of 6.5%, and is followed by the device structure with ZnO:Al showing a conversion efficiency of 6.0%. Suggested energy band diagrams of the devices as well as possible reasons for the observed trends in performance are presented and discussed.

e Acree Technologies Inc., Concord, California Abstract Aluminum-doped zinc oxide, ZnO:Al or AZO, is a well-known n-type transparent conducting oxide with great potential in a number of applications currently dominated by indium tin oxide (ITO). In this study, the optical and electrical properties of AZO thin films deposited on glass and silicon by pulsed filtered cathodic arc deposition are systematically studied. In contrast to magnetron sputtering, this technique does not produce energetic negative ions, and therefore ion damage can be minimized. The quality of the AZO films strongly depends on the growth temperature while only marginal improvements are obtained with post-deposition annealing.

167 two oxygen atoms in order to place an O-MI-O dumbbell unit is parallel with c-axis. All MI layers are linked to the MIIIO2 layers by the O-MI-O dumbbell units. Each oxide ion in the MIIIO2 layer, on the other hand, forms a pseudo-tetrahedral coordination (MIII3MIO) with the neighboring MIII and MI ions [3], thus reduces the nature of non-bonding in the oxide ions and holes are delocalized at the edge of valence band. Moreover, this oxide-layered structure also reduces the cross-linking contribution of MI ions, and thus increases the bandwidth of oxides [1]. This structure also revealed that coordination number of the MI ions is low because of the large separation from oxygen ligands, thus 2p electrons in oxygen ligands and MI d10 electrons form a solid coulombic repulsion. The MI d10 energy levels are being similar to the O 2p level resulted in a high level of mixture.

Figure 1: Schematic illustration of CMVB technique According to valence bond theory, the oxide ions are sp3 hybrid orbital in the valence state of an oxygen (O) atom. There are 2s2 orbital in eight electrons in which conveyed on an oxide ion in four σ co-ordination bonds.

Although the TCOs have a wide range of applications, very little work has been done on the fabrication of p-n junction active device using TCO. This is because most of the TCO are of the n-type and the corresponding p-type TCOs are not systematically investigated. Since the development of p-type TCO is one of the key component for transparent p-n junction-based devices, the formation of p-type TCO based on copper oxide is the main objective in this work. In the literature, most of the techniques used for the formation of TCO film are based on physical method and hence they are expensive and difficult to conduct compared to CSD technique which is simpler with potential for the large scale preparation of thin semiconductor films.

This thesis is dedicated to elucidate the practical limits of modulation doping by implementing a novel doping strategy, which relies on defect related Fermi level pinning in insulators as dopant phase namely ”defect modulation doping”. This approach uses two chemically and structurally dissimilar materials to circumvent the alignment of doping limits. The use of dissimilar materials, which do not have to be conducting on their own, removes the constraint of aligned doping limits. By aligning two dissimilar materials it is therefore, in principle, possible to obtain Fermi levels outside the doping limits in the host material. This is possible by a careful control of the interface properties used to induce previously unattainable charge carrier densities in one of them. Such a situation can, from a thermodynamic point of view, only be achieved if defects in the host material cannot form spontaneously when the Fermi energy is raised during deposition of a modulation layer. The viability of this approach has already been demonstrated by Weidner [8, 9] during his PhD work. He deposited a defective and amorphous insulator material Al 2 O 3 on sputtered SnO 2 thin films, in which the Fermi level in defective Al 2 O 3 pinned and resulted in a Fermi level position outside of the doping limit in SnO 2 . In this work, electrically conducting TCOs 1 shall be obtained by employing modulation doping of sputtered thin films and nanocomposite materials synthesized from undoped TCO hosts and embedded dopant nanoparticles. The defect modulation doping is schematically illustrated in Fig. 1.

Transparent conducting oxides (TCO) constitute a unique class of materials which combine two physical properties together - high optical transparency and high electrical conductivity. These properties are generally considered to be mutually exclusive of each other since high conductivity is a property possessed by metals while insulators are optically transparent. This peculiar combination of physical properties is achieved by generating free electron or hole carriers in a material having a sufficiently large energy band gap (i.e., >∼3.1 eV) so that it is non absorbing or transparent to visible light. The charge carriers are usually generated by doping the insulator with suit- able dopants and also by defects. It is no wonder that this unique material property makes TCOs technologically an important material and TCOs are widely used in commercial applications such as - in liquid crystal display (LCD), plasma and organic light emitting (OLED) displays; touch-screen sensors; thin-film and organic photovoltaics, OLED lighting; low-e windows and smart windows; solar control film etc.

4.4. AGZO: Aluminium and Gallium co-doped Zinc Oxide 126 4.3.5 Conclusions: GZO Doping of Ga into ZnO was successful; up to 6.0 at% Ga, only a single phase was identified by XRD, and only a single environment was observed for each Zn 2p and Ga 2p orbital binding energies from XPS data. Increasing the dopant level did not alter the morphology, but did decrease particle size. The optimal composition as determined by pressing the powder samples into discs and heat treating, pointed to the 3.5 at% GZO sample as being consistently the most conductive. Higher resistivities were observed with both higher and lower dopant levels, above the op- timal 9.1 x 10 −3 Ω cm. This was also close to the 6.0 x 10 −3 Ω cm obtained by ITO as synthesised using the same process and the 7.0 x 10 −3 Ω cm seen in AZO, demonstrating the promise of GZO as an ITO replacement TCO material as made by CHFS. Up-scaling of the synthesis to 330 g h −1 resulted in a minor deterioration of the electrical properties, and a shift in the trend to the optimal nominal dopant level (in the precursor solutions) increasing from 3.5 at% to 4.5 at%.

August 2000 issue of MRS Bulletin is well timed to provide an overview of TCO, included articles cover the industrial perspective, new n-type materials [2] by Tadatsugu Minami, new p-type materials [3] by Hiroshi Kawazoe, Hiroshi Yanagi, Kazushige Ueda, and Hideo Hosono, novel deposition methods, applications and processing of transparent conducting oxides [4] by Brian G. Lewis and David C. Paine, and approaches to developing both an improved basic understanding of the materials themselves as well as models capable of predicting performance limits. There is a renewed interest in research on TCOs, mainly due to its numerous different properties and applications.

Reciprocal space maps showed fully relaxed Ba 0.93 La 0.07 SnO 3 epitaxial layers on SrTiO 3 (001). The crystalline quality of material obtained was evidenced through HR-XRD measurements with a full width at half maximum (FWHM) of 290 arcsec for the Rocking curve of the symmetric (002) peak and 108 arcsec for the asymmetric (103) peak. The band gap of the layers, determined from Reflection measurements employing the Kubelka-Munk method, was estimated as 2.97 - 3.01 eV, i.e. very suitable for the applications envisaged. The layers demonstrated electrical conductivity value of 1024 (Ω·cm) -1 at a free carrier concentration of 2.18×10 21 cm -3 and a high transparency (up to 90%) in the visible and NIR range of spectrum. The Ba 0.93 La 0.07 SnO 3 layers grown could be regarded as a cost-effective and thermally and chemically stable alternative to highly doped ZnO-based transparent conductive oxides and to In 2 O 3 :Sn in applications ranging from solar energy utilization to optoelectronics as well as for the emerging field of transparent and radiation hard electronics.

compared to the experimental range of 2.95–3.30 eV. 13,44–49 PBE + U provides an improved description of the optical band gap compared to experiments, with a calculated optical band gap of 2.7 eV, however, this direct band gap is only in the range of the indirect band gaps reported in experiment. The HSE06 optical band gap is calculated to be 3.75 eV, which is an overestimation of 0.45 eV over the largest experimentally reported optical band gaps for CuCrO 2 . In line with these find- ings, HSE06 has been shown recently to overestimate the band gaps of some transition metal containing ternary oxide systems. 87 Fitting exchange to the band gap is an often-used correction when the hybrid function of choice does not yield the expected band gap, 70,88 however, in this case there are too many uncer- tainties about the exact indirect and direct band gaps of CuCrO 2 , so we have not attempted any ‘‘exchange fitting’’ in this case. The earliest study of the opto-electronic properties of CuCrO 2 by Benko and Koffyberg 40 had reported an indirect band gap of only 1.28 eV. The same authors also studied CuAlO 2 , 57 and