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ALD of ZnO:Ti: Growth Mechanism and Application as an Efficient Transparent Conductive Oxide in Silicon Nanowire Solar Cells
摘要： In the quest for replacement of indium-tin-oxide (ITO), Ti-doped zinc oxide (TZO) films have been synthesized by atomic layer deposition (ALD) and applied as n-type transparent conductive oxide (TCO). TZO thin films were obtained from titanium (IV) i-propoxide (TTIP), diethyl zinc and water, by introducing TiO2 growth cycle in a ZnO matrix. Process parameters such as the order of precursor introduction, the cycle ratio and the film thickness were optimized. The as-deposited films were analyzed for their surface morphology, elemental stoichiometry, optoelectronic properties and crystallinity, using a variety of characterization techniques. The growth mechanism was investigated for the first time by in situ quartz-crystal microbalance measurements. It evidenced different insertion modes of titanium depending on the precursor introduction, as well as the etching of Zn-Et surface groups by TTIP. Resistivity as low as 1.2 × 10-3 Ω cm and transmittance > 80% in the visible range were obtained for 72-nm thick films. Finally, the first application of ALD-TZO as TCO was reported. TZO films were successfully implemented as top electrodes in silicon nanowire solar cells. The unique properties of TZO combined with conformal coverage realized by ALD technique make it possible for the cell to show almost flat EQE response, surpassing the bell-like EQE curve seen in devices with sputtered ITO top electrode.
关键词： TCO,silicon nanowire solar cells,n-type,ZnO:Ti,Atomic Layer Deposition,QCM studies
更新于2025-09-23 15:19:57
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Dynamic space-charge-controlled field emission model of current conduction in metala??insulatora??semiconductor capacitors
摘要： A dynamic space-charge-controlled field emission (SCC-FE) model that considers temporal insulator charge variations caused by voltage stress is developed for analyzing the current conduction in insulators in the entire voltage range of measurement, yielding good agreement between experiments and simulations. The usage of prestressed samples in this analysis is essential for accurately estimating the electron affinities of insulators, yielding 1.65 and 1.93 eV as the estimates for Al2O3 films formed on GaN by atomic-layer deposition (ALD) at 200 and 450 °C, respectively, and 1.65 and 1.83 eV for those on SiO2/Si, respectively. Through the bias instability analysis using the method developed here, the voltage-stress tolerance of both Si and GaN metal–insulator–semiconductor (MIS) capacitors with ALD Al2O3 films was found to be enhanced by the high-temperature (450 °C) ALD. The analysis also revealed the fact that the voltage-stress-induced flatband voltage shift of GaN capacitors with the high-temperature Al2O3 films is mainly caused by the Al2O3 charges near the substrate, hence providing a clue to even better bias stability of the GaN capacitors. With possible applications to other wide-bandgap semiconductor (WBGS) capacitors, the dynamic SCC-FE analysis developed here will play an essential role in analyzing not only gate insulator characteristics but also many reliability issues of various WBGS MIS field-effect transistors.
关键词： Al2O3 films,bias instability,atomic-layer deposition,dynamic space-charge-controlled field emission,metal–insulator–semiconductor capacitors
更新于2025-09-23 15:19:57
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Enhanced operational stability through interfacial modification by active encapsulation of perovskite solar cells
摘要： Encapsulates are, in general, the passive components of any photovoltaic device that provides the required shielding from the externally stimulated degradation. Here we provide comprehensive physical insight depicting a rather non-trivial active nature, in contrast to the supposedly passive, atomic layer deposition (ALD) grown Al2O3 encapsulate layer on the hybrid perovskite [(FA0.83MA0.17)0.95Cs0.05PbI2.5Br0.5] photovoltaic device having the configuration: glass/FTO/SnO2/perovskite/spiro-OMeTAD/Au/(6) Al2O3. By combining various electrical characterization techniques, our experimental observations indicate that the ALD chemistry produces considerable enhancement of the electronic conductivity of the spiro-OMeTAD hole transport medium (HTM), resulting in electronic modification of the perovskite/HTM interface. Subsequently, the modified interface provides better hole extraction and lesser ionic accumulation at the interface, resulting in a significant lowering of the burn-in decay and nearly unchanged charge transport parameters explicitly under the course of continuous operation. Unlike the unencapsulated device, the modified electronic structure in the Al2O3 coated device is essentially the principal reason for better performance stability. Data presented in this communication suggest that the ionic accumulation at the spiro-OMeTAD/perovskite interface triggers the device degradation in the uncoated devices, which is eventually followed by material degradation, which can be avoided by active encapsulation.
关键词： encapsulation,Al2O3,atomic layer deposition,operational stability,perovskite solar cells
更新于2025-09-23 15:19:57
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Atomic layer deposition of zirconium oxide thin film on an optical fiber for cladding light strippers
摘要： Cladding light strippers are essential components in high-power fiber lasers used for removal of unwanted cladding light that can distort the beam quality or even damage the whole fiber laser system. In this study, an Atomic Layer Deposition system was used for the first time to prepare the cladding light stripper devices using a 40 nm thick zirconia layer grown on optical fiber. The thickness of the zirconia coating was confirmed using the Scanning Electron Microscopy (SEM) and the Ellipsometry techniques. The elemental analysis was also performed using the wavelength dispersive X-ray spectroscopy technique. The Raman spectroscopy and XRD data confirm the structure of the atomic layer deposition-grown zirconia thin films to be predominantly amorphous. The cladding light stripper devices formed using the zirconia thin films with the lengths of 8.5 and 15.5 cm were able to strip approximately 30% (~1.5 dB) and 40% (~2.3 dB) of the unwanted cladding light.
关键词： zirconium oxide,atomic layer deposition,cladding light stripper,thin film,Fiber laser
更新于2025-09-23 15:19:57
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Atomic layer deposition of metal oxides for efficient perovskite single-junction and perovskite/silicon tandem solar cells
摘要： Aluminum-doped and undoped zinc oxide films were investigated as potential front and rear contacts of perovskite single and perovskite/silicon tandem solar cells. The films were prepared by atomic layer deposition (ALD) at low (<200 °C) substrate temperatures. The deposited films were crystalline with a single-phase wurtzite structure and exhibit excellent uniformity and low surface roughness which was confirmed by XRD and SEM measurements. Necessary material characterizations allow for realizing high-quality films with low resistivity and high optical transparency at the standard growth rate. Spectroscopic ellipsometry measurements were carried out to extract the complex refractive index of the deposited films, which were used to study the optics of perovskite single junction and perovskite/silicon tandem solar cells. The optics was investigated by three-dimensional finite-difference time-domain simulations. Guidelines are provided on how to realize perovskite solar cells exhibiting high short-circuit current densities. Furthermore, detailed guidelines are given for realizing perovskite/silicon tandem solar cells with short-circuit current densities exceeding 20 mA cm?2 and potential energy conversion efficiencies beyond 31%.
关键词： Zinc oxide,Tandem solar cells,Perovskite solar cells,Atomic layer deposition,Optical simulations
更新于2025-09-23 15:19:57
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Tuning Plasmonic Coupling from Capacitive to Conductive Regimes via Atomic Control of Dielectric Spacing
摘要： The gap length between plasmonic nanoparticles determines the strength of the optical coupling that results in electromagnetic field enhancement for spectroscopic and other applications. Although gap plasmon resonances have been the focus of increasing research interest, experimental observations have primarily been limited to the coupling of spherical nanoparticles that may not provide clear spectral contrast of the optical response as the interaction evolves from capacitive to charge transfer with the gap size decreasing to subnanometer. Here, by taking advantage of the sharp plasmon resonances of colloidal gold nanorods coupled to gold film, we present the spectral evolution of gap plasmon resonance as the particle-film spacing varies from over 30 nm to the touching limit. We find that, the capacitive gap plasmon resonance of the coupled system red shifts and narrows continuously until it vanishes at the quantum tunneling limit, in contrast to the nonlocal and Landau damping effects that are expected to result in relative blue shifting and spectral broadening. When the spacer thickness is further decreased, high order cavity modes appear, and eventually single peak broad resonances that are characteristic of tunneling and direct contact particle-film interaction emerge. The experimental observations show that nanorods are better suited for creating cavity plasmon resonances with high quality factor, and the spectral contrast at the transition provides clarity to develop improved theoretical modeling of optical coupling at subnanometer gap lengths.
关键词： atomic layer deposition,tunneling,plasmon coupling,Particle on metal film,cavity modes,charge transfer,gold nanorods
更新于2025-09-23 15:19:57
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On-wafer fabrication of etched-mirror UV-C laser diodes with the ALD-deposited DBR
摘要： We have demonstrated an on-wafer fabrication process for AlGaN-based UV-C laser diodes (LDs) with etched mirrors and have achieved lasing for 100 ns pulsed current injection at room temperature. A combined process of dry and wet etching was employed to achieve smooth and vertical AlGaN (1(cid:2)100) facets. These etched facets were then uniformly coated with a distributed Bragg re?ector by atomic layer deposition. A remarkable reduction of the lasing threshold current density to 19:6 kA=cm2 was obtained owing to the high re?ectivity of the etched and coated mirror facets. The entire laser diode fabrication process was carried out on a whole 2-in. wafer. We propose this mirror fabrication process as a viable low-cost AlGaN-based UV-C LD production method that is also compatible with highly integrated optoelectronics based on AlN substrates.
关键词： AlGaN,distributed Bragg reflector,atomic layer deposition,etched mirrors,UV-C laser diodes
更新于2025-09-23 15:19:57
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Investigation of interface characteristics of Al2O3/Si under various O2 plasma exposure times during the deposition of Al2O3 by PA-ALD
摘要： Plasma-assisted atomic layer deposition (PA-ALD) is more suitable than thermal atomic layer deposition (ALD) for mass production because of its faster growth rate. However, controlling surface damage caused by plasma during the PA-ALD process is a key issue. In this study, the passivation characteristics of Al2O3 layers deposited by PA-ALD were investigated with various O2 plasma exposure times. The growth per cycle (GPC) during Al2O3 deposition was saturated at approximately 1.4 ?/cycle after an O2 plasma exposure time of 1.5 s, and a refractive index of Al2O3 in the range of 1.65–1.67 was obtained. As the O2 plasma exposure time increased in the Al2O3 deposition process, the passivation properties tended to deteriorate, and as the radio frequency (RF) power increased, the passivation uniformity and the thermal stability of the Al2O3 layer deteriorated. To study the Al2O3/Si interface characteristics, the capacitance-voltage (C-V) and the conductance-voltage (G-V) were measured using a mercury probe, and the ?xed charge density (Qf) and the interface trap density (Dit) were then extracted. The Qf of the Al2O3 layer deposited on a Si wafer by PA-ALD was almost una?ected, but the Dit increased with O2 plasma exposure time. In conclusion, as the O2 plasma exposure time increased during Al2O3 layer deposition by PA-ALD, the Al2O3/Si interface characteristics deteriorated because of plasma surface damage.
关键词： Plasma-assisted atomic layer deposition,Plasma damage,Silicon solar cell,Passivation,Al2O3
更新于2025-09-23 15:19:57
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Mechanism of formation of titanium dioxide crystallites in the reaction of titanium tetrachloride with magnesium hydrosilicate nanotubes
摘要： Explored herein is the first cycle of atomic layer deposition of titanium dioxide from titanium tetrachloride and water vapours on the nanotubular magnesium hydrosilicate Mg3Si2O5(OH)4, a synthetic analogue of chrysotile. The structure and morphology of the products are characterised by X-ray diffraction, infrared spectroscopy, electron microscopy and nitrogen adsorption measurements. A side reaction between chrysotile and hydrogen chloride is followed by in situ gravimetry. At 150 °C, titanium tetrachloride chemisorption is shown to produce a monomolecular layer of titanium–chlorine groups on the surface of the chrysotile nanotube preserving its original crystal structure. By contrast, at higher temperatures, 300–400 °C, the process is complicated by a secondary interaction including dehydroxylation of the substrate and a reaction of released water with titanium tetrachloride to form titanium dioxide crystallites in the free space between nanotubes. Structural transformations of chrysotile lowering its thermal stability and leading to its dehydroxylation are caused by the action of hydrogen chloride, a by-product of titanium tetrachloride chemisorption and titanium dioxide formation.
关键词： Atomic layer deposition,Reaction front advance,Titanium tetrachloride,Hydrogen chloride,Chrysotile (Mg3Si2O5(OH)4) nanotubes
更新于2025-09-23 15:19:57
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Atomic Layer Deposition of Al <sub/>2</sub> O <sub/>3</sub> Using Aluminum Tri-Isopropoxide (ATIP): A Combined Experimental and Theoretical Study
摘要： The aluminum precursor plays a crucial role in the Al2O3 ALD process. Up to date, trimethyl aluminum (TMA) is one of the most widely used precursors in experimental and theoretical studies. However, its application at industrial scale can pose safety risks since it is pyrophoric and extremely reactive with water. Aluminum alkoxides offer a promising alternative, but have received far less attention. A combined theoretical and experimental investigation is carried out on the Al2O3 ALD process using aluminum triisopropoxide (ATIP) as a prototypical example of Al-alkoxide precursors. The experimental results pointed out that the thermal ALD process using ATIP and water has a maximal growth per cycle (GPC) of 1.8 ?/cycle at temperatures of 150°C to 175°C. Based on the in-situ mass spectrometry analysis and DFT calculations, the formation of the alumina film mainly occurs during the water pulse by ligand exchange reactions between water and adsorbed precursors, while during the ATIP pulse only adsorption of ATIP and/or its dissociation occur. Design of heteroleptic precursors containing alkoxide group as basic ligand is challenging, but greatly promising for future industrial scale Al2O3 ALD.
关键词： Al2O3,DFT calculations,Atomic Layer Deposition,Aluminum Triisopropoxide,Ligand Exchange Reactions
更新于2025-09-23 15:19:57