Controlled growth of rutile TiO2 by atomic layer deposition on oxidized ruthenium

Crystalline rutile TiO₂ films were grown by atomic layer deposition on oxidized Ru electrodes using a titanium methoxide as the metal precursor and O₃ as the oxidant. A protective layer of ～0.3 nm TiO₂ grown with H₂O as the oxidant was first deposited in order to avoid etching of the Ru bottom electrode by the O₃ used for the growth of the TiO₂ (bulk) layer. Electrical evaluation of the capacitor stacks with TiO₂ as dielectric, RuO₂/Ru and Pt as the bottom and top electrodes respectively, resulted in superior characteristics of the rutile phase as compared to the anatase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Antireflection ln2O3 coatings of self‐organized TiO2 nanotube layers prepared by atomic layer deposition

We report on the uniform anti‐reflection coating of TiO₂ nanotube layers with a secondary material – indium trioxide (In₂O₃) – by atomic layer deposition (ALD). We provide for the first time the detailed evidence of the ALD deposited coating inside nanotubes for three different tube layers with aspect ratio up to ≈80, which is so far the highest aspect ratio reported for ALD‐processed self‐organized anodic TiO₂ nanotubes. We show that uniform In₂O₃coating of the nanotubes strongly influences the overall reflectance of the layers due to intrinsic properties of In₂O₃. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Low-temperature plasma enhanced atomic layer deposition of large area HfS_2 nanocrystal thin films

Hafnium disulfide(HfS2) is a promising two-dimensional material for scaling electronic devices due to its higher carrier mobility, in which the combination of two-dimensional materials with traditional semiconductors in the framework of CMOS-compatible technology is necessary. We reported on the deposition of HfS2 nanocrystals by remote plasma enhanced atomic layer deposition at low temperature using Hf(N(CH3)(C2H5))4 and H2S as the reaction precursors. Selflimiting reaction behavior was observed at the deposition temperatures ranging from 150℃ to 350℃, and the film thickness increased linearly with the growth cycles. The uniform HfS2 nanocrystal thin films were obtained with the size of nanocrystal grain up to 27 nm. It was demonstrated that higher deposition temperature could enlarge the grain size and improve the HfS2 crystallinity, while causing crystallization of the mixed HfO2 above 450℃. These results suggested that atomic layer deposition is a low-temperature route to synthesize high quality HfS2 nanocrystals for electronic device or electrochemical applications.     

Effective silicon surface passivation by atomic layer deposited Al2O3/TiO2 stacks

In this work atomic layer deposition of Al₂O₃ and TiO₂ has been used to obtain dielectric stacks for passivation of silicon surfaces. Our experiments on n‐ and p‐type silicon wafers deposited by thin Al₂O₃/TiO₂ stacks show that a considerably improved passivation is obtained compared to the Al₂O₃ single layer. For Al₂O₃ films thinner than 20 nm the emitter saturation current density decreases with increasing TiO₂ thickness. Especially the passivation of ultrathin (～5 nm) Al₂O₃ is very effectively enhanced by TiO₂ due to a decreased interface defect density as well as an increased fixed negative charge in the stacks. Hence, the thin Al₂O₃/TiO₂ stacks developed in this work can be used as a passivation coating for Si‐based solar cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Use of atomic layer deposition to improve the stability of silver substrates for in situ,high‐temperature SERS measurements

A method to stabilize silver surface‐enhanced Raman spectroscopy (SERS) substrates for in situ, high‐temperature applications is demonstrated. Silver island films grown by thermal evaporation were coated with a thin layer (from 2.5 to 5 nm) of alumina by atomic layer deposition (ALD), which protects and stabilizes the SERS‐active substrate without eliminating the Raman enhancement. The temporal stability of the alumina‐coated silver island films was examined by measurement of the Raman intensity of rhodamine 6G molecules deposited onto bare and alumina‐coated silver substrates over the course of 34 days. The coated substrates showed almost no change in SERS enhancement, while the uncoated substrates exhibited a significant decrease in Raman intensity. To demonstrate the feasibility of the alumina‐coated silver substrate as a probe of adsorbates and reactions at elevated temperatures, an in situ SERS measurement of calcium nitrate tetrahydrate on bare and alumina‐coated silver was performed at temperatures ranging from 25 to 400 °C. ALD deposition of an ultrathin alumina layer significantly improved the thermal stability of the SERS substrate, thus enabling in situ detection of the dehydration of the calcium nitrate tetrahydrate at an elevated temperature. Despite some loss of Raman signal, the coated substrate exhibited greater thermal stability compared to the uncoated substrate. These experiments show that ALD can be used to synthesize stable SERS substrates capable of measuring adsorbates and processes at high temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

Organic photovoltaics with high stability sustained for 100 days without encapsulation fabricated using atomic layer deposition

ZnO thin films with a rippled surface structure were used as electron‐collecting layers of inverted organic photovoltaics (OPVs). Using additional ultrathin layers of ZnO and TiO₂ fabricated using atomic layer deposition (ALD), not only the power‐conversion efficiency of the OPVs could be increased (up to 3.5%), but also the photovoltaic performance became nearly constant within 100 days without any additional encapsulations of the solar cells under ambient conditions.

     

Influence of annealing temperature on passivation performance of thermal atomic layer deposition Al_2O_3 films

Chemical and field-effect passivation of atomic layer deposition （ALD） Al2O3 films are investigated, mainly by corona charging measurement. The interface structure and material properties are characterized by transmission electron microscopy （TEM） and X-ray photoelectron spectroscopy （XPS）, respectively. Passivation performance is improved remarkably by annealing at temperatures of 450 ℃ and 500 ℃, while the improvement is quite weak at 600 ℃, which can be attributed to the poor quality of chemical passivation. An increase of fixed negative charge density in the films during annealing can be explained by the Al2O3/Si interface structural change. The Al–OH groups play an important role in chemical passivation, and the Al–OH concentration in an as-deposited film subsequently determines the passivation quality of that film when it is annealed, to a certain degree.     

Preparation of tantalum oxide thin films by photo-assisted atomic layer deposition

Tantalum oxide thin films were prepared by photo-assisted atomic layer deposition (Photo-ALD) in the substrate temperature range of 170–400 °C using Ta(OC₂H₅)₅ and H₂O as precursors. The constant growth rates of 0.42 and 0.47 Å per cycle were achieved for the films grown by normal ALD and Photo-ALD, respectively. The increased growth rate in Photo-ALD is probably due to the reactive surface by photon energy and faster surface reaction. In Photo-ALD, however, the constant growth rate started at lower temperature of 30 °C and one cycle time shortened up to 5.7 s than that of normal ALD. The films grown by normal ALD and Photo-ALD were amorphous and very smooth (0.21–0.35 nm) as examined by X-ray diffractometer and atomic force microscopy, respectively. Also, the refractive index was found to be 2.12–2.16 at the substrate temperature of 190–300 °C, similar to that of the film grown by normal ALD. However, the remarkably low leakage current density of 0.6×10⁻⁶ A/cm² to 1×10⁻⁶ A/cm² at applied field of 1 MV/cm is several order of magnitude smaller than that of normal ALD, probably due to the presence of reactive atom species.     

TiO2/Al2O3薄膜的原子层沉积和光学性能分析

采用原子层沉积技术在熔石英和BK7玻璃基片上镀制了TiO2/Al2O3薄膜,沉积温度分别为110℃和280℃。利用X射线粉末衍射仪对膜层微观结构进行了分析研究,并在激光损伤平台上进行了抗激光损伤阈值测量。采用Nomarski微分干涉差显微镜和原子力显微镜对激光损伤后的形貌进行了观察分析。结果表明,采用原子层沉积技术镀制的TiO2/Al2O3增透膜的厚度均匀性较好,Φ50 mm样品的膜层厚度均匀性优于99%;光谱增透效果显著,在1 064 nm处的透过率〉99.8%;在熔石英和BK7基片上,TiO2/Al2O3薄膜在110℃时的激光损伤阈值分别为（6.73±0.47）J/cm2和（6.5±0.46）J/cm2,明显高于在280℃时的损伤阈值。     

Asymmetry in electrical properties of Al‐doped TiO2 film with respect to bias voltage

The energy diagram of RuO₂/Al‐doped TiO₂/RuO₂ structures was estimated from the capacitance–voltage and leakage current density–voltage curves. The Al‐doping profile in TiO₂ film was varied by changing position of the atomic layer deposition cycle of Al₂O₃ during the atomic layer deposition of 9 nm‐thick TiO₂ film. The interface between the TiO₂ film and the RuO₂ electrode containing Al‐doping layer showed a higher Schottky barrier by 0.1 eV compared with the opposite interface without the doping layer. The evolution of various leakage current profiles upon increasing the bias with opposite polarity could be well explained by the asymmetric Schottky barrier. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Stacked and nanolaminated Al2O3/TiO2 for surface passivation and encapsulation of silicon

Silicon solar cells passivated with Al₂O₃ require a capping layer that protects the passivation layer from humidity because of sensitivity of Al₂O₃ to moisture. Al₂O₃/TiO₂ stacks obtained by atomic layer deposition have been known to provide a high level of passivation layers because of their excellent field‐effect passivation. In this work, degradation of this Al₂O₃/TiO₂ stack, when exposed to humidity, is examined, and an attempt is made for a humidity‐resistant encapsulation layer by adding Al₂O₃/TiO₂ nanolaminates that can be deposited in‐situ without breaking vacuum. Placing the nanolaminate on top of the TiO₂ and Al₂O₃ stack is found to lead to almost no degradation even after 10 days of humidity exposure. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Low‐temperature atomic layer deposition of MoOx for silicon heterojunction solar cells

The preparation of high‐quality molybdenum oxide (MoO_x) is demonstrated by plasma‐enhanced atomic layer deposition (ALD) at substrate temperatures down to 50 °C. The films are amorphous, slightly substoichiometric with respect to MoO₃, and free of other elements apart from hydrogen (&11 at%). The films have a high transparency in the visible region and their compatibility with a‐Si:H passivation schemes is demonstrated. It is discussed that these aspects, in conjunction with the low processing temperature and the ability to deposit very thin conformal films, make this ALD process promising for the future application of MoO_x in hole‐selective contacts for silicon heterojunction solar cells. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

等离子增强原子层沉积低温生长AlN薄膜

采用等离子增强原子层沉积技术在单晶硅基体上成功制备了AlN晶态薄膜, 利用椭圆偏振仪、原子力显微镜、小角掠射X射线衍射仪、高分辨透射电子显微镜、 X射线光电子能谱仪对样品的生长速率、表面形貌、晶体结构、薄膜成分进行了表征和分析, 结果表明, 采用等离子增强原子层沉积制备AlN晶态薄膜的最低温度为200 ℃, 薄膜表面平整光滑, 具有六方纤锌矿结构与(100)择优取向, Al_2p与N_1S的特征峰分别为74.1 eV与397.0 eV, 薄膜中Al元素与N元素以Al-N键相结合, 且成分均匀性良好. 关键词： 氮化铝 等离子增强原子层沉积 低温生长 晶态薄膜     

Characterization and application in XRF of HfO_2-coated glass monocapillary based on atomic layer deposition

Coating a glass monocapillary x-ray optics with high-density film is a promising way to improve transmission characteristics. For a long time, it has been a challenge to coat a high-density film in the inside of monocapillary with an extremely high length-to-diameter ratio. In this work, Hf O2 film is deposited on the inner wall of a tapered glass monocapillary with length 9.9 cm, entrance diameter 596.4 μm, and exit diameter 402.3 μm by atomic layer deposition. The coated and uncoated monocapillaries are studied by the transmission process of x-rays with energy from 5 ke V to 100 ke V and the x-ray fluorescence(XRF) spectra of a Mo sample are detected. Improved transmission characteristics have been obtained for the Hf O_2-coated monocapillary. The energy upper limit of focused x-rays increases from 18.1 ke V to 33.0 ke V and the ‘penetration halo' is suppressed to some extent. The XRF spectrum presents two stronger peaks at ～ 17.4 ke V and～ 19.6 ke V which are considered as the characteristic x-rays of Mo K_α and Mo K_β. These results reveal that more higher energy x-rays from the W x-ray tube are totally reflected on the inner wall of the Hf O_2-coated glass monocapillary due to the increase of total reflection critical angle. This work is significant for more applications of monocapillary in higher energy x-ray field.     

Characteristics and properties of metal aluminum thin films prepared by electron cyclotron resonance plasma-assisted atomic layer deposition technology

Metal aluminum (Al) thin films are prepared by 2450 MHz electron cyclotron resonance plasma-assisted atomic layer deposition on glass and p-Si substrates using trimethylaluminum as the precursor and hydrogen as the reductive gas. We focus our attention on the plasma source for the thin-film preparation and annealing of the as-deposited films relative to the surface square resistivity. The square resistivity of as-deposited Al films is greatly reduced after annealing and almost reaches the value of bulk metal. Through chemical and structural analysis, we conclude that the square resistivity is determined by neither the contaminant concentration nor the surface morphology, but by both the crystallinity and crystal size in this process.     

Double‐layer channel structure based ZnO thin‐film transistor grown by atomic layer deposition

A double channel structure has been used by depositing a thin amorphous‐AlZnO (a‐AZO) layer grown by atomic layer deposition between a ZnO channel and a gate dielectric to enhance the electrical stability. The effect of the a‐AZO layer on the electrical stability of a‐AZO/ZnO thin‐film transistors (TFTs) has been investigated under positive gate bias and temperature stress test. The use of the a‐AZO layer with 5 nm thickness resulted in enhanced subthreshold swing and decreased V_th shift under positive gate bias/temperature stress. In addition, the falling rate of the oxide TFT using a‐AZO/ ZnO double channel had a larger value (0.35 eV/V) than that of pure ZnO TFT (0.24 eV/V). These results suggest that the interface trap density between dielectric and channel was reduced by inserting a‐AZO layer at the interface between the channel and the gate insulator, compared with pure ZnO channel. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impact of substrate temperature and film thickness on the interfacial evolution during atomic layer deposition of HfO2 on InP

The effects of both the deposition temperature and the HfO₂ film thickness on the interfacial layer (IL) evolution were studied when tetrakis(ethylmethylamino)hafnium and H₂O based atomic layer deposition (ALD) was performed on InP substrates. While the self‐cleaning effect resulted in an IL‐free structure after formation of ～2 nm thick HfO₂ at 200 °C and 250 °C, substantial IL growth occurred at 300 °C, probably due to simultaneous InP oxidation. Following further growth to ～8 nm at 300 °C, the IL was almost removed and, in particular, a significant In incorporation into the HfO₂ film was observed, which was attributed to IL decomposition and subsequent out‐diffusion of the constituent elements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ternary semiconductor compounds CuInS2 (CIS) thin films synthesized by electrochemical atomic layer deposition (EC-ALD)

In this paper the formation and characterization of the I-III-VI₂ semiconductor compound CuInS₂ (CIS) on gold substrate at room temperature by electrochemical atomic layer deposition (EC-ALD) method are reported. Optimum deposition potentials for each element are determined using cyclic voltammetry (CV) technique and Amperometric I-t method is used to prepare the semiconductor compound. These thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FT-IR). XRD results indicate that the CIS thin films have a (1 1 2) preferred orientation. The XPS analyses of the films reveal that Cu, In and S are present in an atomic ratio of approximately 1:1:2. And their semiconductor band gaps are found to be 1.50 eV by FT-IR.     

Plasmonic tuning of aluminum doped zinc oxide nanostructures by atomic layer deposition

Currently there is a strong interest in plasmonic materials operating in the near‐infrared (NIR), however, conventional metals such as gold and silver possess high optical losses in this region. In this work we demonstrate localized surface plasmon resonances (LSPRs) with low loss in the NIR region by utilizing atomic layer deposition to deposit thin films of aluminium doped zinc oxide onto silicon nanopillars created via nanopshere lithography. The deposited films have excellent conformality and the LSPRs can be tuned from the mid‐infrared to the NIR by controlling the doping concentration, deposition temperature and nanostructure morphology. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Structural study of TiO2 thin films by micro-Raman spectroscopy

The Raman spectroscopy method was used for structural characterization of TiO₂ thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125–425 °C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 °C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 °C and retained this phase even after annealing at 900 °C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 °C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.