P-type ZnO thin films prepared by in situ oxidation of DC sputtered Zn3N2:Ga

The feasibility of a new fabrication route for N and Ga codoped p-type ZnO thin films on glass substrates, consisting of DC sputtering deposition of Zn3N2:Ga precursors followed by in situ oxidation in high purity oxygen, has been studied. The effects of oxidation temperature on the structural, optical and electrical properties of the samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical transmittance and Hall effect measurements. The results were compared to a control film without Ga. XRD analyses revealed that the Zn3N2 films entirely transformed into ZnO films after annealing Zn3N2 films in oxygen over 500 ℃ for 2 h. Hall effect measurements confirmed p-type conduction in N and Ga codoped ZnO films with a low resistivity of 19.8 Ω·cm, a high hole concentration of 4.6 × 1018 cm-3 and a Hall mobility of 0.7 cm2/(V·s). These results demonstrate a promising approach to fabricate low resistivity p-type ZnO with high hole concentration.     

Optoelectronic properties of solution synthesis of carbon nanotube/ZnO:Al:N nanocomposite and its potential as a photocatalyst

A novel multiwalled carbon nanotubes/aluminum–nitrogen co-doped ZnO (MWCNT/ZnO:Al:N) nanocomposite film was synthesized by a sol–gel deposition method and used for the photodegradation of organic dye under UV light illumination. The MWCNT/ZnO:Al:N composite film was extensively characterized through scanning electron microscope (SEM), Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence measurements (PL) and UV–vis spectroscopy. Photocatalytic measurements reveal that the addition of MWCNT enhances photocatalytic degradation of MB by providing conduction path for electron transfer and reactive oxygen groups.     

The effects of carrier gas and substrate temperature on ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on glass substrates in the temperature range of 350–470 °C under an atmosphere of compressed air or nitrogen (N₂) by using ultrasonic spray pyrolysis technique. Structural, electrical and optical properties of the ZnO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical two-probe and optical transmittance measurements. The ZnO films deposited in the range of 350–430 °C were polycrystalline with the wurtzite hexagonal structure having preferred orientation depending on the substrate temperature. The ZnO films deposited below 400 °C had a preferred (100) orientation while those deposited above 400 °C mostly had a preferred (002) orientation. The resistivity values of ZnO films depended on the types of carrier gas. The ZnO thin films deposited under N₂ atmosphere in the range of 370–410 °C showed dense surface morphologies and resistivity values of 0.6–1.1 Ω-cm, a few orders of magnitude lower than those deposited under compressed air. Hydrogen substition in ZnO possibly contributed to decreasing resistivity in ZnO thin films deposited under N₂ gas. The Hall measurements showed that the behavior of ZnO films deposited at 410 °C under the N₂ atmosphere was n-type with a carrier density of 8.9–9.2×10¹⁶ cm^-3 and mobility of ～70 cm²/Vs. ZnO thin films showed transmission values at 550 nm wavelength in a range of 70–80%. The values of band gaps extrapolated from the transmission results showed bandgap shrinkage in an order of milli electron volts in ZnO films deposited under N₂ compared to those deposited under compressed air. The calculation showed that the bandgap reduction was possibly a result of carrier–carrier interactions.     

TaN-TiN binary alloys and superlattices as diffusion barriers for copper interconnects

Binary alloys and superlattices of TaN-TiN thin films were grown on Si(100) substrates with a TiN buffer layer using pulsed laser deposition. A special target assembly was used to manipulate the concentrations of these binary component films. The 60% TaN resulted in a TaN (3 nm)/TiN (2 nm) superlattice, while 30% and 70% TaN generated uniform Ta_xTi_1−xN alloys. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) confirmed the single-crystalline nature of these films. Four-point probe resistivity measurements suggest that these alloy and superlattice films have a lower resistivity than pure single-crystalline TaN films. The Cu-diffusion characteristic studies showed that these materials would have the potential as high-temperature diffusion barriers for Cu in ultra-large-scale integration technology.     

Sol–gel production of ZnO:CO: Effect of post-annealing temperature on its optoelectronic properties

Thin films of ZnO:Co were prepared by a sol–gel process. The microstructure and optoelectronic properties as a function of sintering temperature were studied extensively by optoelectronic characterizations. It was observed from the scanning electron microscopy images that the introduction of Co eliminated the commonly observed wrinkle effect in sol-gel derived films. Structurally, XRD measurements revealed that the derived film were c-axis oriented that enhances as sintering temperature increases upto 500 °C. Electrical measurements confirm that the deposited ZnO:Co thin film is n-type with decreasing resistivity as sintering temperature increases. Optical measurements revealed that the derived films exhibit good transmittance ~82% with a wide band gap ~4.01 eV.     

Synthesis of ZnO: Ge nanocomposite thin films by plasma gas condensation

In this work, we introduce a new method for the synthesis of Ge nanoparticles embedded ZnO thin films that are considered to be a potential candidate for photovoltaic applications. As opposed to current techniques, for the independent preparation of Ge nanoparticles, we propose using Cluster Deposition Source (CDS), which utilizes gas condensation of sputtered Ge atoms. For the synthesis of ZnO thin film host material conventional sputtering technique is employed. In the proposed technique independently synthesized Ge nanoparticles and ZnO thin films are combined into a composite structure on (100) oriented Si substrates. X-ray diffraction (XRD) patterns of the samples have revealed that Ge nanoparticles preferentially settle on (113) planes on top of the (002) oriented ZnO layer. It is realized that Ge nanoparticles with sizes ranging from 16 nm to 20 nm could be embedded into a well-defined ZnO matrix. In fact, transmission electron microscopy (TEM) studies performed on Ge nanoparticles captured on a Cu grids placed just above the substrate during deposition for about 60 s have manifested that Ge nanoparticles reach to ZnO matrix as clusters composed of particles with sizes of about 7–8 nm and then eventually grow larger due to substrate heating implemented during capping layer deposition. Optical absorption measurements have revealed that Ge nanoparticle inclusion lead to an additional absorption edge at about 2.75 eV along with 3.17 eV edge resulting from ZnO host.     

Thickness dependent physical properties of chemically deposited nanocrystalline MgSe thin films deposited at room temperature by solution growth method

Chemical bath deposition method has been employed to deposit nanocrystalline magnesium selenide thin films of thickness 104–292 nm onto glass substrates at room temperature. The deposition bath consists of magnesium chloride, triethanolamine (TEA) and selenium dioxide. The as deposited films were characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), optical absorption, electrical resistivity and thermo-emf measurements. The X-ray diffraction (XRD) studies revealed that the crystallinity of the magnesium selenide thin film increases with thickness. SEM studies reveal that MgSe films exhibit uniform distribution of round shaped grains over the entire substrate surface.The optical band-gap and electrical resistivity of MgSe film decrease as the film thickness increases. Such type of dependence is attributed to the quantum size effect that is observed in nanocrystalline semiconductors.The thermo-emf measurement confirms its p-type conductivity.     

Composite structure of ZnO films coated with reduced graphene oxide: structural,electrical and electrochemical properties

ZnO films coated with reduced graphene oxide (RGO-ZnO) were prepared by a simple chemical approach.The graphene oxide (GO) films transferred onto ZnO films by spin coating were reduced to RGO films by two steps (exposed to hydrazine vapor for 12 h and annealed at 600 ℃).The crystal structures,electrical and photoluminescence properties of RGO-ZnO films on quartz substrates were systematically studied.The SEM images illustrated that RGO layers have successfully been coated on the ZnO films very tightly.The PL properties of RGO-ZnO were studied.PL spectra show two sharp peaks at 390 nm and a broad visible emission around 490 nm.The resistivity of RGO-ZnO films was measured by a Hall measurement system,RGO as nanofiller considerably decrease the resistivity of ZnO films.An electrode was fabricated,using RGO-ZnO films deposited on Si substrate as active materials,for super capacitor application.By comparison of different results,we conclude that the RGO-ZnO composite material couples possess the properties of super capacitor.     

Effect of deposition power in fabrication of highly efficient CdS:O/CdTe thin film solar cell by the magnetron sputtering technique

Polycrystalline II–VI semiconductor materials such as oxygenated CdS have a wide and tunable band gap (≥2.5 eV) which plays an important role in increasing the light absorption capacity of CdTe absorber. In this study, the ultra-thin CdS:O and CdTe films were deposited by the sputtering technique and the optimum condition of deposition power is investigated. The prepared ultra-thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), UV–vis spectrometry, Hall Effect and current–voltage measurements techniques. The complete cell was then fabricated by the sputtering technique with a novel configuration of ‘glass/FTO/ZnO:Sn/CdS:O/CdTe/C:Cu/Ag’. To avoid the pin hole effect, the high resistive ZnO:Sn layer was deposited as a buffer layer in between the FTO and CdS:O films. It has been observed that the cell performance parameters are found to be varied with deposition power of CdO:S films and an overall conversion efficiency of 10.27% was achieved.     

The Influence of Film Thickness on the Transparency and Conductivity of Al-Doped ZnO Thin Films Fabricated by Ion-Beam Sputtering

To evaluate the influence of film thickness on the structural, electrical, and optical properties of Al-doped ZnO (AZO) films, a set of polycrystalline AZO samples with different thickness were deposited on glass substrates by ion-beam sputtering deposition (IBSD). X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive x-ray spectroscopy (EDS), four-point probe measurements, and spectrophotometry were used to characterize the films. XRD showed that all the AZO films had preferred c-axis orientation. The ZnO (110) peak appeared, and the intensity increased, with increasing thickness. All the samples exhibited compressive intrinsic stresses. AFM showed that the grain size along with the root-mean-square (RMS) roughness increased with increasing thickness. The decrease of resistivity is due to the corresponding change in grain size, surface morphology, and chemical composition. The average optical transmittance of the AZO films was over 80%, and a sharp fundamental absorption edge with red-shifting was observed in the visible region. The optical band gap decreased from 3.95 eV to 3.80 eV when the AZO film thickness increased from 100 nm to 500 nm.     

ZnO films deposited on GaAs substrates with a SiO2 thin buffer layer

Sputter deposition of ZnO films on GaAs substrates has been investigated. ZnO films were radio frequency (rf)-magnetron sputter deposited on GaAs substrates with or without SiO₂ thin buffer layers. Deposition parameters such as rf power, substrate-target distance, and gas composition/pressure were optimized to obtain highly c-axis oriented and highly resistive films. Deposited films were characterized by x-ray diffraction, scanning electron microscopy (SEM), capacitance, and resistivity measurements. Thermal stability of sputter-deposited ZnO films (0.5–2.0 μm thick) was tested with a post-deposition heat treatment at 430°C for 10 min, which is similar to a standard ohmic contact alloying condition for GaAs. The ZnO/SiO₂/GaAs films tolerated the heat treatment well while the ZnO/GaAs films disintegrated. The resistivity (10¹¹ Ω-cm) of the ZnO films on SiO₂-buffered GaAs substrates remained high during the heat treatment. The post-deposition anneal treatment also enhances c-axis orientation of the ZnO films dramatically and relieves intrinsic stress almost completely. These improvements are attributed to a reduction of grain boundaries and voids with the anneal treatment as supported by SEM and x-ray diffraction measurement results.     

Visible light active TiO2–ZnO composite films by cerium and fluorine codoping for photocatalytic decontamination

The visible light active Ce/F codoped TiO₂–ZnO composite films with a bad gap of 1.82 eV were successfully prepared though a simple sol–gel method. Experimental results indicated that the composite films showed excellent photocatalytic performance towards photocatalytic oxidation of organic pollutants including formaldehyde, acid naphthol red (ANR) and methyl green (MG). The catalysts were characterized by photoluminescence (PL) spectra, UV–vis diffraction reflectance absorption spectra (DRS), X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy (EDS), and N₂ adsorption/desorption isotherms. The DRS and PL spectra results showed that multi-modification not only induced strong visible light absorption but also reduced the recombination rate of electron–hole pairs. The DTA-TG and XRD results indicated that the crystal type of the TiO₂-based catalyst was mostly stabilized in anatase. The FE-SEM and BET surface area results revealed that the nanocrystalline Ce/F codoped TiO₂–ZnO composite samples with the larger specific surface area were composed of smaller nanoparticles compared to pure TiO₂. The mechanism of the enhanced photocatalytic activity was discussed in this study.     

Investigation of the blue–green emission and UV photosensitivity of Cu-doped ZnO films

Cu-doped zinc oxide (ZnO:Cu) films were deposited on p-Si (100) substrates using radio-frequency reactive magnetron sputtering. The structure and optical properties of the films were characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. XRD and SEM results revealed that ZnO:Cu film had a better preferential orientation along the c-axis compared with pure ZnO film. The chemical state of copper and oxygen in ZnO:Cu films was investigated by XPS. The results suggest that the Cu ion has a mixed univalent and bivalent state. The integrated Cu²⁺/Cu⁺ intensity ratio increased with the O₂ partial pressure. Photoluminescence measurements at room temperature revealed a double peak in the blue regions and a green emission peak. The close relationship between the valence state of Cu ions and the blue–green emission is discussed in detail. A higher photocurrent was observed for ZnO:Cu films under UV illumination. UV photodetectors based on ZnO:Cu films have high sensitivity and fast response and recovery times. Under periodic UV illumination at 380 nm the ZnO:Cu films showed stable photocurrent growth and decay, so the films are potential candidate materials for UV photodetectors.     

Low-temperature metal-organic chemical vapor deposition (LTMOCVD) of device-quality copper films for microelectronic applications

Copper films for potential use in multilevel metallization in ULSIC’s were produced by low temperature (250–350° C) metal-organic chemical vapor deposition (LTMOCVD) in atmospheres of pure H₂ or mixture Ar/H₂ from the β-diketonate precursor bis(1,1,1,5,5,5-hexafluoroacetylacetonato) copper(ll), Cu(hfa)₂. The films were analyzed by x-ray diffraction (XRD), Rutherford backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDXS). The results of these studies showed that the films were uniform, continuous, adherent and highly pure—oxygen and carbon contents were below the detection limits of AES. Four point resistivity measurements showed that the copper films had very low resistivity, as low as 1.9 μΩcm for the films deposited in pure hydrogen atmosphere. Our preliminary results seem to indicate that LTMOCVD is a very attractive technique for copper multilevel metallizations.     

Characterization of ZnO and ZnO:Al films deposited by MOCVD on oriented and amorphous substrates

Zinc oxide (ZnO) and ZnO:Al-doped films were deposited by metal organic chemical vapour deposition (MOCVD) using the Zn(tta)₂·tmeda (H-tta=2-thenoyltrifluoroacetone, tmeda=N,N,N′,N′-tetramethylethylendiamine) and Al(acac)₃ (H-acac=acetylacetone) precursors on different substrates. The deposited layers were characterised by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). Film structure is strongly dependent on the substrate nature and deposition conditions. AFM and XRD measurements show a good film texture and a preferential orientation along the c-axis. The Al concentration of ZnO:Al film has been confirmed by energy dispersive X-ray (EDX) analysis. Optical transparency of these ZnO layers has been studied in order to evaluate their applications as a transparent conducting oxide (TCO) material.     

The Effect of Substrate Material and Postannealing on the Photoluminescence and Piezo Properties of DC-Sputtered ZnO

Abstact Zinc oxide (ZnO) thin films were deposited on various substrates by DC sputtering deposition. Thermal annealing was performed at up to 1,200°C in N₂ for 30 min. The effect was investigated using x-ray diffraction (XRD), photoluminescence (PL) spectra, scanning electron microscopy (SEM), and piezoresponse force microscopy (PFM). The influence on PL response depends both on substrate material and annealing temperature. The PFM images reveal that the ZnO films have inversion domains. While annealing improves the piezoresponse, the inversion domains still persist. The cross-sectional analysis of the inversion domains shows domain boundary widths of approximately 1.5 nm. (Received ...; accepted ...)     

Pulsed Laser Deposition and Electrochemical Characterization of LiFePO4–Ag Composite Thin Films

A simple approach is proposed to enhance the electrical conductivity of olivine‐structured LiFePO₄ thin films by uniformly dispersing small fractions of highly conductive silver (ca. 1.37 wt %) throughout the LiFePO₄ film. In this approach, a highly densified (>85 %) LiFePO₄–Ag target was first fabricated by coating conductive silver nanoparticles onto the surfaces of hydrothermally synthesized LiFePO₄ ultrafine particles by a soft chemical route. Pulsed laser deposition (PLD) was then employed to deposit LiFePO₄–Ag composite thin films on the Si/SiO₂/Ti/Pt substrates. The PLD experimental parameters were optimized to obtain well‐crystallized and olivine‐phase pure LiFePO₄–Ag composite thin films with smooth surfaces and homogeneous thicknesses. X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectrometry (Raman), X‐ray photoelectron spectroscopy (XPS), DC conductivity measurements, cyclic voltammetry(CV), as well as galvanostatic measurements were employed to characterize the as‐obtained LiFePO₄–Ag composite films. The results revealed that after silver incorporation, the olivine LiFePO₄ film cathode shows a superior electrochemical performance with a good combination of moderate specific capacity, stable cycling, and most importantly, a remarkable tolerance against high rates and over‐charging and ‐discharging.     

在柔性衬底上制备透明导电薄膜ZnO:Zr(英文)

采用射频磁控溅射法在室温柔性衬底PET上制备了掺锆氧化锌(ZZO)透明导电薄膜.利用不同方法提高了ZZO薄膜的电阻率而未使其可见光透过率降低.X射线衍射(XRD)和扫描电子显微镜(SEM)表明,ZZO薄膜为六角纤锌矿结构的多晶薄膜.在有机衬底和玻璃衬底上制备ZZO薄膜的择优取向不同,前者为(100)晶面,而后者为(002)晶面.在有ZnO缓冲层的PET衬底上制备的ZZO薄膜电阻率比直接生长在玻璃衬底样品上的小.通过优化参数,在PET衬底上制备出了最小电阻率为1.7×10-3Ω·cm、可见光透过率超过93%的ZZO薄膜.实验表明,镀膜之前在柔性衬底上沉积ZnO缓冲层能有效地提高ZZO薄膜的质量.     

缓冲层厚度对透明导电薄膜ZnO:Zr性能的影响

利用直流磁控溅射法在有ZnO:Zr缓冲层的水冷玻璃衬底上成功制备出了ZnO:Zr透明导电薄膜,缓冲层的厚度介于35～208 nm.利用XRD、SEM、四探针测试仪和紫外-可见分光光度计研究ZnO:Zr薄膜的结构、形貌、电光性能.结果表明,薄膜的颗粒尺寸和电阻率对缓冲层厚度具有较强的依赖性.当缓冲层厚度从35 nm增加到103 nm时,薄膜的颗粒尺寸增大,电阻率减小.而当缓冲层厚度从103 nm增加到208 nm时,薄膜的颗粒尺寸减小,电阻率增大.当缓冲厚度为103 nm时,薄膜的电阻率最小为2.96×10-3 Ω·cm,远小于没有缓冲层时的12.9×10-3 Ω·cm.实验结果表明,在沉积薄膜之前先沉积一层适当的缓冲层是提高ZnO:Zr薄膜质量的一种有效方法.     

Effect of seed layers (Al,Ti) on optical and morphology of Fe-doped ZnO thin film nanowires grown on Si substrate via electron beam evaporation

The effects of Al and Ti seed layers were studied for undoped and Fe-doped ZnO thin films deposited on n-type Si substrates by electron beam (e-beam) evaporation. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The films grown on seed layers showed wurtzite hexagonal crystal nanorod and nanowire structures. A higher angle phase shift was observed in the doped thin films compared to the pristine ZnO films. Microstructural studies confirmed the growth of nanorods and nanowires with average widths of ~32 nm and ~8–29 nm, respectively. The nanostructures were denser and more crystalline on the Al seed layer than on the Ti seed layer for the doped thin films. However, in the undoped thin films, a more crystalline nature was observed on the Ti seeded layer than the Al seeded layer.