In the present investigation we show the effect of Al doping on the length, size, shape, morphology, and sensing property of ZnO nanorods. Effect of Al doping ultimately leads to tuning of electrical and optical properties of ZnO nanorods. Undoped and Al-doped well aligned ZnO nanorods are grown on sputtered ZnO/SiO2/Si (100) pre-grown seed layer substrates by hydrothermal method. The molar ratio of dopant (aluminium nitrate) in the solution, [Al/Zn], is varied from 0.1 % to 3 %. To extract structural and microstructural information we employ field emission scanning electron microscopy and X-ray diffraction techniques. The prepared ZnO nanorods show preferred orientation of ZnO <0001> and are well aligned vertically. The effects of Al doping on the electrical and optical properties are observed by Hall measurement and photoluminescence spectroscopy, respectively, at room temperature. We observe that the diameter and resistivity of the nanorods reach their lowest levels, the carrier concentration becomes high, and emission peak tends to approach the band edge emission of ZnO around 0.5% of Al doping. Sensing behavior of the grown ZnO nanorod samples is tested for H2 gas. The 0.5 mol% Al-doped sample shows highest sensitivity values of ~ 60 % at 250 ˚C and ~ 50 % at 220 ˚C.

ZnO micro/nanocrystals at large scale were synthesized through the thermal evaporation of Al-Zn mixtures under air atmosphere. The effect of synthetic temperature and time on the morphology of the micro/nanocrystals was examined. It was found that the temperature and time affected the morphology of the ZnO crystals. At temperatures below 900 oC, no crystals were synthesized. At a temperature of 1000 oC, ZnO crystals with a rod shape were synthesized. With an increase in temperature from 1000 oC to 1100 oC, the morphology of the crystals changed from rod shape to wire and granular shapes. As the time increased from 2 h to 3 h at 1000 oC, tetrapod-shaped ZnO crystals started to form. XRD patterns showed that the ZnO crystals had a hexagonal wurtzite structure. EDX analysis revealed that the ZnO crystals had high purity. It is believed that the ZnO nanowires were grown via a vapor-solid mechanism because no catalyst particles were observed at the tips of the micro/nanocrystals in the SEM images.

The effect of oxygen pressure on the synthesis of ZnO nanowires by means of melt-oxidation of an Al-Zn mixture was investigated. The samples were prepared in oxygen ambient for 1 h at 1,000˚C under oxygen pressure ranging from 0.5 to 100 Torr. ZnO nanowires were formed at oxygen pressures lower than 10 Torr. As the oxygen pressure increased from 0.5 to 10 Torr, the width of the nanowires increased, but their length decreased. The ZnO nanowires had a needle shape, which became gradually thinner toward the tip. X-ray diffraction patterns showed that the nanowires had a hexagonal wurtzite structure. However, ZnO nanowires were not observed when the oxygen pressure increased from 10 Torr to 100 Torr. In roomtemperature cathodeluminescence spectra of the ZnO nanowires, the intensity of ultra-violet emission at 380 nm increased with decreasing oxygen pressure, which indicated that the lower the oxygen pressure, the better the crystallinity of the ZnO nanowires.

Al-doped ZnO(AZO) thin films were synthesized using atomid layer deposition(ALD), which acurately controlledthe uniform film thickness of the AZO thin films. To investigate the electrical and optical properites of the AZO thin films,AZO films using ALD was controlled to be three different thicknesses (50nm, 100nm, and 150nm). The structural, chemical,electrical, and optical properties of the AZO thin films were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy,field-emssion scanning electron microscopy, atomic force microscopy, Hall measurement system, and UV-Visspectrophotometry. As the thickness of the AZO thin films increased, the crystallinity of the AZO thin films gradually increased,and the surface morphology of the AZO thin films were transformed from a porous structure to a dense structure. The averagesurface roughnesses of the samples using atomic force microscopy were ~3.01nm, ~2.89nm, and ~2.44nm, respectively. Asthe thickness of the AZO filmsincreased, the surface roughness decreased gradually. These results affect the electrical and opticalproperties of AZO thin films. Therefore, the thickest AZO thin films with 150nm exhibited excellent resistivity (~7.00×10−4Ω·cm), high transmittance (~83.2%), and the best FOM (5.71×10−3Ω−1). AZO thin films fabricated using ALD may be usedas a promising cadidate of TCO materials for optoelectronic applications.

Silicon heterojunction solar cells have been studied by many research groups. In this work, silicon heterojunction solar cells having a simple structure of Ag/ZnO:Al/n type a-Si:H/p type c-Si/Al were fabricated. Samples were fabricated to investigate the effect of transparent conductive oxide growth conditions on the interface between ZnO:Al layer and a-Si:H layer. One sample was deposited by ZnO:Al at low working pressure. The other sample was deposited by ZnO:Al at alternating high working pressure and low working pressure. Electrical properties and chemical properties were investigated by light I-V characteristics and AES method, respectively. The light I-V characteristics showed better efficiency on sample deposited by ZnO:Al by alternating high working pressure and low working pressure. Atomic concentrations and relative oxidation states of Si, O, and Zn were analyzed by AES method. For poor efficiency samples, Si was diffused into ZnO:Al layer and O was diffused at the interface of ZnO:Al and Si. Differentiated O KLL spectra, Zn LMM spectra, and Si KLL spectra were used for interface reaction and oxidation state. According to AES spectra, sample deposited by high working pressure was effective at reducing the interface reaction and the Si diffusion. Consequently, the efficiency was improved by suppressing the SiOx formation at the interface.

La doped CuO-ZnO-Al2O3 powders are prepared by sol-gel method with aluminum isopropoxide and primarydistilled water as precursor and solvent. In this synthesized process, the obtained metal oxides caused the precursor such ascopper (II) nitrate hydrate and zinc (II) nitrate hexahydrate were added. To improve the surface areas of La doped CuO-ZnO-Al2O3 powder, sorbitan (z)-mono-9-octadecenoate (Span 80) was added. The synthesized powder was calcined at varioustemperatures. The dopant was found to affect the surface area and particle size of the mixed oxide, in conjunction with thecalcined temperature. The structural analysis and textual properties of the synthesized powder were measured with an X-rayDiffractometer (XRD), a Field-Emission Scanning Electron Microscope (FE-SEM), Bruner-Emmett-Teller surface analysis (BET),Thermogravimetry-Differential Thermal analysis (TG/DTA), 27Al solid state Nuclear Magnetic Resonance (NMR) and transforminfrared microspectroscopy (FT-IR). An increase of surface area with Span 80 was observed on La doped CuO-ZnO-Al2O3powders from 25m2/g to 41m2/g.

Abstract In this study characteristics of Al-doped ZnO thin film by HIPIMS (High power impulse sputtering) are discussed. Deposition speed of HIPIMS with conventional balanced magnetic field is measured at about 3 nm/min, which is 30% of that of conventional RF sputtering process with the same working pressure. To generate additional magnetic flux and increase sputtering speed, electromagnetic coil is mounted at the back side of target. Under unbalanced magnetic flux from electromagnet with 1.5A coil current, deposition speed of AZO thin film is increased from 3 nm/min to 4.4 nm/min. This new value originates from the decline of particles near target surface due to the local magnetic flux going toward substrate from electromagnet. AZO film sputtered by HIPIMS process shows very smooth and dense film surface for which surface roughness is measured from 0.4 nm to 1 nm. There are no voids or defects in morphology of AZO films with varying of magnetic field. When coil current is increased from 0A to 1A, transmittance of AZO thin film decreases from 80% to 77%. Specific resistance is measured at about 2.9×10-2Ω·cm. AZO film shows C-axis oriented structure and its grain size is calculated at about 5.3 nm, which is lower than grain size in conventional sputtering.

Changes in surface morphology and roughness of dc sputtered ZnO:Al/Ag back reflectors by varying the deposition temperature and their influence on the performance of flexible silicon thin film solar cells were systematically investigated. By increasing the deposition temperature from 25˚C to 500˚C, the grain size of Ag thin films increased from 100 nm to 1000 nm and the grain size distribution became irregular, which resulted in an increment of surface roughness from 6.6 nm to 46.6 nm. Even after the 100 nm thick ZnO:Al film deposition, the surface morphology and roughness of the ZnO:Al/Ag double structured back reflectors were the same as those of the Ag layers, meaning that the ZnO:Al films were deposited conformally on the Ag films without unnecessary changes in the surfacefeatures. The diffused reflectance of the back reflectors improved significantly with the increasing grain size and surface roughness of the Ag films, and in particular, an enhanced diffused reflectance in the long wavelength over 800 nm was observed in the Ag back reflectors deposited at 500˚C, which had an irregular grain size distribution of 200-1000 nm and large surface roughness. The improved light scattering properties on the rough ZnO:Al/Ag back reflector surfaces led to an increase of light trapping in the solar cells, and this resulted in a noticeable improvement in the Jsc values from 9.94 mA/cm2 for the flat Ag back reflector at 25˚C to 13.36 mA/cm2 for the rough one at 500˚C. A conversion efficiency of 7.60% (Voc = 0.93, Jsc = 13.36 mA/cm2, FF = 61%) was achieved in the flexible silicon thin film solar cells at this moment.

Various thicknesses of Al-doped ZnO (AZO) films were deposited on glass substrate using pulsed dcmagnetron sputtering with a cylindrical target designed for large-area high-speed deposition. The structural,electrical, and optical properties of the films of various thicknesses were characterized. All deposited AZO filmshave (0002) preferred orientation with the c-axis perpendicular to the substrate. Crystal quality and surfacemorphology of the films changed according to the film thickness. The samples with higher surface roughnessexhibited lower Hall mobility. Analysis of the measured data of the optical band gap and the carrierconcentration revealed that there were no changes for all the film thicknesses. The optical transmittances weremore than 85% regardless of film thickness within the visible wavelength region. The lowest resistivity,4.13×10-4Ω·cm-1, was found in 750nm films with an electron mobility (µ) of 10.6cm2V-1s-1 and a carrierconcentration (n) of 1.42×1021cm-3.

We investigated the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with a thin layer of 1 wt% Al-doped ZnO using rf magnetron sputtering deposition. Morphological studies clearly revealed that the ZnO appeared to form beadshaped crystalline nanoparticles with an average diameter as small as 30 nm, attaching to the surface of the nanotubes. It was found that the NO gas sensing properties of the ZnO-CNT layered composites were dramatically improved over Al-doped ZnO thin films. It is reasoned from these observations that an increase in the surface-to-volume ratio associated with the numerous ZnO “nanobeads” on the surface of the CNTs results in the enhancement of the NO gas sensing properties. The ZnO-CNT layered composite sensors exhibited a maximum sensitivity of 13.7 to 2 ppm NO gas at a temperature of 200˚C and a low NO gas detection limit of 0.2 ppm in dry air.

In this study we investigated the effect of the multi-step texturing process on the electrical and optical properties of hydrogenated Al-doped zinc oxide (HAZO) thin films deposited by rf magnetron sputtering. AZO films on glass were prepared by changing the H2/(Ar+H2) ratio at a low temperature of 150˚C. The prepared HAZO films showed lower resistivity and higher carrier concentration and mobility than those of non-hydrogenated AZO films. After deposition, the surface of the HAZO films was multi-step textured in diluted HCl (0.5%) for the investigation of the change in the optical properties and the surface morphology due to etching. As a result, the HAZO film fabricated under the type III condition showed excellent optical properties with a haze value of 52.3%.

Changes in the surface morphology and light scattering of textured Al doped ZnO thin films on glasssubstrates prepared by rf magnetron sputtering were investigated. As-deposited ZnO:Al films show a hightransmittance of above 80% in the visible range and a low electrical resistivity of 4.5×10-4Ω·cm. The surfacemorphology of textured ZnO:Al films are closely dependent on the deposition parameters of heater temperature,working pressure, and etching time in the etching process. The optimized surface morphology with a cratershape is obtained at a heater temperature of 350oC, working pressure of 0.5 mtorr, and etching time of 45seconds. The optical properties of light transmittance, haze, and angular distribution function (ADF) aresignificantly affected by the resulting surface morphologies of textured films. The film surfaces, havinguniformly size-distributed craters, represent good light scattering properties of high haze and ADF values.Compared with commercial Asahi U (SnO2:F) substrates, the suitability of textured ZnO:Al films as frontelectrode material for amorphous silicon thin film solar cells is also estimated with respect to electrical andoptical properties.

This study examined the effect of growth temperature on the electrical and optical properties ofhydrogenated Al-doped zinc oxide (AZO:H) thin films deposited by rf magnetron sputtering using a ceramictarget (98wt.% ZnO, 2wt.% Al2O3). Various AZO films on glass were prepared by changing the substratetemperature from room temperature to 200oC. It was shown that intentionally incorporated hydrogen plays animportant role on the electrical properties of AZO:H films by increasing free carrier concentration. As a result,in the 2% H2 addition at the growth temperature of 150oC, resistivity of 3.21×10-4Ω·cm, mobility of 21.9cm2/V−s, electric charge carrier concentration of 9.35×1020cm-3 was obtained. The AZO:H films show a hexagonalwurtzite structure preferentially oriented in the (002) crystallographic direction.

Pulsed Current Sintering (PCS) process possesses some problems that need to be resolved. We, therefore aims at understanding phenomena of PCS process by presenting some basic data on in situ sintering behavior of PCS. Special graphite mold equipped with thermo couple and electrodes were designed to measure the temperature, electric current and voltage inside the powder during PCS process. We apply three types of raw materials, especially for ZnO as semiconductor, Al2O3 as non-conductor and WC as good conductor. The electric current and voltage were measured for each powder during PCS process. In addition, their electric resistance properties were calculated.