The changes in structural and optical properties of (ZnO:AlN) thin films fabricated at different RF powers of ZnO target

AlN doped ZnO thin films were prepared on glass and Si (100) substrates by RF sputtering. The ratio of nitrogen (N₂) to Argon (Ar) used to prepare the films was 80:20. The films were deposited at different RF powers of 150 W, 175 W, 200 W, 225 W and 250 W for ZnO target and 200 W for AlN target. XRD results revealed the existence of (002) ZnO phase for RF power of ZnO target above 175 W. However, at the RF power of 150 W, the film exhibited amorphous properties. The prepared films showed transmission values above 70% in the visible range. The average calculated value of energy band gap and the refractive index were 3.43 eV and 2.29 respectively. The green and UV emission peaks were observed from PL spectra. Raman Peaks at 275.49 cm^?1 and 580.17 cm^?1 corresponding to ZnO:N and ZnO:AlN were also observed.     

Electrical contacts to nitrogen incorporated nanocrystalline diamond films

The effect of surface plasma treatment on the nature of the electrical contact to the nitrogen incorporated nanocrystalline diamond (n-NCD) films is reported. Nitrogen incorporated NCD films were grown in a microwave plasma enhanced chemical vapor deposition (MPECVD) reactor using CH₄ (1%)/N₂ (20%)/Ar (79%) gas chemistry. Raman spectra of the films showed features at ∼ 1140 cm^− 1, 1350 cm^− 1(D-band) and 1560 cm^− 1(G-band) respectively with changes in the bonding configuration of G-band after the plasma treatment. Electrical contacts to both untreated and surface plasma treated films are formed by sputtering and patterning Ti/Au metal electrodes. Ohmic nature of these contacts on the untreated films has changed to non-ohmic type after the hydrogen plasma treatment. The linear current–voltage characteristics could not be obtained even after annealing the contacts. The nature of the electrical contacts to these films depends on the surface conditions and the presence of defects and sp² carbon.     

CIGS absorbing layers prepared by RF magnetron sputtering from a single quaternary target

Cu(In_1−xGa_x)Se₂ (CIGS) thin films were prepared by RF magnetron sputtering from a single quaternary target at multiple processing parameters. The structural, compositional, and electrical properties of the as-deposited films were systematically investigated by XRD, Raman, SEM, and Hall effects analysis. The results demonstrate that by adjusting the processing parameters, the CIGS thin films with a preferential orientation along the (112) direction which exhibited single chalcopyrite phase were obtained. The films deposited at relatively higher substrate temperature, sputtering power, and Ar pressure exhibited favorable stoichiometric ratio (Cu/(In+Ga):0.8–0.9 and Ga/(In+Ga):0.25–0.36) with grain size of about 1–1.5 µm, and desirable electrical properties with p-type carrier concentration of 10¹⁶−10¹⁷ cm⁻³ and carrier mobility of 10–60 cm²/Vs. The CIGS layers are expected to fabricate high efficiency thin film solar cells.     

Growth and properties of Cu3SbS4 thin films prepared by a two-stage process for solar cell applications

Cu₃SbS₄ is a promising material for thin film heterojunction solar cells owing to its suitable optical and electrical properties. In this paper, we report the preparation of Cu₃SbS₄ thin films by annealing the Sb₂S₃/CuS stacks, produced by chemical bath deposition, in a graphite box held at different temperatures. The influence of annealing temperature on the growth and properties of these films is investigated. These films are systematically analyzed by evaluating their structural, microstructural, optical and electrical properties using suitable characterization techniques. X-ray diffraction analysis showed that these films exhibit tetragonal crystal structure with the lattice parameters a=0.537 nm and b=1.087 nm. Their crystallite size increases with increasing annealing temperature of the stacks. Raman spectroscopy analysis of these films exhibited modes at 132, 247, 273, 317, 344, 358 and 635 cm⁻¹ due to Cu₃SbS₄ phase. X-ray photoelectron spectroscopy analysis revealed that the films prepared by annealing the stack at 350 °C exhibit a Cu-poor and Sb-rich composition with +1, +5 and −2 oxidation states of Cu, Sb and S, respectively. Morphological studies showed an improvement in the grain size of the films on increasing the annealing temperature. The direct optical band gap of these films was in the range of 0.82–0.85 eV. Hall measurements showed that the films are p-type in nature and their electrical resistivity, hole mobility and hole concentration are in the ranges of 0.14–1.20 Ω-cm, 0.05–2.11 cm² V⁻¹ s⁻¹ and 9.4×10²⁰–1.4×10¹⁹ cm⁻³, respectively. These structural, morphological, optical and electrical properties suggest that Cu₃SbS₄ could be used as an absorber layer for bottom cell in multi-junction solar cells.     

Characteristics of highly (001) oriented (K,Na)NbO3 films grown on LaNiO3 bottom electrodes by RF magnetron sputtering

(K,Na)NbO₃ ferroelectric films were grown on LaNiO₃ coated silicon substrates by RF magnetron sputtering. The conductive LaNiO₃ films acted as seed layers and induced the highly (001) oriented perovskite (K,Na)NbO₃ films. Such films exhibit saturated hysteresis loops and have a remnant polarization (2P_r) of 23 μC/cm², and coercive field (2E_c) of 139 kV/cm. The films showed a fatigue-free behavior up to 10⁹ switching cycles. A high tunability of 65.7% (@300 kV/cm) was obtained in the films. The leakage current density of the films is about 6.0×10^?8 A/cm² at an electric field of 50 kV/cm.     

Effect of oxygen pressure on the p-type conductivity of Ga,P co-doped ZnO thin film grown by pulsed laser deposition

The effect of the oxygen partial pressure on the conductivity of (Ga, P) co-doped ZnO thin films (ZnO:Ga_0.01P_0.02, ZnO:Ga_0.01P_0.04) was investigated. The thin films were grown by using the pulsed laser deposition (PLD) method. As the oxygen partial pressure increased from 1 mTorr to 200 mTorr, the electron carrier concentration of the ZnO:Ga_0.01P_0.04 thin films decreased. Above 200 mTorr, however, the electron carrier concentration increased and a transition from n-type to p-type conductivity was observed. On the other hand, in the case of the ZnO:Ga_0.01P_0.02 thin films, their electron carrier concentration continuously decreased as the oxygen partial pressure increased from 1 to 500 mTorr, showing the typical n-type semi-conductive characteristics. The X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) analyses were used to characterize the n-type to p-type conductivity transitions with increasing oxygen partial pressure.     

From micro to nanocrystalline transition in the diamond formation on porous pure titanium

A novel composite material of nanocrystalline (NCD) and/or microcrystalline (MCD) diamond films grown on porous titanium (Ti) substrate was obtained by hot filament chemical vapor deposition technique. Diamond films were grown using 1.5 vol.% CH₄ in a balanced mixture of Ar/H₂. The grain size control was obtained by varying the argon concentration from 0 up to 90 vol.% at substrate temperature of 870 K. Porous Ti substrates were obtained by powder metallurgy and presented an inter-connected open porosity. Scanning electron microscopy images of diamond/Ti exposed the substrate covered by a continuous textured coating which changed from MCD to NCD morphology; depending on the amount of Ar concentration in the feed gas. Micro-Raman spectra showed the characteristic t-polyacethylene peaks around 1150 cm^− 1 and 1470 cm^− 1, associated to NCD formation for samples grown with Ar concentration higher than 40 vol.%. X-ray diffraction patterns identified the diamond and TiC peaks, where the crystallinity of (111) TiC phase decreased as the Ar amount increased. This behavior was associated to diamond (220) peak increase for films grown with Ar concentration higher than 70 vol.%. Diamond crystallite size was also evaluated from Sherrer's formula in the range of 11 up to 20 nm.     

Piezoelectric properties of highly densified 0.01Pb (Mg1/2W1/2)O3–0.41Pb (Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3+0.1 wt% Y2O3+1.5 wt% ZnO thick films on alumina substrate

This paper reports on the formation of highly densified piezoelectric thick films of 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃+0.1 wt% Y₂O₃+1.5 wt% ZnO (PMW–PNN–PT–PZ+YZ) on alumina substrate by the screen-printing method. To increase the packing density of powder in screen-printing paste, attrition milled nano-scale powder was mixed with ball milled micro-scale powder, while the particle size distribution was properly controlled. Furthermore, the cold isostatic pressing process was used to improve the green density of the piezoelectric thick films. As a result of these processes, the PMW–PNN–PT–PZ+YZ thick film, sintered at 890 °C for 2 h, showed enhanced piezoelectric properties such as P_r=42 μC/cm², E_c=25 kV/cm, and d₃₃=100 pC/N, in comparison with other reports. Such prominent piezoelectric properties of PMW–PNN–PT–PZ+YZ thick films using bi-modal particle distribution and the CIP process can be applied to functional thick films in MEMS applications such as micro actuators and sensors.     

Characterization of Cu(In,Ga)Se2 thin films prepared by RF magnetron sputtering using a single target without selenization

Cu(In_1?xGa_x)Se₂ (CIGS) thin films were prepared using a single quaternary target by RF magnetron sputtering. The effects of deposition parameters on the structural, compositional and electrical properties of the films were examined in order to develop the deposition process without post-deposition selenization. From X-ray diffraction analysis, as the substrate temperature and Ar pressure increased and RF power decreased, the crystallinity of the films improved. The scanning electron microscopy revealed that the grains became uniform and circular shape with columnar structure with increasing the substrate temperature and Ar pressure, and decreasing the RF power. The carrier concentration of CIGS films deposited at the substrate temperature of 500 °C was 2.1 × 10¹⁷ cm^?3 and the resistivity was 27 Ω cm. At the substrate temperature above 500 °C, In and Se contents in CIGS films decreased due to the evaporation and it led to the deterioration of crystallinity. It was confirmed that CIGS thin films deposited at optimal condition had similar atomic ratio to the target value even without post-deposition selenization process.     

Improving the electrical properties of niobium-doped titania sputtering targets by sintering in oxygen-deficient atmospheres

Niobium-doped titania (TNO) film can be used as a transparent conductive oxide (TCO) film due to its excellent conductivity and visible transparency. The performances of TNO sputtering targets are thus critical issues in optimizing sputtered films. This study clarifies the influences of inert and reducing atmospheres on the microstructure, densification, crystal structure, and electrical properties of TNO sputtering targets. The results indicate that a sintering atmosphere of 90% Ar–10% H₂ can result in a lower sintered density, larger grain size, and lower resistivity than can an atmosphere of Ar, followed by one of air. Sintering in 90% Ar–10% H₂ or Ar obviously decreases the resistivity of TiO₂, from >10⁸ Ω cm to <10⁻¹ Ω cm, and the TNO target, from >10¹ Ω cm to <10⁻¹ Ω cm. The resistivity of TNO target sintered at 1200 °C in 90% Ar–10% H₂ is as low as 1.8×10⁻² Ω cm.     

Transparent and high infrared reflection film having sandwich structure of SiO2/Al:ZnO/SiO2

New transparent and high infrared reflection films having the sandwich structure of SiO₂/Al:ZnO(AZO)/SiO₂ were deposited on the soda-lime silicate glass at room temperature by radio frequency (R.F.) magnetron sputtering. The optical and electrical properties of SiO₂ (110 nm)/AZO (860 nm)/SiO₂ (110 nm) sandwich films were compared with those of single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. The results show that these sandwich films exhibit high transmittance of over 85% in the visible light range (380–760 nm), and low reflection rate of below 4.5% in the wavelength range of 350–525 nm, which is not shown in the conventional single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. Further these sandwich films display a low sheet resistance of 20 Ω/sq by sheet resistance formula and high infrared reflection rate of above 80% in the wavelength range of 15–25 μm. In addition, the infrared reflection property of these sandwich films is determined mainly by the AZO film. The outer SiO₂ film can diminish the interference coloring and increase transparency; the inner SiO₂ film improves the adhesion of the coating to the glass substrate and prevents Ca²⁺ and Na⁺ in the glass substrate from entering the AZO film.     

Time dependent growth of ZnO nanoflowers with enhanced field emission properties

Herein, we report the facile growth of ZnO nanoflowers composed of nanorods on silicon substrate by non-catalytic thermal evaporation process. The grown nanoflowers were examined in terms of their morphological, structural, optical and field emission properties. The detailed characterizations revealed that the nanoflowers are grown in high density, possessing well-crystallinity and exhibiting wurtzite hexagonal phase. The Raman-scattering spectrum shows a sharp optical-phonon E₂ mode at 437 cm⁻¹ which confirmed the wurtzite hexagonal phase for the grown nanoflowers. The room-temperature PL spectrum depict a strong ultraviolet emission at 381 nm, revealed good optical properties for the ZnO nanoflowers. The field emission studies revealed that a turn-on field for the ZnO nanoflowers based field emission device was 4.3 V/μm and the emission current density reached to 0.075 mA/cm² at an applied electric field of 7.2 V/μm and exhibit no saturation. The field enhancement factor ‘β’ for the fabricated device was estimated from the F-N plot and found to be ~2.75×10³. Finally, systematic time-dependent experiments were performed to determine the growth process for the formation of ZnO nanoflowers composed of nanorods.     

Structural and optical studies on sol–gel derived ZnO thin films by excimer laser annealing

High-quality polycrystalline ZnO thin films were deposited onto alkali-free glasses at a temperature of 300°C in air ambience by combining sol–gel spin coating and KrF excimer laser annealing. The effects of laser irradiation energy density on the crystallization, microstructure, surface morphology, and optical transmittance of as-prepared ZnO thin films were investigated and compared to the results of thermally annealed ZnO thin films. The crystallinity level and average crystallite size of laser annealed ZnO thin films increased as laser energy density increased. The crystallinity levels and average crystallite size of excimer laser annealed (ELA) thin films were greater than those of the thermally annealed (TA) thin films. However, laser annealed thin films had abnormal grain growth when irradiation energy density was 175 mJ/cm². Experimental results indicated that the optimum irradiation energy density for excimer laser annealing of ZnO sol–gel films was 150 mJ/cm². The ELA 150 thin films had a dense microstructure, an RMS roughness value of 5.30 nm, and an optical band gap of 3.38 eV, close to the band gap of a ZnO crystal (3.4 eV).     

Characterization of luminescent properties of ZnO:Er thin films prepared by rf magnetron sputtering

ZnO:Er thin films were deposited on c-plane sapphire substrates by rf magnetron sputtering and annealed at 700 °C under air and H₂ atmospheres for the luminescent improvement. The effects of sputtering parameters and the annealing conditions on visible and 1.54 μm IR emissions were investigated. Structural and luminescent properties strongly depended on the deposition conditions and annealing atmospheres. By tuning the excitation wavelength, ZnO:Er thin films exhibited a strong emission band at around 465 nm and a weak emission at 525 nm originated from the energy transition of ⁴I_15/2–⁴F_5/2 and ⁴I_15/2–²H_11/2, respectively, while 1.54 μm IR emissions due to ⁴I_15/2–⁴I_13/2 transition.     

Enhanced photocatalytic activity of TiO2-ZnO thin films deposited by dc reactive magnetron sputtering

The effect of deposition conditions on the photocatalytic activity of TiO₂-ZnO thin films was studied. By using a (Ti)₉₀-(Zn)₁₀ alloy target, the samples were deposited at room temperature on glass substrates by dc reactive magnetron sputtering and post-annealed in air at 500 °C. The dependence of the physical properties of the films on the O₂/Ar gas ratio and the deposition working pressure was investigated. XRD patterns showed mainly the formation of the anatase phase of TiO₂. Optical absorption measurements exhibited a blue shift of the band-gap energy with increasing working pressure. XPS spectra indicated the presence of the Ti⁴⁺ and Zn²⁺ oxidation states, which correspond to TiO₂ and ZnO, respectively. The chemical state of Ti was further analyzed by means of the modified Auger parameter, α’, which gave a value of ca. 873 eV. The photocatalytic property of the films was assessed by the degradation of a methylene blue aqueous solution. The maximum photocatalytic performance was observed for the samples deposited at 3.0 mTorr and O₂/Ar gas ratio of 10/90. These results are explained in terms of the structural, optical, and morphological properties of the films.     

p-type cuprous oxide thin films with high conductivity deposited by high power impulse magnetron sputtering

Cu_xO thin films were deposited on glass and silicon substrates by High Power Impulse Magnetron Sputtering (HiPIMS) at room temperature from a metallic copper target. The influence of pulse off-time on the films’ structural, morphological and optoelectronic properties was investigated. It was found that the power intensity applied on the Cu target was strongly affected by pulse off-time, which had an important impact on the films’ composition. Upon increasing the pulse off-time from 500 μs to 3500 μs (pulse on-time fixed at 50 μs), the films’ crystallinity as well as transmittance in the visible region both ameliorate. Meanwhile, the conductivity type changed from n-type to p-type as the films’ composition changed. When the pulse off-time was fixed at 2000 μs, the optimal p-type conductivity of about 3 S × cm⁻¹ was achieved, which is the highest p-type conductivity reported for Cu₂O films in the last few years. The transition of the films’ conductivity type can be utilized for the fabrication of Cu₂O-based p-n homojunction, and may also prove useful in developing other oxide films by using HiPIMS technology.     

Effects of plasma treatments on the nitrogen incorporated nanocrystalline diamond films

The nitrogen incorporated nanocrystalline diamond (NCD) films were grown on n-silicon (100) substrates by microwave plasma enhanced chemical vapor deposition (MPECVD) using CH₄/Ar/N₂ gas chemistry. The effect of surface passivation on the properties of NCD films was investigated by hydrogen and nitrogen-plasma treatments. The crystallinity of the NCD films reduced due to the damage induced by the plasma treatments. From the crystallographic data, it was observed that the intensity of (111) peak of the diamond lattice reduced after the films were exposed to the nitrogen plasma. From Raman spectra, it was observed that the relative intensity of the features associated with the transpolyacetylene (TPA) states decreased after hydrogen-plasma treatment, while such change was not observed after nitrogen-plasma treatment. The hydrogen-plasma treatment has reduced the sp²/sp³ ratio due to preferential etching of the graphitic carbon, while this ratio remained same in both as-grown and nitrogen-plasma treated films. The electrical contacts of the as-grown films changed from ohmic to near Schottky after the plasma treatment. The electrical conductivity reduced from ~ 84 ohm^– 1 cm^− 1 (as-grown) to ~ 10 ohm^– 1 cm^− 1 after hydrogen-plasma treatment, while the change in the conductivity was insignificant after nitrogen-plasma treatment.     

Sputtering deposition of transparent conductive F-doped SnO2 (FTO) thin films in hydrogen-containing atmosphere

F-doped SnO₂ (FTO) thin films have been prepared by sputtering SnO₂-SnF₂ target in Ar+H₂ atmosphere. The effects of H₂/Ar flow ratio on the structural, electrical and optical properties of the films were investigated at two substrate temperatures of 150 and 300 °C and two base pressures of 3.5×10⁻³ and 1.5×10⁻² Pa. The results show that introducing H₂ into sputtering atmosphere can lead to the formation of a FTO film with a (101) preferred orientation and produce oxygen vacancy (V_O) at lower H₂/Ar flow ratios, but SnO phase at higher H₂/Ar flow ratios in the films. Accordingly, the resistivity of the films first decreases and then increases, but the transmittance decreases continuously with increasing H₂/Ar flow ratio. When H₂/Ar flow ratio is increased above a certain value, more amorphous SnO phase forms in the films, resulting in a big decrease in conductivity, transmittance, and band gap (E_g). Increasing substrate temperature can increase the Hall mobility due to the improvement of film crystallinity, but decrease the carrier concentration due to outward-diffusion of fluorine in the films. At a base pressure of 3.5×10⁻³ Pa, high substrate temperature (300 °C) can hinder the formation of SnO and thus improve the transparent conductive properties of the films. At a base pressure of 1.5×10⁻² Pa, the range of H₂/Ar flow ratio for forming the SnO₂ phase and hence for obtaining high transparent conductive FTO films is widened at both substrate temperatures of 150 and 300 °C.     

Graphene quantum dots directly generated from graphite via magnetron sputtering and the application in thin-film transistors

This work presents a novel method to prepare graphene quantum dots (GQDs) directly from graphite. A composite film of GQDs and ZnO was first prepared using the composite target of graphite and ZnO via magnetron sputtering, followed with hydrochloric acid treatment and dialysis. Morphology and optical properties of the GQDs were investigated using a number of techniques. The as-prepared GQDs are 4–12 nm in size and 1–2 nm in thickness. They also exhibited typical excitation-dependent properties as expected in carbon-based quantum dots. To demonstrate the potential applications of GQDs in electronic devices, pure ZnO and GQD–ZnO thin-film transistors (TFTs) using ZrO_x dielectric were fabricated and examined. The ZnO TFT incorporating the GQDs exhibited enhanced performance: an on/off current ratio of 1.7 × 10⁷, a field-effect mobility of 17.7 cm²/Vs, a subthreshold swing voltage of 90 mV/decade. This paper provides an efficient, reproducible and eco-friendly approach for the preparation of monodisperse GQDs directly from graphite. Our results suggest that GQDs fabricated using magnetron sputtering method may envision promising applications in electronic devices.     

Enhancement of piezoelectric and ferroelectric performances in (Na0.85K0.15)0.5Bi0.5TiO3 films with BaTiO3 interlayers

In this work, in order to optimize the electrical performance of (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) thin films, 20 nm-thick BaTiO₃ (BTO) layer was utilized by deliberately coating in the NKBT film-substrate interface or in the NKBT film, i.e., BTO layers coated in sequence with NBKT layers. The BTO layer, especial coated in the NKBT film, was beneficial for crystallization process and more preferable to form a denser film morphology. The BTO-coated NKBT composite films exhibited much enhancement in electrical properties compared to the films without BTO layer. Accordingly, a high effective piezoelectric coefficient d₃₃^* of 75 pm/V and remnant polarization P_r of 22.1 μC/cm², as well as a low leakage current density of 1.2 × 10^?5 A/cm² were obtained in the 460 nm-thick composite film with BTO layers coated in the NBKT film. It meant that this kind of BTO-coated NKBT composite film could perform as a potential candidate for the lead-free piezoelectric applications. The observed enhancement in the electrical properties with the introduction of BTO layer could be mainly explained by the weakened influence of domain pinning in the film-electrode interface and grain boundaries due to the decreased strain in the film-electrode interface and better crystallinity in the highly (110)-oriented NKBT films, thereby enhancing motion of domain-walls.