Reactive Co-sputtering Research Articles

Mechanisms of electrical transition using a conformal MoOx cap on Mo-doped VO2 thermochromics

Mo-doped VO2 thin-films are deposited on the soda-lime glass by a reactive high-power impulse magnetron co-sputtering technique (R-HiPIMS). Rapid thermal annealing at 500 °C for 3 min is performed to achieve the fabrication under low thermal budget. To prevent VO2 from further oxidation, a conformal and semi-conducting MoOx film is applied as the capping layer by the plasma-enhanced atomic layer deposition (PE-ALD). After MoOx film is deposited, an electrical transition in the resistance ratio of 6–10 orders of magnitude has been found, especially for MoOx thicknesses less than 20 nm. A secondary phase of V2O3 plays an important role in abrupt change of current transportation. Also, the hysteresis of optical transition in transmittance at a wavelength of 2500 nm shows that both the width and transition temperature (TC) decrease with increasing the thickness of the MoOx cap. Moreover, the effect of localized surface plasmonic resonance (LSPR) due to the Karst-like structure has been detected by the absorption spectrum. The variations in LSPR peak, such as intensity, blue-shifting, and red-shifting, originated from either excess carrier or structure change are discussed. The high aspect ratio of surface morphology is further examined by atomic force microscopy. In addition, the coverage of MoOx on Mo-doped VO2 concerning the friction behavior is evaluated by lateral force microscopy (LFM), which is helpful in clarifying the responsible mechanisms during TC transition.

Impact of Silver Incorporation and Flash-Lamp-Annealing on the Photocatalytic Response of Sputtered ZnO Films.

Thin films of silver-doped zinc oxide (SZO) were deposited at room temperature using a DC reactive magnetron co-sputtering technique using two independent Zn and Ag targets. The crystallographic structure, chemical composition and surface morphology of SZO films with different silver concentrations were correlated with the photocatalytic (PC) properties. The crystallization of the SZO films was made using millisecond range flash-lamp-annealing (FLA) treatments. FLA induces significant structural ordering of the wurtzite structure and an in-depth redistribution of silver, resulting in the formation of silver agglomerates. The wurtzite ZnO structure is observed for silver contents below 10 at.% where Ag is partially incorporated into the oxide matrix, inducing a decrease in the optical band-gap. Regardless of the silver content, all the as-grown SZO films do not exhibit any significant PC activity. The best PC response is achieved for samples with a relatively low Ag content (2-5 at.%) after FLA treatment. The enhanced PC activity of SZO upon FLA can be attributed to structural ordering and the effective band-gap narrowing through the combination of silver doping and the plasmonic effect caused by the formation of Ag clusters.

Effect of Reactive Magnetron Co-Sputtering on the Microstructures and Optical Characteristics of TiAlN Coating

Effect of Reactive Magnetron Co-Sputtering on the Microstructures and Optical Characteristics of TiAlN Coating

Self-formation of dual-phase nanocomposite Zr–Cu–N coatings based on nanocrystalline ZrN and glassy ZrCu

A novel type of nanocomposite Zr–Cu–N material based on hard nanocrystalline ZrN and amorphous glassy ZrCu was prepared by atom-by-atom deposition using reactive magnetron co-sputtering. The elemental composition of the coatings was systematically controlled over a wide range, so that the stoichiometry of both phases was the same in all coatings and only phase fractions varied. Experimental results obtained using X-ray diffraction and electron microscopies were complemented by thirteen ab-initio simulations for the same coating compositions. We found that the structure of the as-deposited Zr–Cu–N coatings undergoes a gradual transition from an amorphous to nanograined and finally to nanocolumnar structure. When ZrN fraction exceeds 20 mol.%, both phases exhibit the tendency for spontaneous segregation even without heating, forming a heterogenous dual-phase nanocomposite structure. At approximately 50 mol.% ZrN, the ZrN nanocrystals enveloped by a relatively thin amorphous ZrCu phase reach an optimum size (3–5 nm), resulting in a maximum enhancement of hardness by 38 % compared to the rule of mixture. For ZrN fractions > 80 mol.%, hardness and plastic work fraction follow the trend proposed by the rule of mixture and the coatings with a lower hardness but a higher plasticity compared to the ZrN coating are prepared.

Tailoring the structural, optical, hydrophobicity and electrical properties of ZnO thin films by copper doping for self-clean optoelectronic application

Optoelectronic devices such as solar panels, cameras, screens, and sensors frequently suffer reduced performance due to dust accumulation. Incorporating self-cleaning features not only sustains their efficiency but also minimizes maintenance expenses, especially for large or challenging-to-access setups. In this study, copper doped-zinc oxide (CZO) thin films with varying copper (Cu) concentrations were created using the reactive co-sputtering process. These films underwent a comprehensive analysis, including X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy to examine their structure, morphology, and elemental composition. Optical properties were investigated through UV–Vis spectroscopy, while hydrophobicity and electrical characteristics were assessed with contact angle and I–V measurements. Spectroscopic ellipsometry was employed to analyse surface attributes. The results confirmed that as Cu concentrations increased, the crystallite and grain size of ZnO in the films also increased. A red shift in the band gap was observed in UV–Vis spectroscopy, and Cu doping effectively reduced the electrical resistivity of the ZnO thin film. The CZO thin film, with a 60 nm thickness, low roughness (1.49 nm), high optical transmittance (around 80.20 %), a wide band gap (3.22 eV), a substantial contact angle (113°), and low electrical resistivity (5.9 × 105 Ω cm), holds great promise for use in transparent, conductive, and self-cleaning optoelectronic devices.

High performance symmetric supercapacitors based on Au incorporated CrN thin films fabricated by reactive magnetron sputtering

Recently, transition metal nitrides are being investigated extensively as potential supercapacitor material. In the present study, Au incorporated CrN (Au_CrN) thin films have been synthesized using reactive magnetron co-sputtering technique for application as supercapacitor electrode material. Films have been prepared at different Ar to N2 flow rates keeping total deposition pressure constant to achieve the required structural phase in the sample. Electrochemical properties of the deposited materials have been investigated with a three-electrode system in 0.5 M H2SO4 aqueous electrolyte. The CrN thin film deposited under 3:1 Ar: N2 partial pressure or flow rate ratio shows the highest specific capacitance. Upon Au incorporation, the film shows an areal capacitance of 56.8 mFcm−2 at 1.0 mAcm−2discharge current density which is an almost nine-fold enhancement in specific capacitance value compared to pristine CrN sample. Symmetric supercapacitors have also been developed by sandwiching two identical Au_CrN thin film electrodes, which have found to deliver excellent specific capacitance of 86.03 mFcm−2at 1.0 mAcm−2 discharge current density with no decline in capacitance value till 20,000 cycles. Furthermore, it can deliver a high energy density of 52.02mWhcm−2and a power density of 0.12mWcm−2. The electrochemical properties of the supercapacitors fabricated with the Au_CrN thin film electrodes are found to be better than most of the results reported so far in the literature with CrN electrodes. Results of the present study clearly demonstrate that these Au enhanced CrN films prepared by easily scalable and highly reproducible magnetron sputtering technique have great potential as a high capacitance supercapacitor electrode material.

Long Electrical Stability on Dual Acceptor p-Type ZnO:Ag,N Thin Films.

p-type Ag-N dual acceptor doped ZnO thin films with long electrical stability were deposited by DC magnetron reactive co-sputtering technique. After deposition, the films were annealed at 400 °C for one hour in a nitrogen-controlled atmosphere. The deposited films were amorphous. However, after annealing, they crystallize in the typical hexagonal wurtzite structure of ZnO. The Ag-N dual acceptors were incorporated substitutionally in the structure of zinc oxide, and achieving that; the three samples presented the p-type conductivity in the ZnO. Initial electrical properties showed a low resistivity of from 1 to 10-3 Ω·cm, Hall mobility of tens cm2/V·s, and a hole concentration from 1017 to 1019 cm-3. The electrical stability analysis reveals that the p-type conductivity of the ZnO:Ag,N films is very stable and does not revert to n-type, even after 36 months of aging. These results reveal the feasibility of using these films for applications in short-wavelength or transparent optoelectronic devices.

Development of Sb phase change thin films with high thermal stability and low resistance drift by alloying with Se

A single Sb phase demonstrates potential for use in phase change memory devices. However, the rapid crystallization of Sb at room temperature imposes limitations on its practical application. To overcome this issue, Sb is alloyed with Se using a reactive co-sputtering deposition technique, employing both Sb and Sb2Se3 sputter targets. This process results in the formation of Sb-rich Se thin films with varying compositions. Compared to pure Sb, the Sb-rich Se thin films exhibit enhanced thermal stability due to the formation of Sb–Se bonds and reduced resistance drift. In particular, the Sb86.6Se13.4 thin film demonstrates an exceptionally low resistance drift coefficient (0.004), a high crystallization temperature (Tc = 195 °C), a high 10-year data retention temperature (116.3 °C), and a large crystallization activation energy (3.29 eV). Microstructural analysis of the Sb86.6Se13.4 reveals the formation of a trigonal Sb phase with (012) texture at 250 °C, while Sb18Se and Sb2Se3 phases form at 300 °C. Conversely, the Sb98.3Se1.7 thin film shows the formation of the single Sb phase with (001) texture, a Tc of 145 °C, and a low resistance drift coefficient (0.011). Overall, this study demonstrates that the alloying strategy is a viable approach for enhancing thermal stability and reducing resistance drift in Sb-based phase-change materials.

Palladium enhanced electrochemical supercapacitive performance of chromium oxide thin films synthesized by sputtering process

Recently, the use of transition metal oxide electrodes for supercapacitor applications has increased due to the possibility of variable mixed valence states. The present study has established the use of Pd-Cr2O3 composite thin films as a working electrode for high-performance supercapacitors. The reactive dc magnetron co-sputtering method has been used for the fabrication of thin film of Cr2O3 and Pd-Cr2O3 on SS-304 substrate. X-ray diffraction and X-ray photoemission spectroscopy techniques were used to examine the surface chemistry and phase purity of chromium oxide and Pd-Cr2O3 composite thin films. The incorporation of Pd in Cr2O3 delivers a drastic change in the surface morphology. Due to the modified morphology and electronic properties, a noticeable improvement in the electrochemical properties of Pd-Cr2O3 electrode is observed. The obtained value of specific capacitance for this electrode is 401 Fg−1 at 0.1 mAcm−2 scan rate and within the potential window range 0 to +1.2 V. This value of specific capacitance is almost twice in comparison to the Cr2O3 based electrode. The Pd-Cr2O3 composite thin film shows a good cycle retention capability of 8000 cycles with 87.5 % retention. The obtained value of energy density and power density for Pd-Cr2O3 electrode was 80.2 Whkg−1 and 3.23 kWkg−1, respectively at 0.1 mAcm−2. Consequently, this composite material electrode can be seen as a promising advancement for electrodes in supercapacitor devices.

Nanocrystalline Cubic Phase Scandium-Stabilized Zirconia Thin Films.

The cubic zirconia (ZrO2) is attractive for a broad range of applications. However, at room temperature, the cubic phase needs to be stabilized. The most studied stabilization method is the addition of the oxides of trivalent metals, such as Sc2O3. Another method is the stabilization of the cubic phase in nanostructures-nanopowders or nanocrystallites of pure zirconia. We studied the relationship between the size factor and the dopant concentration range for the formation and stabilization of the cubic phase in scandium-stabilized zirconia (ScSZ) films. The thin films of (ZrO2)1-x(Sc2O3)x, with x from 0 to 0.2, were deposited on room-temperature substrates by reactive direct current magnetron co-sputtering. The crystal structure of films with an average crystallite size of 85 Å was cubic at Sc2O3 content from 6.5 to 17.5 mol%, which is much broader than the range of 8-12 mol.% of the conventional deposition methods. The sputtering of ScSZ films on hot substrates resulted in a doubling of crystallite size and a decrease in the cubic phase range to 7.4-11 mol% of Sc2O3 content. This confirmed that the size of crystallites is one of the determining factors for expanding the concentration range for forming and stabilizing the cubic phase of ScSZ films.

Pseudocapacitive Kinetics in Synergistically Coupled MoS2-Mo2N Nanowires with Enhanced Interfaces toward All-Solid-State Flexible Supercapacitors.

Pseudocapacitive kinetics in rationally engineered nanostructures can deliver higher energy and power densities simultaneously. The present report reveals a high-performance all-solid-state flexible symmetric supercapacitor (FSSC) based on MoS2-Mo2N nanowires deposited directly on stainless steel mesh (MoS2-Mo2N/SSM) employing DC reactive magnetron co-sputtering technology. The abundance of synergistically coupled interfaces and junctions between MoS2 nanosheets and Mo2N nanostructures across the nanocomposite results in greater porosity, increased ionic conductivity, and superior electrical conductivity. Consequently, the FSSC device utilizing poly(vinyl alcohol)-sodium sulfate (PVA-Na2SO4) hydrogel electrolyte renders an outstanding cell capacitance of 252.09 F·g-1 (44.12 mF·cm-2) at 0.25 mA·cm-2 and high rate performance within a wide 1.3 V window. Dunn's and b-value analysis reveals significant energy storage by surface-controlled capacitive and pseudocapacitive mechanisms. Remarkably, the symmetric device boosts tremendous energy density ∼10.36 μWh·cm-2 (59.17 Wh·kg-1), superb power density ∼6.5 mW·cm-2 (37.14 kW·kg-1), ultrastable long cyclability (∼93.7% after 10,000 galvanostatic charge-discharge cycles), and impressive mechanical flexibility at 60°, 90°, and 120° bending angles.

Mg incorporation induced microstructural evolution of reactively sputtered GaN epitaxial films to Mg-doped GaN nanorods

Mg-doped GaN films/nanorods were grown epitaxially on c-sapphire by reactive co-sputtering of GaAs and Mg at different N2 percentages in Ar–N2 sputtering atmosphere. Energy dispersive x-ray spectroscopy revealed that the Mg incorporation increases with increase of Mg area coverage of GaAs target, but does not depend on N2 percentage. In comparison to undoped GaN films, Mg-doped GaN displayed substantial decrease of lateral conductivity and electron concentration with the initial incorporation of Mg, indicating p-type doping, but revealed insulating behaviour at larger Mg content. Morphological investigations by scanning electron microscopy have shown that the films grown with 2%–4% Mg area coverages displayed substantially improved columnar structure, compared to undoped GaN films, along with rough and voided surface features at lower N2 percentages. With increase of Mg area coverage to 6%, the growth of vertically aligned and well-separated nanorods, terminating with smooth hexagonal faces was observed in the range of 50%–75% N2 in sputtering atmosphere. High-resolution x-ray diffraction studies confirmed the epitaxial character of Mg-doped GaN films and nanorods, which displayed complete c-axis orientation of crystallites and a mosaic structure, aligned laterally with the c-sapphire lattice. The catalyst-free growth of self-assembled Mg-doped GaN nanorods is attributed to increase of surface energy anisotropy due to the incorporation of Mg. However, with further increase of Mg area coverage to 8%, the nanorods revealed lateral merger, suggesting enhanced radial growth at larger Mg content.

Synthesis and characterization of low-friction W-V-N alloy coatings using reactive magnetron sputtering technique for tribological applications

In recent years, self-lubricating hard coatings have garnered significant interest across various industries such as cutting tools, molds, and manufacturing because of their ability to reduce friction and wear at high temperatures in dry-cutting applications. The present study focuses on synthesis of tungsten-vanadium-nitride (W-V-N) coatings using the reactive magnetron cosputtering technique in an Ar + N2 plasma gas environment. The coating microstructure, surface morphology, wetting behavior, and mechanical properties were characterized by grazing incidence x-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, energy-dispersive spectroscopy, and nanoindentation. Wear resistance properties of the prepared W-V-N alloy coatings were investigated using a ball-on-disk tribometer at two different temperatures. The findings indicate that all W-V-N coatings, regardless of the vanadium content, exhibit a face-centered cubic structure and form a solid solution of W-V-N. Among the coatings studied, W0.68V0.32N exhibited the highest hardness (14.25 GPa) and Young's modulus (257.53 GPa), as well as an excellent wear resistance. Increasing the vanadium content in the W-V-N coating led to a notable reduction in both the specific wear rate and friction coefficient. Moreover, this reduction was more pronounced with an increase in temperature during the wear test. Improvement in the wear properties can be attributed to the formation of Magnéli phases of vanadium oxides on the surface of the coatings. The ability of the W-V-N coating to reduce friction and wear, combined with its improved mechanical properties, makes it a promising candidate for solid lubricating coatings in tribological applications.

Effects of nitrogen flow ratio on the mechanical and anticorrosive properties of cosputtered (TiZrHfTa)Nx films

In this study, TiZrHfTa films were cosputtered through cyclical gradient composition deposition by using four single-element targets connected to direct-current power supplies. Multilayered and columnar structures formed at low and high rotation speeds of the substrate holder (RH), respectively. (TiZrHfTa)Nx thin films were then prepared through reactive cosputtering by using Ar/N2 mixed gas. A high RH value resulted in these films having homogeneous structures. Without the addition of reactive nitrogen gas, the fabricated metallic Ti0.24Zr0.23Hf0.27Ta0.26 film exhibited a valence electron concentration of 4.26, which resulted in the formation of a body-centered cubic (bcc) phase; a hardness of 4.7 GPa; and an elastic modulus of 104 GPa. (TiZrHfTa)Nx films with stoichiometric ratios (x) ranging from 0.59 to 0.97 were obtained by adjusting the reactive gas ratio fN2 (N2/(N2 + Ar)) from 0.1 to 0.7. The introduction of N into the TiZrHfTa crystallites caused the bcc phase to transform into a face-centered cubic phase and enhanced the mechanical properties of the films, with their hardness and elastic modulus increasing to 13.8–25.5 and 235–290 GPa, respectively. Nanoindentation, scratch, Rockwell-C adhesion, and potentiodynamic polarization tests indicated that among the prepared (TiZrHfTa)Nx films, the (Ti0.17Zr0.25Hf0.20Ta0.38)N0.75 film exhibited the best mechanical and anticorrosive properties. Target poisoning accompanied by defect formation affected the mechanical properties of the (TiZrHfTa)Nx films. The anticorrosive properties of the (TiZrHfTa)Nx films were dominated by the high-entropy effect through alloying with Ta and the adhesion strength between the films and substrates.

Binder-free V-doped CrN thin film electrode enables high performance symmetric supercapacitor

Transition metal nitrides (TMNs) are rapidly gaining prominence as attractive supercapacitor electrode materials due to their intriguing properties. Nevertheless, the quest for facile and green fabrication of TMNs electrodes with high supercapacitor performance remains a substantial challenge. In this study, we have successfully designed and prepared the binder-free V-doped CrN thin film electrodes through a one-step reactive magnetron co-sputtering in nitrogen and argon atmosphere without high temperature heating. Our experimental and DFT findings confirm that the V doping increases the number of active sites, enlarges the specific surface area, and enhances the electron concentration and electrical conductivity. Consequently, the CrVN thin film electrodes achieve a remarkable specific capacitance of 22.8 mF cm−2 at 1.0 mA cm−2, along with excellent cycling performance (93.9% capacitance retention after 20,000 cycles at 5.0 mA cm−2). Furthermore, the assembled CrVN symmetric supercapacitor device exhibits a substantial energy density of 11.2 mWh cm−3 and an impressive power density of 7.5 W cm−3, respectively. These encouraging outcomes open new avenues for developing ternary TMNs-based electrodes for high performance supercapacitors.

Unravelling the doping mechanism and origin of carrier limitation in Ti-doped In2O3 films

Ti-doped In2O3 thin films with varying Ti contents are prepared by partial reactive co-sputtering using ceramic In2O3 and metallic Ti targets and characterized by in situ x-ray photoelectron spectroscopy, electrical conductivity, and Hall-effect measurements. For a substrate temperature of 400°C, the carrier concentration increases faster than the Ti content and saturates at ≈7.4×1020cm−3. Based on these results, it is suggested that Ti does not directly act as donor in In2O3 but is rather forming TiO2 precipitates and that the related scavenging of oxygen generates oxygen vacancies in In2O3 as origin of doping. Neutralization of oxygen vacancies is, therefore, suggested to be origin of the limitation of the carrier concentration in Ti-doped In2O3 films.

Deposition and photoluminescence of zinc gallium oxide thin films with varied stoichiometry made by reactive magnetron co-sputtering

This paper reports on the deposition and photoluminescence of amorphous and crystalline thin films of zinc gallium oxide with Ga:Zn atomic ratio varied between 0.3 and 5.7. The films are prepared by reactive direct current magnetron co-sputtering from liquid/solid gallium/zinc targets onto fused quartz substrates; the temperature of the substrate is varied from room temperature (RT) to 800 °C. The sputtering process is effectively controlled by fixing the sputtering power of one of the targets and controlling the power of the other target by plasma optical emission spectroscopy. The method, in conjunction with oxygen flow adjustment, enables the production of near-stoichiometric films at any temperature used. The composition analysis suggests a few at% oxygen deficiency in the films. The resulting deposition rate is at least an order of magnitude higher compared to the commonly used radio-frequency sputtering from a ceramic ZnO:Ga2O3 target. Deposited onto unheated substrates, the films with Ga:Zn ≈ 2 are X-ray amorphous. Well-defined X-ray diffraction peaks of spinel ZnGa2O4 start to appear at a substrate temperature of 300 °C. The surface of the as-deposited films is dense and exhibits a fine-featured structure observed in electron microscopy images. Increasing the deposition temperature from RT to 800 °C eliminates defects and improves crystallinity, which for the films with Ga:Zn ratio close to 2 results in an increase in the optical band gap from 4.6 eV to 5.1 eV. Room temperature photoluminescence established the main peak at 3.1 eV (400 nm); a similar peak in Ga2O3 is ascribed to oxygen-vacancy related transitions. A prominent feature around 2.9 eV (428 nm) is attributed to self-activation center of the octahedral Ga-O groups in the spinel lattice of ZnGa2O4. It was found that photoluminescence from ZnGa2O4 depends significantly on the stoichiometric ratio between Ga and Zn and the deposition/annealing temperature.

Effects of Y and Ho doping on microstructure evolution during oxidation of extraordinary stable Hf-B-Si-Y/Ho-C-N films up to 1500 °C

Hard, and optically transparent amorphous Hf6B12Si29Y2C2N45 and Hf5B13Si25Ho3C2N48 films were prepared by reactive pulsed dc magnetron co-sputtering and annealed up to 1500 °C in air. The evolved microstructures were studied by X-ray diffraction and transmission electron microscopy to understand the Y- and Ho– doping effects on thermal stability and oxidation behavior. A three-layered microstructure developed in both annealed films. A fully oxidized layer formed at the top surface consisting of cubic fluorite Hf(Y/Ho)O2 nanoparticles embedded in an amorphous SiOx-based matrix. The oxide layer is about 36 % thinner compared to undoped films with similar composition [1]. A recrystallized structure formed at the bottom of both films composed mainly of Hf(Y/Ho)N and α-/β-Si3N4. All Hf(Y/Ho)N in the middle layer was oxidized producing vertically oriented Hf(Y/Ho)O2 nanocolumns surrounded by Si3N4 nanocrystalline. The Y- and Ho– doping found to stabilize the cubic fluoride oxide structure and promoted its (1 1 1) columnar texture. The oxidation mechanism of Si3N4 nanodomains occurs via formation of β-SiO2 first followed by its transformation to amorphous SiOx. It is suggested that substitution of Hf4+ with Y3+ and Ho3+ ions within the Hf(Y/Ho)O2 formed an anion vacancy defect structure to preserve charge neutrality affecting the oxidation mechanism in the doped films.

Correlation of sputtering power with microstructure and ionic conductivity in lithium aluminum oxide thin films prepared by reactive co-sputtering

Li–Al–O thin films synthesized via the reactive magnetron co-sputtering have the potential to act as solid-state electrolytes in micro-batteries. In this paper, the constant RF power (155 W) and variable DC power (20–50 W) were applied to lithium (Li) and aluminum (Al) metal targets, respectively, in Ar/O2 atmosphere to produce films with adequate ionic conductivity. The influence of DC sputtering power on the composition, microstructure, band gap energy, ionic conductivity, and dielectric loss of films were studied in detail. X-ray photoelectron spectroscopy (XPS) showed a shift of the Li 1s peak towards higher binding energy with increasing DC power. X-ray diffraction (XRD) spectra confirmed the amorphous state for all as-deposited films, while the post-annealed films at 950 °C contain the γ-LiAlO2 phase. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) images revealed that the increasing DC power had a significant impact on the film morphology, enlarging grain size and increasing surface roughness. Energy dispersive X-ray (EDX) spectroscopy showed that increasing the DC power increased the Al content. The optical properties were examined by ultraviolet–visible (UV–vis) spectroscopy, which indicated that increasing the Al content led to a blue shift of the absorption edge and an increase in the band gap energy (5.40–5.68 eV). Increasing the DC power resulted in an improvement of room-temperature conductivity by two orders of magnitude (∼2.85 × 10−9 S cm−1) and a decrease in the activation energy from 0.54 eV to 0.32 eV. These results suggest that composition and microstructure significantly affect the ionic transport in co-sputtered Li–Al–O films.

Dependence of diode behaviour and photoresponse of Ga-doped ZnO (GZO)/p-Si junction on the carrier concentration of GZO layer

Ga-doped ZnO (GZO)/p-Si junctions were fabricated by reactive co-sputtering of Zn-GaAs target in Ar–O2 atmosphere. Highly degenerate GZO (carrier concentration ∼1021 cm−3) deposited at 4 % O2 forms non-rectifying contact with p-Si. GZO/p-Si diodes fabricated with moderately doped GZO layers deposited at 5 % O2, having carrier concentration ∼1019 cm−3 display low turn-on voltage (≲ 0.5 V) and ideality factor ≈ 2. Measurement of barrier height by temperature dependent I–V and built-in potential by C–V reveal respective values of (0.74 ± 0.07 eV) and (0.44 ± 0.04 eV), suggesting formation of Schottky type diodes. These diodes display nearly linear I–V characteristics under UV illumination, yielding photoresponsivity ∼1 A/W at ± 1 V. In contrast, GZO/p-Si diodes fabricated with lightly doped (non-degenerate) GZO layers deposited at 6–8 % O2, having carrier concentration ∼1018 cm−3, show higher turn-on voltages (4.5–6.5 V) and ideality factors of 2.5–2.7. I–V and C–V measurements reveal nearly equal values of barrier height and built-in potential, indicating formation of n-p heterojunctions, with near-elimination of conduction band discontinuity. Under UV illumination, I–V characteristics of these GZO/p-Si diodes display non-linear behaviour in forward bias and yield photoresponsivity of ∼0.1 A/W at ±1 V.