Growth of CZTS thin films by sulfurization of sputtered single-layered Cu–Zn–Sn metallic precursors from an alloy target

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing single-layered metallic Cu–Zn–Sn precursors which were deposited by DC magnetron sputtering using a Cu–Zn–Sn ternary alloy target. The composition, microstructure and properties of the CZTS thin films prepared under different sputtering pressure and DC power were investigated. The results showed that the sputtering rate of Cu atom increases as the sputtering pressure and DC power increased. The microstructure of CZTS thin films can be optimized by sputtering pressure and DC power. The CZTS thin film prepared under 1 Pa and 30 W showed a pure Kesterite phase and a dense micro-structure. The direct optical band gap of this CZTS thin film was calculated as 1.49 eV with a high optical absorption coefficient over 10⁴ cm^?1. The Hall measurement showed the film is a p-type semiconductor with a resistivity of 1.06 Ω cm, a carrier concentration of 7.904 × 10¹⁷ cm^?3 and a mobility of 7.47 cm² Vs^?1.     

Nitrogen effect on spin-coated ZnO-based p–n homojunctions: structural,optical and electrical characteristics

In this work, ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al homojunctions were deposited by means of spin coating method using precursors obtained by sol gel chemistry. The optical, structural and electrical properties of spin coated undoped and M-doped ZnO thin films (M?=?Al, Ag–N and Al–N) using ammonium hydroxide as a nitrogen source are reported. The films showed the wurtzite type structure with a c-axis (002) preferential orientation. The films showed a surface morphology consisting of wrinkles, which were constituted of nanocrystals in the range of ～?20 nm. The thin films were highly transparent in the visible region of the electromagnetic spectrum. The optical band gap of the films was close to 3.30 eV. Hall Effect measurements indicated that undoped and Al doped ZnO thin films showed an n-type conductivity, whereas ZnO:Al–N and ZnO:Ag–N thin films exhibited p-type conductivity, probably related to the formation of dual acceptor complexes related to nitrogen. Two types of p–n homojunctions (ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al) were fabricated by means of sol–gel spin-coating method. In both cases, a rectifying behavior was observed, as revealed by current–voltage measurements.     

Optimization of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin film absorber layer growth without sulphurization using triethanolamine as complexing agent for thin film solar cells applications

Quaternary kesterite Cu₂ZnSnS₄ (CZTS) thin films have been prepared via a simple spin-coating technique based on a sol–gel precursor of 2-methoxyethanol solution with metal salts and thiourea. Solution processed CZTS thin film growth parameters using complexing agent triethanolamine (TEA) have been investigated. Effects of complexing agent TEA on structural, morphological, optical, electrical and photovoltaic properties of CZTS thin films were systematically investigated. X-ray diffraction and Raman spectroscopy studies reveal that amorphous nature of CZTS thin film changes into polycrystalline with kesterite crystal structure with optimized TEA concentartion. Surface morphology of CZTS films were analyzed by field emission scanning electron microscope and atomic force microscope, which revealed the smooth, uniform, homogeneous and densely packed grains and systematic grain growth formation with varying TEA concentrations. UV–Vis spectra revealed a direct energy band gap ranging from 1.78 to 1.50 eV, which was found to depend upon the TEA concentration. X-ray photoelectron spectroscopy demonstrated stoichiometric atomic ratios of multicationic quaternary CZTS thin film grown without sulphurization. p-type conductivity was confirmed using Hall measurements and the effect of varying concentartion of TEA on electrical and photovoltaic properties are studied. The SLG/FTO/ZnO/CZTS/Al thin film solar cell is fabricated with the CZTS absorber layer grown at optimized TAE concentration of 0.06 M. It shows a power conversion efficiency of 0.87% for a 0.16 cm² area with V_oc = 0.257 mV, J_sc = 8.95 mA/cm² and FF?=?38%.     

Reproducibility and stability of N–Al codoped p-type ZnO thin films

Reproducible and stable p-type ZnO thin films have been prepared by the N–Al codoping method. Secondary ion mass spectroscopy measurements demonstrate that N and Al are incorporated into ZnO. The resistivity, carrier concentration, and Hall mobility are typically of 50–100 Ωcm, 1×10¹⁷–8×10¹⁷ cm⁻³, and 0.1–0.6 cm²/Vs, respectively, for the N–Al codoped p-type ZnO films. Hall measurement, X-ray diffraction, and optical transmission were carried out to investigate the changes of the properties with the storage period. Results show that the p-type characteristics of the N–Al codoped ZnO films are of acceptable reproducibility and stability. In addition, the N–Al codoped p-type ZnO films have good crystallinity and optical quality. The properties are time independent.     

Stable p-type conductivity and enhanced photoconductivity from nitrogen-doped annealed ZnO thin film

We report on the growth of p-type ZnO thin films with improved stability on various substrates and study the photoconductive property of the p-type ZnO films. The nitrogen doped ZnO (N:ZnO) thin films were grown on Si, quartz and alumina substrates by radio frequency magnetron sputtering followed by thermal annealing. Structural studies show that the N:ZnO films possess high crystallinity with c-axis orientation. The as-grown films possess higher lattice constants compared to the undoped films. Besides the high crystallinity, the Raman spectra show clear evidence of nitrogen incorporation in the doped ZnO lattice. A strong UV photoluminescence emission at ~ 380 nm is observed from all the N:ZnO thin films. Prior to post-deposition annealing, p-type conductivity was found to be unstable at room temperature. Post-growth annealing of N:ZnO film on Si substrate shows a relatively stable p-type ZnO with room temperature resistivity of 0.2 Ω cm, Hall mobility of 58 cm²/V s and hole concentration of 1.95 × 10¹⁷ cm^− 3. A homo-junction p-n diode fabricated on the annealed p-type ZnO layer showed rectification behavior in the current-voltage characteristics demonstrating the p-type conduction of the doped layer. Doped ZnO films (annealed) show more than two orders of magnitude enhancement in the photoconductivity as compared to that of the undoped film. The transient photoconductivity measurement with UV light illumination on the doped ZnO film shows a slow photoresponse with bi-exponential growth and bi-exponential decay behaviors. Mechanism of improved photoconductivity and slow photoresponse is discussed based on high mobility of carriers and photodesorption of oxygen molecules in the N:ZnO film, respectively.     

Effects of annealing on thermoelectric properties of Sb2Te3 thin films prepared by radio frequency magnetron sputtering

Antimony telluride (Sb₂Te₃) thin films were deposited on silicon substrates at room temperature (300 K) by radio frequency magnetron sputtering method. The effects of annealing in N₂ atmosphere on their thermoelectric properties were investigated. The microstructure and composition of these films were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. Both of the Seebeck coefficient and Hall coefficient measurement showed that the prepared Sb₂Te₃ thin films were p-type semiconductor materials. By optimizing the annealing temperature, the power factor achieved a maximum value of 18.02 μW cm^?1 K^?2 when the annealing temperature was increased to 523 K for 6 h with a maximum electrical conductivity (1.17 × 10³ S/cm) and moderate Seebeck coefficient (123.9 μV/K).     

Effect of growth temperature on structural, electrical and optical properties of dual ion beam sputtered ZnO thin films

ZnO epitaxial thin films were grown on p-type Si(100) substrates by dual ion beam sputtering deposition system. The crystalline quality, surface morphology, optical and electrical properties of as-deposited ZnO thin films at different growth temperatures were studied. Substrate temperature was varied from 100 to 600 °C at constant oxygen percentage O₂/(O₂ + Ar) % of 66.67 % in a mixed gas of Ar and O₂ with constant chamber pressure of 2.75 × 10^?4 mBar. X-Ray diffraction analyses revealed that all the films had (002) preferred orientation. The minimum value of stress was reported to be ?0.32 × 10¹⁰ dyne/cm² from ZnO film grown at 200 °C. Photoluminescence measurements demonstrated sharp near-band-edge emission (NBE) was observed at ~375 nm along with deep level emission (DLE) in the visible spectral range at room temperature. The DLE Peak was found to have decrement as ZnO growth temperature was increased from 200 to 600 °C. The minimum FWHM of the NBE peak of 16.76 nm was achieved at 600 °C growth temperature. X-Ray photoelectron spectroscopy study revealed presence of oxygen interstitials and vacancies point defects in ZnO film grown at 400 °C. The ZnO thin film was found to be highly resistive when grown at 100 °C. The ZnO films were found to be n-type conducting with decreasing resistivity on increasing substrate temperature from 200 to 500 °C and again increased for film grown at 600 °C. Based on these studies a correlation between native point defects, optical and electrical properties has been established.     

Fabrication and post-anneal activation of p-type ZnMgO:Li film using dc reactive magnetron sputtering

Monodoping Li as acceptor, p-type ZnMgO thin films have been realized via dc reactive magnetron sputtering followed by a thermal anneal process. The conductivity of Li-doped films are transformed from highly resistant to p-type via anneal. This phenomenon may be associated with eliminating of Li_Zn–Li_i complexes and Li_i. The optimized p-type Zn_0.96Mg_0.04O:Li thin film possesses a resistivity of 72.3Ω cm and a carrier concentration of 1.49 × 10¹⁷cm^{− 3}, while the electrical properties of Zn_0.84Mg_0.16O:Li thin film degrade in comparison to Zn_0.96Mg_0.04O:Li thin film. Moreover, the absorption spectra confirm Mg can be a good candidate for band gap engineering in p-type ZnO film.     

Transparent conducting zinc oxide thin film prepared by off-axis rf magnetron sputtering

Highly conducting and transparent ZnO : Al thin films were grown by off-axis rf magnetron sputtering on amorphous silica substrates without any post-deposition annealing. The electrical and optical properties of the films deposited at various substrate temperatures and target to substrate distances were investigated in detail. Optimized ZnO : Al films have conductivity of 2200 S cm^-1 and average transmission in the visible range is higher than 85%. The conductivity and mobility show very little temperature dependence.     

Low-temperature preparation of transparent conductive Al-doped ZnO thin films by a novel sol–gel method

We developed a novel sol–gel method to prepare transparent conductive Al-doped ZnO (AZO) thin film at low temperature. The AZO nanocrystals were prepared by a solvothermal method and then they were dispersed in the monoethanolamine and methanol to form AZO colloids. A (002)-oriented ZnO thin film was used as a nucleation layer to induce the (002)-oriented growth of AZO thin films. The AZO thin films were prepared on Si(100) and fused quartz glass substrates with the (002)-oriented ZnO nucleation layer and annealed at 400 °C for 60 min. All AZO thin films showed (002) orientation. For electrical and optical measurements, the films deposited on glass substrates were post-annealed at 400 °C for 30 min in forming gas (100 % H₂) to improve their conductivity. These samples had high transparency in the visible wavelength range, and also showed good conductivity. A 0.2 mol L^?1 AZO solution with 3 at.% Al content was heated in a Teflon autoclave at 160 °C for 30 min to form AZO nanocrystals, and then the AZO nanocrystals were suspended in the MEA and methanol to obtain the stable AZO colloid. The Al content in the AZO nanocrystals was 2.7 at.%, and the high Al doping coefficient was mainly attributed to the formation of AZO nanocrystals in the autoclave. The AZO thin film using this colloid had the lowest resistivity of 3.89 × 10^?3 Ω cm due to its high carrier concentration of 3.29 × 10²⁰ cm^?3.     

Influence of annealing temperature on structural,electrical and optical properties of undoped zinc oxide thin films

The undoped zinc oxide thin films were grown on quartz substrate at a substrate temperature of 750 °C by radio frequency magnetron sputtering and post annealed at different temperatures (600–800 °C) for a period of 30 min. The influence of annealing temperature on the structure, electrical and optical properties of undoped ZnO thin films was investigated by X-ray diffraction, Hall-effect, photoluminescence and optical transmission measurements. Results indicated that the electrical properties of the thin films were extremely sensitive to the annealing temperature and the conduction type could be changed dramatically from n-type to p-type, and finally changed to weak p-type when the temperature increased from 600 to 800 °C. Electrical and photoluminescence results indicate that native defects, such as oxygen and zinc vacancies, could play an important role in determining the conductivity of these nominally undoped ZnO thin films. The conversion of the conduction type was attributed to the competition between Zn vacancy acceptor and oxygen vacancy and interstitial Zn donors. At an intermediate annealing temperature of 750 °C, the film behaves the best p-type characteristic, which has the lowest resistivity of 12 Ωcm, hall mobility of 2.0 cm²/V s and carrier concentration of 1.5 × 10¹⁷ cm^?3. The photoluminescence results indicated that the Zn vacancy might be responsible for the intrinsic better p-type characteristic in ZnO thin films.     

Characterization of aluminum-doped zinc oxide thin films by RF magnetron sputtering at different substrate temperature and sputtering power

In this study, transparent conductive Al doped zinc oxide (ZnO: Al, AZO) thin films with a thickness of 40 nm were prepared on the Corning glass substrate by radio frequency magnetron sputtering. The properties of the AZO thin films are investigated at different substrate temperatures (from 27 to 150 °C) and sputtering power (from 150 to 250 W). The structural, optical and electrical properties of the AZO thin films were investigated. The optical transmittance of about 78 % (at 415 nm)–92.5 % (at 630 nm) in the visible range and the electrical resistivity of 7 × 10^?4 Ω-cm (175.2 Ω/sq) were obtained at sputtering power of 250 W and substrate temperature of 70 °C. The observed property of the AZO thin films is suitable for transparent conductive electrode applications.     

Effects of growth ambient on electrical properties of Al-N co-doped p-type ZnO films

p-Type zinc oxide thin films with c-axis orientation were prepared in N₂O-O₂ atmosphere by an Al-N co-doping method using reactive magnetron sputtering. Secondary ion mass spectroscopy (SIMS) measurements indicate that as-grown ZnO films were co-doped with Al and N. Hall effect measurements show a dependence of types of conduction, carrier concentration and mobility of as-grown ZnO films on N₂O partial pressure ratios. p-Type ZnO thin films deposited in a N₂O partial ratio of 10% show the highest hole concentration of 1.1×10¹⁷ cm⁻³, the lowest resistivity of about 100 Ω cm, and a low mobility of 0.3 cm² V⁻¹ s⁻¹.     

Effect of Ga doping concentrations,substrate temperatures and working pressures on the electrical and optical properties of ZnO thin films

We fabricated Ga-doped ZnO (GZO) thin films on glass substrate by RF magnetron sputtering method with different conditions of Ga₂O₃ concentration, substrate temperature and working pressure. Next we investigated the electrical, optical and structural properties of the GZO thin films. At a substrate temperature of 300 °C, a working pressure of 1 mTorr, and a Ga₂O₃ concentration of 3 wt%, the GZO thin films showed the lowest resistivity of 3.16 × 10^?4 Ω cm, a carrier concentration of 7.64 × 10²⁰ cm^?3 and a Hall mobility of 25.8 cm²/Vs. Moreover, the GZO thin films exhibited the highest (002) orientation under the same conditions and the full width at half maximum of X-ray peak was 0.34°. All GZO thin films showed the optical transmittance of more than 80 % in the visible range regardless of working conditions. The Burstein–Moss effect was observed by the change of doping concentration of Ga₂O₃. The GZO thin films were fabricated to have the good electrical and optical properties through optimizing doping concentration of Ga₂O₃, substrate temperature, working pressure. Therefore, we confirmed the possibility of application of GZO thin film as transparent conductive oxide used in flat panel display and solar cell.     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

Structural and opto-electric properties of Ga and F codoped ZnO thin films on PC substrates

Ga–F codoped ZnO (GFZO) thin films were firstly prepared on polycarbonate (PC) substrates by MF magnetron sputtering and the results were compared in detail with the Al doped ZnO (AZO) thin films. The influence of dopants on the structural and optoelectric properties of ZnO films was studied. X-ray diffraction and scanning electron microscopy results show that the cracks formed in both GFZO and AZO films due to the high residual stress, originating from the different thermal expansion coefficients between film/substrate. However, the GFZO films show better crystallinity and deliver larger grain size than AZO. A relative low resistivity of 1.4 × 10⁻³ Ω cm and a transmittance of 81% for the GFZO thin films are achieved, better than that of 2.3 × 10⁻² Ω cm and 75% for the AZO films. The results illustrate that the combined effects of Ga–F codoping and smaller crack density can optimise the opto-electric properties of ZnO based thin films.     

Preparation of p-type transparent conducting CuAlO2 thin films by reactive DC sputtering

P-type transparent conducting thin films of copper aluminate were prepared by reactive DC sputtering of a prefabricated target having 1:1 atomic ratio of Cu and Al. Films of CuAlO₂ were deposited on Si (400) and glass substrates. The sputtering was performed in Ar+O₂ (40 vol.%) atmosphere and the substrate temperature was 475 K. X-ray diffraction (XRD) spectra of the films showed the peaks which could be assigned with those of the crystalline CuAlO₂. UV–Visible spectrophotometric measurement showed high transparency of the films in the visible region. Both direct and indirect band gaps were found to exist and their corresponding estimated values were 3.75 and 1.85 eV, respectively. The room temperature conductivity of the film was fairly high and was of the order of 0.22 S cm⁻¹ while the activation energy was ∼0.25 eV. Seebeck coefficient at room temperature gave a value of +115 μV/K confirming the p-type conductivity. Room temperature Hall effect measurement also indicated positive value of Hall coefficient with a value R_H=14.1 cm³/C.     

Growth ambient dependent electrical properties of lithium and nitrogen dual-doped ZnO films prepared by radio-frequency magnetron sputtering

Lithium (Li) and nitrogen (N) dual-doped ZnO films with wurtzite structure were prepared by radio-frequency magnetron sputtering ZnO target with Li₃N in growth ambient of pure Ar and the mixture of Ar and O₂, respectively, and then post annealing techniques. The film showed week p-type conductivity as the ambient was pure Ar, but stable p-type conductivity with a hole concentration of 3.46 × 10¹⁷ cm^− 3, Hall mobility of 5.27 cm²/Vs and resistivity of 3.43 Ω cm when the ambient is the mixture of Ar and O₂ with the molar ratio of 60:1. The stable p-type conductivity is due to substitution of Li for Zn (Li_Zn) and formation of complex of interstitial Li (Li_i) and substitutional N at O site, the former forms a Li_Zn acceptor, and the latter depresses compensation of Li_i donor for Li_Zn acceptor. The level of the Li_Zn acceptor is estimated to be 131.6 meV by using temperature-dependent photoluminescence spectrum measurement and Haynes rule. Mechanism about the effect of the ambient on the conductivity is discussed in the present work.     

Nonlinear optical investigations on Al doping ratio in ZnO thin film under pulsed Nd:YAG laser irradiation

In the present study, it has been reported on the effect of Al doping on linear and nonlinear optical properties of ZnO thin films synthesized by spray pyrolysis method. The structural properties of ZnO thin films with different Al doping levels (0–4 wt%) were analyzed using X-ray diffraction (XRD). The results obtained from XRD analysis indicated that the grain size decreased as the Al doping value increased. The UV–Vis diffused refraction spectroscopy was used for calculation of band gap. The optical band gap of Al-doped ZnO (AZO) thin films is increased from 3.26 to 3.31 eV with increasing the Al content from 0 to 4 wt%. The measurements of nonlinear optical properties of AZO thin films have been performed using a nanosecond Nd:YAG pulse laser at 532 nm by the Z-scan technique. The undoped ZnO thin film exhibits reverse saturation absorption (RSA) whereas the AZO thin films exhibit saturation absorption (SA) that shows RSA to SA process with adding Al to ZnO structure under laser irradiation. On the other hand, all the films showed a self-defocusing phenomenon because the photons of laser stay on below the absorption edge of the ZnO and AZO films. The third-order nonlinear optical susceptibility, χ⁽³⁾, of AZO thin films, was varied from of the order of 10^?5–10^?4 esu. The results suggest that AZO thin films may be promising candidates for nonlinear optical applications.     

Activation of p-type conduction in ZnO:N films by annealing in atomic oxygen

ZnO:N epitaxial films have been grown by reactive magnetron sputtering. The effect of annealing in atomic oxygen on the structural and electrical properties of the ZnO:N films has been studied by X-ray diffraction, atomic force microscopy, Hall effect measurements, and X-ray photoelectron spectroscopy. By annealing at temperatures from 500 to 700°C, we have obtained p-type ZnO:N films with a resistivity of ～57 Ω cm, hole mobility of ～2.7 cm²/(V s), and hole concentration of ～6.8 × 10¹⁷ cm^?3. X-ray photoelectron spectroscopy results suggest that the p-type conductivity of the films is due to a decrease in the concentration of (N₂)_O and V _O donors.