Influence of annealing temperature on the properties of ZnO thin films deposited by thermal evaporation

ZnO thin films were deposited by thermal evaporation of a ZnO powder. The as-deposited films are dark brown, rich zinc and present a low transmittance. Then, these films were annealed in air atmosphere at different temperatures between 100 and 400 °C. Their microstructure and composition were studied using XRD and RBS measurements respectively. By increasing the temperature, it was found that film oxidation starts at 250 °C. XRD peaks related to ZnO appear and peaks related to Zn decrease. At 300 °C, zinc was totally oxidised and the films became totally transparent. The electrical conductivity measurement that were carried out in function of the annealing temperature showed the transition from highly conductive Zn thin film to a lower conductive ZnO thin film. The optical gap (E_g) was deduced from the UV-vis transmittance, and its variation was linked to the formation of ZnO.     

Effects of processing on the electrical and structural properties of spray deposited CdS:In thin films

Polycrystalline CdS:In thin films were prepared by the Spray pyrolysis technique (SP) at a substrate temperature T_s=490 °C. The effects of annealing in nitrogen atmosphere at 400 °C and HCl-etching on the electrical and structural properties of the films were investigated. The electrical properties were studied through the analysis of the I-V curves, while the structural properties were studied through the analysis of the X-ray diffraction (XRD) patterns and the scanning electron microscope (SEM) images. An increase in the films’ resistivity was occurred after annealing and/or HCl-etching, which was accompanied by changes in the XRD patterns and SEM images. These changes were related to a phase change from the mixed (cubic and hexagonal) phase to the hexagonal phase which was expected to occur during the aforementioned processes. The X-ray diffraction (XRD) patterns and the scanning electron microscope images confirm this expectation.     

Investigation of Ni/Ta contacts on 4H silicon carbide upon thermal annealing

Nickel and Tantalum thin films with 3:5 thickness ratios were deposited in succession onto 4H-SiC substrate at room temperature. The samples were then heated in situ in vacuum at 650, 800 or 950 °C for 30 min. Glancing angle X-ray diffraction (XRD), Auger electron spectroscopy (AES) and current-voltage (I-V) technique were used for characterising the interfacial reactions and electrical properties. Amorphous Ni-Ta can be formed by solid-state reaction at 650 °C. The minor dissolved Ni in the Ta metal promotes the reaction between Ta and SiC. With increasing annealing temperature up to 950 °C, the dominant carbide changes from Ta₂C to TaC and a layer structure is developed. Electrical measurements show that ohmic contact is formed after annealing at or above 800 °C.     

Switching phenomenon and optical properties of Se85Te10Bi5 films

Se₈₅Te₁₀Bi₅ films of different thicknesses ranging from 126 to 512 nm have been prepared. Energy-dispersive X-ray (EDX) spectroscopy technique showed that films are nearly stoichiometric. X-ray diffraction (XRD) measurements have showed that the Se₈₅Te₁₀Bi₅ films were amorphous. Electrical conduction activation energy (ΔE_σ) for the obtained films is found to be 0.662 eV independent of thickness in the investigated range. Investigation of the current voltage (I-V) characteristics in amorphous Se₈₅Te₁₀Bi₅ films reveals that it is typical for a memory switch. The switching voltage V_th increases with the increase of the thickness and decreases exponentially with temperature in the range from 298 to 383 K. The switching voltage activation energy (ε) calculated from the temperature dependence of V_th is found to be 0.325 eV. The switching phenomenon in amorphous Se₈₅Te₁₀Bi₅ films is explained according to an electrothermal model for the switching process. The optical constants, the refractive index (n) and the absorption index (k) have been determined from transmittance (T) and reflectance (R) of Se₈₅Te₁₀Bi₅ films. Allowed non-direct transitions with an optical energy gap (E_g^opt) of 1.33 eV have been obtained. ΔE_σ is almost half the obtained value of E_g^opt, which suggested band to band conduction as indicated by Davis and Mott.     

Structural and optical properties of zinc nitride films prepared by rf magnetron sputtering

Zinc nitride films were prepared on quartz substrates by rf magnetron sputtering using pure zinc target in N₂-Ar plasma. X-ray diffraction (XRD) analysis indicates that the films just after deposition are polycrystalline with a cubic structure and a preferred orientation of (4 0 0). X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of N-Zn bonds and the substitution incorporation of oxygen for nitrogen on the surface of the films. The optical band gap is calculated from the transmittance spectra of films just after deposition, and a direct band gap of 1.01 ± 0.02 eV is obtained. Room temperature PL measurement is also performed to investigate the effect of defect on the band gap and quality of the zinc nitride films.     

Characteristics of low-temperature-grown GaN films on Si(111)

In this paper, we report on the characteristics of GaN films grown on Si(111) at a low temperature (200 °C) by electron cyclotron resonance (ECR) plasma-assisted metalorganic chemical vapor deposition (PA-MOCVD). Structural analysis of the GaN films was performed by using scanning electron microscopy (SEM), atomic force miscroscopy (AFM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), and Rutherford backscattering spectrometry (RBS). Post deposition analysis revealed high quality crystalline GaN was obtained at this low temperature. Electrical analysis of the GaN films was done by using current-voltage (I-V) measurements where electrical characterizations were carried on GaN/Si heterojunction and Schottky barrier diodes. Rectification behaviour was observed for the isotype GaN/Si (n-n) heterojunction. Ideality factors and Schottky barrier heights for Ni and Cr Schottky barriers on GaN, were deduced to be 1.4 and 1.7; and 0.62 and 0.64 eV, respectively.     

Optical and electrical properties of thermally evaporated In49Se48Sn3 films

Nearly stoichiometric thin films of In₄₉Se₄₈Sn₃ were deposited at room temperature, by conventional thermal evaporation of the presynthesized materials, onto precleaned glass substrates. The microstructural studies on the as-deposited and annealed films, using transmission electron microscopy and diffraction (TEMD), revealed that the as-deposited films are amorphous in nature, while those annealed at 498 K are crystalline. The optical properties of the investigated films were determined from the transmittance and reflectance data, in the spectral range 650-2500 nm. An analysis of the optical absorption spectra revealed a non-direct energy gap characterizing the amorphous films, while both allowed and forbidden direct energy gaps characterized the crystalline films. The electrical resistance of the deposited films was carried out during heating and cooling cycles in the temperature range 300-600 K. The results show an irreproducible behavior, while after crystallization the results become reproducible. The analysis of the temperature dependence of the resistance (ln(R) vs. 1000/T) for crystalline films shows two straight lines corresponding to both extrinsic and intrinsic conduction. The room temperature I-V characteristics of the as-deposited films sandwiched between similar Ag metal electrodes shows an ohmic behavior, while non-ohmic behavior attributed to space charge limited conduction has been observed when the films are sandwiched between dissimilar Ag/Al metal electrodes.     

Effect of indium incorporation on properties of SnS thin films prepared by spray pyrolysis

Tin sulphide (SnS) thin films were deposited on glass substrate at different substrate temperature (T_s = 325 °C, 350 °C and 375 °C) by pyrolytic decomposition using stannous chloride and thiourea as precursor solutions. Also, indium-doped SnS thin films were prepared by using InCl₃ as dopant source. The dopant concentration [In/Sn] was varied from 2 at% to 6 at%. The XRD analysis revealed that the films were polycrystalline in nature having orthorhombic crystal structure with a preferred grain orientation along (1 1 1) plane. Due to In doping, the orientation of the grains in the (1 1 1) plane was found to be deteriorated. Atomic force microscopy (AFM) measurements revealed that the surface roughness of the films decreased due to indium doping. The optical properties were investigated by measuring the transmittance characteristics which were used to find the optical band gap energy, refractive index and extinction coefficient. The energy band gap value was decreased from 1.60 to 1.43 eV with increasing In concentration. The photoluminescence (PL) measurements of thin films showed strong emission band centered at 760 nm. Using Hall Effect measurements electrical resistivity, carrier concentration and Hall mobility have been determined.     

Structural, optical properties and VCNR mechanisms in vacuum evaporated iodine doped ZnSe thin films

Iodine doped ZnSe thin films were prepared onto uncoated and aluminium (Al) coated glass substrates using vacuum evaporation technique under a vacuum of 3 × 10⁻⁵ Torr. The composition, structural, optical and electrical properties of the deposited films were analyzed using Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and study of I-V characteristics, respectively. In the RBS analysis, the composition of the deposited film is calculated as ZnSeI_0.003. The X-ray diffractograms reveals the cubic structure of the film oriented along (1 1 1) direction. The structural parameters such as crystallite size, strain and dislocation density values are calculated as 32.98 nm, 1.193 × 10⁻³ lin⁻² m⁻⁴ and 9.55 × 10¹⁴ lin/m², respectively. Spectroscopic ellipsometric (SE) measurements were also presented for the prepared iodine doped ZnSe thin films. The optical band gap value of the deposited films was calculated as 2.681 eV by using the optical transmittance measurements and the results are discussed. In the electrical studies, the deposited films exhibit the VCNR conduction mechanism. The iodine doped ZnSe films show the non-linear I-V characteristics and switching phenomena.     

Ultraviolet photoconductive detector based on Al doped ZnO films prepared by sol-gel method

We report a study on the fabrication and characterization of ultraviolet photodetectors based on ZnO:Al films. Using sol-gel technique, highly c-axis oriented ZnO films with 5 mol% Al doping were deposited on Si(1 1 1) substrates. The photoconductive UV detectors based on ZnO:Al thin films, having a metal-semiconductor-metal (MSM) structure with interdigital (IDT) configuration, were fabricated by using Au as a contact metal. The characteristics of dark and photocurrent of the UV detector and the UV photoresponse of the detector were investigated. The linear current-voltage (I-V) characteristics under both forward and reverse bias exhibit ohmic metal-semiconductor contacts. Under illumination using monochromatic light with a wavelength of 350 nm, photo-generated current was measured at 58.05 μA at a bias of 6 V. The detector exhibits an evident wide-range spectral responsivity and shows a trend similar to that in transmittance and photoluminescence spectrum.     

Spray pyrolytic synthesis of large area NiOx thin films from aqueous nickel acetate solutions

Non-stoichiometric nickel oxide thin films were prepared by pyrolytic decomposition of aerosol droplets of aqueous nickel acetate solution. Conventional un-nebulized spray pyrolysis system was used for the synthesis of thin films. The fine droplets were atomized by employing compressed air as carrier gas and allowed to decompose onto pre-heated Sn doped In₂O₃ (ITO) coated glass. The preparative parameters such as substrate temperature, solution concentration, distance from spray-nozzle to substrate, pressure of carrier air, etc., were optimized to obtain large area, uniform, thin films. The appropriate substrate temperature was selected after thermo-gravimetric analysis of nickel acetate. The temperature range of 330-420 °C was investigated for pyrolysis. Structural studies using X-ray diffraction (XRD) show the formation of cubic NiO. Morphological aspects of the films as-prepared and air annealed films have been studied by employing scanning electron microscopy. The optical absorption studies give direct band gap equal to 3.61 eV. The compositional analysis was carried out from the elemental depth profiles employing Auger electron spectroscopy. These indicate the formation of non-stoichiometric nickel oxide thin films. By studying I-V characteristics in alkaline electrolyte, electrocatalytic activity is tested.     

Influence of temperature annealing on optical properties of SrTiO3/BaTiO3 multilayered films on indium tin oxide

We have prepared SrTiO₃/BaTiO₃ thin films with multilayered structures deposited on indium tin oxide (ITO) coated glass by a sol-gel deposition and heating at 300-650 °C. The optical properties were obtained by UV-vis spectroscopy. The films show a high transmittance (approximately 85%) in the visible region. The optical band gap of the films is tunable in the 3.64-4.19 eV range by varying the annealing temperature. An abrupt decrease towards the bulk band gap value is observed at annealing temperatures above 600 °C. The multilayered film annealed at 650 ° C exhibited the maximum refractive index of 2.09-1.91 in the 450-750 nm wavelength range. The XRD and AFM results indicate that the films annealed above 600 ° C are substantially more crystalline than the films prepared at lower temperatures which were used to change their optical band gap and complex refractive index to an extent that depended on the annealing temperature.     

A study on the optical and electrical properties of direct-patternable ZnO films incorporated various contents of Pt nanoparticles

Platinum nanoparticles were synthesized by the methanol reduction method, and their size was controlled to 3 nm on average using PVP [poly(N-vinyl-2-pyrrolidon)] as a protecting unit. Various contents of Pt nanoparticles were incorporated into ZnO solutions which were synthesized by a sol-gel process. ZnO films with Pt nanoparticles of various content were annealed at 500 °C and 600 °C for 1 h. The crystallinity increased with the annealing temperature and also slightly with the content of Pt nanoparticles. The sheet resistance of ZnO films decreased with the incorporation of Pt nanoparticles, however the decreasing behavior was not maintained with increasing content of Pt nanoparticles. A shift of valence band maximum energy of ZnO film with Pt nanoparticles to higher energy was also observed due to electron transfer from Pt nanoparticles to ZnO film. The optical transmittance was 88 ± 2% in the visible region for all the ZnO films. Well-defined 60 μm wide direct-patterned ZnO films containing Pt nanoparticles of 0.5 atomic percent could be formed without using dry etching process.     

Annealing temperature effect on the structural, optical and electrical properties of ZnS thin films

Zinc sulfide thin films were prepared on glass substrates at room temperature using a chemical bath deposition method. The obtained films were annealed at temperatures ranging from 100 to 500 °C in steps of 100 °C for 1 h. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray analysis (EDX), optical absorption spectra, and electrical measurements. X-ray diffraction analysis indicates that the deposited films have an amorphous structure, but after being annealed at 500 °C, they change to slightly polycrystalline. The optical constants such as the refractive index (n_r), the extinction coefficient (k), and the real (ε₁) and imaginary (ε₂) parts of the dielectric constant are calculated depending on the annealing temperature. Aside from the ohmic characteristics of the I-V curve, a nonlinear I-V curve owing to the Schottky contact is also found, and the barrier heights (?_bn) for Au/n-ZnS and In/n-ZnS heterojunctions are calculated. The conductivity type was identified by the hot-probe technique.     

Characterization of the low temperature dopant activation behavior at NiSi/silicon interface formed by implant into silicide method

Process temperature and thermal budget control are very important for high-k dielectric device manufacturing. This work focuses on the characteristics of low temperature activated nickel silicide/silicon (M/S) interface formed by implant into silicide (IIS) method. By combining SIMS, C-V, I-V, and AFM measurements in this work, it provides a clear picture that the high dopant activation ratio can be achieved at low temperature (below 600 °C) by IIS method. From SIMS and C-V measurements, high dopant activation behavior is exhibited, and from I-V measurement, the ohmic contact behavior at the M/S junction is showed. AFM inspection displays that under 2nd RTA 700 °C 30 s no agglomeration occurs. These results suggest that IIS method has the potential to integrate with high-k dielectric due to its low process temperature. It gives an alternate for future device integration.     

Optical properties of Al-doped ZnO thin films by ellipsometry

Al-doped ZnO thin films (AZO) were prepared on Si (1 0 0) substrates by using sub-molecule doping technique. The Al content was controlled by varying Al sputtering time. The as-prepared samples were annealed in vacuum chamber at 800 °C for 30 min. From the XRD observations, it is found that all films exhibit only the (0 0 2) peak, suggesting that they have c-axis preferred orientation. The average transmittance of the visible light is above 80%. Spectroscopic ellipsometry was used to extract the optical constants of the films. The absorption coefficient and the energy gap were then calculated. The results show that the absorption edge initially blue-shifts and then red-shifts with increase of Al content.     

Effects of growth temperature on Li-N dual-doped p-type ZnO thin films prepared by pulsed laser deposition

Li-N dual-doped p-type ZnO (ZnO:(Li,N)) thin films have been prepared by pulsed laser deposition. The introduction of Li and N was confirmed by secondary ion mass spectrometry measurements. The structural, electrical, and optical properties as a function of growth temperature were investigated in detail. The lowest room-temperature resistivity of 3.99 Ω cm was achieved at the optimal temperature of 450 °C, with a Hall mobility of 0.17 cm²/V s and hole concentration of 9.12 × 10¹⁸ cm⁻³. The ZnO:(Li,N) films exhibited good crystal quality with a complete c-axis orientation, a high transmittance (about 90%) in the visible region, and a predominant UV emission at room temperature. The two-layer-structure p-ZnO:(Li,N)/n-ZnO homojunctions were fabricated on a sapphire substrate. The current-voltage characteristics exhibited the rectifying behavior of a typical p-n junction.     

Structural and optical properties of Au-implanted ZnO films

The structural and luminescence related optical behaviours of Au ion implanted ZnO films grown by magnetic sputtering and their post implantation annealing behaviours in the temperature range of 100-700 °C have been investigated. Optical absorption and transmittance spectra of the films indicate that band edge of Au-implanted ZnO has shifted to high energy range and optical band gap has increased, because the sharp difference of thermal expansion induces the lattice mismatch between ZnO and SiO₂. PL spectra reveal that UV and visible luminescence bands of ZnO films can be improved after thermal annealing due to recovery of defects and Au ions incorporation. Importantly, green luminescence band of 530 nm has been only observed in the Au-implanted and subsequently annealed ZnO films and it enhances with the increasing annealing temperature, which can be related to Au atoms or clusters in ZnO films. Furthermore, X-ray photoelectron spectroscopy measurements reveal that the Au⁰ is dominant state in Au implanted and annealed ZnO films. Possible mechanisms, such as optical transitions of Au atoms or clusters and deep level luminescence of ZnO, have been proposed for green emission.     

Structural and optoelectronic properties of antimony tin sulphide thin films deposited by thermal evaporation techniques

Thin films of SnSb₂S₄ have been prepared on glass substrate by using thermal evaporation techniques. The films were annealed in argon gas at low pressure in sealed glass ampoules at 85 °C, 150 °C, 275 °C and 325 °C. XRD of the films reveal that the low temperature annealed films are poly crystalline while the as deposited films and high annealed films are in amorphous states. There is no adequate variation in the photoconductivity response of the amorphous and crystalline phases. The transmittance of the films is low and having no transmittance below 740 nm. The band gap calculated by ellipsometry technique is in the range of 1.82–3.1 eV. The films have n-type conductivity but the film annealed at 325 °C show p-type conductivity.     

Properties of ZnO thin films deposited on (glass,ITO and ZnO:Al) substrates

ZnO thin films were deposited on glass, ITO (In₂O₃; Sn) and on ZnO:Al coated glass by spray pyrolysis. The substrates were heated at 350 °C. Structural characterization by X-ray diffraction (XRD) measurements shows that films crystallize in hexagonal structure with a preferential orientation along (0 0 2) direction. XRD peak-shift analysis revealed that films deposited on glass substrate (−0.173) were compressive, however, films deposited onto ITO (0.691) and on ZnO:Al (0.345) were tensile. Scanning electron microscopies (SEM) show that the morphologies of surface are porous in the form of nanopillars. The transmittance spectra indicated that the films of ZnO/ITO/glass and ZnO/ZnO:Al/glass exhibit a transmittance around 80% in the visible region. An empirical relationship modeled by theoretical numerical models has been presented for estimating refractive indices (n) relative to energy gap. All models indicate that the refractive index deceases with increasing energy band gap (E_g).