Electrical characterization of nanocrystalline SnSe and ZnSe thin films: effect of annealing

In this paper, experimental data on the electrical properties of as deposited and annealed nanocrystalline SnSe and ZnSe thin films are reported. The thin films of SnSe and ZnSe are deposited on glass substrate by chemical bath deposition method. The films are studied before and after thermal annealing at temperatures 473 K for 1 h. This annealing is done in vacuum of 2?×?10^?3 mbar. The various electrical parameters like dark conductivity, photoconductivity, activation energy, photosensitivity and carrier life time have been measured on these films before and after annealing.     

Annealing effect of ZnO/Au/ZnO transparent conductive films

Au intermediate ZnO (ZAZ) thin films were prepared by radio frequency and direct current magnetron sputtering on glass substrates and then vacuum annealed. The thickness of each layer of the ZAZ films was set at 50 nm, 3 nm, and 47 nm, respectively. The structural, electrical, and optical properties of ZAZ films were investigated with respect to the variation of annealing temperature.As-deposited AZO films showed X-ray diffraction peaks corresponding to ZnO (002) and Au (111) planes and those peak intensities increased with post-deposition vacuum annealing. The optical and electrical properties of the films were strongly influenced by post-deposition annealing. Although the optical transmittance of the films deteriorated with an Au interlayer, as-deposited ZAZ films showed a low resistivity of 2.0 × 10⁻⁴ Ω cm, and the films annealed at 300 °C had a lower resistivity of 9.8 × 10⁻⁵ Ω cm. The work function of the films increased with annealing temperature, and the films annealed at 300 °C had a higher work function of 4.1 eV than the films annealed at 150 °C. The experimental results indicate that vacuum-annealed ZAZ films are attractive candidates for use as transparent electrodes in large area electronic applications such as solar cells and large area displays.     

Highly transparent and conducting In doped CdO synthesized by sol-gel solution processing

Cadmium oxide (CdO) is a much-studied wide gap semiconductor with an inherent high mobility of?>?100 cm²/Vs, high electron concentration of?>?10²¹ cm^?3 and a wide optical transparency window of?>?1800 nm. These unique properties make CdO a potential transparent conductor for full spectrum photovoltaics. However, in order to achieve optimum material properties for optoelectronic applications, CdO was grown by vacuum-based physical or chemical vapor deposition methods. In this work, we explored the application of a low-cost sol-gel spin coating method to achieve highly conducting and transparent CdO thin films doped with 0–10% In (CdO:In). We find that while as-grown CdO:In films are nanocrystalline/amorphous with a high resistivity of?~?1 Ω-cm, polycrystalline and highly conducting films can be obtained after optimized annealing at?≥?400 °C. However, the electron concentration n saturates at?~?5?×?10²⁰ cm^?3 for In concentration?>?5% (or N_In?~?1.9?×?10²¹ cm^?3). This low activation of In may be attributed to the high density of native defects and/or impurities incorporated in the sol-gel process. With 5% In doping, we obtained a low resistivity of ρ?~?2.5?×?10^–4 Ω-cm and a high mobility μ?~?50 cm²/Vs. These values of σ and µ are better than those reported for other TCOs synthesized by solution processes and comparable to conventional commercial TCOs grown by physical vapor deposition methods. Benefiting from their high mobility, these sol-gel CdO:In films are optically transparent over a wide spectral range up to λ?>?1800 nm, making them promising as transparent conductors for optoelectronic devices utilizing the infrared photons.

     

Impact of various irradiation photon energies and gamma doses on the optical properties of ZnSe nanostructure thin film

ZnSe thin films were prepared by thermal evaporation technique under high vacuum (10⁻⁶ Torr) at 300 K and different film thickness. The structure of thin films was measured using grazing incident in-plane X-ray diffraction (GIIXD) and shows single phase zinc blende structure. The particle sizes of the deposited films were estimated for low film thickness by TEM and high film thickness by GIIXD. The particle size of ZnSe films was decreased from ~8.53 to 3.93 nm as film thickness lowered from 200 to 20 nm which ensures the nanocrystalline structure. The optical transmission (T) and reflection (R) in the wavelength range 190–2,500 nm for irradiated and unirradiated ZnSe thin films under investigation were measured. The effect of irradiation of different energies in range (0.1–1.25 MeV) from X-ray, ¹³⁷Cs and ⁶⁰Co irradiation sources were studied for ZnSe thin films of 100 and 200 nm thicknesses. The dependence of the absorption spectra and refractive index were investigated for different energies irradiation sources. The ZnSe films show direct allowed interband transition. The effect of particle size of nanocrystalline ZnSe thin films for unirradiated and irradiated by gamma (γ) doses from ¹³⁷Cs on the optical properties was studied. Both the optical energy bandwidth and absorption coefficient (α) were found to be (γ) dose dependent.     

Effect of vacuum annealing and hydrogenation on ZnSe/Mn multilayer diluted magnetic semiconductor thin films

Multilayer thin films of ZnSe/Mn diluted magnetic semiconductor have been physically deposited onto a glass substrate using thermal evaporation technique and vacuum annealed at 333 K for 1 h at base pressure of 10⁻⁵ Torr. These thin films have been hydrogenated at different pressures (15-45 psi) for half an hour at room temperature. Hydrogenation process has been performed for as- grown as well as annealed thin films and named as-grown hydrogenated and annealed hydrogenated DMS thin films respectively. Structural characteristics of as-grown and vacuum annealed thin films have been performed by X-ray diffractometer. Current-voltage measurement has been studied for both as- grown hydrogenated and annealed hydrogenated DMS thin films by Keithly electrometer. X-ray diffraction pattern has been revealed nanocrystalline single phase of cubic zinc blende structure of film. Due to the annealing the conductivity has been found to be increased indicating the mixing of multilayer whereas the conductivity for as-grown hydrogenated and annealed hydrogenated ZnSe/Mn DMS thin films was found to be reduced indicating the electronic passivation effect of hydrogenation. Raman spectra of as-grown and annealed hydrogenated samples have been taken to see the presence of hydrogen in these samples. Surface topography of as-grown and annealed multilayer thin films has been confirmed by optical microscopy. Surface topography of annealed hydrogenated samples clearly shows the effect of hydrogenation at the surface.     

Effect of Vacuum and O2 Annealing Treatments on Structural and Magnetic Properties of La0.5Ca0.5MnO3 Thin Films

La_0.5Ca_0.5MnO₃ films with a nominal thickness of 80 nm were epitaxially grown on (001) SrTiO₃ and SrLaAlO₄ substrates by the pulsed laser deposition technique. The magnetic moment of the films was observed to depend strongly on the oxygen stoichiometry, tuned by heat treatments in vacuum and O₂ environments. A distinctly larger out-of-plane lattice parameter was measured for the vacuum-annealed films due to transformation of some Mn⁴⁺ ions to Mn³⁺. Both the variations in the magnetic moment and out-of-plane lattice parameter during vacuum annealing can be recovered by subsequent heat treatments in O₂ environment. In this study, it is shown that the enhancement of the magnetic moment via O₂ annealing is considerably less prominent than the respective improvement obtained by the application of compressive epitaxial strain.     

Study of structural,optical and electrical parameters of ZnSe powder and thin films

Nanocrystalline ZnSe powder and thin film forms have been synthesized via chemical bath deposition technique. The ZnSe thin films are deposited onto ultrasonically clean glass substrates in an aqueous alkaline medium using sodium selenosulphate as Se^2? ion source. The ZnSe powder and thin film are characterized by structural, optical and electrical properties. It is confirmed from X-ray diffraction study that cubic phase is present in ZnSe thin film form with (111) as preferred orientation and hexagonal phase is present in ZnSe powder form with (100) as preferred orientation. Optical absorption measurement indicates the existence of direct allowed optical transition with a wide energy gap and blue shift in the fundamental edge has been observed in both cases. The optical band gap of ZnSe powder is greater than the thin film. The electrical conductivity (both dark and photoconductivity) measurements are also carried out in different temperature range and variation in activation energy has been calculated.     

Effect of a ZnSe Layer on the Thermochromic Properties of MoO3 Thin Films

The effect of a ZnSe layer on the thermochromic properties of MoO₃ thin films was investigated. ZnSe/MoO₃ and MoO₃ thin films were deposited by thermal evaporation in vacuum of MoO₃ and ZnSe powders. Photoacoustic spectra of the films indicated that the thermochromic response for the ZnSe/MoO₃ bilayer system was more accentuated, with respect to the MoO₃ sample, for temperature treatments above 150?°C. This result is explained in terms of the injection of electrons from the II?CVI semiconductor to the oxide film.     

Electrical Properties and Leakage Current Mechanisms of Bi<Subscript>3.2</Subscript>Gd<Subscript>0.8</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films Prepared by a Sol-Gel Method

Bi_3.2Gd_0.8Ti₃O₁₂ (BGTO) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates using the sol-gel method and rapid thermal annealing in an oxygen atmosphere. The effects of annealing temperature (500–800°C) on microstructure and electrical properties of thin films were investigated. X-ray diffraction analysis shows that the BGT thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The intensities of (117) peaks increases with increasing annealing temperature. The leakage current density (J) was 3.69×10⁻⁸ A/cm² at 200 kV/cm. It was found that the leakage current was affected not only by the microstructure but also by the interface between the Pt electrode and BGTO thin films. In the low electric field region, the leakage current was controlled by Poole–Frenkel emission. In addition, the mechanism can be explained by Schottky emission from the Pt electrode in the high electric field region.     

Deposition of AgGaS<Subscript>2</Subscript> thin films by double source thermal evaporation technique

In this study, polycrystalline AgGaS₂ thin films were deposited by the sequential evaporation of AgGaS₂ and Ag sources with thermal evaporation technique. Thermal treatment in nitrogen atmosphere for 5 min up to 700 °C was applied to the deposited thin films and that resulted in the mono phase AgGaS₂ thin films without the participation of any other minor phase. Structural and compositional analyses showed the structure of the films completely changes with annealing process. The measurements of transmittance and reflectance allowed us to calculate the band gap of films lying in 2.65 and 2.79 eV depending on annealing temperature. The changes in the structure with annealing process also modify the electrical properties of the films. The resistivity of the samples varied in between 2 × 10³ and 9 × 10⁶ (Ω-cm). The room temperature mobility depending on the increasing annealing temperature was in the range of 6.7–37 (cm² V⁻¹ s⁻¹) with the changes in carrier concentrations lying in 5.7 × 10¹³–2.5 × 10¹⁰ cm⁻³. Mobility-temperature dependence was also analyzed to determine the scattering mechanisms in the studied temperature range with annealing. The variations in the electrical parameters of the films were discussed in terms of their structural changes.     

Investigation of structural,optical and electrical properties of (Ti,Nb)Ox thin films deposited by high energy reactive magnetron sputtering

In this work the results of investigations of the titanium-niobium oxides thin films have been reported. The thin films were manufactured with the aid of a modified reactive magnetron sputtering process. The aim of the research was the analysis of structural, optical and electrical properties of the deposited thin films. Additionally, the influence of post-process annealing on the properties of studied coatings has been presented. The as-deposited coatings were amorphous, while annealing at 873 K caused a structural change to the mixture of TiO₂ anatase-rutile phases. The prepared thin films exhibited good transparency with transmission level of ca. 50 % and low resistivity varying from 2 Ωcm to 5×10^?2 Ωcm, depending on the time and temperature of annealing. What is worth to emphasize, the sign of Seebeck coefficient changed after the annealing process from the electron to hole type electrical conduction.     

Effects of annealing atmosphere on microstructure and ferroelectric properties of praseodymium-doped Bi4Ti3O12 thin films prepared by sol-gel method

Praseodymium-substituted bismuth titanate (Bi_3.2Pr_0.8Ti₃O₁₂, BPTO) thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by spin coating with a sol-gel technology and rapid thermal annealing. The effects of annealing atmospheres (vacuum, ambient atmosphere and oxygen) on the growth and properties of thin films were investigated. The results show that the intensity of the (117) diffraction peak of Bi_3.2Pr_0.8Ti₃O₁₂ film annealed in oxygen is stronger than those annealed in ambient atmosphere and vacuum. The XRD spectra demonstrated that a highly (117) orientation could be obtained when the Bi_3.2Pr_0.8Ti₃O₁₂ thin film was annealed in an oxygen-sufficient environment. The BPTO thin films annealed in oxygen atmosphere exhibits the maximum remanent polarization (2P_r) of 49 μC/cm² and a low coercive field (2E_c) of 130 kV/cm, fatigue free characteristics up to ≧ 10¹¹ switching cycles. These results indicate that the BPTO thin film is useful in nonvolatile ferroelectric random access memory applications.     

Cold-walled,in-situ sulfurization of Cu–In alloys

This article reports cold-walled, in-situ sulfurization of Cu₁₁In₉ for the formation of CuInS₂. The deposition of the precursor Cu–In layered films, the thermal annealing of the layered films, and the subsequent sulfurization of the annealed films were all performed in chamber without breaking the vacuum. The sulfurization was conducted at various pressures and temperatures under a 10% H₂S/Ar mixture. Conversion of the Cu₁₁In₉ phase to the desired CuInS₂ phase was achieved in 1 h at 146.7 Pa and 550 °C or at 1000 Pa and 450 °C. The CuInS₂ films obtained show low resistivity of the order of 10^? 1 Ω-cm and absorbance > 90%. A CuInS₂ film with a rougher surface exhibits a higher absorption coefficient.     

Effect of temperature on microstructure and electrical properties of TaSi2 thin films grown on Si substrates

Tantalum silicide (TaSi₂) thin films were deposited on n-type silicon single crystal substrates using a dual electron-gun system and with Ta and Si targets. The thicknesses of TaSi₂ thin films considered in this study are in the range 200-500 nm, respectively. The TaSi₂/Si samples were annealed at temperature 1173 K for 2 h in a vacuum of 10⁻⁸ mbar. The structure of the tantalum silicide thin films was investigated by X-ray diffraction (XRD). X-ray diffraction results show changes in the structure of TaSi₂ thin films from amorphous to crystalline after annealing. According to XRD analysis, a complete conversion to single-phase disilicide TaSi₂ was achieved from a sample composition of Ta:Si = 1:2. DC conductivity was measured for the TaSi₂ thin films in the temperature range 300-900 K before and after annealing. It has been observed that the DC conductivity and activation energy was affected by changing the TaSi₂ film thickness and by annealing. The experimental results indicate that, the conduction phenomena of the investigated sample proceeded via two distinct mechanisms. The first one in the low-temperature range T < 500 K can be described by thermally-assisted tunneling of the carriers in the localized states near the band edge. The value of the pre-exponential factor before and after annealing is less than 10⁴ Ω⁻¹ cm⁻¹. The other process appears in the high temperature region T > 500 K, where thermally activated conduction occurs through the extended states. Here the value of the pre-exponential factor before and after annealing is larger than 10⁴ Ω⁻¹ cm⁻¹. The conductivity is greater in the crystalline phase than in the amorphous phase. The activation energy ΔE for our films before and after annealing is increased with increasing film thickness.     

Engineering of Superconducting Ba1?x K x BiO3 Thin Films: Novel Electrochemical Route

A novel electrochemical processing technique was used to prepare thin films of Ba_1?x K _x BiO_3??? . The course of action consists of co-deposition of Ba, K, and Bi metals from single electrolytic bath at ?2.1?V_SCE followed by annealing at 175?°C in vacuum and air to control the quantity of K in the film. The desired metal stoichiometries were obtained by adjusting the electrolytic bath composition empirically. The nucleation and growth mechanism of the electro-deposit is found to be of progressive type. Well-connected and compact grain growth was observed after annealing. The crystallinity and purity of phase in the film annealed in vacuum is found be better than sample annealed in air. The superconductivity in the sample processed in vacuum and air is seen at 26?K with the width of 1.3?K and at 18.4?K with width 6?K. Electrodeposited thin films processed in vacuum exhibit current densities of the order to 6.1×10⁴?A?cm^?2 at 5?K.     

Properties of n-type ZnN thin films as channel for transparent thin film transistors

In this work we fabricated, by rf magnetron sputtering from a ZnN target, zinc nitride thin films and examined their properties in order to be used as channel layer in thin film transistors. The films were deposited at 100 W rf power and the Ar pressure was 5 mTorr. The zinc nitride thin films were n-type, and depending on the thickness they exhibited low resistivity (10-10^− 2 Ohm?cm), high carrier concentration (10¹⁸-10²⁰ cm^− 3) and very low transmittance values due to the excess zinc in their structure. After annealing at 300 °C, in flowing nitrogen, the films became more conductive, but annealing at higher temperatures deteriorated the electrical properties and became transparent. Transparent thin film transistor having zinc nitride as channel layer exhibited promising transistor characteristics after nitrogen annealing. Improvements in output transistor characteristics due to both material (zinc nitride) and transistor optimization are addressed.     

Microstructural, mechanical and magnetic properties of shape memory alloy Ni55Mn23Ga22 thin films deposited by radio-frequency magnetron sputtering

The near-stoichiometric Ni₂MnGa ferromagnetic alloys are one of the smart materials, that are of a great interest when they are deposited as a thin film by r.f. sputtering. These thin films of shape memory alloys are prospective materials for micro and nanosystem applications. However, the properties of the shape memory polycrystalline thin films depend strongly on their structure and internal stress, which develop during the sputtering process as well as during the post-deposition annealing treatment. In this study, about 1 μm Ni₅₅Mn₂₃Ga₂₂ thin films were deposited in the range 0,45 to 1,2 Pa of Ar pressure and P = 40 to 120 W. Their composition, crystallographic structure, internal stress and stress gradient, indentation modulus, hardness, deflection induced by magnetic field and magnetic properties were systematically studied as a function of the temperature of the silicon substrate ranging from 298 to 873 K and the vacuum annealing treatment at 873 K for 21,6 ks and 36 ks. A silicon wafer having a native amorphous thin SiO_x buffer layer was used as a substrate. This substrate influences the microstructure of the films and blocks the diffusion process during the heat treatment.The crystal structure of the martensitic phase in each film was changed systematically from bct or 10 M or 14 M. In addition, the evolution of the mechanical properties such as mean stress, stress gradient, roughness, hardness and indentation modulus with the temperature (of substrate or of heat treatment) were measured and correlated to crystal structure and morphology changes.Moreover, it has been shown that it is necessary to associate a high temperature (873 K) annealing during a long time (21 ks and 36 ks) to obtain good ferromagnetic properties. Thus, for the well annealed films (36 ks at 873 K) the magnetostrain is about - 170 ppm for a magnetic field of 1 MA m^- 1 applied along the beams.As a conclusion, the response of free-standing magnetic shape memory films to a magnetic field of 0,2 MA m^- 1 depends strongly on the martensitic structure, internal mechanical stress (mean and gradient) and magnetic properties. The free-standing annealed film at 873 K for 36 ks points out a considerable magnetic actuation associated with bct or 10 M or 14 M martensitic structures.     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Effect of acetic acid and water content in the spray solution on structural,morphological, optical and electrical properties of Al and In co-doped zinc oxide thin films

Aluminium and indium co-doped zinc oxide (AIZO) thin films were deposited using ultrasonic spray pyrolysis. Depositions were performed by varying the acetic acid and water content in the spraying solution which resulted in the formation of different nanostructures like hexagons, flowers, chisels, curved nanostructures, hexagonal pyramids, super grown hexagons, and inter-connected nanostructures. Further, the physical properties such as structural, optical, electrical, and surface texture parameters were examined. The structural studies showed that films were of crystalline nature, with different crystallite sizes and grown with a preferential orientation along (002) plane. The optical transmittance assessments proved that films were highly transparent (>?80%) in the visible region. The electrical sheet resistance was found to be in the range 29–1K Ω/□. Surface parameters like average roughness, root mean square roughness, and peak-valley height values helped to understand the homogeneity of the thin films. Finally, the suitability of AIZO films for transparent conductive oxide applications were tested by estimating the figure of merit (FOM). Among the different solution conditions, films fabricated using a starting solution containing 25 ml of acetic acid and 25 ml of water exhibited the lowest resistivity (2.47?±?0.03?×?10^?3 Ω-cm) along with the highest FOM (5.83?±?0.42?×?10^?3/Ω).     

The photoluminescence and optical constant of ZnSe/SiO2 thin films prepared by sol–gel process

In this paper, ZnSe/SiO₂ thin films were prepared by sol–gel process. X-ray diffraction results indicate that the phase structure of ZnSe particles embedded in SiO₂ thin films is sphalerite (cubic ZnS). The dependence of ellipsometric angle ψ on wavelength λ of ZnSe/SiO₂ thin films was investigated by spectroscopic ellipsometers. The optical constant, thickness, porosity and the concentration of ZnSe/SiO₂ composite thin films were fitted according to Maxwell–Garnett effective medium theory. The thickness of ZnSe/SiO₂ thin films was also measured by surface profile. The photoluminescence properties of ZnSe/SiO₂ thin films were investigated by fluorescence spectrometer. The photoluminescence results reveal that the emission peak at 487 nm (2.5 eV) excited by 395 nm corresponds to the band-to-band emission of sphalerite ZnSe crystal (2.58 eV). Strong free exciton emission and other emission peaks corresponding to ZnSe lattice defects are also observed.