The structural,optical, and electrical properties of vacuum evaporated Cu-doped ZnTe polycrystalline thin films

We have studied the structural, optical, and electrical properties of thermally evaporated, Cu-doped, ZnTe thin films as a function of Cu concentration and post-deposition annealing temperature. X-ray diffraction measurements showed that the ZnTe films evaporated on room temperature substrates were characterized by an average grain size of 300Å with a (111) preferred orientation. Optical absorption measurements yielded a bandgap of 2.21 eV for undoped ZnTe. A bandgap shrinkage was observed for the Cu-doped films. The dark resistivity of the as-deposited ZnTe decreased by more than three orders of magnitude as the Cu concentration was increased from 4 to 8 at.% and decreased to less than 1 ohm-cm after annealing at 260°C. For films doped with 6–7 at.% Cu, an increase of resistivity was also observed during annealing at 150–200°C. The activation energy of the dark conductivity was measured as a function of Cu concentration and annealing temperature. Hall measurements yielded hole mobility values in the range between 0.1 and 1 cm²/V·s for both as-deposited and annealed films. Solar cells with a CdS/CdTe/ZnTe/metal structure were fabricated using Cudoped ZnTe as a back contact layer on electrodeposited CdTe. Fill factors approaching 0.75 and energy conversion efficiencies as high as 12.1% were obtained.     

Impact of substrate temperature on the structural,optical and electrical properties of thermally evaporated SnS thin films

Tin Sulfide thin films were deposited on soda lime glass substrates at three different substrate temperatures using thermal evaporation technique. The impact of substrate temperature on the deposited films has been studied thoroughly. Surface morphology was modified with the substrate temperature. XRD spectra shows orthorhombic end-centered type SnS having (1 1 0) orientation. The crystallite size increases with the increase in the substrate temperature. At a high substrate temperature (450 °C) small grains form on the surface and crystallinity decreases. The effect of substrate temperature on optical and electrical properties has been studied using UV–Vis–NIR Spectrophotometer and Hall effect respectively. With the increase in the substrate temperature there is a substantial decrease in the transmittance and bandgap value. Refractive index (n), dielectric constant (ε₁) and extinction co-efficient (k) have also been calculated for different substrate temperatures.     

Effects of Sb,Zn doping on structural,electrical and optical properties of SnO2 thin films

Highly transparent, low resistive pure and Sb, Zn doped nanostructured SnO₂ thin films have been successfully prepared on glass substrates at 400° C by spray pyrolysis method. Structural, electrical and optical properties of pure and Sb, Zn doped SnO₂ thin films are studied in detail. Powder X-ray diffraction confirms the phase purity, increase in crystallinity, size of the grains (90–45 nm), polycrystalline nature and tetragonal rutile structure of thin films. The scanning electron microscopy reveals the continuous change in surface morphology of thin films and size of the grains decrease due to Sb, Zn doping in to SnO₂. The optical transmission spectra of SnO₂ films as a function of wavelength confirm that the optical transmission increases with Sb, Zn doping remarkably. The optical band gap of undoped film is found to be 4.27 eV and decreases with Sb, Zn doping to 4.19 eV, 4.07 eV respectively. The results of electrical measurements indicate that the sheet resistance of the deposited films improves with Sb, Zn doping. The Hall measurements confirm that the films are degenerate n-type semiconductors.     

Influence of deposition rate on the structural,optical and electrical properties of electron beam evaporated SnO2 thin films for transparent conducting electrode applications

The role of deposition rate in the structural,optical and electrical properties of SnO2 thin films deposited by electron beam evaporation method is investigated by varying the deposition powers viz.50,75,and 100 W.The structural characterization of the films is done by X-ray diffraction (XRD) technique.The surface morphology of the films is studied by scanning electron microscopy (SEM).Rutherford back scattering (RBS) measurements revealed the thickness of the films ranging from 200 nm to 400 and also a change in the concentration of oxygen vacancies which is found to be the maximum in the film deposited at the lowest deposition rate.Optical absorption spectrum is recorded using the UV-V is spectroscopy and the films are found to be transparent in nature.A shift in the absorption edge is observed and is attributed to a different level of allowed energy states in conduction band minimum.The Hall effect and electrical measurements show a variation in the carrier concentrations,mobility and resistivity of the films.In order to explore a better compromise in electrical and optical properties for transparent electrode applications,skin depths calculations are also done to find the optimized values of carrier concentration and mobility.     

Effect of the substrate temperature on the electrical and structural properties of spray-deposited SnO2:F thin films

SnO₂:F thin films were prepared by the spray pyrolysis (SP) technique at substrate temperature in the range 360–480 °C. The effect of varying the substrate temperature on the electrical and structural properties of the films was investigated by studying the I–V characteristics, the X-ray diffraction patterns (XRD), and the scanning electron microscope images (SEM). The I–V characteristics of the films were improved by increasing the substrate temperature, i.e. the resistivity of the films had decreased from 98 to 0.22 Ω cm. The X-ray diffraction patterns taken at 400 and 480 °C showed that the films are polycrystalline and two directions of crystal growth appeared in the difractogram of the film deposited at the lower substrate temperature, which correspond to the reflections from the (1 1 0) and (2 0 0) planes. With the increase in the substrate temperature a new direction of crystal growth appeared, which corresponds to the reflection from the (1 0 1) plane. Also the (1 1 0) and (2 0 0) lines were slightly grown at the higher substrate temperature, which means the crystal growth was enhanced and the grain size had increased. The SEM images confirmed these results and showed larger grains and more crystallization for the higher substrate temperature too.     

Effect of annealing temperature on structural,electrical and optical properties of spray pyrolytic nanocrystalline CdO thin films

Nanocrystalline CdO thin films were prepared onto a glass substrate at substrate temperature of 300 °C by a spray pyrolysis technique. Grown films were annealed at 250, 350, 450 and 550 °C for 2.5 h and studied by the X-ray diffraction, Hall voltage measurement, UV-spectroscopy, and scanning electron microscope. The X-ray diffraction study confirms the cubic structure of as-deposited and annealed films. The grain size increases whereas the dislocation density decreases with increasing annealing temperature. The Hall measurement confirms that CdO is an n-type semiconductor. The carrier density and mobility increase with increasing annealing temperature up to 450 °C. The temperature dependent dc resistivity of as-deposited film shows metallic behavior from room temperature to 370 K after which it is semiconducting in nature. The metallic behavior completely washed out by annealing the samples at different temperatures. Optical transmittance and band gap energy of the films are found to decrease with increasing annealing temperature and the highest transmittance is found in near infrared region. The refractive index and optical conductivity of the CdO thin films enhanced by annealing. Scanning electron microscopy confirms formation of nano-structured CdO thin films with clear grain boundary.     

Characterization of vacuum evaporated CdTe thin films prepared at ambient temperature

Polycrystalline cadmium telluride (CdTe) thin films were prepared by vacuum evaporation on glass substrates at ambient temperature. X-ray diffraction pattern (XRD) showed that the films are polycrystalline with predominant zinc blend structure. A strong reflection from the (111) plane of the cubic phase was seen beside two weak reflections from the (220) and (311) planes of the same phase. Three very weak lines that are characteristic of elemental tellurium were also observed. The average grain size was estimated by using Sherrer's formula and found to be 24±1 nm. The scanning electron microscope (SEM) image showed a uniform surface with submicron grain size. The difference between grain size obtained from Sherrer's formula and that observed in the SEM micrograph means that each grain consists of a large number of smaller crystallites. The composition of the films was explored by using energy dispersive spectroscopy (EDS), which revealed that the surfaces of the films have excess tellurium. The transmittance was measured in the wavelength range λ=400–1100 nm and used to estimate the optical bandgap energy E_g which was found to be E_g=1.48±0.01 eV. The absorption coefficient was calculated and plotted against the photon's energy and tailing in the bandgap was observed. This tailing was found to follow the empirical Urbach rule. The width of the tail was estimated and related to localized states. The linear current–voltage (I–V) plots were used to find the resistivity ρ, where a value of ρ=2.10×10⁶ Ω cm was obtained.     

Effects of substrate temperature on electrical and structural properties of copper thin films

This paper addresses the effects of substrate temperature on electrical and structural properties of dc magnetron sputter-deposited copper (Cu) thin films on p-type silicon. Copper films of 80 and 500 nm were deposited from Cu target in argon ambient gas pressure of 3.6 mTorr at different substrate temperatures ranging from room temperature to 250 °C. The electrical and structural properties of the Cu films were investigated by four-point probe and atomic force microscopy. Results from our experiment show that the increase in substrate temperature generally promotes the grain growth of the Cu films of both thicknesses. The RMS roughness as well as the lateral feature size increase with the substrate temperature, which is associated with the increase in the grain size. On the other hand, the resistivity for 80 nm Cu film decreases to less than 5 μΩ-cm at the substrate temperature of 100 °C, and further increase in the substrate temperature has not significantly decreased the film resistivity. For the 500 nm Cu films, the increase in the grain size with the substrate temperature does not conform to the film resistivity for these Cu films, which show no significant change over the substrate temperature range. Possible mechanisms of substrate-temperature-dependent microstructure formation of these Cu films are discussed in this paper, which explain the interrelationship of grain growth and film resistivity with elevated substrate temperature.     

Effect of Ar ion irradiation on structural and optical properties of e-beam evaporated cadmium telluride thin films

CdTe thin films were prepared using e-beam evaporation technique. The prepared films were irradiated by Ar⁺ ions at different fluencies using multipurpose aluminum (Al) probe as in-situ. This could also be used in ion bombardment for cleaning the substrate prior to coating. The as grown and Ar⁺ ion irradiated films were confirmed to be of polycrystalline nature with X-ray technique. Ar⁺ ion irradiation enhances the growth of (1 1 1) oriented CdTe crystals and the Cd enrichment on the surface of CdTe thin films. Higher Ar⁺ ion flux helps to grow (2 2 0) oriented CdTe thin film. A considerable change in structural parameters like crystallite size, lattice parameter, internal strain, etc. could be observed as a result of high Ar⁺ ion flux. The applied in-plan stress in both as grown and irradiated film was identified to be of tensile nature. The applied stress was observed between 0.016 and 0.067 GPa for all Ar⁺ ion irradiated samples. As a result of the Ar⁺ ion irradiation, the in-plan stress varies between 1.38×10⁹ and 5.58×10⁹ dyn/cm². The observed bad gap was increased for higher Ar⁺ ion flux. It shows the effect of Ar⁺ ion irradiation on the modifications of optical properties. The observed results were encouraging on the use of simple multipurpose Al probe for Ar⁺ ion irradiation process as in-situ.     

Annealing temperature dependent structural and optical properties of electrodeposited CdSe thin films

Cadmium selenide films were synthesized using simple electrodeposition method on indium tin oxide coated glass substrates. The synthesized films were post annealed at 200 °C, 300 °C and 400 °C. X-ray diffraction of the films showed the hexagonal structure with crystallite size <3 nm for as deposited films and 3–25 nm for annealed films. The surface morphology of films using field emission scanning electron microscopy showed granular surface. The high resolution transmission electron microscopy of a crystallite of the film revealed lattice fringes which measured lattice spacing of 3.13 Å corresponding to (002) plane, indicating the lattice contraction effect, due to small size of CdSe nanocrystallite. The calculation of optical band gap using UV–visible absorption spectrum showed strong red-shift with increase in crystallite size, indicating to the charge confinement in CdSe nanocrystallite.     

Effect of annealing temperature on optical and electrical properties of lead sulfide thin films

Lead sulfide (PbS) thin films with 150 nm thickness were prepared onto ultra-clean quartz substrate by the RF-sputtering deposition method. Deposited thin films of PbS were annealed at different temperatures 100 °C, 150 °C, 200 °C, 250 °C and 300 °C. X-ray diffraction pattern of thin films revealed that thin films crystallized at 150 °C. Crystalline thin films had cubic phase and rock salt structure. The average crystallite size of crystalline thin films was 22 nm, 28 nm and 29 nm for 150 °C, 200 °C and 250 °C respectively. From 150 °C to 250 °C increase in annealing temperature leads to increase in crystallite arrangement. FESEM images of thin films revealed that crystallite arrangement improved by increasing annealing temperature up to 250 °C. Increase in DC electrical conductivity by increasing temperature confirmed the semiconductor nature of crystalline thin films. Increase in dark current by increasing annealing temperature showed the effect of crystallite arrangement on carrier transport. Photosensitivity decreased by increasing annealing temperature for crystalline thin films that it was explained at the base of thermal quenching of photoconductivity and adsorption of oxygen at the surface of thin films that leads to the formation of PbO at higher temperatures.     

Investigation of the optical and structural properties of thermally evaporated cadmium sulphide thin films on polyethylene terephthalate substrate

Cadmium sulphide (CdS) thin films of different thicknesses ranging from 100 to 400 nm were prepared on polyethylene terephthalate (PET) substrates at room temperature by thermal evaporation technique in vacuum of about 3×10⁻⁵ Torr. The structural characterisation was carried out by X-ray diffraction (XRD). These studies confirm the proper phase formation of the cadmium sulphide structure. The root mean square (RMS) roughness of the films was measured using atomic-force microscopy. The root mean square roughness of the films increases as the film thickness increases. The energy gap of CdS on PET substrates was determined through the optical transmission method using an ultraviolet–visible spectrophotometer. The optical band gap values of CdS thin films slightly increase as the film thickness increases. The optical band gap energy was found to be in the range of 2.41–2.56 eV.     

Effect of Co doping on structural, optical, electrical and thermal properties of nanostructured ZnO thin films

Nanocrystalline Zn1-x CoxO(where x varies from 0 to 0.04 in steps of 0.01) thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 ℃. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11–36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped Zn O. The transmittance increases with increasing Co doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2C absorption bands corresponding to intraionic d–d shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force measurement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 K and they become n-type semiconductors.     

Effect of substrate temperature on structural,morphological, optical and electrical properties of MnIn2S4 thin films prepared by nebulizer spray pyrolysis technique

Manganese indium sulphide (MnIn₂S₄) thin films were deposited using an aqueous solution of MnCl₂, InCl₃ and (NH₂)₂CS in the molar ratio 1:2:4 by simple chemical spray pyrolysis technique. The thin film substrates were annealed in the temperature range between 250 and 350 °C to study their various physical properties. The structural properties as studied by X-ray diffraction showed that MnIn₂S₄ thin films have cubic spinel structure. The formation of cube and needle shaped grains was clearly observed from FE-SEM analysis. The energy dispersive spectrum (EDS) predicts the presence of Mn, In and S in the synthesized thin film. From the optical studies, it is analyzed that the maximum absorption co-efficient is in the order between 10⁴ and 10⁵ cm⁻¹ and the maximum transmittance (75%) was noted in the visible and infrared regions. It is noted that, the band gap energy decreases (from 3.20 to 2.77 eV) with an increase of substrate temperature (from 250 to 350 °C). The observations from photoluminescence studies confirm the emission of blue, green, yellow and red bands which corresponds to the wavelength range 370–680 nm. Moreover, from the electrical studies, it is observed that, as the substrate temperature increases the conductivity also increases in the range 0.29–0.41×10⁻⁴ Ω⁻¹ m⁻¹. This confirms the highly semiconducting nature of the film. The thickness of the films was also measured and the values ranged between 537 nm (250 °C) to 483 nm (350 °C). This indicates that, as the substrate temperature increases, the thickness of the film decreases. From the present study, it is reported that the MnIn₂S₄ thin films are polycrystalline in nature and can be used as a suitable ternary semiconductor material for photovoltaic applications.     

Influence of working pressure on the structural,optical and electrical properties of sputter deposited AZO thin films

Highly oriented crystalline aluminum doped zinc oxide (AZO) films were sputter deposited on glass substrates and a systematic investigation on the as deposited and etched films was reported for its further application in silicon thin film solar cell. Influence of the deposition pressure (from 2 to 8 mTorr) and post-annealing temperature (at 400 °C for 5 min) on the structural, optical and electrical properties of the as-deposited and etched samples were analyzed. The optimum condition for its reproducibility and large area deposition is determined and found that the depositions made at 8 mTorr at 200 W having the distance from source to substrate of 9 cm. All the AZO films exhibited a c-axis preferred orientation perpendicular to the substrate and their crystallinity was improved after annealing. From the XRD pattern the grain size, stress and strain of the films were evaluated and there is no drastic variation. Optical transmittance, resistivity, Hall mobility and carrier concentration for the as deposited and etched-annealed films were found to improve from 79 to 82%; 2.97 to 3.14×10⁻⁴ Ω cm; 25 to 38 cm²/V s; 8.39 to 5.96×10²⁰/cm³ respectively. Based on the triangle diagram between figure of merit and Hall mobility, we obtained a balance of point between the electrical and optical properties to select the deposition condition of film for device application.     

Effect of thickness on the structural,optical and electrical properties of RF magnetron sputtered GZO thin films

Gallium-doped zinc oxide (GZO) thin films with very high conductivity and transparency were successfully deposited by RF magnetron sputtering at a substrate temperature of 400 °C. The dependence of the film properties over the thickness was investigated. X-ray diffraction (XRD) results revealed the polycrystalline nature of the films with hexagonal wurtzite structure having preferential orientation along [001] direction normal to the substrate. The lowest resistivity obtained from electrical studies was 5.4×10⁻⁴ Ω cm. The optical properties were studied using a UV–vis spectrophotometer and the average transmittance in the visible region (400–700 nm) was found to be 92%, relative to the transmittance of a soda–lime glass reference for a GZO film of thickness 495 nm and also the transparency of the films decreases in the near IR region of the spectra. The mobility of the films showed a linear dependence with crystallite size. GZO film of thickness 495 nm with the highest figure of merit indicates that the GZO film is suitable as an ideal transparent conducting oxide (TCO) material for solar cell applications.     

Influence of substrate temperature on structural and optical properties of RF sputtered ZnMnO thin films

The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering method. The properties of ZnMnO thin films were investigated by high-resolution x-ray diffractometer (HRXRD),atomic force microscopy (AFM), UV-Vis spectrometer and room temperature photoluminescence (PL), under the influence of substrate temperature. The substrate temperature was varied from 300, 400 and 500°C. With increasing the substrate temperature, the structure of the films changed from cubic to hexagonal. The cubic ZnMnO thin films grown along [210] direction, while the hexagonal ones grown along [002] direction. The changes in surface morphology provided a proof on the structural transition. Also, decrease and increase of optical band gap is associated with cubic or hexagonal structure of the films.

     

The influence of substrate temperature on the structural and optical properties of ZnS thin films

Thin films of ZnS were deposited on soda lime glass substrates by a modified close-space sublimation technique. The change in optical and structural properties of the films deposited at various substrate temperatures (150–450°C) was investigated. X-ray diffraction spectra showed that films were polycrystalline in nature having cubic structure oriented only along (111) plan. The crystallinity of films increased with the substrate temperature up to 250°C. However, crystallinity decreased with further increase of substrate temperature and films became amorphous at 450°C. The atomic force microscopy data revealed that the films become more uniform and dense with the increase of substrate temperature. Optical properties of the films were determined from the transmittance data using Swanepoel model. It was observed that the energy band gap is increased from 3.52 to 3.65 eV and refractive index of the films are decreased with the increase of substrate temperature. Moreover, considerable improvement in blue response of the films was noticed with increasing substrate temperature.     

Structural,electrical and optical properties of sintered SnO2 pellets

Tin dioxide (SnO₂) powder was prepared by the co-precipitation method using SnCl₂ solution as a precursor. The powder was then pelletized and sintered. Structural characterization of the samples with XRD confirmed that all the pellets were of SnO₂ having polycrystalline nature with the crystallite size of the order of 90 nm. SEM-EDAX was used to confirm the morphology and composition of the samples. The measurements of electrical properties were carried out in the frequency range of 100 Hz to 100 kHz at various fixed temperatures from 40 °C to 160 °C. The a.c. conductivity and the dielectric constant were found to be dependent on both frequency and temperature. The frequency and temperature dependent conduction properties of SnO₂ are found to be in accordance with correlated barrier hoping model. Infrared and visible spectroscopic studies show that a strong vibration band characteristic of the SnO₂ stretching mode was present at around 620 cm^?1 and the samples exhibited optical transmittance in the visible range.