The Al-doping and post-annealing treatment effects on the structural and optical properties of ZnO:Al thin films deposited on Si substrate

Al-doped ZnO (ZnO:Al) thin films with different Al contents were deposited on Si substrates using the radio frequency reactive magnetron sputtering technique. X-ray diffraction (XRD) measurements showed that the crystallinity of the films was promoted by appropriate Al content (0.75 wt.%). Then the ZnO:Al film with Al content of 0.75 wt.% was annealed in vacuum at different temperatures. XRD patterns revealed that the residual compressive stress decreased at higher annealing temperatures. While the surface roughness of the ZnO:Al film annealed at 300 °C became smoother, those of the ZnO:Al films annealed at 600 and 750 °C became rougher. The photoluminescence (PL) measurements at room temperature revealed a violet, two blue and a green emission. The origin of these emissions was discussed and the mechanism of violet and blue emission of ZnO:Al thin films were suggested. We concluded that the defect centers are mainly ascribed to antisite oxygen and interstitial Zn in annealed (in vacuum) ZnO:Al films.     

Rapid thermal annealing effects on the structural and optical properties of ZnO films deposited on Si substrates

The structural and optical properties of ZnO films deposited on Si substrate following rapid thermal annealing (RTA) have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. After RTA treatment, the XRD spectra have shown an effective relaxation of the residual compressive stress, an increase of the intensity and narrowing of the full-width at half-maximum (FWHM) of the (0 0 2) diffraction peak of the as-grown ZnO film. AFM images show roughening of the film surface due to increase of grain size after RTA. The PL spectrum reveals a significant improvement in the UV luminescence of ZnO films following RTA at 800 °C for 1 min.     

Structural, optical and electrical properties of Al-N codoped ZnO films by RF-assisted MOCVD method

N-doped ZnO films were produced using N₂ as N source by metal-organic chemical vapor deposition (MOCVD) system which has been improved with radio-frequency (RF)-assisted equipments. The data of secondary ion mass spectroscopy (SIMS) indicate that the concentration of N in N-doped ZnO films is around 5 × 10²⁰ cm⁻³, implying that sufficient incorporation of N into ZnO can be obtained by RF-assisted equipment. On this basis, the structural, optical and electrical properties of Al-N codoped ZnO films were studied. Then, the effect of RF power on crystal quality, surface morphologies, optical properties was analyzed using X-ray diffraction, atomic force microscopy and photo-luminescence methods. The results illustrate that the RF plasma is the key factor for the improvement of crystal quality. Then the observation of A⁰X recombination associated with N_O acceptor in low-temperature PL spectrum proved that some N atoms have occupied the positions of O atoms in ZnO films. Hall measurements shown that p-type ZnO film deposited on quartz glasses was obtained when RF power was 150 W for the Al-N codoped ZnO films, while the resistivity of N-doped ZnO films was rather high. Compared with the Al-doped ZnO film, the obviously increased resistivity of codoped films indicates that the formation of N_O acceptors compensate some donors in ZnO films effectively.     

The morphology and optical properties of Cr-doped ZnO films grown using the magnetron co-sputtering method

Undoped ZnO and Zn_0.9Cr_0.1O films were prepared on Al₂O₃ (0 0 0 1) substrates using the magnetron co-sputtering technique. X-ray diffraction scans show that all films exhibit nearly single-phase wurtzite structure with c-axis orientation. Both chromium doping and growth ambient have a significant impact on the lattice constants and nucleation processes in ZnO film. A large quantity of subgrains (10 nm in size) has been observed on Zn_0.9Cr_0.1O film grown under Ar + O₂, while irregular plateau-like grains 40-50 nm in size were observed on Zn_0.9Cr_0.1O film grown under Ar + N₂. The ultraviolet-visible transmittance and optical bandgap of all films were also examined. The photoluminescence spectra of all films exhibit a broad emission located around 400 nm, which is composed of one weak ultraviolet luminescence and another rather intense near-violet one, as determined by Gaussian peak fitting. The near-violet emission centered on 400 nm might originate from the electron transition between the band tail state levels of surface defects and/or lattice imperfection in the ZnO film.     

Microstructures and optical properties of Cu-doped ZnO films prepared by radio frequency reactive magnetron sputtering

Pure and Cu-doped ZnO (ZnO:Cu) thin films were deposited on glass substrates using radio frequency (RF) reactive magnetron sputtering. The effect of substrate temperature on the crystallization behavior and optical properties of the ZnO:Cu films have been studied. The crystal structures, surface morphology and optical properties of the films were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer, respectively. The results indicated that ZnO films showed a stronger preferred orientation toward the c-axis and a more uniform grain size after Cu-doping. As for ZnO:Cu films, the full width at half maxima (FWHM) of (0 0 2) diffraction peaks decreased first and then increased, reaching a minimum of about 0.42° at 350 °C and the compressive stress of ZnO:Cu decreased gradually with the increase of substrate temperature. The photoluminescence (PL) spectra measured at room temperature revealed two blue and two green emissions. Intense blue-green luminescence was obtained from the sample deposited at higher substrate temperature. Finally, we discussed the influence of annealing temperature on the structural and optical properties of ZnO:Cu films. The quality of ZnO:Cu film was markedly improved and the intensity of blue peak (∼485 nm) and green peak (∼527 nm) increased noticeably after annealing. The origin of these emissions was discussed.     

Structure and optical properties of ZnS thin films grown by glancing angle deposition

The glancing angle deposition (GLAD) technique was used to deposit ZnS films by electron beam evaporation method. The cross sectional scanning electron microscopy (SEM) image illustrated a highly orientated microstructure composed of slanted column. The atomic force microscopy (AFM) analysis indicated that incident flux angle had significant effects on the nodule size and surface roughness. Under identical nominal thickness, the actual thickness of the GLAD films is related to the incident flux angle. The refractive index and in-plane birefringence of the GLAD ZnS films were discussed, and the maximum birefringence Δn = 0.036 was obtained at incident flux angle of α = 80°. Therefore, the glancing angle deposition technique is a promising way to create a columnar structure with enhanced birefringent property.     

Structural and optical properties of ZnO thin films prepared by sol-gel method with different thickness

In this work, ZnO thin films with different thickness were prepared by sol-gel method on glass substrates and the structural and optical properties of these films were studied by X-ray diffractometer, atomic force microscope, UV-visible spectrophotometer, ellipsometer and fluorophotometer, respectively. The structural analyses show that all the samples have a wurtzite structure and are preferentially oriented along the c-axis perpendicular to the substrate surface. The growth process of highly c-axis oriented ZnO thin films derived from sol-gel method is a self-template process. With the increase of film thickness, the structural disorder decreases and the crystalline quality of the films is gradually improved. A transition of crystal growth mode from vertical growth to lateral growth is observed and the transition point is found between 270 and 360 nm thickness. The optical analyses show that with the increase of film thickness, both the refractive index and ultraviolet emission intensity are improved. However, the transmittance in the visible range is hardly influenced by the film thickness, and the averages are all above 80%.     

Modifications in structural and optical properties of Mn-ion implanted CdS thin films

In this paper, we report on modifications in structural and optical properties of CdS thin films due to 190 keV Mn-ion implantation at 573 K. Mn-ion implantation induces disorder in the lattice, but does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. The optical band gap was found to decrease with increasing ion fluence. This is explained on the basis of band tailing due to the creation of localized energy states generated by structural disorder. Enhancement in the Raman scattering intensity has been attributed to the enhancement in the surface roughness due to increasing ion fluence. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d-d (⁴T₁ → ⁶A₁) transition of tetrahedrally coordinated Mn²⁺ ions.     

Dependence of film thickness on the structural and optical properties of ZnO thin films

ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10⁻⁴ Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.     

Synthesis, effect of capping agents, structural, optical and photoluminescence properties of ZnO nanoparticles

Zinc oxide nanoparticles were synthesized using chemical method in alcohol base. During synthesis three capping agents, i.e. triethanolamine (TEA), oleic acid and thioglycerol, were used and the effect of concentrations was analyzed for their effectiveness in limiting the particle growth. Thermal stability of ZnO nanoparticles prepared using TEA, oleic acid and thioglycerol capping agents, was studied using thermogravimetric analyzer (TGA). ZnO nanoparticles capped with TEA showed maximum weight loss. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for structural and morphological characterization of ZnO nanoparticles. Particle size was evaluated using effective mass approximation method from UV-vis spectroscopy and Scherrer's formula from XRD patterns. XRD analysis revealed single crystal ZnO nanoparticles of size 12-20 nm in case of TEA capping. TEA, oleic acid and thioglycerol capped synthesized ZnO nanoparticles were investigated at room temperature photoluminescence for three excitation wavelengths i.e. 304, 322 and 325 nm, showing strong peaks at about 471 nm when excited at 322 and 325 nm whereas strong peak was observed at 411 for 304 nm excitation.     

Effects of cooling rate and post-heat treatment on properties of ZnO thin films deposited by sol-gel method

Sol-gel spin-coated ZnO thin films are cooled with different rates after the pre-heat treatment. Atomic force microscopy (AFM), X-ray diffraction (XRD), Raman, and photoluminescence (PL) were carried out to investigate the effects of the cooling rate during pre-heat treatment on structural and optical properties of the ZnO thin films. The ZnO thin films cooled slowly exhibit mountain chain structure while the ones cooled rapidly have smooth surface. The ZnO thin films cooled rapidly have higher c-axis orientation compared to the ones cooled slowly. The narrower and the higher near-band-edge emission (NBE) peaks are observed in the ZnO thin films cooled rapidly.     

Ar irradiation of Si nanocrystal-doped SiO2: Evolution of photoluminescence

We report the evolution of photoluminescence (PL) of Si nanocrystals (nc-Si) embedded in a matrix of SiO₂ during Ar⁺ ion bombardment. The integrated intensity of nc-Si PL falls down drastically before the Ar⁺ ion fluence of 10¹⁵ ions cm⁻², and then decreases slowly with the increasing ion fluence. At the meantime, the PL peak position blueshifts steadily before the fluence of 10¹⁵ ions cm⁻², and then changes in an oscillatory manner. Also it is found that the nc-Si PL of the Ar⁺-irradiated sample can be partly recovered after annealing at 800 °C in nitrogen, but can be almost totally recovered after annealing in oxygen. The results confirm that the ion irradiation-induced defects are made up of oxygen vacancies, which absorb light strongly. The oscillatory peak shift of nc-Si can be related to a size-distance distribution of nc-Si in SiO₂.     

Fabrication and optical properties of SnS thin films by SILAR method

Although the fabrication of tin disulfide thin films by SILAR method is quiet common, there is, however, no report is available on the growth of SnS thin film using above technique. In the present work, SnS films of 0.20 μm thickness were grown on glass and ITO substrates by SILAR method using SnSO₄ and Na₂S solution. The as-grown films were smooth and strongly adherent to the substrate. XRD confirmed the deposition of SnS thin films. Scanning electron micrograph revealed almost equal distribution of the particle size well covered on the surface of the substrate. EDAX showed that as-grown SnS films were slightly rich in tin component while UV-vis transmission spectra exhibited high absorption in the visible region. The intense and sharp emission peaks at 680 and 825 nm (near band edge emission) dominated the photoluminescence spectra.     

Influence of annealing temperature on structural, optical and magnetic properties of Mn-doped ZnO thin films prepared by sol-gel method

Thin films of Zn_1−xMn_xO (x=0.01) diluted magnetic semiconductor were prepared on Si (1 0 0) substrates by the sol-gel method. The influence of annealing temperature on the structural, optical and magnetic properties was studied by X-ray diffraction (XRD), atom force microscopy (AFM), photoluminescence (PL) and SQUID magnetometer (MPMS, Quantum Design). The XRD spectrum shows that all the films are single crystalline with (0 0 2) preferential orientation along c-axis, indicating there are not any secondary phases. The atomic force microscopy images show the surfaces morphologies change greatly with an increase in annealing temperature. PL spectra reveal that the films marginally shift the near band-edge (NBE) position due to stress. The magnetic measurements of the films using SQUID clearly indicate the room temperature ferromagnetic behavior, and the Curie temperature of the samples is above room temperature. X-ray photoelectron spectroscopy (XPS) patterns suggest that Mn²⁺ ions were successfully incorporated into the lattice position of Zn²⁺ ions in ZnO host. It is also found that the post-annealing treatment can affect the ferromagnetic behavior of the films effectively.     

The influence of substrate on the properties of Er2O3 films grown by magnetron sputtering

The structural properties and the room temperature luminescence of Er₂O₃ thin films deposited by RF magnetron sputtering have been studied. Films characterized by good morphological properties have been obtained by using a SiO₂ interlayer between the film and the Si substrate. The evolution of the properties of the Er₂O₃ films due to rapid thermal annealing processes in O₂ ambient performed at temperatures in the range 800-1200 °C has been investigated in details. The existence of well-defined annealing conditions (temperature of 1100 °C or higher) allowing to avoid the occurrence of extensive chemical reactions with the oxidized substrate has been demonstrated and an increase of the photoluminescence (PL) intensity by about a factor of 40 with respect to the as deposited material has been observed. The enhanced efficiency of the photon emission process has been correlated with the longer lifetime of the PL signal. The same annealing processes are less effective when Er₂O₃ is deposited on Si. In this latter case interfacial reactions and pit formation occur, leading to a material characterized by stronger non-radiative phenomena that limit the PL efficiency.     

Temperature effect on the electrical, structural and optical properties of N-doped ZnO films by plasma-free metal organic chemical vapor deposition

N-doped p-type ZnO films were grown by plasma-free metal-organic chemical vapor deposition (MOCVD). The effect of substrate temperature on the electrical, optical, and structural properties of the N-doped ZnO films was investigated by Hall-effect, photoluminescence, X-ray diffraction measurements. The electrical properties of the films were extremely sensitive to the substrate temperature and the conduction type could be reversed in a narrow range from 380 °C to 420 °C. Based on X-ray photoelectron spectroscopy, a high compensation effect in the N-doped ZnO films grown by plasma-free MOCVD was suggested to explain the temperature-dependent phenomenon.     

Crystallization of amorphous Ge2Sb2Te5 films induced by a single femtosecond laser pulse

Crystallization is achieved in amorphous Ge₂Sb₂Te₅ films upon irradiation with a single femtosecond laser pulse. Transmission electron microscopy images evidence the morphology of the crystallized spot which depends on the fluence of the femtosecond laser pulse. Fine crystalline grains are induced at low fluence, and the coarse crystalline grains are obtained at high fluence. At the damage fluence, ablation of the films occurs.     

Structure and electrical properties of CdIn2O4 thin films prepared by DC reactive magnetron sputtering

CdIn₂O₄ thin films were prepared by direct-current (DC) reactive magnetron sputtering. The structure, surface morphology and the chemical composition of the thin films were analyzed by X-ray diffraction (XRD), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The electrical properties of the films prepared in different oxygen concentration and annealing treatment were determined, and the effects of the preparing conditions on the structure and electrical properties were also explored. It indicates that the CdIn₂O₄ thin films with uniform and dense surface morphology contain mainly CdIn₂O₄, In₂O₃ phases, and CdO phase is also observed. The XPS analysis confirms the films are in oxygen-deficient state. The electrical properties of these films significantly depend on the preparing conditions, the resistivity of the films with the oxygen concentration of 4.29% is 2.95 × 10⁻⁴ Ω cm and the Hall mobility is as high as 60.32 cm²/V s. Annealing treatment can improve the electrical performance of the films.     

Fabrication of high hole-carrier density p-type ZnO thin films by N-Al co-doping

In order to obtain p-type ZnO thin films, effect of atomic ratio of Zn:N:Al on the electronic and structural characteristic of ZnO thin films was investigated. Hall measurement indicated that with the increase of Al doping, conductive type of as-grown ZnO thin films changed from n-type to p-type and then to n-type again, reasons are discussed in details. Results of X-ray diffraction revealed that co-doped ZnO thin films have similar crystallization characteristic (0 0 2 preferential orientation) like that of un-doping. However, SEM measurement indicated that co-doped ZnO thin films have different surface morphology compared with un-doped ZnO thin films. p-type ZnO thin films with high hole concentration were obtained on glass (4.6 × 10¹⁸ cm⁻³) and n-type silicon (7.51 × 10¹⁹ cm⁻³), respectively.     

Post-annealing effect upon optical properties of electron beam evaporated molybdenum oxide thin films

Molybdenum oxide (MoO₃) thin films were deposited by electron beam evaporation. The chemical composition, microstructure, optical and electrical properties of MoO₃ thin films depend on the annealing temperature and ambient atmosphere. X-ray diffraction (XRD) shows that crystalline MoO₃ films can be obtained at various post-annealing temperatures from 200 to 500 °C in N₂ and O₂. X-ray photoelectron spectroscopy (XPS) results reveal that the O-1s emission peak was shifted slightly toward lower binding energies as the annealing temperature in N₂ was increased. The oxygen vacancies and conductivity of MoO₃ film increased with the annealing temperature. However, when the MoO₃ films were annealed in an atmosphere of O₂, the optical transmission, the O/Mo ratio and the photon energy increased with the annealing temperature. The results differ from those for films annealed in a N₂ atmosphere.