A parametric study of AlN thin films grown by pulsed laser deposition

High quality AlN thin films were grown at 200–450°C on sapphire substrates by laser ablation of Al targets in nitrogen reactive atmosphere. The nitrogen pressure was varied between 10⁻³ and 10⁻¹ mbar. The reactive gas pressure during irradiation and the temperature of the substrate were found to essentially influence the quality of the layers. X-ray diffraction analysis evidenced the formation of highly orientated layers for a very restrictive set of parameters. Other analysis techniques, like X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, optical transmission spectroscopy have been used to evidence the good stoichiometry and purity of the films. The characteristics of these films were compared with those of AlN thin films deposited in similar experimental conditions, on Si (100) and Si (111) substrates.     

Highly oriented metallic SmS films on Si(100) grown by pulsed laser deposition

Stoichiometric and highly oriented in (100) direction SmS films in the metallic phase have been grown on Si(100) substrate at room temperature by pulsed laser deposition (PLD) as revealed from lattice parameter, reflectivity and electrical resistivity measurements. Above-critical compressive stress P = 0.9 GPa in as grown film was determined from sample curvature measurements and attributed to stress building up in PLD process further accompanied by stress due to SmS versus Si lattice parameter mismatch. Stress relaxation and subsequent metal-to-semiconductor phase transition occurred following annealing at T = 900 K as evident from consistent changes of SmS/Si sample curvature, structural, optical and electrical properties.     

Low-temperature deposition of iridium thin films by pulsed laser deposition

Extremely smooth iridium (Ir) thin films were deposited on Si(1 0 0) substrate at lower temperature than 300 °C by pulsed laser deposition (PLD) technique using Ir target in a vacuum atmosphere. The crystal orientation, surface morphology, and resistivity of the Ir thin films were systematically determined as a function of substrate temperature. Well-crystallized and single-phase Ir thin films with (1 1 1) preferred orientation were obtained at substrate temperature of 200-300 °C. The surface roughness increased with the increasing of substrate temperature. Likewise, the room-temperature resistivity of Ir thin films decreased with increasing substrate temperature, showing a low value of (10.7±0.1) μΩ cm at 300 °C.     

ZnO thin films prepared by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by pulsed laser deposition (PLD) in an oxygen-reactive atmosphere. The structural, optical, and electrical properties of the as-prepared thin films were studied in dependence of substrate temperature and oxygen pressure. High quality polycrystalline ZnO films with hexagonal wurtzite structure were deposited at substrate temperatures of 100 and 300 °C. The RMS roughness of the deposited oxide films was found to be in the range 2-9 nm and was only slightly dependent on substrate temperature and oxygen pressure. Electrical measurements indicated a decrease of film resistivity with the increase of substrate temperature and the decrease of oxygen pressure. The ZnO films exhibited high transmittance of 90% and their energy band gap and thickness were in the range 3.26-3.30 eV and 256-627 nm, respectively.     

Microstructure and magnetic properties of zinc ferrite thin films produced by pulsed laser deposition

Zinc ferrite thin films were deposited from a target of zinc ferrite onto a MgO substrate using XeCl excimer laser operating at 308 nm and frequency of 30 Hz. The crystallographic characterizations of the films were performed using X-ray diffraction (XRD). Microstructure, surface morphology, chemical composition and grain size, as well as surface roughness were obtained from scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). The magnetic properties of the thin films were studied in the temperature range 5–300 K and in fields of up to 5 T using SQUID magnetometry. Data on temperature and field dependence of magnetization provide a strong evidence for superparamagnetism. Paper presented at 8 AGM of MRSI, BARC, Mumbai, 1997.     

Structural and textural characterization of LiFePO4 thin films prepared by pulsed laser deposition on Si substrates

LiFePO₄ thin films were grown on silicon (100) substrates by pulsed laser deposition using Traditional Geometry (TG) and Off-Axis Geometry (OAG) deposition chambers. We examined and compared the structure and composition of the so formed thin films. The nails observed on the OAG-film present an amorphous “body” and a crystallized “head”. The Fe/P ratio determined using energy dispersive spectrometry combined with high angle annular dark field images reveals a metallic iron heart surrounded by LiFePO₄ shell. On the other hand, the protuberances on TG-film are pure iron. The focused ion beam prepared cross-section of the film suggests the presence of iron particles and iron dendritic like filaments inside the LiFePO₄ layer.     

ITO thin films deposited by advanced pulsed laser deposition

Indium tin oxide thin films were deposited by computer assisted advanced PLD method in order to obtain transparent, conductive and homogeneous films on a large area. The films were deposited on glass substrates. We studied the influence of the temperature (room temperature (RT)-180 °C), pressure (1-6 × 10^− 2 Torr), laser fluence (1-4 J/cm²) and wavelength (266-355 nm) on the film properties. The deposition rate, roughness, film structure, optical transmission, electrical conductivity measurements were done. We deposited uniform ITO thin films (thickness 100-600 nm, roughness 5-10 nm) between RT and 180 °C on a large area (5 × 5 cm²). The films have electrical resistivity of 8 × 10^− 4 Ω cm at RT, 5 × 10^− 4 Ω cm at 180 °C and an optical transmission in the visible range, around 89%.     

Composition controlling of KNbO3 thin films prepared by pulsed laser deposition

The composition of KNbO₃ thin films prepared by pulsed laser deposition is crucially influenced by the deposition configuration. In the present study, the composition of KNbO₃ thin films grown on Si (100) substrates by pulsed laser ablation was tried to be controlled by adjusting the target-substrate distance and the oblique angle of substrate from the plume axial direction. It was found that the K deficiency in the films can be effectively avoided by setting the substrate at an appropriate oblique angle from the plume axial direction. The stoichiometric KNbO₃ thin films with a K/Nb molar ratio of 0.98 were successfully obtained, where the substrates were set at an oblique angle of 3-12° from the plume axis while the target-substrate distance was kept at 40 mm.     

High quality amorphous indium zinc oxide thin films synthesized by pulsed laser deposition

Indium zinc oxide films were grown from targets with two different In atomic concentration [In/(In + Zn)] of 40% and 80% by the pulsed laser deposition technique on glass substrates from room temperature up to 100 °C. X-ray diffraction and reflectometry investigations showed that films were amorphous and dense. Thin films (thickness < 100 nm) exhibited higher optical transmittance and resistivities than thick films (thickness > 1000 nm), probably caused by a significant decrease of oxygen vacancies due to atmosphere exposure. Films deposited from the In rich target under an oxygen pressure of 1 Pa exhibited optical transmittance higher than 85%, resistivities around 5- 7 × 10^− 4 Ω cm and mobilities in the 47-54 cm²/V s range.     

Production of porous carbon thin films by pulsed laser deposition

Pulsed laser deposition (PLD) has been used together with the Glancing Angle Deposition (GLAD) technique [1 and 2] for the first time to produce highly porous structured films. A laser produced carbon plasma and vapour plume was deposited at a highly oblique incident angle onto rotating Si substrates, resulting in films exhibiting high bulk porosity and controlled columnar microstructure. By varying the substrate rotation rate, the shape of the microcolumns can be tailored. These results extend the versatility of the GLAD process to materials not readily deposited by means of traditional physical vapour deposition techniques.     

Effects of deposition parameters on the crystallinity of CeO2 thin films deposited on Si(100) substrates by r.f.-magnetron sputtering

Deposition temperature, r.f.-power and seed layer deposition time were important parameters effecting the crystallinity of CeO₂ thin films deposited by r.f.-magnetron sputtering on Si(100) substrates. The CeO₂ (200) peak was notable for a deposition temperature above 600°C. With decreased r.f.-power and thus lower deposition rate, the intensity of the CeO₂(200) peak increased. When the seed layer deposition time was less than 20 s, the CeO₂(200) peak dominated. Transmission electron microscopy (TEM) diffraction revealed that the deposited CeO₂ thin film had a polycrystalline structure. Annealing at 950°C in O₂ atmosphere for 30 min increased and sharpened the CeO₂(200) peak.     

Synthesis of SrSnO3 thin films by pulsed laser deposition: Influence of substrate and deposition temperature

SrSnO₃ thin films were prepared by pulsed laser deposition on amorphous silica and single crystal substrates of R-sapphire, (100)LaAlO₃ and (100)SrTiO₃. High quality epitaxial (100) oriented films were obtained on LaAlO₃ and SrTiO₃ while a texture was revealed for films on sapphire deposited at the same deposition temperature of 700 °C. Amorphous films were obtained on silica but a post annealing at 800 °C induced crystallization with a random orientation. The screening of deposition temperature showed epitaxial features on SrTiO₃ from 650 °C while no crystallization was observed at 600 °C. The influence of substrate and deposition temperature was confirmed by Scanning Electron Microscopy and Atomic Force Microscopy observations.     

Temperature-dependent growth of pulsed-laser-deposited bismuth thin films on glass substrates

Bismuth thin films were grown by pulsed-laser deposition on glass substrates with the substrate temperature from − 40 °C to 200 °C. The structure of the films was characterized by X-ray diffraction. The surface morphology was studied by atomic force microscopy and X-ray reflectivity. The electrical properties of the films were probed by Hall and van der Pauw measurements. We observed changes in the orientation, grain size and roughness of the bismuth films as a function of the substrate temperature. In particular, at − 30 °C, the surface roughness was drastically reduced, leading to very smooth bismuth films with highly (111)-preferred orientation. Furthermore, the preferred orientation disappeared at around − 40 °C.     

Comparison of high-pressure dc-sputtering and pulsed laser deposition of superconducting YBa2Cu3O x thin films

Superconducting YBa₂Cu₃O_x thin films were deposited on NdGaO₃ (110) substrates using two different techniques: dc sputtering at high oxygen pressure and pulsed laser deposition. The structure, electrical properties, and surface morphology of the obtained films were compared. The superior crystal quality of dc-sputtered films fabricated at the same temperature and at oxygen pressure of the same range as for laser-deposited films can be explained by a lower deposition rate providing time for recrystallization processes. The re-evaporation becomes significant for dc sputtering at high deposition temperatures and results in Badeficient films. The high mobility of atoms on the surface of the growing film during laser deposition helps in the formation of smoothc-oriented areas of the film.     

Pulsed laser deposition and characterization of Hf-based high-k dielectric thin films

The continuous downward scaling of the complementary metal oxide semiconductor (CMOS) devices has enabled the Si-based semiconductor industry to meet the technological requirements such as high performance and low power consumption. However, the ever-shrinking dimensions of the active device, metal-oxide-semiconductor-field-effect-transistor (MOSFET), in the circuit create other physical challenges. The industry standard SiO₂ for the gate region is reaching to its physical limits. New materials with higher dielectric constant are needed to replace the silicon dioxide in these gate regions. One of the candidates for this replacement is Hf-based oxides. In this project, we have used pulsed laser deposition (PLD) to synthesize Hf-based high-k dielectric films on Si single crystal substrates with varying deposition parameters and mixtures of HfO₂ and ZrO₂ then used X-ray absorption fine-structure spectroscopy (XAFS) in order to probe the local structure around the Hf metal. The local structural information extracted through XAFS has been correlated with the deposition parameters such as the substrate temperature and the HfO₂, to ZrO₂ ratio in the mixtures.     

Growth and characterization of LiNiVO4 thin film cathode by pulsed laser deposition

Crystallized LiNiVO₄ thin films have been prepared by pulsed laser deposition and their physical and electrochemical properties have been studied. With the increase of deposition temperatures and oxygen pressures, the crystallization became better, but accompanied with large sizes of grains. The initial discharge capacity of the film deposited at 873 K and 40 Pa of oxygen was just around 7.2 μA h/cm² μm when it was cycled between 3.0 and 4.8 V with a current density of 10 μA h/cm². Cyclic voltammetry at a sweep rate of 0.1 mV/s showed a main anodic peak at 4.20 V, a weak anodic peak at 4.59 V and a cathodic peak located at 3.73 V. Based on the linear relationship between the peak currents of cathodic peaks and the square roots of scan rates, the diffusion coefficient was estimated to be about 2.3 × 10^− 15 cm²/s. Electrochemical impedance spectra revealed high charge-transfer resistance of Li-ion, such as about 9000 Ω at 4.0 V. The extremely slow Li-ion diffusion and high charge-transfer resistance indicate that the electrochemical reaction in LiNiVO₄ thin films is sluggish.     

Controlled growth and characteristics of single-phase Cu2O and CuO films by pulsed laser deposition

Copper oxide, Cu₂O and CuO, thin films have been synthesized on Si (100) substrates using pulsed laser deposition method. The influences of substrate temperature and oxygen pressure on the structural properties of copper oxide films were discussed. The X-ray diffraction results show that the structure of the films changes from Cu₂O to CuO phase with the increasing of the oxygen pressure. It is also found that the (200) and (111) preferred Cu₂O films can be modified by changing substrate temperature. The formation of Cu₂O and CuO films are further identified by Fourier transform infrared spectroscopy. For the Cu₂O films, X-ray photoelectron spectroscopic studies indicate the presence of CuO on the surface. In addition, the optical gaps of Cu₂O and CuO films have been determined by measuring the transmittance and reflectance spectra.     

A study of microstructural and optical properties of nanocrystalline ceria thin films prepared by pulsed laser deposition

Thin films of cerium oxide (CeO₂) have been deposited on (100) Si substrates using pulsed laser deposition technique at various substrate temperatures from room temperature (RT) to 973 K at an optimized oxygen partial pressure of 3 Pa. Structural, morphological and optical properties have been carried out using X-ray diffraction (XRD), Raman, ellipsometry and atomic force microscopy techniques. XRD results showed that the deposited films are polycrystalline with cubic structure. At room temperature, the film showed preferred orientation along (111) plane, while at higher temperatures, it exhibited preferred orientation along (200). The crystallite sizes were calculated and were found to be in the range 17-52 nm. The texture coefficient for (200) reflection increased until 573 K, and then decreased in the temperature range 673-973 K. The Raman peak appeared at 463 cm^− 1 due to the F_2g active mode also confirmed the formation of CeO₂ with a cubic structure. There was a systematic variation in the Raman peak intensity, frequency shift and line broadening with the increase of temperature. The ellipsometry studies showed that the refractive index and band gap increased from 2.2 to 2.6 and 3.4 to 3.6 eV, respectively with increasing substrate temperature from RT to 973 K.     

Effect of oxygen pressure on the structural and optical properties of ZnO thin films on Si (111) by PLD

ZnO thin films were grown on Si (111) substrates by pulsed laser deposition (PLD) at various oxygen pressures in order to investigate the structural and optical properties of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The structural and morphological properties of the films were investigated by XRD and AFM measurements, respectively. The results suggest that films grown at 20 Pa and 50 Pa have excellent UV emission and high-quality crystallinity. The research of PL spectra indicates that UV emission is due to excitonic combination, the green band is due to the replacing of Zn in the crystal lattice for O and the blue band is due to the O vacancies.