Growth of cubic and hexagonal CdTe thin films by pulsed laser deposition

The paper reports the growth of cadmium telluride (CdTe) thin films by pulsed laser deposition (PLD) using excimer laser (KrF, λ=248 nm, 10 Hz) on corning 7059 glass and SnO₂-coated glass (SnO₂/glass) substrates at different substrate temperatures (T_s) and at different laser energy pulses. Single crystal target CdTe was used for deposition of thin films. With 30 min deposition time, 1.8- to ∼3-μm-thick films were obtained up to 200 °C substrate temperature. However, the film re-evaporates from the substrate surface at temperatures >275 °C. Atomic force microscopy (AFM) shows an average grain size ∼0.3 μm. X-ray diffraction analysis confirms the formation of CdTe cubic phase at all pulse energies except at 200 mJ. At 200 mJ laser energy, the films show hexagonal phase. Optical properties of CdTe were also investigated and the band gap of CdTe films were found as 1.54 eV for hexagonal phase and ∼1.6 eV for cubic phase.     

Growth of polycrystalline InP thin films by the pulsed laser deposition technique

The growth of polycrystalline InP films on glass substrates by the pulsed laser deposition technique is reported. Optimal growth conditions as high vacuum and relatively low substrate temperature were necessary to obtain stoichiometric InP layers. Structural and morphological characterizations of the samples are shown. X-ray diffraction shows that the stoichiometric InP films were face-centered cubic with preferred orientation of the crystallites over the (111) plane and mean grain size of about 60 nm. We also discuss the consequences of adverse growth conditions as bad vacuum and high substrate temperature on the film stoichiometry.     

Growth and characterization of non-polar ZnO thin films by pulsed laser deposition

Non-polar ZnO thin films were fabricated on r-plane sapphire substrates by pulsed laser deposition at various temperatures from 100 to 500 °C. The effects of the substrate temperature on structural, morphological and optical properties of the films were investigated. Based on the X-ray diffraction analysis, the ZnO thin films grown at 300, 400 and 500 °C exhibited the non-polar (a-plane) orientation and those deposited below 300 °C exhibited polar (c-plane) orientation. In the optical properties of non-polar ZnO films, there were two photoluminescence peaks detected. The peaks (near-band edge emission, blue emission) are due to electron transitions from band-to-band and shallow donor level to valence band, respectively.     

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.     

Growth of Ti:sapphire single crystal thin films by pulsed laser deposition

This paper documents the growth of single crystal Ti:sapphire thin films, typically 10 μm thick, on undoped sapphire substrates using pulsed laser deposition from a Ti:sapphire single crystal target with a doping level of 0.1 wt.% Ti₂O₃. These thin films are shown to have very high crystal quality using ion beam channelling and X-ray diffraction techniques. The degree of titanium incorporation into the films is investigated using inductively coupled plasma mass spectrometry and particle induced X-ray emission. These techniques show that levels of up to 0.08 wt.% Ti₂O₃ are present in the deposited layers.     

InGaZnO thin films grown by pulsed laser deposition

We fabricated InGaZnO (IGZO) ceramic target (In: Ga: Zn = 1: 1: 4 in atomic ratio) using solid-state reaction at ambient atmosphere, and deposited IGZO thin films on quartz glass at room temperature under various oxygen partial pressures using the pulsed laser deposition method. Influence of oxygen pressure on crystal structure, surface morphology, optical and electrical properties were investigated. It was found that all the films deposited at room temperature exhibit amorphous structure. On the other hand, the physical properties of the films like transparency, electron mobility, and free-electron concentration were found to be correlated to the oxygen pressure during the deposition and in turn to the possible oxygen vacancies or metallic interstitials in the films. The analysis of X-ray photoelectron spectra (XPS) of the films indicated that there are no metallic 3d states of In, Ga and Zn, suggesting that oxygen vacancies could be main defects that affect physical properties of the films.     

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.     

Thickness dependent magnetic properties of BiFeO3 thin films prepared by pulsed laser deposition

BiFe_1 ? xMn_xO₃ thin films having thickness 65 and 130 nm was fabricated on LAO substrates using pulsed laser deposition technique and its structural and magnetic properties were examined. Atomic force microscopy images confirmed that, as the thickness of the films increases the particles size also increases resulting in the decrease of magnetization. The possible cause for the lowering of magnetization with film thickness was discussed. Increase of spontaneous magnetization in BiFeO₃ at room temperature was observed with Mn substitution for Fe. The blocking temperature was found to decrease with increasing film thickness.     

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.     

Nanoporous films obtained by sacrificial layer pulsed laser deposition

Integration of solid state gas sensors and solid oxide fuel cells into third generation microelectronic products requires the development of unique fabrication methods. Highly porous electrodes, critical to the performance of many gas dependent devices, typically require harsh production methods and high sintering temperatures that are incompatible with a variety of platforms including those based on silicon or glass. In this study, an alternative procedure for overcoming these problems has been developed. It is based on the synthesis of nano-porous films at reduced fabrication temperatures by means of the Sacrificial Layer Pulsed Laser Deposition (SL-PLD). SL-PLD utilizes simultaneous oxide and carbon deposition to deposit thin dense films. These amorphous films are then transformed into nano-porous perovskite films by thermal annealing in ambient air at 600 ºC. In this paper, an alternative process for the development of nano-porous thin films at reduced fabrication temperatures is presented. It takes advantage of the low temperatures needed for both carbon burn-off and the structural transformation of many perovskite oxides. This alternative method for thin film fabrication opens the possibility for low temperature fabrication of porous ceramic materials.     

脉冲激光沉积法制备Pt薄膜的研究

采用脉冲激光沉积技术在(0001)取向的蓝宝石基片上外延生长了Pt单晶薄膜,研究了沉积温度和激光能量对Pt薄膜的晶体结构,表面形貌及电学性能的影响规律.X射线衍射(XRD)分析结果表明,在沉积温度650℃、激光脉冲频率1Hz和激光能量280mJ的条件下,制备得到的Pt(111)单晶薄膜,其(111)面ω摇摆曲线半高宽(FWHM)仅为0.068°.原子力显微镜(AFM)分析表明外延的Pt薄膜表面具有原子级平整度,其表面均方根粗糙度(RMS)约为1.776nm.四探针电阻测试结果显示薄膜方阻为1/962Ω/□,满足铁电薄膜的制备工艺对Pt底电极的要求.     

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%.     

Structural and magnetic properties of Co-Ga co-doped ZnO thin films fabricated by pulsed laser deposition

Co-Ga co-doped ZnO films were fabricated by pulsed laser deposition on quartz substrates. The obtained films exhibited a wurtzite structure with c-axes growth preference. Optical measurements showed the presence of the cobalt ions in a tetrahedral crystal field, which proved that the Co ion substitution in the ZnO lattice, acting as magnetic cation. Hall measurements indicated that the films were n-type conductive with the electron concentrations of ~ 10²⁰/cm³. This value was much higher than that of the Co-doped films, suggesting the effective incorporation of Ga in the films. Room temperature ferromagnetism was observed for the Ga-Co co-doped thin films.     

脉冲激光沉积制备立方AlN薄膜的研究

采用脉冲激光沉积(PLD)方法,在SrTiO3(100)衬底上在650℃、10Pa N2条件下成功制备了立方结构的AlN薄膜.高能电子衍射(RHEED)及X射线衍射(XRD)分析表明立方AlN和SrTiO3的外延关系为AlN[100]∥SrTiO3[100]和AlN(200)∥SrTiO3(100).其AlN(200)衍射峰的摇摆曲线半高宽(FWHM)为0.44°,说明薄膜结晶性能良好.原子力显微镜(AFM)表明外延的立方AlN薄膜表面具有原子级平整度,其表面均方根粗糙度(RMS)为0.674nm.通过X光电子能谱(XPS)分析AlN薄膜表面成分,结果表明AlN薄膜表面没有被氧化.     

脉冲激光沉积氮化铝薄膜的电学性能研究

采用脉冲激光沉积(PLD)技术在硅片上合成了AlN薄膜.X射线衍射(XRD)结果证实制备的AlN薄膜具有(002)择优取向的六方纤锌矿晶体结构,并且结晶质量随Si衬底温度的提高而改善.电流-电压(I-V)、电容-电压(C-V)、极化曲线结果表明室温生长的AlN薄膜的击穿场强约2.5MV/cm,同时呈现明显的极化现象(类铁电),对应矫顽场强为150kV/cm,剩余极化为0.002C/m2.晶态AlN存在较强的自发极化,薄膜中可动电荷密度高,据此提出了动态电荷模型,指出较大的AlN薄膜极化回线是由于可动电荷在电场中的再分布形成的,因而有别于铁电材料.     

Surface morphology of AlN films synthesized by pulsed laser deposition

Surface morphology of AlN films, synthesized on Si substrates by pulsed laser deposition, has been examined by recording atomic-force-microscopy (AFM) images. The influence of N₂ ambient pressure, ranging from 5 × 10⁻⁴ Pa to 10 Pa, is reflected well in the alteration of the surface roughness and size of crystallites of the AlN films. A tendency of a decrease in the surface roughness with increasing N₂ pressure was observed, which also correlates with the polycrystalline structure of the films. Deposition in vacuum resulted in the highest surface roughness due to the large size of crystallites emerging from the surface, while increasing the nitrogen pressure yielded smaller crystallites and a smoother film surface. The presented results could be useful for applications of pulsed laser deposited AlN in different optical and acoustic devices, where the crystalline quality of the AlN films and the surface is very important.     

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.     

Synthesis of amorphous silicon carbonitride films by pulsed laser deposition

Silicon carbonitride (SiC_xN_y) films were grown on silicon substrates using the pulsed laser deposition (PLD) technique. A silicon carbide (SiC) target was ablated by the beam of a KrF excimer laser in a nitrogen (N₂) background gas. The morphology, structure, composition, as well as the optical and mechanical properties of the coatings were investigated as functions of the N₂ pressure (1–30 mtorr) and substrate temperature (250–650 °C). Smooth, amorphous films were obtained for all the processing parameters. The concentration of nitrogen in the deposits was found to increase when increasing the N₂ pressure, while the silicon and carbon concentrations decreased concurrently. At a N₂ gas pressure of 30 mtorr, a nitrogen content in the range of 28–34 at.% was obtained. Two growth regimes were identified as a function of the N₂ pressure. For a pressure up to 10 mtorr, highly dense and homogeneous films were observed, while textured deposits were obtained at higher pressures. The latter regime was characterized by an oxygen contamination of the coatings, whose severity increased when increasing the N₂ pressure or when reducing the deposition temperature. The hardness of the films was found to be a function of the growth regime; the highest values of the hardness were obtained in the low-pressure regime, in the range of 27–42 GPa.     

Al-doped ZnO films by pulsed laser deposition at room temperature

Polycrystalline Al-doped ZnO films with good photoluminescence property were successfully deposited on quartz glass substrates by pulsed laser deposition (PLD) at room temperature. The films were obtained by ablating a metallic target (Zn:Al 3 wt%) at various laser energy densities (1.0-2.1 J/cm²) in oxygen atmosphere (9 Pa). The structure of the films was characterized by XRD. Ultraviolet photoluminescence centered at 359-361 nm was observed in the room temperature PL spectra of the Al-doped ZnO films.     

Nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition

Nano-polycrystalline vanadium oxide thin films have been successfully produced by pulsed laser deposition on Si(100) substrates using a pure vanadium target in an oxygen atmosphere. The vanadium oxide thin film is amorphous when deposited at relatively low substrate temperature (500 degrees C) and enhancing substrate temperature (600-800 degrees C) appears to be efficient in crystallizing VOx thin films. Nano-polycrystalline V3O7 thin film has been achieved when deposited at oxygen pressure of 8 Pa and substrate temperature of 600 degrees C. Nano-polycrystalline VO2 thin films with a preferred (011) orientation have been obtained when deposited at oxygen pressure of 0.8 Pa and substrate temperatures of 600-800 degrees C. The vanadium oxide thin films deposited at high oxygen pressure (8 Pa) reveal a mix-valence of V5+ and V4+, while the VOx thin films deposited at low oxygen pressure (0.8 Pa) display a valence of V4+. The nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition have smooth surface with high qualities of mean crystallite size ranging from 30 to 230 nm and Ra ranging from 1.5 to 22.2 nm. Relative low substrate temperature and oxygen pressure are benifit to aquire nano-polycrystalline VOx thin films with small grain size and low surface roughness.