Reactive Electron Beam Evaporation Technique Research Articles

Annealing effects on microstructure and laser-induced damage threshold of HfO2/SiO2 multilayer mirrors.

HfO2/SiO2 periodic multilayer high reflection mirrors have been prepared by a reactive electron-beam evaporation technique. The deposited mirrors were annealed in the temperature range from 300°C to 500°C. The effects of annealing on optical, microstructural, and laser-induced damage characteristics of the mirrors have been investigated. The high reflection band of the mirror shifts toward a shorter wavelength with increasing annealing temperature. As-deposited and annealed mirrors show polycrystalline structure with a monoclinic phase of HfO2. Crystalinity and grain size increase upon annealing. The laser-induced damage threshold (LIDT) has been assessed using a 532 nm pulsed laser at a pulse width of 7 ns. The LIDT value of the multilayer mirror increases from 44.1 J/cm2 to 77.6 J/cm2 with annealing up to 400°C. The improvement of LIDT with annealing is explained through oxygen vacancy defects as well as grain-size-dependent thermal conductivity. Finally, the observed laser damage morphology, such as circular scalds and ablated multilayer stacks with terrace structure, are analyzed.

Optical properties and laser damage threshold of HfO2–SiO2 mixed composite thin films

HfO(2)-SiO(2) mixed composite thin films have been deposited on fused silica substrate by co-evaporation of HfO(2) and SiO(2) through the reactive electron-beam evaporation technique. The composition-dependent refractive index and the absorption coefficient have been analyzed using different effective medium approximation (EMA) models in order to evaluate the suitability of these models for such mixed composite thin films. The discrepancies between experimentally determined and EMA-computed values are explained through microstructural and morphological evolutions observed in these mixed composite films. Finally, the dependence of the laser damage threshold as a function of silica content has been investigated, and the improved laser-induced damage threshold for films having more than 80% silica content has been explained through the defect-assisted multiphoton ionization process.

Structural and optical properties of Cr doped ZnO crystalline thin films deposited by reactive electron beam evaporation technique

ZnO and Cr-doped ZnO thin films are grown on to glass substrates using reactive electron beam (e-beam) evaporation technique. Variation of structural, morphological, and optical properties with Cr doping is investigated. X-ray diffraction (XRD) studies show that the films are polycrystalline in nature with single phase. Energy dispersive spectroscopy (EDS) results demonstrate that Cr ions are substitutionally incorporated into ZnO. Atomic force microscopy (AFM) reveals that the films present a compact surface and root mean squared (RMS) roughness increased with Cr contents. The optical band gap energy Eg of the films has been determined using Transmission data by spectrophotometer and ellipsometry. The band gap energy found to be decreased with increasing Cr doping concentration. The optical constants (refractive index, extinction coefficient) are calculated using ellipsometry and found to increase with Cr doping concentration.

Structure and Optical Properties of ZnO Thin Films Prepared by Reactive e- Beam Evaporation

Zinc oxide has been used as transparent and conducting oxide film in solar cells and electrochromic devices. In this work, ZnO thin films have been deposited by reactive electron beam evaporation technique with argonoxygen plasma assistance. The films have been deposited on glass substrate. After the deposition, the films were annealed at 550ºC during 2 hours in an oxidant atmosphere to improve its optical properties. The films were characterized by atomic force microscopy, UV/VIS/NIR spectroscopy and X-ray diffraction. The films are adherent and present high roughness, low transmittance and low crystallinity. After the thermochemical treatment there was an increase in optical transmittance, in crystallinity and a decrease of the absorption coefficient in the visible spectral region. Furthermore, the results of atomic force microscopy and DRX indicate that this treatment promotes a significant change of the surface texture and of the grain size.

Indium doped silver oxide thin films prepared by reactive electron beam evaporation technique: electrical properties

The indium doped silver oxide thin films have been prepared at 275 °C on soda lime glass and silicon substrates by reactive electron beam evaporation technique; the deposition rate has been varied (by varying the electron beam current) in the range 0.94–16.88 nm/s keeping the oxygen flow rate constant. These films are polycrystalline. The electrical resistivity for these films decreases with increasing deposition rate. The AIO films prepared with a deposition rate of 5.7 nm/s show near p-type conductivity. The work function has been measured on these films by contact potential method using Kelvin Probe. The surface morphology of the films has been evaluated using atomic force microscopy (AFM). The roles of indium doping and oxygen vacancies in the electrical properties of these films have been analyzed; the ionized impurity scattering is the dominant mechanism controlling the electrical conduction in these films.

WEAK LOCALIZATION EFFECTS IN METASTABLE SUPERSTRUCTURE NIOBIUM NITRIDE

Single-phase metastable α″-niobium nitride thin films have been synthesized on glass substrates by controlled reactive electron beam evaporation technique and are characterized by X-ray diffraction technique. The transport properties down to low temperatures have also been measured. The temperature dependence of resistivity has a minimum at 132 K and shows a remarkable change in the behavior below 25 K. These have been analyzed in the framework of weak localization effects. The analysis shows that the resistance minimum arises on account of three-dimensional weak localization and there is a cross-over to the two-dimensional weak localization regime at lower temperatures.

Fabrication and characterisation of high quality ZnO thin films by reactive electron beam evaporation technique

High quality zinc oxide thin films have been deposited on silicon substrates by reactive e-beam evaporation in an oxygen environment. The effect of the growth temperature and air annealing on the structural, optical and electrical properties has been investigated. X-ray diffraction measurements have shown that ZnO films are highly c-axis-oriented and that the linewidth of the (002) peak is sensitive to the variation of substrate temperature. The optimum growth temperature has been observed at 300°C. Raman spectroscopy has been found to be an efficient tool to evaluate the residual stress in the as-grown ZnO films from the position of the E2 (high) mode. On the other hand, the vanishing of the 574cm−1. Raman feature after annealing has been explained as due to an increase of grain size and the reduction of O-vacancy and Zn interstitial. The SEM images have shown that the surfaces of the electron beam evaporated ZnO became smoother for the growth temperatures higher than 300°C. The optical transmittance is the highest at 300°C and has been increased after annealing in air showing an improvement of the optical quality. Finally, the maximum electrical resistivity has been found at 300°C, which explains its relation with the crystal quality and increased from 5.8×10−2Ωcm to reach an approximate value of 109Ωcm after annealing at 750°C.

Characterization and Raman investigations on high-quality ZnO thin films fabricated by reactive electron beam evaporation technique

High-quality zinc oxide thin films have been evaporated by reactive e-beam in an oxygen environment. Photoluminescence (PL) on ZnO evaporated at 300 °C reveals an enhancement of the ultraviolet near band edge emission at 3.28 eV and shows the smallest full-width at half-maximum of the NBE peak about 150 meV, proving that the optimum growth temperature is 300 °C. X-ray diffraction measurements have shown that ZnO films are highly c-axis-oriented and that the linewidth of the (0 0 2) peak is sensitive to the variation of substrate temperature. The best crystallinity occurred at 300 °C, correlating with the PL measurements. The optical transmittance is the highest at 300 °C and has been increased after annealing in air, showing an improvement of the optical quality. Raman spectroscopy has been found to be an efficient tool to evaluate the residual stress in the as-grown ZnO films from the position of the E 2 (high) mode. On the other hand, the vanishing of the 574 cm −1 Raman feature after annealing has been explained as due to an increase of grain size and the reduction of O vacancy and Zn interstitial. A model has been developed in this work to determinate the normal mode frequencies from Fourier analysis by considering the five force constants starting from the five elastic constants of the material. The vibrational modes at about 100, 435 and 1123 cm −1 have been found from the model for a ZnO thickness of 0.3 μm.

Synthesis of P-type transparent conducting silver:indium oxide (AIO) thin films by reactive electron beam evaporation technique

Present paper reports the synthesis, electrical and optical properties of p-type conducting and transparent silver indium oxide (AIO) thin films prepared on glass substrates by reactive electron beam evaporation technique at three substrate temperatures (50, 200 and 250 °C) and at five evaporation rates (0.05 to 16.0 nm/s). The source material is pure powders of Ag 2O:In 2O 3=50:50 mol%. The AIO films are amorphous. The films, though not corresponding to Delafossite crystal structure, exhibit p-type conductivity, when prepared at an evaporation rate of 0.05 nm/s at all the three substrate temperatures. With increasing filament current, it is observed that (i) the electrical resistivity decreases and (ii) the refractive index of the films (at 632.8 nm, and is in the range: 1.219–1.211) decreases. The work function (effective Fermi level) has been measured on these samples by Kelvin Probe method. The results are explained on the basis of partial ionic charge and localization of covalent bonds in the AIO thin films.

Carrier transport mechanism in indium tin oxide (ITO)/silicon heterojunctions: effect of chlorine

Transparent-conducting-oxide (TCO)-based photovoltaic junctions have shown complexity in the transport phenomena at the interface. The present study is an attempt to understand the effect of chlorine at the interface between indium tin oxide (ITO) and Si. The ITO/Si junctions have been prepared by depositing transparent and conducting tin-doped indium oxide (ITO) thin films on as-cleaned and chlorine-treated single-crystal p-type and n-type silicon substrates using the reactive electron-beam evaporation technique. ITO/n-Si junctions have shown photovoltaic properties. The photoconversion efficiency of these junctions is observed to increase from 2.3% to 5.5% under chlorine treatment. The transport mechanism across these junctions has been studied by current–voltage (I–V , both dark and illuminated) and capacitance–voltage (C–V ) characterisation techniques. The carrier transport mechanism is found to be dominated by recombination at the depletion region for the junctions prepared with chlorine treatment, whereas for the other junctions, the thermionic process seems to be prominent. The unrealistic barrier heights observed in these junctions by the C–V technique confirms the complex nature of the interface.

P-type transparent conducting In2O3–Ag2O thin films prepared by reactive electron beam evaporation technique

The transparent and conducting oxide thin films are all, so far, n type. In the present article, we report the results of thin films of In2O3+Ag2O which have shown p-type conductivity and transparency in the visible range. These films are prepared on glass substrates by reactive electron beam evaporation technique at a substrate temperature of 180 °C and at a chamber pressure of 2.5×10−4 Torr with oxygen. The evaporation rate is varied by controlling the electron beam current in the range: 30–100 mA keeping the voltage at 3.8 kV. The starting material is a mixture of In2O3 and Ag2O powder (of purity 99.99%). Two compositions of Ag2O in the starting material: 20% and 40% by weight have been studied. All the films grown at higher evaporation rate are polycrystalline. The electrical and optical properties of the films show very interesting behavior. The type of conductivity (p or n) in these films is observed to be dependent upon the evaporation rate. The best values for p-type films observed in the present investigation are for the 80:20 composition at an evaporation rate 42 A/min: Hall mobility: 8.2 cm2/V s, resistivity: 22.5 Ω cm and transparency at 500 nm: 34%. The data are analyzed in the light of electronegativity equalization and partial negative charge concepts to understand the physics of the p-type conduction.

Electrical characterization of electron beam evaporated indium tin oxide/indium phosphide junctions

The electrical properties of Indium tin oxide(ITO)/p-indium phosphide (InP) junctions prepared at different temperatures by reactive electron beam evaporation technique have been studied. A maximum of 10.0% photo conversion efficiency under 100 mW cm−2 illumination (without front metal grid and antireflection coating) has been observed. Analyses of the results indicate an interfacial oxide layer consisting of indium oxide and indium orthophosphate and the ITO/p-InP junction correspond to the semiconductor-insulator-semiconductor SIS model. An attempt has been made to understand the nature of the interfacial layer.

Studies on the electrical and optical properties of reactive electron beam evaporated indium tin oxide films

Highly conducting ( rho =2.5*10-4 Omega cm) and transparent (92%) tin-doped indium oxide (ITO) films have been prepared by a reactive electron beam evaporation technique; the dependence of these properties on the substrate temperature (150-275 degrees C) and tin doping (0-15% by weight) has been studied. Hall mobility in the films has been found to increase with substrate temperature and decrease with the addition of tin. An attempt has been made to distinguish the different scattering mechanisms responsible for electrical conduction; it is found that the grain boundary scattering is negligibly small in these films. An analysis of the optical data has been made to evaluate the broadening parameter and the Burstein-Moss shift in optical band gaps.

Optical and structural characterization of evaporated zirconia films

Thin films of zirconia have been deposited using a reactive electron beam evaporation technique onto unheated alumina and fused silica substrates. The films were post annealed in the range 300–850 °C. The influence of post-deposition conditions on the optical properties like refractive index and absorption and nonoptical properties like structure have been studied. The structural transitions were determined using infrared (IR) absorption and x-ray diffraction. Preliminary results of studies on the correlation between x-ray diffraction and IR absorption data for structural characterization are reported. It has been shown that the refractive index values change considerably with each structural transition, although the optical absorption does not seem to be very adversely affected by post-deposition annealing. Post-deposition annealing resulted in the formation of the cubic phase at 500 °C which transformed to the tetragonal phase at 700 °C and finally monoclinic phase at 800 °C. The above-mentioned phases were only the major phases and post-deposition annealing did not result in single-phase material.