Tayloring of the Schottky barrier height of Pt-Ir mixed silicide infrared detectors

 Pt-Ir silicide Schottky diodes were formed by e-beam evaporation of Pt and Ir onto p-Si(100) substrates in high vacuum with subsequent RTA-annealing at temperatures in the range of 300 to 500 °C. Rutherford Backscattering Spectrometry (RBS) and infrared photoresponse (PR) measurements were performed to determine the composition and the infrared electrooptical properties of the resulting films. Coevaporated Pt-Ir films are demixed during silicidation and form a PtSi layer at the interface to the silicon substrate. The Schottky barrier height is that of a pure PtSi film. Ir deposited prior to Pt exhibits Pt diffusion through the Ir layer. Only when the Ir film is reacted to IrSi by in situ annealing prior to Pt deposition, a mixed Ir-Pt silicide Schottky barrier is obtained. Infrared photoemission then yields intermediate Schottky barrier heights between those of PtSi and IrSi. From a detailed analysis of the photoemission characteristics, it is concluded that the intermediate barrier height is due to an area average of PtSi and IrSi grains which coexist at the Si interface. Received: 29 May 1996/Accepted: 12 August 1996     

Nanometer-microscopy of the electron transmission through an ultrathin (3–22 nm) Au film and of the Au-Si schottky barrier height

Direct imaging with nanometer scale resolution of the Schottky barrier height and of the ballistic transmission of electrons through an ultrathin metal film is demonstrated for the first time. The images are obtained by applying a new pixel-by-pixel evaluation method to the ballistic electron emission spectroscopy (BEES). We find a laterally uniform Schottky barrier height _B=0.88 eV for ultrathin (3–22 nm) Au films evaporated on Si. The transmission coefficient is strongly correlated with the island structure of the Au film. A transmission decay length =14 nm is determined by a statistical analysis of the transmission coefficient with variation of the film thickness.     

Band structure and valence-band offset of HfO2 thin film on?Si?substrate from photoemission spectroscopy

Synchrotron radiation photoemission spectroscopy and optical transmission spectrum measurements have been performed on an HfO₂ thin film grown on a Si(100) substrate to determine the band structure of the HfO₂/Si stack. The result shows a valence-band offset of 2.5 eV and a conduction-band offset of 2.2 eV for the HfO₂/Si interface. The Schottky barrier height between Au and HfO₂ is obtained from current density–voltage measurement. The characterization reveals that the dominant conduction mechanism in the region of low field under gate injection is Schottky emission. The energy-band diagram of an Au–HfO₂–Si MOS stack was obtained from these results.     

Infrared photoemission of holes from ultrathin (3–20 nm) Pt/Ir-compound silicide films into silicon

The infrared responsivity is measured at low temperature on Schottky barrier detectors having ultrathin (3–20 nm) PtSi, IrSi, and compound silicide films as a metal electrode on p-type silicon. The total yield for internal hole photoemission is 1% per incident photon for PtSi and 0.1% for IrSi at a wavelength of =4 m. The cut-of wavelengths are =5.4 m and =8.2 m for PtSi and IrSi, respectively. The compound silicides fabricated by sequential evaporation of Pt and Ir and subsequent annealing at T=450° C show characteristics identical to that of PtSi.A Monte Carlo computer modelling is performed to simulate the scattering mechanisms in the thin silicide film leading to hole photoemission across the Schottky barrier into silicon. The optimum emission yield is observed for ultrathin films of the order of a few nanometers. The optimum film thickness is close to the escape depth d _esc2–3×L _el5 nm which scales with the mean free path L _el for quasi elastic scattering. The enhancement of the internal photoemission in ultrathin silicide films is predominantly due to the increase of the optical photoexcitation density rather than to an increase of the electrical emission yield in thin films.     

The electronic and chemical structure of the a-B(3)CO(0.5):H(y)-to-metal interface from photoemission spectroscopy: implications for Schottky barrier heights

The electronic and chemical structure of the metal-to-semiconductor interface was studied by photoemission spectroscopy for evaporated Cr, Ti, Al and Cu overlayers on sputter-cleaned as-deposited and thermally treated thin films of amorphous hydrogenated boron carbide (a-B(x)C:H(y)) grown by plasma-enhanced chemical vapor deposition. The films were found to contain ～10% oxygen in the bulk and to have approximate bulk stoichiometries of a-B(3)CO(0.5):H(y). Measured work functions of 4.7/4.5?eV and valence band maxima to Fermi level energy gaps of 0.80/0.66?eV for the films (as-deposited/thermally treated) led to predicted Schottky barrier heights of 1.0/0.7?eV for Cr, 1.2/0.9?eV for Ti, 1.2/0.9?eV for Al, and 0.9/0.6?eV for Cu. The Cr interface was found to contain a thick partial metal oxide layer, dominated by the wide-bandgap semiconductor Cr(2)O(3), expected to lead to an increased Schottky barrier at the junction and the formation of a space-charge region in the a-B(3)CO(0.5):H (y) layer. Analysis of the Ti interface revealed a thick layer of metal oxide, comprising metallic TiO and Ti (2)O (3), expected to decrease the barrier height. A thinner, insulating Al(2)O(3) layer was observed at the Al-to-a-B(3)CO(0.5):H(y) interface, expected to lead to tunnel junction behavior. Finally, no metal oxides or other new chemical species were evident at the Cu-to-a-B(3)CO(0.5):H(y) interface in either the core level or valence band photoemission spectra, wherein characteristic metallic Cu features were observed at very thin overlayer coverages. These results highlight the importance of thin-film bulk oxygen content on the metal-to-semiconductor junction character as well as the use of Cu as a potential Ohmic contact material for amorphous hydrogenated boron carbide semiconductor devices such as high-efficiency direct-conversion solid-state neutron detectors.     

Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si

Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films were prepared at room temperature via reactive magnetron sputtering using a W₂B target at various N₂/(Ar + N₂) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement, cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at 500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity diffusion barrier material for copper interconnects.     

Structural, optical and electrical properties of tin oxide thin film deposited by APCVD method

Tin oxide (SnO₂) thin films have been grown on glass substrates using atmospheric pressure chemical vapour deposition (APCVD) method. During the deposition, the substrate temperature was kept at 400°C–500°C. The structural properties, surface morphology and chemical composition of the deposited film were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and Rutherford back scattering (RBS) spectrum. XRD pattern showed that the preferred orientation was (110) having tetragonal structure. The optical properties of the films were studied by measuring the transmittance, absorbance and reflectance spectra between λ = 254 nm to 1400 nm and the optical constants were calculated. Typical SnO₂ film transmits ∼ 94% of visible light. The electrical properties of the films were studied using four-probe method and Hall-voltage measurement experiment. The films showed room temperature conductivity in the range 1.08 × 10² to 1.69 × 10² Ω⁻¹cm⁻¹.     

Preferential regrowth of indium–tin oxide (ITO) films deposited on GaN (0001) by rf-magnetron sputter

Effects of thermal treatments on the electrical properties and microstructures of indium–tin oxide (ITO)/GaN contacts have been investigated using a rf-magnetron sputter deposition followed by rapid thermal annealing. ITO films annealed at 800 °C revealed Schottky contact characteristics with a barrier height corresponding to ITO’s work function of 4.62 eV. The evolution of electrical properties of ITO/GaN contacts was attributed to the preferential regrowth of In₂O₃ (222)//GaN (0001) with an ideal metal–semiconductor Schottky contact. The feasible use of ITO/GaN as a transparent Schottky contact would be realized by the enhanced regrowth of In₂O₃ at high temperature. Received: 1 September 2000 / Accepted: 15 November 2000 / Published online: 28 February 2001     

Structural and optical properties of amorphous Sb2S3 thin films deposited by vacuum thermal evaporation method

Sb₂S₃ thin films have been deposited by vacuum thermal evaporation onto glass substrates at various substrate temperatures in the range of 30–240 °C. Crushed powder of the synthesized Sb₂S₃ was used as raw material for the vacuum thermal evaporation. The structural investigation performed by means of X-ray diffraction (XRD) showed that the all as-deposited films present an amorphous structure and all the films were highly resistive. The reflectance and transmittance of the films are measured in the incident wavelength range 300–1800 nm. The absorption coefficient spectral analysis revealed the existence of long and wide band tails of the localized states in the low absorption region. The band tails width is calculated and found to be varying between 0.024 and 0.032 eV. The analysis of the absorption coefficient in the high absorption region revealed two direct forbidden band gaps between 1.78–1.98 eV and 1.86–2.08 eV.     

Phase transformation of Ni/Si thin films induced by nanoindentation and annealing

Thin Ni/Si films are prepared by depositing a Ni layer with a thickness of 100 nm on a Si (100) substrate. The as-deposited thin-film specimens are indented to a maximum depth of 500 nm using a nanoindentation technique and are then annealed at temperatures of 200°C, 300°C, 500°C and 800°C for 2 min. The microstructural changes and phases induced in the various specimens are observed using transmission electron microscopy (TEM) and micro-Raman scattering spectroscopy (RSS). Based on the load-displacement data obtained in the nanoindentation tests, the hardness and Young’s modulus of the as-deposited specimens are found to be 13 GPa and 177 GPa, respectively. The microstructural observations reveal that the nanoindentation process prompts the transformation of the indentation-affected zone of the silicon substrate from a diamond cubic structure to a mixed structure comprising amorphous phase and metastable Si III and Si XII phases. Following annealing at temperatures of 200∼500°C, the indented zone contains either a mixture of amorphous phase and Si III and Si XII phases, or Si III and Si XII phases only, depending on the annealing temperature. In addition, the annealing process prompts the formation of nickel silicide phases at the Ni/Si interface or within the indentation zone. The composition of these phases depends on the annealing temperature. Specifically, Ni₂Si is formed at a temperature of 200°C, NiSi is formed at a temperature of 300°C and 500°C, and NiSi₂ is formed at 800°C.     

Laser mass spectrometry study of the properties of fullerene structures

Fullerene films grown by various methods are studied using mass spectrometry. The mass spectra of the films formed onto an aluminum foil using thermal deposition (TD) or supersonic molecular beam (SMB) exhibit a small change in the mass peak distribution in the C₁₂₀ dimer range as compared to the initial fullerene powder during desorption by laser radiation irrespective of the radiation wavelength (λ = 259, 518 nm). Under the action of laser radiation with wavelength λ = 259 nm, fullerene films grown on a silicon substrate with an SMB also exhibit a small change in the mass peak distribution in the C₁₂₀ dimer range. At λ = 518 nm, the mass peak distribution in the dimer range shifts significantly toward small masses, so that the intensity maximum corresponds to M ≅ C₁₀₂. This fact is assumed to be related to the polymerization of an SMB fullerene film caused by heating due to the absorption of laser radiation with a wavelength λ = 518 nm.     

In situ photoemission study of the contact formation of (Ba,Sr)TiO3 with Cu and Au

The contact formation of (Ba,Sr)TiO₃ thin films and SrTiO₃ single crystals with Cu and Au have been studied using X-ray and ultraviolet photoelectron spectroscopy with in situ sample preparation. During metal deposition a partial reduction of the substrate occurs. The Fermi level at the interface is found to be close to the conduction band minimum, indicating small Schottky barrier heights (< 0.2 eV).     

Influence of rapid thermal annealing on electrical and structural properties of double metal structure Au/Ni/n-InP (1 1 1) diodes

The effect of rapid thermal annealing on the electrical and structural properties of Ni/Au Schottky contacts on n-InP have been investigated by current–voltage (I–V), capacitance–voltage (C–V), auger electron spectroscopy (AES) and X-ray diffraction (XRD) techniques. The Au/Ni/n-InP Schottky contacts are rapid thermally annealed in the temperature range of 200–500 °C for a duration of 1 min. The Schottky barrier height of as-deposited Ni/Au Schottky contact has been found to be 0.50 eV (I–V) and 0.86 eV (C–V), respectively. It has been found that the Schottky barrier height decreased with increasing annealing temperature as compared to as-deposited sample. The barrier height values obtained are 0.43 eV (I–V), 0.72 eV (C–V) for the samples annealed at 200 °C, 0.45 eV (I–V) and 0.73 eV (C–V) for those at 400 °C. Further increase in annealing temperature to 500 °C the barrier height slightly increased to 0.46 eV (I–V) and 0.78 eV (C–V) compared to the values obtained for the samples annealed at 200 °C and 400 °C. AES and XRD studies showed the formation of indium phases at the Ni/Au and InP interface and may be the reason for the increase in barrier height. The AFM results showed that there is no significant degradation in the surface morphology (rms roughness of 1.56 nm) of the contact even after annealing at 500 °C.     

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y₂O₃:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm² and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y₂O₃:Eu was formed. The Y₂O₃:Eu film irradiated by the ArF laser at 80 mJ/cm² and 500°C showed typical PL spectra of Eu³⁺ ions with cubic symmetry and a ⁵D₀→⁷F₂ transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.     

An exploratory study of the reactive Ni-GaAs (1 1 0) interface

Soft X-ray photoemission spectroscopy measurements have been carried out on cleaved n-type GaAs (1 1 0) surfaces covered with Ni overlayers ranging in thickness from 0.05 to 53 Å. The results of these room temperature measurements show that we have band bending effects occurring in conjunction with strong interfacial chemical reactions. Deconvolution of the Ga 3d core line into substrate and metallic components shows dissolution of the substrate at the interface with Ga diffusing into the surface of the metal overlayer for the intermediate coverages (1–15 Å). Observation of the As 3d core level shows out-diffusion of As to the surface over the entire Ni coverage range. Using this deconvolution scheme we are able to follow the band bending of the Schottky barrier formed here up to the 8 Å coverage. The Schottky barrier height is 1.0 ± 0.1 eV for this overlayer thickness.     

Fractional Josephson vortices: oscillating macroscopic spins

Photon-induced band bending changes and subsequent relaxation at the buried insulator/semiconductor interface of BaF₂/Si(001) have been investigated. This is achieved by creating free charge carriers through absorption of a visible pump laser pulse (λ=532 nm, E=2.33 eV) in the silicon, followed by time resolved photoelectron spectroscopy using vacuum-ultraviolet synchrotron radiation (E=18 eV) as a probe of the BaF₂ valence band (VB). Since the excitation takes place in the semiconductor and the probe photoemission signal originates from the BaF₂, the relaxation at the interface has been probed. PACS 41.60.Ap; 33.60.Cv; 79.60.Jv; 73.40.Qv     

Photoconductivity studies on amorphous and crystalline TiO<Subscript>2</Subscript> films doped with gold nanoparticles

In this work, amorphous and crystalline TiO₂ films were synthesized by the sol–gel process at room temperature. The TiO₂ films were doped with gold nanoparticles. The films were spin-coated on glass wafers. The crystalline samples were annealed at 100°C for 30 minutes and sintered at 520°C for 2 h. All films were characterized using X-ray diffraction, transmission electronic microscopy and UV-Vis absorption spectroscopy. Two crystalline phases, anatase and rutile, were formed in the matrix TiO₂ and TiO₂/Au. An absorption peak was located at 570 nm (amorphous) and 645 nm (anatase). Photoconductivity studies were performed on these films. The experimental data were fitted with straight lines at darkness and under illumination at 515 nm and 645 nm. This indicates an ohmic behavior. Crystalline TiO₂/Au films are more photoconductive than the amorphous ones.     

Effect of process parameters and post-deposition annealing on the microwave dielectric and optical properties of pulsed laser deposited Bi<Subscript>1.5</Subscript>Zn<Subscript>1.0</Subscript>Nb<Subscript>1.5</Subscript>O<Subscript>7</Subscript> thin films

Bismuth Zinc niobate (Bi_1.5Zn_1.0Nb_1.5O₇) thin films were deposited by pulsed laser deposition (PLD) method on fused silica substrates at different oxygen pressures. The structural, microwave dielectric and optical properties of these thin films were systematically studied for both the as-deposited and the annealed films at 600°C. The as-deposited films were all amorphous in nature but crystallized on annealing at 600°C in air. The surface morphology as studied by atomic force microscopy (AFM) reveals ultra-fine grains in the case of as-deposited thin films and cluster grain morphology on annealing. The as-deposited films exhibit refractive index in the range of 2.36–2.53 (at a wavelength of 750 nm) with an optical absorption edge value of 3.30–3.52 eV and a maximum dielectric constant of 11 at 12.15 GHz. On annealing the films at 600°C they crystallize to the cubic pyrochlore structure accompanied by an increase in band gap, refractive index and microwave dielectric constant.     

Electrical and structural properties of a stacked metal layer contact to n-InP

In this study, we found that the double metal contact structure in Pt/Al/n-InP diodes provides better rectification characteristics than conventional single-metal/n-InP Schottky diodes. The effective barrier height was measured to be 0.67 eV for a 400 °C-annealed Pt/Al/n-InP diode sample. The increase in the barrier height is attributed to the formation of Al₂O₃ at the metal/n-InP contact interface during thermal annealing. The formation of the phase Al₂O₃ phase was monitored by X-ray diffraction (XRD) analysis. The corresponding element profiles of Al and O were also confirmed at the metal/n-InP contact interface using secondary ion mass spectrum (SIMS) analysis. The lowering of the Schottky barrier height due to the inhomogeneity at the metal/n-InP junction is also discussed on the basis of the TE theory. The distribution of local effective Schottky barrier heights was explained by a model incorporating the existence of double Gaussian barrier heights, which represent the high barrier and low barrier of the full distribution in the temperature ranges of 83-198 and 198-300 K.     

PEDOT:PSS Schottky contacts on annealed ZnO films

Polycrystalline ZnO and ITO films on SiO₂ substrates are prepared by radio frequency (RF) reactive magnetron sputtering. Schottky contacts are fabricated on ZnO films by spin coating with a high conducting polymer, poly(3, 4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) as the metal electrodes. The current-voltage measurements for samples on unannealed ZnO films exhibit rectifying behaviours with a barrier height of 0.72 eV (n=1.93). The current for the sample is improved by two orders of magnitude at 1 V after annealing ZnO film at 850 ℃, whose barrier height is 0.75 eV with an ideality factor of 1.12. X-ray diffraction, atomic force microscopy and scanning electron microscopy are used to study the properties of the PEDOT:PSS/ZnO/ITO/SiO₂. The results are useful for applications such as metal-semiconductor field-effect transistors and UV photodetectors.