Intrinsic stress fracture energy measurements for PECVD thin films in the SiOxCyNz:H system

The fracture energies of a series of tensile plasma-enhanced chemical vapor deposited low dielectric constant (low-k) SiO_xC_y:H, SiO_xN_y:H and SiN_x:H thin films were calculated by determining the critical thickness at which spontaneous cracking occurred. The fracture energies determined for the SiO_xC_y:H films were in the range of 2-3 J/m², whereas for the SiO_xN_y:H and SiN_x:H films, the calculated fracture energies were higher and ranged from 5 to 14 J/m². For the SiO_xN_y:H and SiN_x:H films, the addition of nitrogen was not found to significantly increase the fracture energy of the SiON films relative to pure SiO₂. The fracture toughness, however, was improved due to the increase in modulus from the addition of nitrogen. Overall, the fracture energies determined by this method were found to be consistent with those determined by other techniques.     

On the charge transport mechanism in n-InSb films

The structure of the conduction band bottom of polycrystalline and recrystallized n-InSb films grown on silicon dioxide substrates has been studied by measuring the temperature dependence of the electrical conductivity in the intrinsic conductivity range. Linear dependences lnσ=f(10³/T) with different slopes can be observed in heterogeneous semiconductors in the intrinsic conductivity range. The percolation level has been determined from the average of ΔE ₁, ΔE ₂, ..., ΔE _n to be 0.165 eV for polycrystalline and 0.2 eV for recrystallized films.     

Structural and optical properties of copper enriched ZnSe thin films prepared by closed space sublimation technique

Thin films of Zn_1?xCu_xSe (0.00≤x≤0.20) have been prepared by the closed space sublimation technique. Various structural and optical properties have been investigated through X-ray diffraction (XRD), atomic force microscopy (AFM), spectrophotometry, spectroscopic ellipsometry (SE) and Fourier transform infrared spectroscopy (FTIR). The effect of Cu concentration has been observed on the physical properties of Zn_1?xCu_xSe films for varying concentrations of copper. X-ray diffraction patterns show that the films are polycrystalline having preferential orientation along the (111) plane. Full width at half maximum (FWHM) values obtained by XRD show that FWHM decreases up to 10% copper concentration while an opposite trend has been observed beyond this concentration. RMS values calculated by AFM shows that the deposited films have smooth morphology; crystallinity improves with increasing Cu concentration and optimum results are shown with 10% Cu concentration. Various optical parameters i.e. absorption coefficient (α), extinction coefficient (k), reflectance (R), refractive index (n), optical conductivity (σ_op) and electrical conductivity (σ_el) have been determined using transmission spectra at different copper concentrations. From the reflection spectra it is observed that reflectance increases with the increase of copper concentration. The band gap energy has been determined using k spectra at various copper concentrations through spectroscopic ellipsometry. It is found that the band gap energy of the films decreases with the increase of copper concentration while dielectric constant increases. FTIR analysis revealed that the characteristic ZnSe bond stretching–vibrating mode occurs at 670.8 cm^?1.     

Properties of ZnO Thin Films Codoped with Lithium and Phosphorus

The properties of ZnO thin films codoped with lithium and phosphorus have been characterized. The films were deposited from high-purity ZnO and Li₃PO₄ solid targets onto c-plane sapphire substrates by radiofrequency (RF) magnetron sputtering. A substrate temperature of 900°C was determined as optimum for depositing undoped ZnO films with background electron concentration of 9.9 × 10¹⁵ cm^?3 as the buffer layer on the sapphire substrate. Postdeposition annealing was carried out using rapid thermal processing in O₂ at temperatures ranging from 500°C to 1000°C for 3 min. Analyses performed using low-temperature photoluminescence spectroscopy measurements revealed luminescence peaks at 3.356 eV, 3.307 eV, 3.248 eV, and 3.203 eV at 12 K for the codoped samples. X-ray diffraction 2θ-scans showed a single peak at about 34.4° with full-width at half-maximum of about 0.09°. Hall-effect measurements revealed initial p-type conductivities, but these were unstable and toggled between p-type and n-type over time with Hall concentrations that varied between 2.05 × 10¹³ cm^?3 and 2.89 × 10¹⁵ cm^?3. The fluctuation in the carrier type could be due to lateral inhomogeneity in the hole concentration caused by stacking faults in the films. An additional cause could be the small Hall voltages in the measurements, which could be significantly impacted by even small spikes in signal noise inherent in the measurements.     

Thin titanium oxide films deposited by e-beam evaporation with additional rapid thermal oxidation and annealing for ISFET applications

Titanium oxide (TiO₂) has been extensively applied in the medical area due to its proved biocompatibility with human cells [1]. This work presents the characterization of titanium oxide thin films as a potential dielectric to be applied in ion sensitive field-effect transistors. The films were obtained by rapid thermal oxidation and annealing (at 300, 600, 960 and 1200 °C) of thin titanium films of different thicknesses (5 nm, 10 nm and 20 nm) deposited by e-beam evaporation on silicon wafers. These films were analyzed as-deposited and after annealing in forming gas for 25 min by Ellipsometry, Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (RAMAN), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectroscopy (RBS) and Ti-K edge X-ray Absorption Near Edge Structure (XANES). Thin film thickness, roughness, surface grain sizes, refractive indexes and oxygen concentration depend on the oxidation and annealing temperature. Structural characterization showed mainly presence of the crystalline rutile phase, however, other oxides such Ti₂O₃, an interfacial SiO₂ layer between the dielectric and the substrate and the anatase crystalline phase of TiO₂ films were also identified. Electrical characteristics were obtained by means of I-V and C-V measured curves of Al/Si/TiO_x/Al capacitors. These curves showed that the films had high dielectric constants between 12 and 33, interface charge density of about 10¹⁰/cm² and leakage current density between 1 and 10⁻⁴ A/cm². Field-effect transistors were fabricated in order to analyze I_D x V_DS and log I_D × Bias curves. Early voltage value of −1629 V, R_OUT value of 215 MΩ and slope of 100 mV/dec were determined for the 20 nm TiO_x film thermally treated at 960 °C.     

Electrical properties of uncontaminated PbTe films on mica substrates prepared by molecular beam deposition

Uncontaminated PbTe films were prepared by molecular beam deposition under clean conditions in a uhv environment and the film properties were measured in situ. The carrier concentration was found to be determined by source conditions and values between 10¹⁶ cm^?3 (intrinsic level) and n = 5 × 10¹⁸cm^?3 could be obtained in a controllable manner. A low temperature anneal enabled bulk value Hall mobilities (1750 cm² V^?1 sec^?1 at 300 K) to be obtained at room temperature and above which indicated that surface scattering in the films was predominantly specular. The mobility at low temperatures (down to 100 K) was limited by small potential barriers located at the double-positioned grain boundaries which were present in the film. Field effect measurements indicated the potential barriers arose from a continuous distribution of band gap states situated in the grain boundaries. These states had a fairly uniform density (? 10¹²cm^?2 (kT)^?1) but there was some increase towards the conduction band edge. They also limited the field effect mobility (μ_FE) to ?0.5 bulk value, giving μ_FE ? 800cm² (volt sec)^?1 for films with carr concentrations above 5 × 10¹⁷ cm^?3. By exposure to low pressures of oxygen the carrier concentrations in annealed n-type films could be reduced to near intrinsic values with no associated degradation in the electrical properties. This indicated that the films were not compensated with the native p-type defect.     

Explaining the effects of processing on the electrical properties of PEDOT:PSS

By simultaneously measuring the Seebeck coefficient and the conductivity in differently processed PEDOT:PSS films, fundamental understanding is gained on how commonly used processing methods improve the conductivity of PEDOT:PSS. Use of a high boiling solvent (HBS) enhances the conductivity by 3 orders of magnitude, as is well-known. Simultaneously, the Seebeck coefficient S remains largely unaffected, which is shown to imply that the conductivity is improved by enhanced connectivity between PEDOT-rich filaments within the film, rather than by improved conductivity of the separate PEDOT filaments. Post-treatment of PEDOT:PSS films by washing with H₂SO₄ leads to a similarly enhanced conductivity and a significant reduction in the layer thickness. This reduction strikingly corresponds to the initial PSS ratio in the PEDOT:PSS films, which suggests removal and replacement of PSS in PEDOT:PSS by HSO₄⁻ or SO₄²⁻ after washing. Like for the HBS treatment, this improves the connectivity between PEDOT filaments. Depending on whether the H₂SO₄ treatment is or is not preceded by an HBS treatment also the intra-filament transport is affected. We show that by characterization of S and σ it is possible to obtain more fundamental understanding of the effects of processing on the (thermo)electrical characteristics of PEDOT:PSS.     

Effect of deposition methods on dielectric breakdown strength of PECVD low-k carbon doped silicon dioxide dielectric thin films

The effect of deposition methods on dielectric breakdown strength of PECVD low-k dielectric carbon doped silicon dioxide films is investigated. I-V measurements were performed using metal-insulator semiconductor structures for carbon doped silicon dioxide thin films with various thicknesses by single deposition station and six sequential deposition systems. I-t measurements are also performed for films with the thickness of 32 nm prepared using both deposition methods. Comparison studies have been carried out for the thickness dependence, temperature dependence, conduction mechanism and time dependence of dielectric breakdown for carbon doped silicon dioxide with single layer and six sub-layers. Results demonstrated that both films follow the newly obtained relationship between dielectric strength E_B and thickness d, i.e. E_B∝(d−d_c)⁻ⁿ, but with a lower exponential factor n and a larger thickness limit d_c for films with six sub-layers. It is also demonstrated that films with six sub-layers have a higher dielectric strength in all the thickness and temperature ranges, a thickness independent thermal behavior and a longer lifetime under constant voltage stressing. This indicates that by tuning the deposition methods smaller thickness with desired dielectric properties can be achieved.     

GaN Power Schottky Diodes with Drift Layers Grown on Four Substrates

We have examined the performance of gallium nitride (GaN) high-power Schottky diodes fabricated on unintentionally doped (UID) metalorganic chemical vapor deposition (MOCVD) films grown simultaneously on four substrates ranging in threading dislocation density from 5 × 10³ cm ^{- 2} to 10¹⁰ cm ^{- 2}. The substrates were an intentionally doped and a UID freestanding hydride vapor phase epitaxy substrate, an MOCVD GaN template grown on a sapphire wafer, and a bulk GaN substrate grown via an ammonothermal method. Capacitance–voltage (C–V) results showed the carrier concentration was ～2 × 10¹⁶ cm^?3 for films grown on each of the four substrates. With that doping level, the theoretical breakdown voltage (V _b) is ～1600 V. However, measured V _b for the devices tested on each of the four substrates fell short of this value. Also, the breakdown voltages across each of the four substrates were not substantially different. This result was especially surprising for films grown on bulk GaN substrates, because of their superior crystal quality, as determined from their x-ray rocking curve widths. Simple probability calculations showed that most of the diodes tested on the bulk substrate did not cover a single threading dislocation. Although optimization of edge-termination schemes is likely to improve V _b, we believe that point defects, not threading dislocations, are the main reason for the reduced performance of these devices.     

High Tc superconducting three-pole parallel-coupled bandpass filters made from laser ablated YBa2Cu3O7 − δ thin films

We have investigated three-pole parallel-coupled bandpass filters with fractional bandwidths of about 6% and 3% at a center frequency of 10.5 GHz utilizing high T_c superconducting YBa₂Cu₃O_{7 − δ} thin films. The films were deposited on LaAlO₃ substrates by pulsed laser ablation. Microwave responses of the filters were measured as a function of temperature and input power. The performance of the 3% bandwidth filter exhibits low insertion losses of about 0.48 dB and 0.79 dB at 20 K and 77 K, respectively. The insertion loss in the 6% bandwidth filter was 0.96 dB at 77 K. Both filters showed return losses better than 15 dB. High T_c superconducting bandpass filters showed good reproducibility. They were also compared with equivalent gold filters which showed insertion losses of more than 8 dB at 77 K.     

Electron diffraction study of the phase formation of Tl-Fe-Se and kinetics of phase transformations of films TlFeSe2

The conditions of phase formation in the Tl-Fe-Se system and the crystallization kinetics of amorphous TlFeSe₂ films are investigated by electron-diffraction structural analysis and kinematic electronography. It is shown that the crystallization of amorphous TlFeSe₂ films is described by the analytical expression of kinetic phase-transformation curves V _t = V ₀[1 ? exp(kt ^m )]. The growth dimensionality during the crystallization of amorphous TlFeSe₂ equal to three and the activation energies of nucleation and crystal growth are determined.     

Structural and optical properties of ZnO films produced by a nonvacuum chemical technique

Zinc-oxide films are grown by a new nonvacuum chemical method: the pyrolysis of zinc acetylacetonate at a temperature of 280–300°C. The structural, phonon, and emission properties of the ZnO films are studied by X-ray diffraction analysis, scanning electron microscopy, Raman measurements, and photoluminescence spectroscopy. The high-intensity (0002) peak recorded in the X-ray diffraction spectra indicate the predominant orientation of crystallites in the (0001) direction in the ZnO films. From analysis of the E ₂ ^high mode in the Raman spectrum of the ZnO films, the elastic strains ? _zz (～3.2 × 10^?3) and the quality of the crystal structure are determined. The characteristics of the pyrolytic ZnO films are compared with the corresponding characteristics of ZnO films grown by molecular-beam epitaxy. As a result, the possibility of growing polycrystalline ZnO films of rather high quality by a practically feasible low-temperature technique is demonstrated.     

Post-annealing Effect on Microstructures and Thermoelectric Properties of Bi0.45Sb1.55Te3 Thin Films Deposited by Co-sputtering

p-Type Bi_0.45Sb_1.55Te₃ thermoelectric (TE) thin films have been prepared at room temperature by a magnetron cosputtering process. The effect of postannealing on the microstructure and TE properties of Bi_0.45Sb_1.55Te₃ films has been investigated in the temperature range from room temperature to 350°C. x-Ray diffraction analysis shows that the annealed films have polycrystalline rhombohedral crystal structure, and the average grain size increases from 36?nm to 64?nm with increasing annealing temperature from room temperature to 350°C. Electron probe microanalysis shows that annealing above 250°C can cause Te reevaporation, which induces porous thin films and dramatically affects electrical transport properties of the thin films. TE properties of the films have been investigated at room temperature. The hole concentration shows a trend from descent to ascent and has a minimum value at the annealing temperature of 200°C, while the Seebeck coefficient shows an opposite trend and a maximum value of 245?μV?K^?1. The electrical resistivity monotonically decreases from 19.8?mΩ?cm to 1.4?mΩ?cm with increasing annealing temperature. Correspondingly, a maximum value of power factor, 27.4?μW?K^?2?cm^?1, was obtained at the annealing temperature of 250°C.     

Sulfur stoichiometry driven chalcopyrite and pyrite structure of spray pyrolyzed Cu-alloyed FeS2 thin films

We report on fabrication of Cu_xFe_1−xS₂ (CFS) thin films using chemical spray pyrolysis followed by post-sulfurization. Post-sulfurized CFS films were grown with compact and good crystalline texture. The sulfur stoichiometry in CFS films was found to be crucial for determination of its crystal structure. The sulfur deficient CFS films were driven to chalcopyrite CFS (CH-CFS) structure whereas the sulfur cured CFS films were grown with Cu-incorporated pyrite CFS (P-CFS) structure which was confirmed by X-ray diffraction and Raman spectroscopy analysis along with UV–vis spectroscopy measurement. Electrical characterizations of both types of CFS films revealed p-type conductivity with carrier concentration in the range of 10¹⁸–10²⁰ cm⁻³ and mobility of 0.5–9 cm² V⁻¹ s⁻¹. The band gaps of CFS films of CH-CFS structure (0.885–0.949 eV) were found to be less than that of P-CFS structure (0.966–1.156 eV), which indicates its potential application for thermoelectric and photovoltaic devices.     

Influence of Sn content on properties of ZnO:SnO2 thin films deposited by ultrasonic spray pyrolysis

The present work is devoted to the preparation of zinc oxide (ZnO): tin oxide (SnO₂) thin films by ultrasonic spray technique. A set of films are deposited using a solution formed with zinc acetate and tin chloride salts mixture with varied weight ratio R=[Sn/(Zn+Sn)]. The ratio R is varied from 0 to 100% in order to investigate the influence of Sn concentration on the physical properties of ZnO:SnO₂ films. The X rays diffraction (XRD) analysis indicated that films are composed of ZnO and SnO₂ distinct phases without any alloys or spinnel phase formations. The average grain size of crystallites varies with the ratio R from 17 to 20 nm for SnO₂ and from 24 to 40 nm for ZnO. The obtained films are highly transparent with a transmission coefficient equal to 80%. An increase in Sn concentration increases both the effective band gap energy from 3.2 to 4.01 eV and the photoluminescence intensity peak assigned defects to SnO₂. The films electrical characterization indicated that films are resistive. Their resistivities vary between 1.2×10² and 3.3×10⁴ (Ω cm). The higher resistivity is measured in film deposited with a ratio R equal to 50%.     

Synthesis and Characterization of Magnesium-Alloyed Hematite Thin Films

We have synthesized pure and Mg-alloyed hematite thin films on F-doped, SnO₂-coated glass substrates by radiofrequency magnetron cosputtering of iron oxide with and without MgO sources in mixed Ar/O₂ and mixed N₂/O₂ ambient. We found that hematite films deposited in N₂/O₂ ambient exhibited much poorer crystallinity than those deposited in Ar/O₂ ambient. We determined that Mg alloying led to increased crystallinity and bandgap. Furthermore, we found that Mg alloying inverted the type of conductivity of the thin films: pure hematite thin films exhibited n-type conductivity, whereas Mg-alloyed hematite thin films exhibited p-type conductivity.     

Electrical characteristics of r.f.-sputtered CdTe thin-films for photovoltaic applications

A method of preparing self-doped p- and n-type and In-doped n-type CdTe thin-films for photovoltaic applications has been developed using r.f. sputtering. Ohmic contacts to n-type films with contact resistivity less than 10^?2 Ω — cm² have been obtained. Schottky barrier diode test devices, formed by evaporation of various metals including Au on n-CdTe films, have been examined for electrical and photovoltaic evaluation of the sputtered films. Although S.B. diodes based on In doped films, prepared under Cd overpressure, show promising electrical and photovoltaic performance (V_oc ～ 315 mV, I_sc ～ 4.6mA/cm²), much improvement remains to be made by further control of dopant concentration and structural details of films.     

Temperature effect on the physical properties of CuIn11S17 thin films for photovoltaic applications

CuIn₁₁S₁₇ compound was synthesized by horizontal Bridgman method using high-purity copper, indium and sulfur elements. CuIn₁₁S₁₇ thin films were prepared by high vacuum evaporation on glass substrates. The glass substrates were heated at 30, 100 and 200 °C. The structural properties of the powder and the films were investigated using X-ray diffraction (XRD). XRD analysis of thin films revealed that the sample deposited at a room temperature was amorphous in nature while those deposited on heated substrates were polycrystalline with a preferred orientation along the (311) plane of the spinel phase. Ultraviolet–visible (UV–vis) spectroscopy was used to study the optical properties of thin films. The results showed that CuIn₁₁S₁₇ thin films have high absorption coefficient α in the visible range (10⁵–10⁶ cm⁻¹). The band gap E_g of the films decrease from 2.30 to 1.98 eV with increasing the substrate temperature (T_s) from 30 to 200 °C. We exploited the models of Swanepoel, Wemple–DiDomenico and Spitzer–Fan for the analysis of the dispersion of the refractive index n and the determination of the optical constants of the films. Hot probe method showed that CuIn₁₁S₁₇ films deposited at T_s=30 °C and T_s=100 °C are p-type conductivity whereas the sample deposited at T_s=200 °C is highly compensated.     

Diamond-Like Carbon Films Obtained by the Method of High-Frequency Diode Sputtering

Conditions for fabrication of diamond-like carbon films on the surface of oxidized single-crystalline silicon using the technique of high-frequency diode sputtering of graphite target are determined. It has been found that the deposited films have amorphous structure. The Raman spectroscopy technique has been used to show the presence of carbon phases with sp²- and sp³-hybridization, the ratio between which can be controlled by the growth conditions.     

Dislocation electrical conductivity of synthetic diamond films

A relationship between the electric resistance of single-crystal homoepitaxial and polycrystalline diamond films and their internal structure has been investigated. It is established that the electrical conductivity of undoped homoepitaxial and polycrystalline diamond films is directly related to the dislocation density in them. A relation linking the resistivity ρ (～10¹³–10¹⁵ Ω cm) with the dislocation density Γ (～10¹⁴?4 × 10¹⁶ m^?2) is obtained. The character of this correlation is similar for both groups of homoepitaxial and polycrystalline diamond films. Thin (～1–8 μm) homoepitaxial and polycrystalline diamond films with small-angle dislocation boundaries between mosaic blocks exhibit dislocation conductivity. The activation energy of dislocation acceptor centers was calculated from the temperature dependence of the conductivity and was found to be ～0.3 eV. The conduction of thick diamond films (h > 10 μm) with the resistivity ρ ≈ 10⁸ Ω cm is determined by the conduction of intercrystallite boundaries, which have a nondiamond hydrogenated structure. The electronic properties of the diamond films are compared with those of natural semiconductor diamonds of types IIb and Ic, in which dislocation acceptor centers have activation energies in the range 0.2–0.35 eV and are responsible for hole conduction.