Influence of oxygen partial pressure on the properties of undoped InOx films deposited at room temperature by rf-PERTE

Transparent and conductive/semiconductive undoped indium oxide (InO_x) thin films were deposited at room temperature. The deposition technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied between 3 × 10^?2 and 1.3 × 10^?1 Pa. Undoped InO_x films, 100 nm thick, deposited at the oxygen partial pressure of 6 × 10^?2 Pa show a conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7 eV and an electrical conductivity of about 1100 (Ω cm)^?1. For oxygen pressures greater than 6 × 10^?2 Pa, semiconductive films are obtained, maintaining the visible transmittance. Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6 × 10^?2 Pa show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases.     

Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl2O4) ceramic target

Using a highly conductive ZnO(ZnAl₂O₄) ceramic target, c-axis-oriented transparent conductive ZnO:Al₂O₃ (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10⁻⁴ Ω cm and can be further reduced to as low as 1.5×10⁻⁴ Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10⁻⁵ Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).     

Structural change of laser-irradiated Ge2Sb2Te5 films studied by electrical property measurement

Sheet resistance of laser-irradiated Ge₂Sb₂Te₅ thin films prepared by magnetron sputtering was measured by the four-point probe method. With increasing laser power the sheet resistance undergoes an abrupt drop from 10⁷ to 10³ Ω/□ at about 580 mW. The abrupt drop in resistance is due to the structural change from amorphous to crystalline state as revealed by X-ray diffraction (XRD) study of the samples around the abrupt change point. Crystallized dots were also formed in the amorphous Ge₂Sb₂Te₅ films by focused short pulse laser-irradiated, the resistivities at the crystallized dots and the non-crystallized area are 3.375 × 10^?3 and 2.725 Ω m, sheet resistance is 3.37 × 10⁴ and 2.725 × 10⁷ Ω/□ respectively, deduced from the I–V curves that is obtained by conductive atomic force microscope (C-AFM).     

Optical properties and infrared-to-visible upconversion in Er3+-doped GeO2–Bi2O3 and GeO2–PbO–Bi2O3 glasses

Luminescence properties and upconversion studies of germanate glasses in ternary GeO₂–PbO–Bi₂O₃ and binary GeO₂–Bi₂O₃ systems containing Er₂O₃ (0.1–1.0 wt%) are presented for the first time. The Judd-Ofelt parameters found for these glasses are: Ω₂ = 4.50 × 10⁻²⁰ cm², Ω₄ = 1.55 × 10⁻²⁰ cm² and Ω₆ = 0.69 × 10⁻²⁰ cm² for binary glasses and Ω₂ = 4.44 × 10⁻²⁰ cm², Ω₄ = 1.82 × 10⁻²⁰ cm² and Ω₆ = 0.39 × 10⁻²⁰ cm² for ternary glasses. The refractive index of these glasses is found to be ∼2. The transition ⁴I_13/2 → ⁴I_15/2 is peaked at ∼1.53 μm and shows a radiative lifetime around 5 ms. Both systems exhibit similar emission cross-section at 1.53 μm around 0.8 × 10⁻²⁰ cm². Upconverted green emission at ∼530 nm (²H_11/2 → ⁴I_15/2) and ∼550 nm (⁴S_3/2 → ⁴I_15/2) and red emission at ∼668 nm (⁴F_9/2 → ⁴I_15/2) are observed under 980 nm cw excitation. Our results suggest that these glasses are promising candidates for applications in photonics.     

Sol–gel derived highly transparent and conducting yttrium doped ZnO films

This paper reports the structural, electrical and optical properties of Yttrium doped zinc oxide (YZO) thin films deposited on Corning (7059) glass substrates by spin coating technique. A precursor solution of ZnO, 0.2 M in concentration was prepared from zinc acetate dissolved in anhydrous ethanol with diethanolamine as a sol gel stabilizer. Yttrium nitrate hexahydrate (Y₂NO₃ · 6H₂O) was used as the dopant (3 wt%) in the present study. The films of different thickness in the range (200–500 nm) were prepared. The films were annealed in air at 450 °C for 1 h. It was observed that the c-axis orientation improves and the grain size increases as is indicated by an increase in intensity of the (0 0 2) peak and the decrease in the FWHM with the increase of film thickness. The resistivity decreased sharply from 2.8 × 10⁻² to 5.8 × 10⁻³ Ω-cm as the thickness increased from 200 to 500 nm. However, the average transmittance decreased from 87% to 82.6% as the film thickness increased to 500 nm. The lowest sheet resistance of ∼120 Ω/□ was obtained for the 500 nm thick film.     

Amorphous tungsten-doped In2O3 transparent conductive films deposited at room temperature from metallic target

Amorphous tungsten-doped In₂O₃ (IWO) films were deposited from a metallic target by dc magnetron sputtering at room temperature. Both oxygen partial pressure and sputtering power have significant effects on the electrical and optical properties of the films. The as-deposited IWO films with the optimum resistivity of 5.8 × 10^?4 Ω·cm and the average optical transmittance of 92.3% from 400 to 700 nm were obtained at a W content of 1 wt%. The average transmittance in the near infrared region (700–2500 nm) is 84.6–92.8% for amorphous IWO prepared under varied oxygen partial pressure. The mobility of the IWO films reaches its highest value of 30.3 cm² V^?1 s^?1 with the carrier concentration of 1.6 × 10²⁰ cm^?3, confirming their potential application as transparent conductive oxide films in various flexible devices.     

Effect of annealing temperature on the optical and electrical properties of aluminum doped ZnO films

Aluminum doped ZnO thin films were successfully deposited on the silicon substrates by spin coating method. The effects of an annealing temperature on electrical and optical properties were investigated for 1.5 at.% of aluminum. Refractive index profile has been obtained for the film annealed at 350 °C using ellipsometry and it has shown minimum refractive index of 1.95 and maximum value of 2.1. Thickness profile shows quite good uniformity of the film having minimum thickness value of 30.1 nm and maximum value of 34.5 nm. Maximum conductivity value obtained was 4.63 Ω^?1-cm^?1 for the film annealed at 350 °C. Maximum carrier density of 2.20 × 10¹⁷ cm^?3 was deduced from the Hall measurement and Fourier transform infrared spectroscopy clearly reveals major peak at 407 cm^?1 in the spectra associated with the ZnO bond.     

Transparent thin film transistors based on indium oxide semiconductor

Indium oxide films were deposited by radio-frequency plasma enhanced reactive thermal evaporation (rf-PERTE). The combined use of rf power and oxygen pressure allowed the control of the crystallite size in the film, changing the optical and electrical properties. The films obtained have electrical resistivity ranging from 13.7 to 1.7 × 10⁷ Ω cm. Transparent TFTs made with those films as semiconducting and conducting layers, respectively, present threshold voltages near 2 V and on/off ratios of 10⁴.     

Solid–liquid interfacial energy of neopentylglycol solid solution in equilibrium with neopentylglycol–(D) camphor eutectic liquid

The grain boundary groove shapes for equilibrated solid neopentylglycol (NPG) solution (NPG–3 mol% D-camphor) in equilibrium with the NPG–DC eutectic liquid (NPG–36.1 mol% D-camphor) have been directly observed using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Г), solid–liquid interfacial energy (σ_SL) of NPG solid solution have been determined to be (7.5±0.7)×10^?8 K m and (8.1±1.2)×10^?3 J m^?2, respectively. The Gibbs–Thomson coefficient versus T_mΩ^1/3, where Ω is the volume per atom was also plotted by linear regression for some organic transparent materials and the average value of coefficient (τ) for nonmetallic materials was obtained to be 0.32 from graph of the Gibbs–Thomson coefficient versus T_mΩ^1/3. The grain boundary energy of solid NPG solution phase has been determined to be (14.6±2.3)×10^?3 J m^?2 from the observed grain boundary groove shapes. The ratio of thermal conductivity of equilibrated eutectic liquid to thermal conductivity of solid NPG solution was also measured to be 0.80.     

A novel structured plastic substrate for light confinement in thin film silicon solar cells by a geometric optical effect

We present a novel method to achieve light trapping in thin film silicon solar cells. Unlike the commonly used surface textures, such as Asahi U-type TCO, that rely on light scattering phenomena, we employ embossed periodically arranged micro-pyramidal structures with feature sizes much larger than the wavelength of visible light. Angular resolved transmission of light through these substrates indeed showed diffraction patterns, unlike in the case of Asahi U-type substrates, which show angular resolved scattering. Single junction amorphous silicon (a-Si) solar cells made at 125 °C on the embossed structured polycarbonate (PC) substrates showed an increase in current density by 24% compared to a similar solar cell on a flat substrate. The band gap and thickness of the i-layer made by VHF PECVD are 1.9 eV and 270 nm respectively. A double p-layer (nc-Si:H/a-Si:H) was used to make proper contact with ZnO:Al TCO.Numerical modeling, called DokterDEP was performed to fit the dark and light current–voltage parameters and understand the characteristics of the cell. The output parameters from the modeling suggest that the cells have excellent built-in potential (V_bi). However, a rather high recombination voltage, V_μ, affects the FF and short circuit current density (J_sc) for the cells on Asahi as well as for the cells on PC. A rather high parallel resistance ? 1 MΩ cm² (obtained from the modeling) infers that there is no significant shunt leakage, which is often observed for solar cells made at low temperatures on rough substrates. An efficiency of more than 6% for a cell on PC shows enormous potential of this type of light trapping structures.     

Effect of silver doping on the electrical properties of a-Sb2Se3

This paper reports the effect of Ag-doping on electrical properties of a-Sb₂Se₃ in the temperature range 230–340 K and frequency range 5–100 kHz. The variation of transport properties with thermal doping has been studied. Ag-doping produces two homogeneous phases in the sample, which are found to be voltage dependent in the temperature range studied and frequency dependent in lower frequency region (0.1–10 kHz). Activation energy E_g and C′ [= σ₀ exp (γ/k), where γ, is the temperature coefficient of the band gap] calculated from dc conductivity has been found to vary from (0.42 ± 0.01) eV to (0.26 ± 0.01) eV and (4.11 ± 0.01) × 10⁻⁵ to (2.90 ± 0.02) × 10⁻⁶ Ω⁻¹ cm⁻¹ respectively. Ag-doping can be used to make the sample useful in device applications.     

Growth kinetics and boron doping of very high Ge content SiGe for source/drain engineering

We have studied the in-situ boron doping of high Ge content Si_1?xGe_x layers (x=0.3, 0.4 and 0.5). These layers have been grown at low pressure (20 Torr) and low temperature (600–650 °C) with a heavily chlorinated chemistry on blanket Si(0 0 1) substrates. Such a chemistry yields a full selectivity versus SiO₂ (isolation) and Si₃N₄ (sidewall spacers) on patterned wafers with gate stacks. We have quantified the impact of the diborane flow on the SiGe layer crystalline quality, its resistivity, the SiGe:B growth rate and the apparent Ge concentration. Resistivity values lower than 1 mΩ cm are easily achieved, all the more so for high Ge content layers. The SiGe growth rate increases and the apparent Ge concentration (from X-ray diffraction) decreases as the diborane flow increases. B atoms (much smaller than Si or Ge) indeed partially compensate the compressive strain in the SiGe:B layers. We have also probed the in-situ boron and phosphorus doping of Si at 750 °C, 20 Torr with a heavily chlorinated chemistry. The B ions concentration increases linearly with the diborane flow, then saturates at a value close to 4×10¹⁹ cm^?3. By contrast, the P ions concentration increases sub-linearly with the phosphine flow, with a maximum value close to 9×10¹⁸ cm^?3. Adding diborane (phosphine) to the gaseous mixture leads to a sharp increase (decrease) of the Si:B (the Si:P) growth rates, which has to be taken into account in device layers. All the know-how acquired will be most handy for the formation of in-situ doped recessed or raised sources and drains in metal-oxide semiconductor devices.     

Vapor growth and characterization of pyrite (FeS2) doped with Co,Ni, and As: Variations in semiconducting properties

Pyrite (FeS₂) crystals doped with As, Ni and Co were synthesized with chemical vapor transport over an 18 cm horizontal gradient of 700–600 °C in evacuated quartz tubes, from a mixture of FeS and S, with FeBr₃ as a transport agent. Sulfur fugacity and thus S:Fe stoichiometry was constrained by the Fe_1−xS/FeS_2−y buffer. As, Ni and Co concentrations were ∼3–800 ppm, ∼200–1500 ppm and ∼ 450–3700 ppm, respectively.Semiconducting properties were measured at room temperature using a van der Pauw and Hall measurement system. Ni and Co-doped pyrite are n-type while As-doped pyrite tends to be p-type. Resistivity for Co-doped pyrite ranged from 0.009 to 0.02 Ω cm while for Ni- and As-doped pyrite, resistivity ranged from 2 to 17 Ω cm. Undoped pyrite resistivity ranged from 15 to 85 Ω cm. Carrier concentration was similar for undoped and Ni-doped pyrite, ranging from 10¹⁵ to 10^16.6 cm⁻³, while for Co-doped pyrite it ranged from 10^18.7 to 10^19.3 cm⁻³ and for As-doped pyrite it ranged from 10¹⁴ to 10¹⁸ cm⁻³. Hall mobility was similar for Co and Ni-doped pyrite ranging from 60 to 270 cm² v⁻¹ s⁻¹ while for undoped pyrite it ranged from 8 to 70 cm² v⁻¹ s⁻¹. Hall mobility for As-doped pyrite ranged from 55.0 to 0.2 cm² v⁻¹ s⁻¹ for electrons and from 0.1 to 11.3 cm² v⁻¹ s⁻¹ for holes with the exception of one sample (of 22). These values should be viewed more as trends than as definitive. The results obtained for Ni, Co, and undoped pyrite are similar to those reported in the literature while results for As-doped synthetic pyrite have not previously been reported.     

Photoelectric features of vacuum-deposited a-Si:H/Alq3 blends

Using three electrode vacuum system for glow discharge of 5% SiH₄ + 95% Ar gas mixture together with thermal evaporation of phosphorus or boric aced, the n- and p-type a-Si:H layers have been deposited. By co-evaporation of phosphorus or boric aced the conductivity of a-Si:H layers was changed in 10^?11–10^?3 Ω^?1 cm^?1 or 10^?11 –10^?8 Ω^?1 cm^?1 range, respectively. Blends of a-Si:H and tris-(8-hydroxyquinoline) aluminum (Alq₃) have been vacuum-deposited by simultaneous glow discharge of 5% SiH₄ + 95 % Ar gas mixture and thermal co-evaporation of Alq₃. Photoluminescence spectrum of a-Si:H/Alq₃ blend coincident with one of Alq₃ was observed at room temperature.     

Structural,electrical and optical properties of in-situ phosphorous-doped Ge layers

We have studied the impact of temperature and pressure on the structural and electronic properties of Ge:P layers grown with GeH₄+PH₃ on thick Ge buffers, themselves on Si(0 0 1). The maximum phosphorous atomic concentration [P] exponentially decreased as the growth temperature increased, irrespective of pressure (20 Torr, 100 Torr or 250 Torr). The highest values were however achieved at 100 Torr (3.6×10²⁰ cm^?3 at 400 °C, 2.5×10¹⁹ cm^?3 at 600 °C and 10¹⁹ cm^?3 at 750 °C). P atomic depth profiles, “box-like” at 400 °C, became trapezoidal at 600 °C and 750 °C, most likely because of surface segregation. The increase at 100 Torr of [P] with the PH₃ mass-flow, almost linear at 400 °C, saturated quite rapidly at much lower values at 600 °C and 750 °C. Adding PH₃ had however almost no impact on the Ge growth rate (be it at 400 °C or 750 °C). A growth temperature of 400 °C yielded Ge:P layers tensily-strained on the Ge buffers underneath, with a very high concentration of substitutional P atoms (5.4×10²⁰ cm^?3). Such layers were however rough and of rather low crystalline quality in X-ray Diffraction. Ge:P layers grown at 600 °C and 750 °C had the same lattice parameter and smooth surface morphology as the Ge:B buffers underneath, most likely because of lower P atomic concentrations (2.5×10¹⁹ cm^?3 and 10¹⁹ cm^?3, respectively). Four point probe measurements showed that almost all P atoms were electrically active at 600 °C and 750 °C (1/4th at 400 °C). Finally, room temperature photoluminescence measurements confirmed that high temperature Ge:P layers were of high optical quality, with a direct bandgap peak either slightly less intense (750 °C) or more intense (600 °C) than similar thickness intrinsic Ge layers. In contrast, highly phosphorous-doped Ge layers grown at 400 °C were of poor optical quality, in line with structural and electrical results.     

Role of oxygen in structural properties of annealed CuAlO2 films

CuAlO₂ films were sputtered on quartz substrates at different oxygen partial pressures (OPP) and carried out the annealing at 900 °C for 5 h in N₂ ambient. The structural properties of these films have been studied in detail by X-ray diffraction, Raman spectroscopy, and atomic force microscopy. Annealed CuAlO₂ films are grown along the (0 0 1) preferential orientation. The film deposited at 20% OPP demonstrates the excellent crystalline behavior and the smallest electrical resistivity (41.8 Ω cm). At higher OPP, the crystalline behavior begins to degenerate up to the amorphous state at 60% OPP, and some micro-caves presented in the film surface become larger and deeper with the increase in OPP. We believe that the negative thermal expansion behavior associated with excess oxygen atoms is the primary responsibility for the change in structural properties.     

Conductivity percolation transition of Agx(Ge0.25Se0.75)100−x glasses

The ionic conductivity of several chalcogenide glasses increases abruptly with mobile ion addition from values typical of insulating materials (10⁻¹⁶–10⁻¹⁴ Ω⁻¹ cm⁻¹) to values of fast ionic conductors (10⁻⁷–10⁻¹ Ω⁻¹ cm⁻¹). This change is produced in a limited concentration range pointing to a percolation process. In a previous work [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259] the transition from semiconductor to fast ionic conductor of Ag_x(Ge_0.25Se_0.75)_100−x glasses was detected at x¹ ≅ 10 at.% in the form of a steep change in the conductivity. Ag_x(Ge_0.25Se_0.75)_100−x glasses with x ⩽ 25 at.%, prepared by a melt quenching method, are investigated by impedance spectroscopy in the frequency range 5 Hz–2 MHz at different temperatures, T, from room temperature to 363 K and by DC measurements at room temperature. The conductivity of the glasses, σ, was obtained as a function of silver concentration and temperature. For x ⩾ 10 at.% our results are in agreement with those reported by Kawasaki et al. [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259]. The percolation transition was observed in the range 7 ⩽ x ⩽ 8. The temperature dependence of the ionic conductivity follows an Arrhenius type equation σ = (σ_o/T) · exp(−E_σ/kT). The activation energy of the ionic conductivity, E_σ, and the pre-exponential term, σ_o, are calculated. The results are discussed in connection with other chalcogenide and chalcohalide systems and linked with the glass structures.     

Electrical conductivity and single oscillator model properties of amorphous CuSe semiconductor thin film

The structural, optical dispersion and electrical conductivity properties of the CuSe thin film have been investigated using X-ray diffraction, electrical and optical characterization methods. X-ray diffraction results indicate that CuSe thin film has an amorphous structure. The electrical conductivity of the CuSe film increases with increasing temperature. The activation energy and room temperature conductivity values of the film were found to be 1.32 meV and 3.89 × 10⁻³ S/cm, respectively. The refractive index dispersion of the thin film obeys the single oscillator model and single oscillator parameters were determined. The E_o, n_∞, and S_o values of the CuSe thin film were found to be 5.08 eV, 3.55 and 1.92 × 10¹⁴ m⁻², respectively. The obtained results suggest that CuSe film is an amorphous semiconductor.     

Bond character,optical properties and ionic conductivity of Li2O/B2O3/SiO2/Al2O3 glass: Effect of structural substitution of Li2O for LiCl

A glass of composition (20 ? x)Li₂O–xLiCl–65B₂O₃–10SiO₂–5Al₂O₃ where 0 ? x ? 12.5 wt% is prepared using the normal melt-quenching technique. The optical constants and electrical conductivity and their correlation are investigated, furnished and discussed with the substitution of Li₂O for LiCl. The mechanism of the optical absorption and the calculated Urbach energy follow the rule of phonon-assisted transitions. The ionic conduction mechanism is determined by activation energy process. Substitution up to 10 wt% LiCl provides high ionic conductivity (1.9 × 10^?2 Ω^?1 m^?1) due to the high average electronegativity of LiCl which increases the polarizability of lithium ions. The small cation–anion distance approach confirmed the enhancement in ionic conductivity of LiCl containing glass compared to that of Li₂O. Due to the large size of Cl^? ions, there is an expansion of the lattice which in turn broadens the available path windows. For 12.5 wt% LiCl, anomalous density behavior is observed and a reduction in conductivity is occurred, σ = 5.4 × 10^?3 Ω^?1 m^?1. Owing to the model of bond fluctuation, the reduction is attributed to the increase in the alkali halide concentration which creates bottlenecks that hinder the motion of Li⁺ ions. The ionic conductivity character is strongly supported by the behavior of the glass ionicity factor, density, molar volume, refractive index, average boron–boron separation, molar refraction, metallization criterion and non-bridging oxygen concentration of the studied glass.     

Growth and characterization of zirconium oxide thin films on silicon substrate

The growth and characterization of zirconium oxide (ZrO₂) thin films prepared by thermal oxidation of a deposited Zr metal layer on SiO₂/Si were investigated. Uniform ZrO₂ thin film with smooth surface morphology was obtained. The thermal ZrO₂ films showed a polycrystalline structure. The dielectric constant of the ZrO₂ film has been shown to be 23, and the equivalent oxide thickness (EOT) of the ZrO₂ stacked oxide is in the range of 3.38–5.43 nm. MOS capacitors with ZrO₂ dielectric stack show extremely low leakage current density, less than 10^?6 A/cm² at ?4 V. Consequently, using this method, high-quality ZrO₂ films could be fabricated at oxidation temperature as low as 600 °C.