Synthesis of n-type boron phosphide films and formation of Schottky diode: Al/n-BP/Sb

Phosphorous rich BP in thin film form was deposited onto fused silica substrates by co-evaporating boron (99.99%) and phosphorous (99.995%) from a tantalum boat and indirectly heated alumina crucible, respectively. Schottky diode structures for n-type BP (Al/n-BP/Sb) were fabricated out of these films. Corresponding current-voltage and capacitance-voltage characteristics of the Schottky diodes were recorded and analyzed in the light of the existing theories.     

Effects of annealing on morphological,structural and electrical properties of thermally evaporated WO3 thin films

Tungsten trioxide (WO₃) thin films were prepared by thermal evaporation method onto quartz substrates at room temperature. Effect of annealing temperature (from 200 to 800 °C) to morphology, crystallographic structure and electrical properties were investigated. In order to investigate the temperature dependant resistivity properties of the films dark current–voltage measurements were done at the temperatures of 30, 60, 90, 120 and 150 °C. From the AFM pictures it is seen that the increasing annealing temperature causes an increase in grain sizes. At elevated temperatures the grains combine to each other and thus form continuous and homogenous surfaces. From the XRD patterns it was seen that the as-prepared and annealed films at 200, 300, 310 and 320 °C were amorphous. On the other hand at 330 °C and higher temperatures the films were found as in crystallized structures (monoclinic phase). From the current–voltage measurements it was seen that the contacts areohmic and the current increased with increasing temperatures. From the calculated values it was seen that the produced films shows good semiconducting nature.     

The influence of interfacial barrier engineering on the resistance switching of In2O3：SnO2/TiO2/In2O3：SnO2 device

The I-V characteristics of In2O3：SnO2/TiO2/In2O3：SnO2 junctions with different interracial barriers are inves- tigated by comparing experiments. A two-step resistance switching process is found for samples with two interfacial barriers produced by specific thermal treatment on the interfaces. The nonsynchronous occurrence of conducting filament formation through the oxide bulk and the reduction in the interracial barrier due to the migration of oxygen vacancies under the electric field is supposed to explain the two-step resistive switching process. The unique switching properties of the device, based on interracial barrier engineering, could be exploited for novel applications in nonvolatile memory devices.     

Electronic and interface state density distribution properties of Ag/p-Si Schottky diode

Electronic and interface state distribution properties of Ag/p-Si Schottky diode have been investigated. The diode indicates non-ideal current-voltage behavior with an ideality factor greater than unity. The capacitance-voltage (C-V) characteristic is linear in reverse bias indicating rectification behavior and charge density within depletion layer is uniform. From I-V and C-V characteristics, junction parameters such as diode ideality factor and barrier height were found as 1.66 and ?_B(I-V) = 0.84 eV (?_B(C-V) = 0.90 eV), respectively. The interface state density N_ss and relaxation time τ of the Schottky diode were determined by means of Schottky capacitance spectroscopy method. The results show the presence of thin interfacial layer between the metal and semiconductor.     

Investigation of CdS and CdTe thin films and influence of CdCl2 on CdTe/CdS structure

CdTe/CdS heterojunction solar cell structure has been fabricated using simple, easy and low-cost methods. To fabricate this structure, CdS and CdTe thin films are deposited onto FTO-coated conducting glass substrates by chemical bath deposition (CBD) and electrodeposition method, respectively. The optimized growth conditions are chosen for both CdS and CdTe films by investigating the optical, structural and morphological properties of both the as-deposited and annealed films. Optical measurement showed that CdS films have higher transmittance and lower absorbance, and CdTe films have lower transmittance and higher absorbance in the near infrared region. The band gap of CdS films is estimated to lie in the range 2.29–2.41 eV and that of CdTe films is in the range 1.53–1.55 eV. X-ray diffraction (XRD) study reveals that CdS and CdTe films are polycrystalline with preferential orientation of (1 1 1) plane. Scanning electron microscopy (SEM) study reveals that both films are smooth, void-free and uniformly distributed over the surface of the substrate. Fabricated CdTe/CdS structure showed the anticipated rectifying behaviour, and the rectifying behaviour is observed to improve due to CdCl₂ treatment.     

Effect of annealing temperature on the structural and electrical properties of SrBi2Ta2O9 thin films for memory-based applications

Ferroelectric SrBi₂Ta₂O₉ (SBT) thin films were grown on p-type (1 0 0) Si substrates by radio frequency sputtering technique. The crystallinity of the films was studied using grazing incidence X-ray diffraction pattern. The spectra showed the films were polycrystalline with dominant orientation along (1 1 5) plane. The surface morphology was investigated by atomic force microscope. The chemical composition was studied by Rutherford back-scattering, which yielded a near stoichiometric composition of SBT. The capacitance–voltage characteristics of Al/SBT/Si capacitors measured at 100 kHz showed a hysteresis nature with a clockwise rotation and the memory window of the hysteresis loop was 0.88 V with the gate voltage ±5 V. The interface trap density was calculated by using Hills method at room temperature and a value in the order of 10¹¹–10¹² eV⁻¹ cm⁻² was found depending on the crystallization temperature at midgap region.     

Optical and electrical characterization of TiO2 nanotube arrays on titanium substrate

Novel oriented aligned TiO₂ nanotube (TN) arrays were fabricated by anodizing titanium foil in 0.5% HF electrolyte solution. It is indicated that the sizes of the TNs greatly depended on the applied voltages to some extent. The electrical properties of the TN arrays were characterized by current-voltage (I-V) measurements. It exhibits a nonlinear, asymmetric I-V characterization, which can be explained that there exists an n-type semiconductor/metal Schottky barrier diode between TN arrays and titanium substrate interface. The absorption edges shift towards shorter wavelengths with the decrease of the anodizing voltages, which is attributed to the quantum size effects. At room temperature, a novel wide PL band consisting of four overlapped peaks was observed in the photoluminescence (PL) measurements of the TN arrays. Such peaks were proposed to be resulted from the direct transition X₁ → X₂/X₁, indirect transition Γ₁ → X₂/X₁, self-trapped excitons and oxygen vacancies, respectively.     

Annealing effect on CdS/SnO2 films grown by chemical bath deposition

The extensive investigation of the annealing effect in nitrogen atmosphere on the structural optical and electrical properties of chemically deposited CdS films on SnO₂ has been performed. The as-deposited film shows 2.45 eV band gap (E_g) and decreases with increasing annealing temperature. The film annealed at 623 K having pure hexagonal phase (a = 4.14 Å, c = 6.71 Å for [1 0 0] plane) and E_g = 2.36 eV shows 10 times higher conductivity for all temperature range, and shows two different activation energies E_a = 0.114 eV and E_a = 0.033 eV for the temperature range 395 K ≤ T ≤ 515 K and 515 K ≤ T ≤ 585 K, respectively. The structural parameters such as dislocation density, strain and optical parameters such as absorption and extinction coefficient are calculated and compared for all the films.     

The effect of temperature on the electrical characteristics of Ti/n-GaAs Schottky diodes

Schottky diodes still attract researchers as they are used in various device applications. This study provides I–V characteristics of Ti/n-GaAs (80–300 K). Higher barrier height (Φ_B0) values were obtained for higher temperatures, whereas the ideality factor exhibited the opposite behavior. This was associated with a barrier inhomogeneity at the Ti/GaAs interface, which has a Gaussian distribution (GD). The mean barrier height values calculated from the modified Richardson and Φ_B0 - q/2 kT plots were found to be 0.584 eV and 0.575 eV in the temperature range of 80–160 K. They were found as 1.041 eV and 1.033 eV between 180 K and 300 K, respectively. The modified Richardson constant value, on the other hand, was calculated as 22.06 A cm⁻² K⁻² (80–160 K) and 13.167 A cm⁻² K⁻² (180–300 K). These values are higher than the theoretical value for n-GaAs, which is 8.16 A cm⁻² K⁻². This difference may stem from intense inhomogeneity at the Ti/n-GaAs interface.     

Annealing temperature influence on electrical properties of ion beam sputtered Bi2Te3 thin films

Ion beam sputtering process was used to deposit n-type fine-grained Bi₂Te₃ thin films on BK7 glass substrates at room temperature. In order to enhance the thermoelectric properties, thin films are annealed at the temperatures ranging from 100 to 400 °C. X-ray diffraction (XRD) shows that the films have preferred orientations in the c-axis direction. It is confirmed that grain growth and crystallization along the c-axis are enhanced as the annealing temperature increased. However, broad impurity peaks related to some oxygen traces increase when the annealing temperature reached 400 °C. Thermoelectric properties of Bi₂Te₃ thin films were investigated at room temperature. The Bi₂Te₃ thin films, including as-deposited, exhibit the Seebeck coefficients of −90 to −168 μV K⁻¹ and the electrical conductivities of 3.92×10²-7.20×10² S cm⁻¹ after annealing. The Bi₂Te₃ film with a maximum power factor of 1.10×10⁻³ Wm⁻¹ K⁻² is achieved when annealed at 300 °C. As a result, both structural and transport properties have been found to be strongly affected by annealing treatment. It was considered that the annealing conditions reduce the number of potential scattering sites at grain boundaries and defects, thus improving the thermoelectric properties.     

SnO2:Zr薄膜对SO2气体的光学气敏特性研究

采用双靶反应溅射制得SnO₂:Zr薄膜,并对它作了150°C下SO₂气敏光学特性试验,首次发现在适当工艺条件下制得的SnO₂:Zr薄膜在近红外波段(1.7～3μm)对SO₂气体具有明显的光学气敏特性,在2.65μm附近透过率上升幅度达10%左右.Zr的引入增强了SnO₂薄膜对SO₂的吸附能力.用二次离子质谱对吸附SO₂前后的薄膜作了组分相对含量分析.本实验结果对今后研究高性能SO₂气敏传感器有一定的价值.     

Studies on the structural and electrical properties of F-doped SnO2 film prepared by APCVD

Fluorine-doped tin oxide films (SnO₂:F, FTO) were deposited by atmosphere pressure chemical vapor deposition (APCVD) on Na-Ca-Si glass coated with a diffusion barrier layer of SiO_xC_y. The effects of post-heating time at 700 °C on the structural and electrical properties of SnO₂:F films were investigated. The results showed that SnO₂:F films were polycrystalline with tetragonal SnO₂ structure, SnO phase was present in SnO₂ film, and abnormal grain growth was observed. The element distribution in the film depth was measured with X-ray photoelectron spectroscopy (XPS) and revealed that when the heating time increased from 202 s to 262 s, the oxygen content in the surface increased from 78.63% to 83.38%. The resistivity increased from 3.13 × 10⁻⁴ for as-deposited films to 4.73 × 10⁻⁴ Ω cm when post-heated for 262 s. Hall mobility is limited by the ionized impurity scattering rather than the grain boundary scattering.     

Effect of heating on electrical transport in AlGaN/GaN Schottky barrier diodes on Si substrate

Thermal properties of the AlGaN/GaN Schottky barrier diodes were investigated, using a pulsed-IV measurement technique. The thermally degraded mobility in the DC-bias configuration was restored, when the pulse-bias voltages were applied. It was observed that heat generation was minimized, using a pulse width of 500 ns and pulse period of 10 ms. For the SBDs consisting of 5 μm of anode–cathode distance, on-resistance measured by the pulse-IV and DC-IV were 1.6 and 6.2 Ω-mm, respectively. We also demonstrated the device-width dependence of the thermal properties of the SBDs. We found that the performance of the power devices can be greatly influenced by the heat generation.     

The influence of substrate temperature on the morphology, optical and electrical properties of thermal-evaporated ZnTe Thin Films

The structural, morphological, optical and electrical properties of ZnTe films deposited by evaporation were investigated as a function of substrate temperature (at −123 and 27 °C) and post-deposition annealing temperature (at 200, 300 and 400 °C). It was determined that films deposited at both substrate temperatures were polycrystalline in nature with zinc-blende structure and a strong (1 1 1) texture. A small Te peak was detected in XRD spectra for both substrate temperatures, indicating that as-deposited ZnTe films were slightly rich in Te. Larger grains and a tighter grain size distribution were obtained with increased substrate temperature. Scanning electron microscopy (SEM) studies showed that the microstructures of the as-deposited films agreed well with the expectations from structure zone model. Post-deposition annealing induced further grain growth and tightened the grain size distribution. Annealing at 400 °C resulted in randomization in the texture of films deposited at both substrate temperatures. Optical spectroscopy results of the films indicated that the optical band gap value increased from 2.13 to 2.16 eV with increased substrate temperature. Increasing the annealing temperature sharpened the band-edge. Resistivity measurements showed that the resistivity of films deposited at substrate temperatures of −123 and 27 °C were 32 Ω cm, and 1.0 × 10⁴ Ω cm, respectively with corresponding carrier concentrations of 8.9 × 10¹⁵ cm⁻³ and 1.5 × 10¹⁴ cm⁻³. Annealing caused opposite changes in the film resistivity between the samples prepared at substrate temperatures of −123 and 27 °C.     

肖特基势垒对CdS/CdTe薄膜电池J-V暗性能的影响

采用数学模拟方法分析了不同背接触势垒高度(φ_b) 对于CdS/CdTe薄膜电池的J-V(电流密度-电压)方程的影响, 得出了势垒高度与roll-over的变化对应关系. 采用相应Cu/Mo背电极的CdS/CdTe薄膜电池在220-300 K的变温J-V曲线的数值分析与理论分析相对照, 分析了背势垒对于J-V曲线拟合参数的影响. 修正了φ_b 与反向饱和电流(J_b0)关系式, 理论与实验符合得非常好. 关键词： CdS/CdTe薄膜 伏安特性 肖特基势垒 roll-over     

The enhanced photocatalytic activity of CdS/TiO2 nanocomposites by controlling CdS dispersion on TiO2 nanotubes

CdS/TiO₂ nanocomposites were prepared via a simple wet chemical method, and characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their ability to degrade Acid Rhodamine B was investigated under visible light irradiation. The results indicate that CdS/TiO₂ nanocomposite with a mass ratio of 4:1(TiO₂:CdS) showed high photocatalytic activity and the CdS loaded on TiO₂ nanotube surface exhibited a hexagonal phase. The dispersion of CdS on TiO₂ nanotube surface had an important effect on the degradation efficiency of pollutant, which provides a strategy for practical industry application.     

Effect of anode area on the sensing mechanism of vertical GaN Schottky barrier diode temperature sensor

Effect of anode area on temperature sensing ability is investigated for a vertical GaN Schottky-barrier-diode sensor. The current-voltage-temperature characteristics are comparable to each other for Schottky barrier diodes with different anode areas, excepting the series resistance. In the sub-threshold region, the contribution of series resistance on the sensitivity can be ignored due to the relatively small current. The sensitivity is dominated by the current density. A large anode area is helpful for enhancing the sensitivity at the same current level. In the fully turn-on region, the contribution of series resistance dominates the sensitivity. Unfortunately, a large series resistance degrades the temperature error and linearity, implying that a larger anode area will help to decrease the series resistance and to improve the sensing ability.     

Optical and electrical properties of SnO2:Sb thin films deposited by oblique angle deposition

The antimony doped tin oxide (SnO₂:Sb) (ATO) thin films were prepared by oblique angle electron beam evaporation technique. X-ray diffraction, field emission scanning electron microscopy, UV-vis-NIR spectrophotometer and four-point probe resistor were employed to characterize the structure, morphology, optical and electrical properties. The results show that oblique angle deposition ATO thin films with tilted columns structure are anisotropic. The in-plane birefringence of optical anisotropy is up to 0.035 at α = 70°, which means that it is suitable as wave plate and polarizer. The electrical anisotropy of sheet resistance shows that the sheet resistance parallel to the deposition plane is larger than that perpendicular to the deposition plane and it can be changed from 900 Ω/□ to 3500 Ω/□ for deposition angle from 40° to 85°, which means that the sheet resistance can be effectively tuned by changing the deposition angle. Additionally, the sandwich structure of SiO₂ buffer layer plus normal ATO films and oblique angle deposition ATO films can reduce the resistance, which can balance the optical and electrical anisotropy. It is suggested that oblique angle deposition ATO thin films can be used as transparent conductive thin films in solar cell, anti-foggy windows and multifunctional carrier in liquid crystal display.     

Dependence of photocurrent on UV wavelength in ZnO/Pt bottom-contact Schottky diode

We fabricated the bottom-contacted ZnO/Pt Schottky diode and investigated the dependence of its photocurrent on the wavelength of illuminated ultraviolet (UV) light source. The bottom-contacted Schottky diode was devised by growing (000l) ZnO on (111) Pt, and the fabricated device showed a strong dependence on the UV wavelength for its photo-response characteristics. When longer-wavelength-UV (e.g., UV-A) was illuminated on the device, the photo-current was increased by a factor of 200, compared to that under illumination of shorter-wavelength-UV (e.g., UV-C). The behavior is attributed to the wavelength-dependent UV penetration depth for ZnO.     

Micro-structural and temperature dependent electrical characterization of Ni/GaN Schottky barrier diodes

Micro-structural investigation of Ni/GaN Schottky barrier diodes has been carried out using high-resolution transmission electron microscopy and electron diffraction spectrum in order to emphasize the role of Ni/GaN interface in controlling the Schottky diode behavior. Variable temperature Hall effect measurement of GaN samples along with the current–voltage (I–V) characteristics of Ni/n-GaN Schottky barrier diodes have been measured in 100–380 K temperature range. Results are analyzed in terms of thermionic emission theory by incorporating the concept of barrier inhomogeneity at the metal/semiconductor interface. The observed anomaly of temperature dependence of Schottky barrier height and ideality factor are explained by invoking two sets of Gaussian distribution of SBH in the temperature ranges of 100–180 K and 220–380 K, respectively. The value of A** (effective Richardson constant) as determined from the modified Richardson plot is 29.2 A/(cm² K²), which shows an excellent agreement with the theoretical value (26.4 A/(cm² K²)) in the temperature range of 220–380 K.