Investigation of diode parameters using I-V and C-V characteristics of In/SiO2/p-Si (MIS) Schottky diodes

A study on interface states density distribution and characteristic parameters of the In/SiO₂/p-Si (MIS) capacitor has been made. The thickness of the SiO₂ film obtained from the measurement of the corrected capacitance in the strong accumulation region for MIS Schottky diodes was 220 Å. The diode parameters from the forward bias I-V characteristics such as ideality factor, series resistance and barrier heights were found to be 1.75, 106-112 Ω and 0.592 eV, respectively. The energy distribution of the interface state density D_it was determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density obtained using the I-V characteristics had an exponential growth, with bias towards the top of the valance band, from 9.44×10¹³ eV⁻¹ cm⁻² in 0.329-E_v eV to 1.11×10¹³ eV⁻¹ cm⁻² in 0.527-E_v eV at room temperature. Furthermore, the values of interface state density D_it obtained by the Hill-Coleman method from the C-V characteristics range from 52.9×10¹³ to 1.11×10¹³ eV⁻¹ cm⁻² at a frequency range of 30kHz-1 MHz. These values of D_it and R_s were responsible for the non-ideal behaviour of I-V and C-V characteristics.     

Electron energy loss spectra from polycrystalline Cr and Cr2O3 before and after surface reduction by Ar bombardment

Electron energy loss spectra (ELS) have been obtained from polycrystalline Cr and Cr₂O₃ before and after surface reduction by 2 keV Ar⁺ bombardment. The primary electron energy used in the ELS measurements was systematically varied from 100 to 1150 eV in order to distinguish surface versus bulk loss processes. Two predominant loss features in the ELS spectra obtained from Cr metal at 9.0 and 23.0 eV are assigned to the surface and bulk plasmon excitations, respectively, and a number of other features arising from single electron transitions from both the bulk and surface Cr 3d bands to higher-lying states in the conduction band are also present. The ELS spectra obtained from Cr₂O₃ exhibit features that originate from both interband transitions and charge-transfer transitions between the Cr and O ions as well as the bulk plasmon at 24.4 eV. The ELS feature at 4.0 eV arises from a charge-transfer transition between the oxygen and chromium ions in the two surface layers beneath the chemisorbed oxygen layer, and the ELS feature at 9.8 eV arises from a similar transition involving the chemisorbed oxygen atoms. The intensity of the ELS peak at 9.8 eV decreases after Ar⁺ sputtering due to the removal of chemisorbed oxygen atoms. Sputtering also increases the number of Cr²⁺ states on the surface, which in turn increases the intensity of the 4.0 eV feature. Furthermore, the ELS spectra obtained from the sputtered Cr₂O₃ surface exhibit features characteristic of both Cr⁰ and Cr₂O₃, indicating that Ar⁺ sputtering reduces Cr₂O₃. The fact that neither the surface- nor the bulk-plasmon features of Cr⁰ can be observed in the ELS spectra obtained from sputtered Cr₂O₃ while the loss features due to Cr⁰ interband transitions are clearly present indicates that Cr⁰ atoms form small clusters lacking a bulk metallic nature during Ar⁺ bombardment of Cr₂O₃.     

Influence of postdeposition annealing on structural properties and electrical characteristics of thin Tm2O3 and Tm2Ti2O7 dielectrics

We describe the structural properties and electrical characteristics of thin thulium oxide (Tm₂O₃) and thulium titanium oxide (Tm₂Ti₂O₇) as gate dielectrics deposited on silicon substrates through reactive sputtering. The structural and morphological features of these films were explored by X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy, measurements. It is found that the Tm₂Ti₂O₇ film annealed at 800 °C exhibited a thinner capacitance equivalent thickness of 19.8 Å, a lower interface trap density of 8.37 × 10¹¹ eV⁻¹ cm⁻², and a smaller hysteresis voltage of ∼4 mV than the other conditions. We attribute this behavior to the Ti incorporated into the Tm₂O₃ film improving the interfacial layer and the surface roughness. This film also shows negligible degrees of charge trapping at high electric field stress.     

Characterization of Y2O3 gate dielectric on n-GaAs substrates

Physical and electrical properties of sputtered deposited Y₂O₃ films on NH₄OH treated n-GaAs substrate are investigated. The as-deposited films and interfacial layer formation have been analyzed by using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). It is found that directly deposited Y₂O₃ on n-GaAs exhibits excellent electrical properties with low frequency dispersion (<5%), hysteresis voltage (0.24 V), and interface trap density (3 × 10¹² eV⁻¹ cm⁻²). The results show that the deposition of Y₂O₃ on n-GaAs can be an effective way to improve the interface quality by the suppression on native oxides formation, especially arsenic oxide which causes Fermi level pinning at high-k/GaAs interface. The Al/Y₂O₃/n-GaAs stack with an equivalent oxide thickness (EOT) of 2.1 nm shows a leakage current density of 3.6 × 10⁻⁶ A cm⁻² at a V_FB of 1 V. While the low-field leakage current conduction mechanism has been found to be dominated by the Schottky emission, Poole-Frenkel emission takes over at high electric fields. The energy band alignment of Y₂O₃ films on n-GaAs substrate is extracted from detailed XPS measurements. The valence and conduction band offsets at Y₂O₃/n-GaAs interfaces are found to be 2.14 and 2.21 eV, respectively.     

Exchange bias in thin-film (Co/Pt)3/Cr2O3 multilayers

We have fabricated exchange-biased Co/Pt layers ((0.3 nm/1.5 nm)×3) on (0 0 1)-oriented Cr₂O₃ thin films. The multilayered films showed extremely smooth surfaces and interfaces with root mean square roughness of ≈0.3 nm for 10 μm×10 μm area. The Cr₂O₃ films display sufficient insulation with a relative low leakage current (1.17×10⁻² A/cm² at 380 MV/m) at room temperature which allowed us to apply electric field as high as 77 MV/m. We find that the sign of the exchange bias and the shape of the hysteresis loops of the out-of-plane magnetized Co/Pt layers can be delicately controlled by adjusting the magnetic field cooling process through the Néel temperature of Cr₂O₃. No clear evidence of the effect of electric field and the electric field cooling was detected on the exchange bias for fields as high as 77 MV/m. We place the upper bound of the shift in exchange bias field due to electric field cooling to be 5 Oe at 250 K.     

Stabilization of a very high-k crystalline ZrO2 phase by post deposition annealing of atomic layer deposited ZrO2/La2O3 dielectrics on germanium

The impact of the ZrO₂/La₂O₃ film thickness ratio and the post deposition annealing in the temperature range between 400 °C and 600 °C on the electrical properties of ultrathin ZrO₂/La₂O₃ high-k dielectrics grown by atomic layer deposition on (1 0 0) germanium is investigated. As-deposited stacks have a relative dielectric constant of 24 which is increased to a value of 35 after annealing at 500 °C due to the stabilization of tetragonal/cubic ZrO₂ phases. This effect depends on the absolute thickness of ZrO₂ within the dielectric stack and is limited due to possible interfacial reactions at the oxide/Ge interface. We show that adequate processing leads to very high-k dielectrics with EOT values below 1 nm, leakage current densities in the range of 0.01 A/cm², and interface trap densities in the range of 2-5 × 10¹² eV⁻¹ cm⁻².     

Influence of [S2O3]/[Sm] on Sm2S3 thin films deposited by liquid phase deposition method on self-assembled monolayers

Sm₂S₃ thin films were prepared on Si (1 0 0) substrates using SmCl₃ and Na₂S₂O₃ as precursors by liquid phase deposition method on self-assembled monolayers. The influence of the molar concentration ratio of [S₂O₃²⁻]/[Sm³⁺] on the phase compositions, surface morphologies and optical properties of the as-deposited films were investigated. The as-deposited Sm₂S₃ thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible (UV-vis) and photoluminescence spectrum (PL). Results show that it is important to control the [S₂O₃²⁻]/[Sm³⁺] during the deposition process and monophase Sm₂S₃ thin films with orientation growth along (0 1 1) direction can be achieved when [S₂O₃²⁻]/[Sm³⁺] = 2.0, pH 3.0, with citric acid as a template agent. The as-deposited thin films exhibit a dense and crystalline surface morphology. Good transmittance in the visible spectrum and excellent absorbency of ultraviolet light of the thin films are observed, and the band gap of the thin films first decrease and then increase with the increase of the [S₂O₃²⁻]/[Sm³⁺]. The as-deposited thin films also exhibit red photoluminescence properties under visible light excitation. With the increase of the [S₂O₃²⁻]/[Sm³⁺] in the deposition solution, the PL properties of Sm₂S₃ thin films are obviously improved.     

Electrical properties vs. microstructure of nanocrystallized V2O5-P2O5 glasses — An extended temperature range study

An electronically conducting nanomaterial was synthesized by nanocrystallization of a 90V₂O₅·10P₂O₅ glass and its electrical properties were studied in an extended temperature range from − 170 to + 400 °C. The conductivity of the prepared nanomaterial reaches 2 ? 10^− 1 S cm^− 1 at 400 °C and 2 ? 10^− 3 S cm^− 1 at room temperature. It is higher than that of the original glass by a factor of 25 at room temperature and more than 100 below − 80 °C. A key role in the conductivity enhancement was ascribed to the material's microstructure, and in particular to the presence of the large number of small (ca. 20 nm) grains of crystalline V₂O₅. The observed conductivity dependencies are discussed in terms of the Mott's theory of the electronic hopping transport in disordered systems. Since V₂O₅ is known for its ability to intercalate lithium, the presented results might be helpful in the development of cathode materials for Li-ion batteries.     

Interface properties of an O2 annealed Au/Ni/n-Al0.18Ga0.82N Schottky contact

We oxidized a Ni/Au metal bi-layer contact fabricated on HVPE Al_0.18Ga_0.82N from 373 K to 573 K in 100 K steps. In the range 1 kHz to 2 MHz, the Capacitance–Voltage–Frequency (C–V–f) measurements reveal a frequency dispersion of the capacitance and the presence of an anomalous peak at 0.4 V owing to the presence of interface states in the as deposited contact system. The dispersion was progressively removed by O₂ anneals from temperatures as low as 373 K. These changes are accompanied by an improvement in the overall quality of the Schottky system: the ideality factor, n, improves from 2.09 to 1.26; the Schottky barrier height (SBH), determined by the Norde [1] method, increases from 0.72 eV to 1.54 eV. From the Nicollian and Goetzberger model [2], we calculated the energy distribution of the density of interface states, N_SS. Around 1 eV above the Al_0.18Ga_0.82N valence band, N_SS, decreases from 2.3×10¹² eV⁻¹ cm⁻² for the un-annealed diodes to 1.3×10¹² eV⁻¹ cm⁻² after the 573 K anneal. Our results suggest the formation of an insulating NiO leading to a MIS structure for the oxidized Au/Ni/Al_0.18Ga_0.82N contact.     

Study on the photocatalytic activity of K2La2Ti3O10 doped with zinc(Zn)

The layered perovskite type oxides, K₂La₂Ti₃O₁₀ and zinc(Zn)-doped K₂La₂Ti₃O₁₀ were prepared by sol-gel method and were characterized by power X-ray diffraction, UV-vis diffuse reflectance and X-ray photoelectron spectroscopy. The photocatalytic activity for water splitting of the catalyst powders was investigated with I⁻ as electron donor under ultraviolet and visible light irradiation respectively. The electronic structure of the powders has been analyzed by the first principles calculation, which reveals the photo responses in the visible region and the improvement of the photocatalytic activity of K₂La₂Ti₃O₁₀. Conclusions were made that zinc(Zn)-doped K₂La₂Ti₃O₁₀ exhibited higher reactivity for hydrogen production. When I⁻ was used as electron donor, the optimum doping concentration of zinc(Zn) was found to be 0.015:1 (n_Zn:n_Ti). The average hydrogen production rates were 126.6 μmol/(gcat h) under ultraviolet irradiation and 55.5 μmol/(gcat h) under visible light irradiation which were raised by 131% and 251% compared with undoped K₂La₂Ti₃O₁₀ photocatalyst, respectively.     

Spectral properties of Nd-doped Sr3Ga2Ge4O14 crystal

Neodymium doped strontium gallogermanate crystals were grown successfully by the Bridgman technique. The linear thermal expansion coefficients for the c- and a-axes were measured as 5.8 × 10⁻⁶ °C⁻¹ and 6.5 × 10⁻⁶ °C⁻¹. Absorption spectra, and fluorescence spectra, as well as fluorescence decay curves of Nd³⁺-doped Sr₃Ga₂Ge₄O₁₄ crystal, have been recorded at room temperature and used to calculate the absorption and stimulated emission cross-sections. Based on the Judd-Ofelt theory, three intensity parameters were obtained. The luminescent quantum efficiency of the ⁴F_3/2 level was determined to be approximately 73.8% for this material. Compared with other Nd³⁺-doped laser crystals, Nd³⁺-doped Sr₃Ga₂Ge₄O₁₄ crystal displays special laser properties due to its disorder structure.     

Crystallization of 21.25Gd2O3-63.75MoO3-15B2O3 glass induced by femtosecond laser at the repetition rate of 250 kHz

We report the formation of β′-Gd₂(MoO₄)₃ (GMO) crystal on the surface of the 21.25Gd₂O₃-63.75MoO₃-15B₂O₃ glass, induced by 250 kHz, 800 nm femtosecond laser irradiation. The morphology of the modified region in the glass was clearly examined by scanning electron microscopy (SEM). By micro-Raman spectra, the laser-induced crystals were confirmed to be GMO phases and it is found that these crystals have a strong dependence on the number and power of the femtosecond laser pulses. When the irradiation laser power was 900 mW, not only the Raman peaks of GMO crystals but also some new peaks at 214 cm⁻¹, 240 cm⁻¹, 466 cm⁻¹, 664 cm⁻¹ and 994 cm⁻¹which belong to the MoO₃ crystals were observed. The possible mechanisms are proposed to explain these phenomena.     

Synthesis and characterization of TiO2/Fe2O3 core-shell nanocomposition film and their photoelectrochemical property

TiO₂/Fe₂O₃ core-shell nanocomposition film has been fabricated via two-step method. TiO₂ nanorod arrays are synthesized by a facile hydrothermal method, and followed by Fe₂O₃ nanoparticles deposited on TiO₂ nanorod arrays through an ordinary chemical bath deposition. The phase structures, morphologies, particle size, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer. The results confirm that Fe₂O₃ nanoparticles of mean size ca. 10 nm coated on the surface of TiO2 NRs. After depositing Fe₂O₃, UV-vis absorption property is induces the shift to the visible-light range, the annealing temperature of 600 °C is the best condition for UV-vis absorption property of TiO₂/Fe₂O₃ nanocomposite film, and increasing Fe content, optical activity are enhanced one by one. The photoelectrochemical (PEC) performances of the as-prepared composite nanorods are determined by measuring the photo-generated currents under illumination of UV-vis light. The TiO₂ NRs modified by Fe₂O₃ show the photocurrent value of 1.36 mA/cm² at 0 V vs Ag/AgCl, which is higher than those of unmodified TiO₂ NRs.     

A novel chemical synthesis and characterization of Mn3O4 thin films for supercapacitor application

Mn₃O₄ thin films have been prepared by novel chemical successive ionic layer adsorption and reaction (SILAR) method. Further these films were characterized for their structural, morphological and optical properties by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), field emission scanning electron microscopy (FESEM), wettability test and optical absorption studies. The XRD pattern showed that the Mn₃O₄ films exhibit tetragonal hausmannite structure. Formation of manganese oxide compound was confirmed from FTIR studies. The optical absorption showed existence of direct optical band gap of energy 2.30 eV. Mn₃O₄ film surface showed hydrophilic nature with water contact angle of 55°. The supercapacitive properties of Mn₃O₄ thin film investigated in 1 M Na₂SO₄ electrolyte showed maximum supercapacitance of 314 F g⁻¹ at scan rate 5 mV s⁻¹.     

Characterization of single-crystalline In2O3 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

Epitaxial In₂O₃ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). The films were deposited at different substrate temperatures (450-750 °C). The film deposited at 650 °C has the best crystalline quality, and observation of the interface area shows a clear cube-on-cube epitaxial relationship of In₂O₃(1 0 0)||YSZ(1 0 0) with In₂O₃[0 0 1]||YSZ[0 0 1]. The Hall mobility of the single-crystalline In₂O₃ film deposited at 650 °C is as high as 66.5 cm² V⁻¹ s⁻¹ with carrier concentration of 1.5 × 10¹⁹ cm⁻³ and resistivity of 6.3 × 10⁻³ Ω cm. The absolute average transmittance of the obtained films in the visible range exceeds 95%.     

Luminescence of ZnWO4 and CdWO4 thin films prepared by spray pyrolysis

Thin films of ZnWO₄ and CdWO₄ were prepared by spray pyrolysis and the structural, optical, and luminescence properties were investigated. Both ZnWO₄ and CdWO₄ thin films showed a broad blue-green emission band. The broad band of ZnWO₄ films was centered at 495 nm (2.51 eV) consisted of three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 540 nm (2.30 eV). The broad band of CdWO₄ films at 495 nm (2.51 eV) could be decomposed to three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 545 nm (2.28 eV). These results are consistent with emission from the WO₆⁶⁻ molecular complex. The luminance and efficiency for ZnWO₄ film at 5 kV and 57 μA/cm² were 48 cd/m² and 0.22 lm/w, respectively, and for CdWO₄ film the values were 420 cd/m² and 1.9 lm/w.     

Synthesis and ion conductivity of (Bi2O3)0.75(Dy2O3)0.25 ceramics with grain sizes from the nano to the micro scale

Using (Bi₂O₃)_0.75(Dy₂O₃)_0.25 nano-powder synthesized by reverse titration co-precipitation method as raw material, dense ceramics were sintered by both Spark Plasma Sintering (SPS) and pressureless sintering. According to the predominance area diagram of Bi-O binary system, the sintering conditions under SPS were optimized. (Bi₂O₃)_0.75(Dy₂O₃)_0.25 ceramics with relative density higher than 95% and an average grain size of 20 nm were sintered in only 10 min up to 500 °C. During the pressureless sintering process, the grain growth behavior of (Bi₂O₃)_0.75(Dy₂O₃)_0.25 followed a parabolic trend, expressed as D² − D₀² = Kt, and the apparent activation energy of grain growth was found to be 284 kJ mol^− 1. Dense (Bi₂O₃)_0.75(Dy₂O₃)_0.25 ceramics with different grain sizes were obtained, and the effect of grain size on ion conductivity was investigated by impedance spectroscopy. It was shown that the total ion conductivity was not affected by the grain size down to 100 nm, however lower conductivity was measured for the sample with the smallest grain size (20 nm). But, although only the δ phase was evidenced by X-ray diffraction for this sample, a closer inspection by Raman spectroscopy revealed traces of α-Bi₂O₃.     

Rovibrational spectrum and potential energy surface of the N2-N2O van der Waals complex

The rovibrational spectrum of the N₂-N₂O van der Waals complex has been recorded in the N₂O ν₁ region (∼1285 cm⁻¹) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. The observed transitions together with the data observed previously in the N₂O ν₃ region are analyzed using a Watson S-reduced asymmetric rotor Hamiltonian. The rotational and centrifugal distortion constants for the ground and excited vibrational states are accurately determined. The band-origin of the spectrum is determined to be 1285.73964(14) cm⁻¹. A restricted two-dimensional intermolecular potential energy surface for a planar structure of N₂-N₂O has been calculated at the CCSD(T) level of theory with the aug-cc-pVDZ basis sets and a set of mid-bond functions. With the intermolecular distance fixed at the ground state value R = 3.6926 Å, the potential has a global minimum with a well depth of 326.64 cm⁻¹ at θ_N2 = 11.0° and θ_N2O = 84.3° and has a saddle point with a barrier height of 204.61 cm⁻¹ at θ_N2 = 97.4° and θ_N2O = 92.2°, where θ_N2(θ_N2O) is the enclosed angle between the N-N axis (N-N-O axis) and the intermolecular axis.     

Current-voltage characteristics of Au/GaN/GaAs structure

Au/GaN/n-GaAs structure has been fabricated by the electrochemically anodic nitridation method for providing an evidence of achievement of stable electronic passivation of n-doped GaAs surface. The change of the electronic properties of the GaAs surface induced by the nitridation process has been studied by means of current-voltage (I-V) characterizations on Schottky barrier diodes (SBDs) shaped on gallium nitride/gallium arsenide structure. Au/GaN/n-GaAs Schottky diode that showed rectifying behavior with an ideality factor value of 2.06 and barrier height value of 0.73 eV obeys a metal-interfacial layer-semiconductor (MIS) configuration rather than an ideal Schottky diode due to the existence of GaN at the Au/GaAs interfacial layer. The formation of the GaN interfacial layer for the stable passivation of gallium arsenide surface is investigated through calculation of the interface state density N_ss with and without taking into account the series resistance R_s. While the interface state density calculated without taking into account R_s has increased exponentially with bias from 2.2×10¹² cm⁻² eV⁻¹ in (E_c−0.48) eV to 3.85×10¹² cm⁻² eV⁻¹ in (E_c−0.32) eV of n-GaAs, the N_ss obtained taking into account the series resistance has remained constant with a value of 2.2×10¹² cm⁻² eV⁻¹ in the same interval. This has been attributed to the passivation of the n-doped GaAs surface with the formation of the GaN interfacial layer.     

Preparation and characterization of SnO2 nanoparticles using high power pulsed laser

Tin dioxide (SnO₂) nanoparticles having 3 nm size were synthesized by irradiating pure tin metal using high power Nd:YAG laser in deionized water. Formation of nano-SnO₂ crystallites was confirmed by X-ray diffraction (XRD) and AFM study. UV-vis absorption spectral studies showed a peak at 240 nm. FTIR spectrum showed a band in the range of 400-700 cm⁻¹ which was assigned to Sn-O antisymmetric vibrations. Photoluminescence spectrum of synthesized SnO₂ nanoparticles showed peak corresponding to 3.175, 2.901 and 2.613 eV respectively.