Fabrication of nano-floating gate memories through atomic layer deposition incorporated with chemically-synthesized ZnO-nanocrystals

Nano-floating gate memories made of Al₂O₃/ZnO/Al₂O₃ nanostructures were fabricated with chemically-driven ZnO nanocrystals embedded into high-k Al₂O₃ thin films prepared through atomic layer deposition. The memory characteristics were analyzed through high-frequency capacitance–voltage measurement and current–voltage characteristics, along with high-resolution images of the aforementioned structures. The dotted ZnO nanocrystals function as charge-trapping/detrapping centers, inducing a very large memory window of 5.34 V. The defective nature of ZnO was optimally adjusted into the energy-band diagrams in combination with the tunneling and control layers of the robust Al₂O₃ thin films. The measured memory characteristics exhibited superior retention features derived from the charge-trapping/detrapping behaviors.     

Application of MEH-PPV/SnO<Subscript>2</Subscript> bilayer as hybrid solar cell

The effects of oxygen content in the sputtering gas on the crystallographic and optoelectronic properties of 210 nm-thick Zr–doped In₂O₃ (Zr–In₂O₃) films by rf magnetron sputtering were initially studied. The results of X-ray diffraction show that the Zr–In₂O₃ films grown on glass substrates exhibit mixed crystallographic orientations. Moreover, the Zr–In₂O₃ film grown in an Ar atmosphere promotes the appearance of crystallographic orientation of (222). The surface of the Zr–In₂O₃ film becomes rougher as the oxygen content in the sputtering gas decreases; the current images obtained by conductive atomic force microscopy reveal that the surfaces of the Zr–In₂O₃ films exhibit a distribution of coexisting conducting and nonconducting regions, and that the area of the nonconducting surface increases with the oxygen content in the sputtering gas. The resistivity is minimized to 3.51×10⁻⁴ Ω cm when the Zr–In₂O₃ film is grown in an Ar atmosphere and the average transmittance in the visible light region is ∼85%. The optical band gap decreases as the oxygen content in the sputtering gas increases.     

Epitaxial combination of NdBa2Cu3O7−δ /SrTiO3: growth characteristics, structure, and parameters

We have studied the growth characteristics, structure, and parameters of the epitaxial heterostructures (001)NdBa₂Cu₃O_7−δ /(100)SrTiO₃/(001)NdBa₂Cu₃O_7−δ grown by laser ablation on a (100)LaAlO₃ substrate with a thin (∼2 nm) YBa₂Cu₃O_7−δ intermediate layer. The use of an YBa₂Cu₃O_7−δ intermediate layer promotes layered growth of the (200 nm) NdBa₂Cu₃O_7−δ layer, whose free-surface roughness is 4–5 nm. The resistance of the NdBa₂Cu₃O_7−δ layers began to fall off abruptly at T=92 K, and at T≈87 K it vanished completely. The critical current density in the NdBa₂Cu₃O_7−δ layers at T=76 K exceeded 10⁶ cm² A/cm². The dielectric constant of the (400 nm) SrTiO₃ layer sandwiched between the NdBa₂Cu₃O_7−δ epitaxial layers grew by roughly threefold as the temperature was lowered in the interval 300–4.2 K. When a bias voltage of ±2.5V was applied to the NdBa₂Cu₃O_7−δ electrodes, the relative dielectric constant of the (400 nm) SrTiO₃ intermediate layer fell from 1150 to 400 (T=32 K, f=100 kHz). The conductivity of the SrTiO₃ intermediate layer in the direction perpendicular to the substrate plane increased with temperature and the electric field strength. Fiz. Tverd. Tela (St. Petersburg) 41, 395–403 (March 1999)     

Highly transparent Ag doped In2O3 electrodes with high work function for organic solar cells

We report highly transparent Ag-doped In₂O₃ (IAO) films with high work function for use as transparent anodes in organic solar cells (OSCs). The electrical, optical, structural, and morphological properties of IAO films and their work function were investigated as a function of the rapid thermal annealing (RTA) temperature. At an RTA temperature of 600 °C, the IAO film showed a sheet resistance of 23.12 Ohm/square, an optical transmittance of 79.28%, and a work function of 5.21 eV, similar to conventional Sn-doped In₂O₃ (ITO) films. The low resistivity of the IAO film was closely related to oxygen vacancies caused by Ag suboxide formation in the In₂O₃ matrix. A bulk-heterojunction OSC with the optimized IAO anode showed performance comparable to that of an OSC with a reference ITO anode, indicating that the IAO films is a promising anode material for use in OSCs.     

Preparation of LaGaO<Subscript>3</Subscript> thin film for intermediate temperature SOFC by screen printing method (I)

La-doped ceria (Ce_0.6La_0.4O_1.8 [LDC]) has been reported to be an effective buffer layer material for preventing the chemical reaction between Sr- and Mg-doped LaGaO₃ (LSGM) electrolyte and Ni-based anode during sintering. However, it seems difficult to achieve a high power density on the cell using LDC buffer layer because of its low sintering and electrical conducting properties. In this study, effects of various sintering additives such as MgO, SrO, In₂O₃, Ga₂O₃, ZrO₂, and LSGM oxide powders were studied for improving sintering density and electrical conductivity of LDC. Sintering property, phase formation, and electrical conductivity varied with the sintering agents. Addition of SrO, Ga₂O₃, or LSGM enhanced the sintering density of LDC while LSGM addition was effective to increase the electrical conductivity. LSGM sintering aid was inert with LDC accompanying no chemical reaction after sintering at 1,623 K. Therefore, it was considered that a small amount of LSGM addition as a sintering agent was desirable for improving sintering and electrical properties of LDC. Furthermore, a single cell using LSGM-added LDC buffer layer and LSGM electrolyte film was fabricated by a screen printing method after co-firing at 1,623 K. The obtained cell showed an almost theoretical open circuit voltage and a high maximum power density (0.725 W cm⁻²) at 973 K.     

Impacts of Ti on electrical properties of Ge metal–oxide–semiconductor capacitors with ultrathin high-k LaTiON gate dielectric

Ge Metal–Oxide–Semiconductor (MOS) capacitors with LaON gate dielectric incorporating different Ti contents are fabricated and their electrical properties are measured and compared. It is found that Ti incorporation can increase the dielectric permittivity, and the higher the Ti content, the larger is the permittivity. However, the interfacial and gate-leakage properties become poorer as the Ti content increases. Therefore, optimization of Ti content is important in order to obtain a good trade-off among the electrical properties of the device. For the studied range of the Ti/La₂O₃ ratio, a suitable Ti/La₂O₃ ratio of 14.7% results in a high relative permittivity of 24.6, low interface-state density of 3.1×10¹¹ eV⁻¹ cm⁻², and relatively low gate-leakage current density of 2.0×10⁻³ A cm⁻² at a gate voltage of 1 V.     

Characteristics of p-type ZnO:As thin films prepared by the ampoule-tube method and ZnO p–n homojunction

A p-type ZnO thin film was prepared using arsenic diffusion via the ampoule-tube method. This was followed by fabrication of a ZnO p–n homojunction using n-type ZnO and characterization of the device properties. The ZnO thin film exhibited p-type characteristics, with a resistivity of 2.19×10⁻³ Ω cm, a carrier concentration of 1.73×10²⁰/cm³, and a mobility of 26.7 cm²/V s. Secondary ion mass spectrometer analysis confirmed that in- and out-diffusion occurred simultaneously from the external As source and the GaAs substrate. The device exhibited the rectification characteristics of a typical p–n junction; the forward voltage at 20 mA was approximately 5.5 V. The reverse-bias leakage current was very low—0.1 mA for −10 V; the breakdown voltage was −11 V. The ampoule-tube method for fabricating p-type ZnO thin films may be useful in producing ultraviolet ZnO LEDs and other ZnO-based devices.     

The sensitivity and dynamic response of field ionization gas sensor based on ZnO nanorods

Field ionization gas sensors based on ZnO nanorods (50–300 nm in diameter, and 3–8 μm in length) with and without a buffer layer were fabricated, and the influence of the orientation of nano-ZnO on the ionization response of devices was discussed, including the sensitivity and dynamic response of the ZnO nanorods with preferential orientation. The results indicated that ZnO nanorods as sensor anode could dramatically decrease the breakdown voltage. The XRD and SEM images illustrated that nano-ZnO with a ZnO buffer layer displayed high c-axis orientation, which helps to significantly reduce the breakdown voltage. Device A based on ZnO nanorods with a ZnO buffer layer could distinguish toluene and acetone. The dynamic responses of device A to the NO _x compounds presented the sensitivity of 0.045 ± 0.007 ppm/pA and the response speed within 17–40 s, and indicated a linear relationship between NO _x concentration and current response at low NO _x concentrations. In addition, the dynamic responses to benzene, isopropyl alcohol, ethanol, and methanol reveals that the device has higher sensitivity to gas with larger static polarizability and lower ionization energy.     

Indium oxide nanostructures

In this report we review the growth of indium oxide (In₂O₃) nanostructures, including octahedral nanocrystals (NCs), nanobelts (NBs), nanosheets (NSs), and nanowires (NWs), by hot-wall chemical vapor deposition (HW-CVD). This system is highly controllable, allowing the user to easily access different growth regimes – each corresponding to the growth of a different nanostructure – by changing growth variables of the HW-CVD system. Hot-wall CVD produces crystalline nanostructures; here we present a survey of microstructural characterizations of the four types of In₂O₃ nanostructures using transmission- and scanning-electron microscopy. Interestingly, the In₂O₃ nanostructures have different preferred growth directions: NCs have (111) faces, NBs are predominantly (200), and NWs are predominantly (110). We end the review by discussing the current shortcomings of HW-CVD growth of In₂O₃ nanostructures. PACS 61.46.-w; 61.82.Rx; 73.31.Hb; 81.02.-b     

Studies on chemical stability in CO2 and H2O and electrical conductivity of perovskite-type Ba3In2Zr1?xCexO8 (x?= 0, 0.5, 1)

We report the synthesis, structure, microstructure, chemical stability in H₂O and CO₂, and electrical transport properties of an oxide ion-conducting perovskite-related structure Ba₃In₂MO₈ (M = Zr, Ce, Zr_0.5Ce_0.5). Powder X-ray diffraction confirmed the formation of a simple cubic perovskite-like structure for Ba₃In₂ZrO₈ (a = 4.205(9) ?), Ba₃In₂CeO₈ (a = 4.234(1) ?), and Ba₃In₂Zr_0.5Ce_0.5O₈ (a = 4.285(8) ?). The increase in lattice constant is consistent with the Shannon’s ionic radius trend. Among the three samples investigated, Ba₃In₂ZrO₈ was found to be stable against reaction with pure CO₂ at elevated temperature, while the Ce and 1:1 Zr and Ce compounds were unstable at 600 °C. Ba₃In₂ZrO₈, Ba₃In₂CeO₈, and Ba₃In₂Zr_0.5Ce_0.5O₈ were found to be chemically unstable in H₂O at about 50 °C. The bulk electrical conductivity of the samples prepared at different temperatures was found to be nearly the same; the total conductivity (bulk + grain–boundary + electrode) seems to change with sintering temperature. Both Ba₃In₂ZrO₈ and Ba₃In₂CeO₈, prepared at 1,400 °C, exhibited comparable electrical conductivity of about 6 × 10⁻³ S cm⁻¹ at 800 °C, which is comparable to that of conventional Y₂O₃-doped ZrO₂ electrolyte. These compounds are very promising electroltes, provided that their chemical and mechnical stabitities are improved without losing any ionic conductivity.     

Implantation of the 111In/Cd Probe as InO− Ion for Radioisotope Tracer Studies

A radioisotope ion implanter has been developed using a cesium-sputtering, negative ion source, which offers versatility and sustained operation. Employing the molecular ¹¹¹In¹⁶O⁻ ion, μCi activities of the radioisotope probe ¹¹¹In/Cd have been implanted into different material hosts. The implanted tracer activity has been shown to be sufficient for LTNO, NMRON and PAC. A new NMRON resonance for ¹¹¹InAg was observed at 75.08 MHz. In₂O₃ powder performed well as the radioisotope carrier in the ion source, with the ratio of radioisotope and parasitic ion current being typically 4 × 10⁻⁴.     

Strain accumulation in InAs/In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As quantum dots

The effect of strain accumulation in the InAs/In _x Ga_1−x As quantum dots (QDs) system was studied in this work. It was found that strain in the In _x Ga_1−x As layer accumulation in the QD layer. This effect resulted in a dramatic reduction of growth mode transition thickness of the QD layer. For InAs/In_0.25Ga_0.75As QDs, critical thickness is measured to be as low as 1.08 ML. The experimental results in this work highlight the importance of strain accumulation in the design and fabrication of QD-based devices with metamorphic buffer layer involved.     

Strain accumulation in InAs/In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As quantum dots

The effect of strain accumulation in the InAs/In _x Ga_1−x As quantum dots (QDs) system was studied in this work. We found strain in the In _x Ga_1−x As layer with accumulation in the QD layer. This effect resulted in a dramatic reduction of growth-mode transition thickness of the QD layer. For InAs/In_0.25Ga_0.75As QDs, critical thickness is measured to be as low as 1.08 ML. The experimental results in this work highlight the importance of strain accumulation in the design and fabrication of QD-based devices with metamorphic buffer layer involved.     

Evaluation of the electrical capacitance of M,O2/O2− interfaces (M=Pt, Au, Pd, In2O3; O2− = zirconia based electrolyte) exhibiting constant phase element behavior

The behavior of the electrode systems M,O₂/O² (M = porous Pd, Pt, A and dense In₂O₃; O²⁻ = ZrO₂-based single-crystal solid electrolyte) was studied by means of impedance measurements. The examination of the Pt,O₂/O²⁻ electrode system showed that the constant phase element (CPE) can be attributed to a nonuniform distribution of current at the electrode surface. It was observed that the CPE parameters n and B in the expression Y_CPE = B (jω)ⁿ may be related by B=(C_dl)ⁿ (R_Ω)_n-1, where C_dl is the double layer capacitance and R_Ω the resistance of the electrolyte in the cell. Then, C_dl of the electrode - electrolyte interface could be determined. The specific C_dl of the oxidized noble metals and india electrodes is nearly one order of magnitude lower than C_dl of the electrodes in the metallic state. The C_dl value of all the electrodes studied depends little or is independent of temperature and oxygen pressure. It is concluded that the Helmholtz model of double layer structure does not contradict the C_dl behavior.     

Synthesis,structural and ellipsometric evaluation of oxygen-deficient and nearly stoichiometric zinc oxide and indium oxide nanowires/nanoparticles

Oxygen-deficient (OD) and nearly stoichiometric (NST) ZnO and In₂O₃ nanowires/nanoparticles were synthesized by chemical vapor deposition on Au-coated silicon substrates. The OD ZnO and OD In₂O₃ nanowires were synthesized at 750 and 950°C, respectively, using Ar flow at ambient pressure. A mixture of flowing Ar and O₂ was used for synthesizing NST ZnO nanowires and NST In₂O₃ nanoparticles. Growth of OD ZnO nanowires and NST In₂O₃ nanoparticles was found to be via a vapor–solid (VS) mechanism and the growth of NST ZnO nanowires was via a vapor–liquid–solid mechanism (VLS). However, it was uncertain whether the growth of OD In₂O₃ nanowires was via a VS or VLS mechanism. The optical constants, thickness and surface roughness of the prepared nanostructured films were determined by spectroscopic ellipsometry measurements. A three-layered model was used to fit the calculated data to the experimental ellipsometric spectra. The refractive index of OD ZnO, NST ZnO nanowires and NST In₂O₃ nanoparticles films displayed normal dispersion behavior. The calculated optical band gap values for OD ZnO, NST ZnO, OD In₂O₃ nanowires and NST In₂O₃ nanoparticles films were 3.03, 3.55, 2.81 and 3.52?eV, respectively.     

Structure and properties of GZO thin films grown on ZnO buffer layers

Thin gallium-doped zinc oxide (in GZO the Ga₂O₃ contents are approximately 3 wt%) films having different ZnO buffer layers were deposited using radio frequency (rf) magnetron sputtering. The use of a grey-based Taguchi method to determine the processing parameters of ZnO buffer layer deposition has been studied by considering multiple performance characteristics. A Taguchi method with an L₉ orthogonal array, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) is employed to investigate the performance characteristics in the deposition operations. The effect and optimization of ZnO buffer deposition parameters (rf power, sputtering pressure, thickness, and annealing) on the structure, morphology, electrical resistivity, and optical transmittance of the GZO films are studied. Annealing treatment and reduction in thickness resulted in a decrease in root-mean-square (RMS) surface roughness of the ZnO buffer layer. Using the optimal ZnO buffer layer obtained by the application of the grey-based Taguchi method, the electrical resistivity of GZO films was decreased from 2.94×10⁻³ to 9.44×10⁻⁴ Ω cm and the optical transmittance in the visible region was slightly increased from 84.81% to 85.82%.     

Growth of InN thin films on ZnO substrate by plasma-assisted molecular beam epitaxy

We have studied the microstructure property of InN epitaxial films grown on ZnO substrate by plasma-assisted molecular beam epitaxy. We found that the In₂O₃ compound was produced on ZnO substrate and many pits were formed on the InN films when InN was directly grown on ZnO substrate with the N/In flux ratio less than 40. We demonstrated that the quality of InN film was significantly improved when the In₂O₃ layer was used as a buffer to prevent the reaction between In and the ZnO substrate.     

Enhanced field emission from pulsed laser deposited nanocrystalline ZnO thin films on Re and W

Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm² and 9.3 mA/cm² has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87 and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×10⁵ cm⁻¹ and 2.16×10⁵ cm⁻¹ for pointed and 3.2×10⁴ and 1.74×10⁴ for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical applications in field-emission-based electron sources.     

Spectroscopic ellipsometry modeling of ZnO thin films with various O2 partial pressures

ZnO films were deposited on thermally oxidized SiO₂/p-type Si (100) substrates and glass substrates by DC magnetron sputtering using a metal Zn target. Three types of samples were prepared with various O₂/(Ar + O₂) ratios (O₂ partial pressure) of 20%, 50%, and 80%. The properties of these ZnO thin films were investigated using X-ray diffraction (XRD), optical transmittance, atomic force microscopy (AFM), and spectroscopic ellipsometry in the spectral region of 1.7–3.1 eV. The structural and optical properties of ZnO thin films were affected by O₂ partial pressure. Relationships between crystallinity, the ZnO surface roughness layer, and the refractive index (n) were investigated with varying O₂ partial pressure. It was shown that the spectroscopic ellipsometry extracted parameters well represented the ZnO thin film characteristics for different O₂ partial pressures.     

Microstructure and electrode properties of La0.6Sr0.4Co0.2Fe0.8O3-δ spin-coated on Ce0.8Sm0.2O2?δ electrolyte

Fine and uniform La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ powder was synthesized by a glycine–nitrate combustion process. La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ electrodes were prepared on dense Ce_0.8Sm_0.2O_2−δ electrolyte substrates using a spin-coating technique by sintering at 900–1,000 °C. The electrode properties of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ were investigated by electrochemical impedance spectroscopy and chronopotentiometry techniques with respect to preparation conditions and the resulting microstructures. The results indicate a significant effect of the microstructure on the electrode processes and polarization characteristics. The oxygen adsorption and dissociation process acted as a larger contribution to the overall electrode polarization R _p in magnitude compared with the charge transfer process due to relatively low porosity levels of the electrodes. It was detected that the grain size of the electrodes exhibited a crucial role on the electrocatalytic reactivity. At 800 °C, the electrode sintered at 950 °C attained a polarization resistance of 0.18 Ω cm², an overpotential of 27 mV at a current density of 200 mA cm⁻², and an exchange current density of 308 mA cm⁻².