Conduction in MIM structures with an organic monomolecular layer at high electric fields

The influence of one organic monolayer (30 Å thick) on the electronic conduction through Al/Al₂O₃/Al structures at very high d.c. electric fields (E > 10⁶ V cm^?1) between 20 and 120°C was studied.One interposed monolayer reduces the injected current from aluminium into alumina by a factor of 100–1000. This reduction in the conduction current cannot be explained by one single potential barrier associated with the organic layer. It is necessary to take into account the presence of a natural oxide layer on the counterelectrode and the trapping of electrons in the organic layer or at the interface.     

Internal photoemission in Ge/sapphire/metal structures

Photoemission experiments on Ge/(single-crystal Al₂O₃)/metal structures are reported. The electronic barrier height between aluminium, silver or germanium and single-crystal Al₂O₃ were determined from the spectral response of the photoemission and were found to be 3.20 ± 0.03 eV, 3.81 ± 0.03 eV and 4.01 ± 0.03 eV respectively. Values for μτ (the product of the mobility and the lifetime) and the mean range of injected electrons in Al₂O₃ were determined from steady-state photocurrent-voltage characteristics measured on Ge/Al₂O₃/Al and Al/Al₂O₃/Al structures with a sapphire (Al₂O₃) thickness of 150–250 μm for electric fields in the range from 10² to 2 × 10⁴ V cm^-1. A mean value of 8.4 × 10^-6 cm² V^-1 was deduced for μτ from measurements made on several samples. Measurements made on samples with semitransparent aluminium electrodes of different thicknesses showed that the relative importance of a possible extrinsic photoconductivity component due to charges related to defect centres must be less than the 10% of the measured photocurrent.     

Dielectric properties of YSZ high-k thin films fabricated at low temperature by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) films were deposited on Pt-coated silicon substrates and directly on n-type Si substrates, respectively, by pulsed laser deposition (PLD) technique using a YSZ (5 mol% Y₂O₃-stabilized ZrO₂) ceramic target. The YSZ films were deposited in 1.5×10⁻² Pa O₂ ambient at 300 °C and in situ post-annealed at 400 °C. X-ray diffraction (XRD) and differential thermal analysis measurements demonstrated that YSZ remained amorphous. The dielectric constant of amorphous YSZ was determined to be about 26.4 by measuring Pt/YSZ/Pt capacitor structure. The 6-nm-thick amorphous YSZ films with an equivalent oxide thickness (EOT) of 1.46 nm and a low leakage current of 7.58×10⁻⁵ A/cm² at 1 V gate voltage exhibit good electrical properties. YSZ thin films fabricated at low temperature 300 °C have satisfactory dielectric properties and could be a candidate of high-k gate dielectrics.     

Enhanced leakage current properties of HfO2/GaN gate dielectric stack by introducing an ultrathin buffer layer

The band alignments of HfO₂/GaN, HfO₂/SiO₂/GaN and HfO₂/Al₂O₃/GaN gate dielectric stacks were comparatively investigated by using X-ray photoelectron spectroscopy. It was observed that the introduction of an ultrathin buffer layer film (SiO₂ or Al₂O₃) in HfO₂/GaN stack can make the band alignments more symmetrical with larger barrier height as identified by the valence band offsets and electron energy loss spectrum measurements. At room temperature, the leakage current density as function of temperature is 4.1 × 10^?6, 3 × 10^?7 and 9.8 × 10^?8 A cm^?2 at the bias of 1 V for the HfO₂/GaN, HfO₂/Al₂O₃/GaN and HfO₂/SiO₂/GaN gate dielectric stacks, correspondingly. With temperature increase from room temperature to 300 °C, the HfO₂/SiO₂/GaN gate dielectric stack exhibits lowest lower leakage current density than that of others. The HfO₂/GaN high-k gate dielectric stack with an ultrathin SiO₂ buffer layer appears to be a promising candidate for future GaN based high temperature metal-oxide-semiconductor (MOS) devices applications.     

Structural,morphological and optoelectronic properties of porous silicon combined alumina coating film deposited by PLD

Pulsed laser deposition of Al₂O₃ onto porous silicon (PS) is shown to provide excellent passivation of multi-crystalline silicon surfaces intended for solar cells applications. Surface passivation and reflectivity are investigated before and after the deposition of various nominal thicknesses of Al₂O₃ ranging from isolated nanoparticles to ~80 nm-thick films. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 1 to 130 μs at a minority carrier density (Δn) of 1?×?10¹³ cm^?3. However, passivation scheme provide a significant decrease in the reflectivity; it’s reduced from 28% to about 5% after Al₂O₃/PS coating.     

Ni-Al-O diffusion barrier layer for high-κ metal-oxide-semiconductor capacitor

Using amorphous Ni-Al-O (a-Ni-Al-O) thin film as the intermediate layer, poly-crystalline Er₂O₃ thin film was grown on a-Ni-Al-O/Si (p-type) via laser molecular beam epitaxy, forming the Er₂O₃/Ni-Al-O gate stack. It was found that the mean dielectric constant of the Er₂O₃/Ni-Al-O gate stack with an equivalent oxide thickness of 1.5 nm is about 17-23, the interfacial states density is about 3.16 × 10¹² cm⁻² and the stack gate leakage current density is as small as 4.1 × 10^− 6 A/cm². Furthermore, The insertion of the Ni-Al-O thin film between the Er₂O₃ gate dielectric and p-Si substrate prevents the oxygen from being out-diffused, which significantly improved the stability of gate stack, showing that the Er₂O₃/Ni-Al-O gate stack thin film could be used as an ideal gate oxide layer for the future Metal Oxide Semiconductor Field Effect Transistors.     

Band alignment of metal-oxide-semiconductor structure by internal photoemission spectroscopy and spectroscopic ellipsometry

In this paper, we will provide an overview of the internal photoemission (IPE) and the significance of this technique when combined with spectroscopic ellipsometry (SE) to investigate the interfacial electronic properties of heterostructures. In particular, the main interest is focused on the electron transport mechanism and properties at and near the interface of the technologically important metal-oxide-semiconductor (MOS) devices. Not until recently, IPE and SE have become important metrology tools in band offset characterization for the MOS materials. The most common and straightforward application of IPE and SE is to determine how the Fermi level of the metal, and the conduction and valence bands of the semiconductor align with those of the oxide of the MOS structure. For demonstration, we will present the results recently obtained on a set of MOS devices consisting of metal gate / high-k dielectric stack / Si and III-V high mobility substrate. The examples include [TaN/TaSiN] metal gate / [HfO₂/SiO₂] dielectric stack / Si substrate and Al metal gate / Al₂O₃ dielectric / In_xGa_1 − xAs substrate.     

Charge trapping characteristics of Al2O3/Al-rich Al2O3/SiO2 stacked films fabricated by radio-frequency magnetron co-sputtering

A thin-film structure comprising Al₂O₃/Al-rich Al₂O₃/SiO₂ was fabricated on Si substrate. We used radio-frequency magnetron co-sputtering with Al metal plates set on an Al₂O₃ target to fabricate the Al-rich Al₂O₃ thin film, which is used as a charge storage layer for nonvolatile Al₂O₃ memory. We investigated the charge trapping characteristics of the film. When the applied voltage between the gate and the substrate is increased, the hysteresis window of capacitance-voltage (C-V) characteristics becomes larger, which is caused by the charge trapping in the film. For a fabricated Al-O capacitor structure, we clarified experimentally that the maximum capacitance in the C-V hysteresis agrees well with the series capacitance of insulators and that the minimum capacitance agrees well with the series capacitance of the semiconductor depletion layer and stacked insulator. When the Al content in the Al-rich Al₂O₃ is increased, a large charge trap density is obtained. When the Al content in the Al-O is changed from 40 to 58%, the charge trap density increases from 0 to 18 × 10¹⁸ cm^− 3, which is 2.6 times larger than that of the trap memory using SiN as the charge storage layer. The device structure would be promising for low-cost nonvolatile memory.     

Growth and characterization of Al2O3 insulator gate on p-InP and p-Si by metallorganic chemical vapour deposition at low temperatures

Metallorganic chemical vapour deposition of Al₂O₃ from Al(O-C₃H₇)₃ via pyrolysis at low (280 °C) temperature was investigated with the goal of producing high quality Al₂O₃/p-InP (1 0 0) and Al₂O₃/p-Si (1 0 0) interfaces. Ellipsometer measurements of Al₂O₃ have determined the refractive index of the film to be about 1.55. Room temperature capacitance-voltage measurements were used to characterize the electrical properties of the structures after metal gate electrodes have been deposited. Low temperature conductance-voltage measurements were also carried out to investigate the quality of the Al₂O₃/InP interfaces. The interface state densities Al₂O₃/p-InP and Al₂O₃/p-Si determined from deep-level transient spectroscopy were approximately 10¹² eV^–1 cm^–2 and 10¹¹ eV^–1 cm^–2.     

Structure,conduction mechanisms and multiferroic properties of (Sm,Cr) co-doped Bi0.89Sm0.11Fe0.97Cr0.03O3–NiFe2O4 composition thin films

(Sm, Cr) co-doped Bi_0.89Sm_0.11Fe_0.97 Cr_0.03O₃ (BSFC)–NiFe₂O₄ (NFO) composition thin films were successfully prepared on FTO/glass (SnO₂:F) substrates via a sol–gel method. The structure, surface morphology, leakage current, ferroelectricity and ferromagnetism of BSFC–NFO composition thin film have been investigated. X-ray diffraction analysis indicates that the thin film is polycrystalline and consisted of a rhombohedral perovskite (R3m space group) BiFeO₃ phase and a cubic (Fd-3m space group) inverse spinel NiFe₂O₄ phase. The BSFC–NFO composition thin film is promising in practical application because of its well saturated ferromagnetic (Ms = 19.45 emu/cm³) and ferroelectric (Pr = 39 µC/cm²) hysteresis loops with low order of leakage current density (J = 6.73 × 10^?6 A/cm², at an applied electric field of 100 kV/cm). Which suggest the ferroelectric and ferromagnetic properties can be improved by this composition thin film structure. Moreover, the various conduction mechanisms of BSFC–NFO composition thin film have also been studied.     

Monocrystalline silicon surface passivation by Al2O3/porous silicon combined treatment

In this paper, we report on the effect of Al₂O₃/porous silicon combined treatment on the surface passivation of monocrystalline silicon (c-Si). Al₂O₃ films with a thickness of 5, 20 and 80 nm are deposited by pulsed laser deposition (PLD). It was demonstrated that Al₂O₃ coating is a very interesting low temperature solution for surface passivation. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 2 μs to 7 μs at a minority carrier density (Δn) of 1 × 10¹⁵ cm^?3 and the reflectivity reduce from 28% to about 7% after Al₂O₃/PS coating.     

Properties of MgB2 Thin Films Deposited on Different Substrates Prepared by Ex-Situ Annealing Process

MgB₂ thin films were deposited on MgO (100) substrate and r-plane Al₂O₃ $(1\bar{1}02)$ substrate by ex-situ annealing of boron film in magnesium vapor. The thickness of ex-situ annealed MgB₂ films is approximately 600 nm according to data observation by ellipsometer. The magnetic properties of samples were determined using a vibrating sample magnetometer. The magnetic field dependence of the critical current density J _c was calculated from M–H loops and also the magnetic field dependence of F _p was compared for the different temperature ranges from 5 to 25 K. The critical current density J _c was found to be around 1.0×10⁶ A/cm² and 1.7×10⁶ A/cm² in zero field at 5 K for MgB₂ films deposited on MgO and r-plane Al₂O₃ substrates, respectively. It was found that the critical current density of the film deposited on MgO became stronger than that of r-plane Al₂O₃ in the magnetic field. The superconducting transition temperature was determined by ac susceptibility measurement using physical properties measurement system. ac susceptibility measurements for MgB₂ films deposited on MgO and r-plane Al₂O₃ substrates were performed as a function of temperatures at constant frequency and ac field amplitude in the absence of dc bias field. The critical current densities as a function of temperature were estimated from the ac susceptibility data.     

Sintering, densification and crystallization of Ca–Al–B–Si–O glass/Al2O3 composites for LTCC application

Ca–Al–B–Si–O glass/Al₂O₃ composites were prepared based on the borosilicate glass powders (D₅₀ = 2.84) and Al₂O₃ ceramic powders (D₅₀ = 3.26), and the sintering, densification, crystallization of samples were investigated. The shrinkage of sample starts to have a sharp increase at 600 °C. The shrinkage of sample starts to have a further rapid increase after the glass softening temperature of about 713 °C. Glass/Al₂O₃ composites can be sintered at 875 °C/15 min and exhibit better properties of a relative density of 98.4 %, a λ value of 2.89 W/mK, a ε _r value of 7.82 and a tan δ value of 5.3 × 10^?4. The interface between glass and Al₂O₃ grains and the interface between anorthite and glass phase depicts a good compatibility according to transmission electron microcopy test. It is the low sintering temperature, high density and good compatibility with Ag electrodes that, guarantee borosilicate glass/Al₂O₃ composites suitable for low temperature co-fired ceramic materials.     

Metal/nonpolar <Emphasis Type="Italic">m</Emphasis>-plane ZnO contacts with and without thin Al<Subscript>2</Subscript>O<Subscript>3</Subscript> interlayer deposited by atomic layer deposition

Using the temperature dependent current–voltage (I–V) measurements, the electrical properties of Au/nonpolar m-plane ZnO Schottky diodes with an Al₂O₃ interlayer prepared by atomic layer deposition (ALD) was investigated. With an Al₂O₃ interlayer, it was found to have higher barrier heights and higher rectifying ratio. Modified Richardson plots produced effective Richardson constants of 30.0 and 37.6 Acm^?2K^?2 for the samples with and without Al₂O₃ interlayer, respectively, which are similar to the theoretical value of 32.0 Acm^??2K^??2 for n-ZnO. Scanning transmission electron microscope (STEM) results showed that the oxygen-contained layer on ZnO surface degraded the film quality of subsequently deposited Al₂O₃ layer. In addition, the inter-diffusion of Au and Al atoms into ZnO subsurface region also modulated the electrical properties of Au/ZnO contacts.     

Influence of alkalinity on particle size distribution and crystalline structure in synthesis of zeolite beta

Influence of alkalinity (OH^-/SiO₂) on particle size distribution and crystalline structure in synthesis of zeolite beta at a short crystallization period (60 h) has been studied. The results indicate that the highest crystallinity of synthetic zeolite beta at alkalinity of 0.24, 0.35 occurs when Al₂O₃·H₂O and NaAlO₂ are respectively used as aluminium sources. At an alkalinity higher than 0.39, zeolite beta can not be obtained when Al₂O₃·H₂O is used as aluminium source. The difference of particle sizes between zeolite beta synthesized from gels of different alkalinity is 0.7–0.8 μm. The widest particle size distribution of zeolite beta synthesized occurs when the alkalinity is 0.23–0.24. Along with the increase of the alkalinity, zeolite beta synthesized changes as follows: vibration peak of 1071 cm⁻¹ by IR moves to a higher position, the framework Si/Al ratio determined by ²⁹Si MAS NMR first increases gradually and then decreases, but the change of OhAl/TdAl ratio determined by ²⁷Al MAS NMR is contrary to that of the framework of the Si/Al ratio. In addition, the Si(O⁻) site existing in the TEA-β is confirmed by NMR, and the mechanism of alkalinity influencing crystallization is discussed.     

Electrical Spin Injection from Ferromagnetic Nanocontacts into Nondegenerated Silicon at Low Temperatures

We present results on the magnetoresistance of the system Ni/Al₂O₃/Si/Al₂O₃/Ni fabricated in lateral nanostructures. The substrate n-type Si is a nondegenerated semiconductor with a doping level of 10¹⁵ cm^?3. The results are presented between 11 and 30 K, where the electrical resistivity of the semiconductor varies about 4 orders of magnitude. The reduction of magnetoresistance at 30 K is consistent with the standard theory for spin injection between a metal and a semiconductor. By fitting the data with $e^{ - t_{N} / L_{\mathrm{SD}}}$ , the diffusion condition, as a function of the channel length t _N , where the magnetoresistance takes place, we deduced the values of spin diffusion length L _SD and spin lifetime τ _s .     

磁控溅射Al掺杂Al2O3薄膜耐蚀性能研究

采用中频电源反应溅射在Si和SS304不锈钢表面制备两种不同成分的Al-O涂层,利用X射线衍射、扫描电镜、纳米压痕仪、电化学工作站和Cu装饰实验对涂层的结构及性能进行了分析。结果表明:室温下制备的涂层,掺Al后沉积速率是纯Al_2O_3的10倍,两种非晶涂层截面无明显的形貌特征,纯Al_2O_3涂层表面有微裂纹存在,掺杂Al的Al_2O_3涂层表现出更为优异的耐腐蚀性能,这与其表面的Al发生钝化氧化反应有关。     

Structure transition and multiferroic properties of Mn-doped BiFeO3 thin films

Pure BiFeO₃ (BFO) and Mn-doped BiFe_1?yMn_yO₃ thin films were prepared on FTO/glass (SnO₂: F) substrates by using a sol–gel method. The effects of Mn-doping on the structure and electric properties of the BFO thin films were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the Mn-doped BiFe_0.96Mn_0.04O₃ (BFMO) thin film. The Rietveld refined XRD patterns conform the trigonal (R3c: H) and tetragonal (P422) symmetry for the BFO and BFMO thin films, respectively. The structure transition and the mixed valences of Mn ions substantially improve the electric properties of the BFMO thin film. The remnant polarization (P _r) of the BFMO thin film was 105.86 μC/cm² at 1 kHz in the applied electric field of 865 kV/cm. At an applied electric field of 150 kV/cm, the leakage current density of BFMO thin film is 1.42 × 10^?5 A/cm². It is about two orders of magnitude lower than that of the pure BFO thin film (1.25 × 10^?3 A/cm²). And the enhanced saturated magnetization of the BFMO thin film is 4.45 emu/cm³.     

Conduction in thin films of r.f. reactively sputtered zinc sulphide

Experiments on d.c. electrical conduction in thin films of r.f. reactively sputtered zinc sulphide (thicknesses from 100 to 1000 Å) sandwiched between Al and Au are described. For an electric field between 10⁵ and 10⁶ V cm^-1, the plot of log J versus √V is linear; the thermal evolution of the current is described by log J ～T^-1/3. It is therefore assumed that the electrical conduction is due to the emission of electrons from defects into the conduction band of the zinc sulphide.