Some properties of metal/insulator/semiconductor structures with BN and carbon thin layers formed by the reactive pulse plasma method on silicon or SiO2 substrates and annealing effects

Thin layers (100–300 nm) of BN and diamond-like carbon were produced by the reactive pulse plasma method. On the basis of measurements and analysis of electrical properties of metal/insulator/semiconductor (MIS) capacitors, with a BN or carbon layer acting as the dielectric and silicon as the semiconductor, operating parameters were identified for the BN/Si and C/Si structures. A double layer of thermal SiO₂ and either BN or carbon was also used as a dielectric. The structures produced were subjected to annealing at temperatures from 100 to 500°C in N₂ and O₂ atmospheres.Using the spectral investigation method, BN and carbon layers produced on quartz and KBr substrates were examined for their probable composition (IR absorption analysis), absorption coefficient α and refractive index n. After annealing at temperatures of 300–400°C, a marked improvement in the electrical performance of MIS structures was found as well as storage of charge in the double-layer dielectric structures. Hydrogen and oxygen were also found to be present in the test layers. On the basis of the analysis of the electrical characteristics it is assumed that dehydrogenation of the layers during thermal treatment is one of the reasons why their electrical properties tend to vary with time.     

Field effect studies on p-type PbTe metal/insulator/semiconductor structures

Field effect studies on metal/insulator/semiconductor structures of Ag/mica/p-PbTe were made in the temperature range 120–300 K. It was observed that the effect of a negative voltage is to decrease the Hall coefficient, the Hall mobility and the defect scattering mobility. A positive gate voltage has the opposite effect and to a smaller extent. These results are explained on the basis of accumulation and depletion of charges induced by the field at the surface.     

Electrical properties of InSb metal/insulator/semiconductor diodes prepared by photochemical vapour deposition

Thin SiO₂ films were prepared by photochemical vapour deposition. IR absorption and Auger electron spectroscopy showed that the dominant components of the oxide are silicon and oxygen with a small amount of hydrogen. Metal/insulator/semiconductor (MIS) capacitors were constructed on InSb substrates. Capacitance-voltage characteristics of the MIS capacitors were measured, and a midgap interface state density of the order of 10¹² cm^-2 eV^-1 was determined. The amount of hysteresis observed was found to be about 10% of the inversion bias voltage. Annealing studies were also conducted to improve the electrical properties. After annealing, the midgap interface state density was reduced to 5 × 10¹¹ cm^-2 eV^-1 and the amount of hysteresis reduced to 5% of the inversion bias voltage.     

Hysteresis in metal insulator semiconductor structures with high temperature annealed ZrO2/SiOx layers

Hysteresis behaviour in sandwich structure — zirconium oxide/chemical silicon oxide, annealed at temperature of 850 °C in oxygen ambient, was studied. Formation of thin ZrSi_xO_y layer due to the high temperature annealing was found. Metal-insulator-semiconductor (MIS) capacitors using ZrO₂/ZrSi_xO_y/SiO_x insulator were studied. High-frequency capacitance-voltage (HF C-V), current-voltage (I-V) and current-time (I-t) measurements were carried out on the Al/ZrO₂/ZrSi_xO_y/SiO_x/Si capacitors.Two leakage current components were identified — tunneling current component at high electric fields and transient current component at low fields. The transient leakage currents are due to charge trapping phenomena. The measured I-t characteristics are related with charging/discharging and dielectric relaxation phenomena. A counter-clockwise HF C-V hysteresis, larger than 2 V at thickness of the stack structure of about 50 nm was observed.Metal-insulator-semiconductor field effect transistors (MISFETs) using ZrO₂/ZrSi_xO_y/SiO_x-gate insulator were studied. P-channel MISFETs with aluminum gate electrode were fabricated on standard n-type silicon substrates. Due to charging/discharging phenomena in the gate dielectric the transistors can be switched between On- and Off-state with the polarity of applied stress voltage.     

WCCo/cBN composites produced by pulse plasma sintering method

WCCo/cBN composites have been considered as a next-generation material for use in cutting-tool edges, being characterized by an optimal combination of hardness and toughness. They can be used instead of WCCo/diamond composites in machining of iron-based materials. The major challenge in sintering these composites is to produce a well-bonded interface between the WCCo matrix and cBN particles. In this study, WCCo/cBN composites were fabricated by the pulse plasma sintering technique. The aim of this work is to obtain sintered parts with density near the theoretical value and with very good contact between the cBN particles and WCCo matrix. cBN/cemented carbide containing 30 vol.% of cBN particles was produced using a mixture of 6 and 12 wt.% Co-added WC powder, with WC grain size of 0.4 μm and cBN powder with grain size ranging from 4 to 40 μm. Scanning electron microscopy (SEM) observations of the microstructure and diffraction phase examinations did not show the presence of hBN phase. The specific heating conditions used to consolidate the material using high-current pulses hamper the transformation of cBN into hBN and ensure a strong bond between the cBN particles and the cemented carbide matrix. Fractures through the WCCo/cBN composite showed that only few cBN particles were torn out from the cemented carbide matrix, with most of them having been cleaved along the fracture plane. This provides evidence that the bond at the WCCo/cBN interface is mechanically strong. Composites sintered at temperature of 1,200 °C under pressure of 100 MPa for 5 min had density near the theoretical value. Increase of the sintering temperature to 1,200 °C resulted in an increase of the hardness to 2,330 HK1 for the WC6Co/cBN(1/3) composite and to 2,160 HK1 for the WC6Co/cBN(37/44) composite.     

Characterization of TBP containing polysiloxane membrane/insulator/semiconductor structures for hexavalent chromium detection

A hexavalent chromium-sensitive EMIS sensor (electrolyte membrane insulator semiconductor sensor) is prepared by deposition of a tributylphosphate (TBP) ionophore-containing siloprene membrane on a Si/SiO₂/Si₃N₄ structure. The developed EMIS sensor was studied by means of impedance spectroscopy, capacitance–voltage, X-ray photoelectron spectrometry and FT-IR spectroscopy. From the flat-band shift of the EMIS structure, the nersntian response to the anionic species Cr₂O₇⁻ was demonstrated. The linear range of detection is 10^− 4 M to 10^− 1 M and the detection limit is 10^− 5 M. Sulfate and chloride anions are shown not to be interfering whereas carbonate ions present a pK^pot equal to 0.19.     

Transformations in a metal/insulator/semiconductor structure with an amorphous insulator film caused by contacts

The thermodynamic criteria for and structural consequences of interphase interactions at the boundaries of adjacent layers in an Nb/a-Nb₂O₅/MnO₂ (where a indicates amorphous) metal/insulator/semiconductor (MIS) structure were analysed and studied as an example of the behaviour of similar MIS structures. It was shown experimentally that the interaction in the thin insulator film induced a permanent electrochemical breakdown of the MIS structure which was followed by a step-like electrothermal breakdown under certain conditions. The relation between transformations in the ionic and electronic subsystems of the MIS structure at both stages of its relaxation into a state of thermodynamic equilibrium was investigated. A mechanism was proposed for the electroforming of the film, and investigations of the current-controlled negative resistance and bistable memory switching were performed.     

Photoelectric properties of substituted silicon phthalocyanine Langmuir-Blodgett film Schottky barrier and metal/insulator/semiconductor devices

The fabrication of Schottky barrier structures by evaporating aluminium onto Langmuir-Blodgett films of a substituted silicon phthalocyanine is described. The electrical characteristics of the resulting diodes are similar to those obtained using other thin film techniques and indicate that the substituted silicon phthalocyanine is a p-type semiconductor. We also show that Langmuir-Blodgett films of this material can be effectively used to control the forward current in Au/n-Si diodes. Photovoltaic measurements are reported for both these and the Schottky barrier devices.     

Photoluminescence properties of nanocrystalline AlN layers grown by pulse plasma assisted CVD

In this work, results of photoluminescence and absorption measurements on pulse plasma assisted CVD layers of AlN are presented. We studied nanocrystalline layers grown on silicon substrate at a temperature of 300 K. The efficient photoluminescence of nanocrystalline AlN layers, obtained under non optimal conditions, i.e. relatively low excitation energy, seems to be promising for light emitting applications of this material.     

Structure and mechanical properties of Mo-N/Cu films produced by inductively coupled plasma reactive sputtering

Mo-N/Cu films were deposited on silicon and steel substrates by inductively coupled plasma sputtering using Mo-Cu alloy targets having different Cu concentrations. The structure and mechanical properties of the Mo-N/Cu films were investigated. The (200)-oriented γ-Mo₂N-Cu films were obtained at a nitrogen flow rate higher than 1.5 sccm, whereas metallic films were deposited at a nitrogen flow rate lower than 1 sccm. Cu contents in the films increased from 3 at.% to 8 at.% with corresponding increase in Cu concentrations in the target from 5 at.% to 20 at.%. Hardness of the films varied between 19 and 35 GPa as the Cu concentration and nitrogen flow rate were changed. HRTEM and XPS analyses showed that Mo-N/Cu films consisted of γ-Mo₂N grains lower than 10 nm in size and a copper amorphous phase. The minimum value of coefficient of friction (CoF) of the films was 0.17 when the film tested by alumina ball.     

Electrical properties of plasma-deposited polysiloxane and metal/plasma polysiloxane/GaAs structures

Thin films of polymer were grown on metallized glass or GaAs substrates using plasma polymerization of hexamethyldisiloxane ((CH₃)₃SiOSi(CH₃)₃). Results concerning the electrical properties of the polymer sandwiched between two metal electrodes are first reported and then those of metal/(plasma polymer)/GaAs structures are presented. On the basis of their electrical behaviour, the possibility of using plasma polymer films as a passivating layer for III–V compounds is discussed.Step response experiments were carried out on metal/(plasma polymer)/metal structures. Both transient and steady state currents were recorded as a function of the electric field, the temperature, the nature of the electrodes and the applied pressure. At low fields the transient current is produced by dipolar orientation. At higher fields the dielectric response becomes non-linear and a space charge builds up in the films.The steady state behaviour involves electronic transport. It is a bulk-controlled process limited by a Poole-Frenkel mechanism.In the case of metal/(plasma polymer)/GaAs structures the density of states at the polymer-GaAs interface features a U-shaped distribution with a minimum of 10¹² states eV^-1 cm^-2 located 1.1 eV below the conduction band of the semiconductor.     

Structural,electrical and optical properties of CuxS layers produced by reactive r.f. sputtering

Thin films of Cu_xS (0.3–0.5μm thick) were produced by r.f. sputtering using hydrogen and H₂S as additives to the sputter gas argon. The electrical resistivity and the optical properties of the films show marked changes when the concentration of the reactive part of the sputter gas exceeds 1%. These changes correspond to a variation in the chemical composition of the Cu_xS layers. The films are polycrystalline and consist of a mixture crystallographic phases that are not in thermodynamic equilibrium in all of the sputtered layers.     

The structure and mechanical properties of carbon layers formed by crystallization from pulse plasma

The structure of amorphous carbon layers thicker than 10 µm, obtained from a pulse plasma has been studied. Their hardness, friction coefficient and response to the action of a uniaxial force were determined. The conclusions from X-ray diffraction data, especially from the atomic radial distribution, from annealing experiments and from investigation of the mechanical properties are complementary to one another.     

Optical properties of TiNx produced by reactive evaporation and reactive ion-beam sputtering

Thin films of titanium nitride are produced by activated reactive evaporation and reactive ion-beam sputtering. The optical constants n and k are calculated over the wavelength region 400–700 nm and vacuum-to-air changes are investigated. It is found that substantial modification of the optical properties occurs as a result of water sorption and oxidation in the bulk of the films.     

Basic properties of apatite cement containing spherical tetracalcium phosphate made with plasma melting method

Apatite cement (AC) can be injected through syringe and forms apatite mass. Therefore, AC is very useful for a minimally invasive surgical operation aimed for the reconstruction of bone defects. However, injectability of current AC is not satisfactory for its clinical use. In this investigation, therefore, spherical tetracalcium phosphate (s-TTCP) was prepared with plasma melting method and its effect on injectability were evaluated as well as other basic properties of AC. We found much better handling property and injectability when we used s-TTCP as a component of AC (s-AC). For example, cement spread area used as an index of consistency of the s-AC paste was 512 mm2 whereas that of ordinary AC with irregular TTCP (i-AC) was 158 mm2 when powder to liquid mixing ratio was 2.5. However, diametral tensile strength of set s-AC (1.4 MPa) was significantly lower than that of set i-AC (10.7 MPa) when the powder to liquid ratio was 4.0. X-ray powder diffraction analysis revealed limited formation of apatite in the case of s-AC. Although there are some drawbacks, we feel the use of spherical particle is very useful to improve the injectability of AC. Therefore, it is important to find suitable method to prepare spherical powder as the component of AC.     

金刚石膜中黑色缺陷形成过程的计算机模拟

多晶金刚石膜中的黑色缺陷是影响材料光学、电学性能的一种重要缺陷。利用水平集方法对黑色缺陷的形成过程进行了模拟。模拟的基本假设为:黑色缺陷形成的基本条件为相邻晶粒间的晶界环境使活性气体扩散的过程难以进行,形成了一种形如峡谷状的、相邻晶面夹角30°的局部环境。金刚石膜的生长参数α2d值由1.3改变为1.5,在其晶粒表面{11}面上形成孪晶。孪晶的长大促进了黑色缺陷的形成。     

Dense outer layers formed by plasma treatments of silica coatings produced by the sol–gel method

Silica gel coatings prepared by the sol-gel method were subjected to low-temperature plasma treatments in air and argon. This was found to give rise to the formation of a dense outer layer, whose thickness increased with the duration of the treatment and decreased when the pressure in the plasma chamber was reduced. The formation of a dense layer in the coatings was confirmed from measurements of the overall thickness and the refractive index by ellipsometry, and also from TEM examination and light transmission experiments. The coatings were found to contain an uppermost layer of alumina, which was formed through secondary sputtering of aluminium from the electrodes in the plasma chamber. The concentration of alumina in the mixture with silica decreased through the thickness of the coating and became zero at a distance slightly smaller than the overall thickness of the dense layer. The thickness of the dense layer was found to be slightly higher with argon than with air plasma treatments. Whereas the aluminium concentration through the thickness of the coating was the same for the two types of treatment, a carbon residue was found only in the case of argon plasma treatments. The composition of the underlying silica layers was found to correspond to SiO_1.6. This revised version was published online in November 2006 with corrections to the Cover Date.     

Formation of detonation diamond layers on silicon by the aerosol method

An aerosol method for deposition of nanometer-thick layers of detonation diamonds has been developed. Application of a suspension of deagglomerated diamond particles onto substrates from an aerosol provides deposition of small-size drops, with the ultrasonic spraying of the suspension precluding formation of secondary agglomerates of nanodiamond particles in the course of sample drying. The layers are promising for high-precision studies of the structure and chemical composition of the surface of isolated nanodiamond particles.