Electrical properties of evaporated polycrystalline Ge thin-films

Electrical properties of Ge thin films evaporated on Si₃N₄ CVD-coated Si substrate were improved by introducing a heat treatment after the deposition of Ge films. Evaporation conditions were optimized by changing the substrate temperature and deposition rate, and then, heat treatment was performed. At substrate temperatures during the evaporation lower than 300 °C and higher than 400 °C, deposited films were amorphous and polycrystalline, respectively. At substrate temperatures lower than 400 °C, Ge films were evaporated without degrading the surface roughness. The Hall mobility of films evaporated at room temperature increased with increasing the substrate and heating temperature and showed about 400 cm² V⁻¹ s⁻¹ for the hole concentration of 4 × 10¹⁷ cm⁻³ at the heating temperature of 900 °C. This value was almost comparable to that of p-type Ge single crystal.     

Effects of temperature,thickness and atmosphere on mixing in Au-Ti bilayer thin films

The interdiffusion and intermetallic compound formation of Au-Ti bilayer thin films annealed at 125 to 350 °C have been investigated. The bilayer thin films were prepared through electron beam deposition at comparatively low temperature. The interdiffusion of annealed specimens was examined by measuring electrical resistance and the depth-composition profile, and by observation using a transmission electron microscope. Interdiffusion between the thin films was detected at temperature above 175°C in a vacuum of 10^–4 Pa. The starting temperature at which interdiffusion occurred decreases with lowering annealing vacuum. The intermetallic compounds AuTi, Au₄Ti, Au₂Ti and Ti₃Au form during annealing at over 250 °C. The activation energies of Au in Ti and Ti in Au obtained by the penetration depth are approximately 0.45 and 0.41 eV, respectively. These measurements indicate that the diffusion is controlled by a short-circuit mechanism. The diffusion of Ti species in Au depends on the annealing vacuum and Au thickness.     

Auger electron spectroscopy of high-speed-deformed Ni/Cu layers

Ni/Cu double- and multilayers subjected to high-speed deformation were investigated by Auger electron spectroscopy (AES) using depth profiling. Ni and Cu thin films were alternately deposited on a 0.3 mm thick Ni substrate using RF magnetron sputtering. The thickness of the double-layer was 90 nm, while that of the multilayer was 160 nm. High-speed compression was performed using bullet masses from 30.0 to 57.4 g at varying bullet speeds between 16.8 and 48.5 m s⁻¹. The strain rate ranged from 6.7×10⁴ to 8.4×10⁵ s⁻¹. Upon high-speed deformation, the thickness of the Ni/Cu double-layer was reduced to about 80% of its original value. The Cu thin film was compressed to a greater extent relative to the Ni thin film (by about 15%), which may be due to the difference in malleability between the two metals. At a strain rate of 8.4×10⁵ s⁻¹, the Ni/Cu double-layer virtually disappeared. Ni/Cu interdiffusion was enhanced by high-speed deformation. The degree of interdiffusion appeared to be greater at lower strain rates. Cu_0.5Ni_0.5 and Cu_0.75Ni_0.25 thin film alloys formed in the high-speed-deformed multilayer sample, indicating that high-speed compression could potentially be used to prepare thin film metal alloys.     

Deformation behavior and microstructural evolution during the semi-solid compression of Al–4Cu–Mg alloy

The effects of the process parameters, including deformation temperature and strain rate, on the deformation behavior and microstructure of an Al–4Cu–Mg alloy, have been investigated through isothermal compression. Experiments were conducted at deformation temperatures of 540 °C, 560 °C, and 580 °C, strain rates of 1 s⁻¹, 1×10⁻¹ s⁻¹, 1×10⁻² s⁻¹, and 1×10⁻³ s⁻¹, and height reductions of 20%, 40%, and 60%. The experimental results show that deformation temperature and strain rate have significant effect on the peak flow stress. The flow stress decreases with an increase of deformation temperature and/or a decrease of the strain rate. Above a critical value of the deformation temperature, the flow stress quickly reaches a steady value. Experimental materials A and B have equiaxed and irregular grains, respectively, prior to deformation. The microstructures vary with the process parameters in the semi-solid state. For material B, the irregular grains transform to equiaxed grains in the process of semi-solid deformation, which improves the deformation behavior.     

Direct liquid injection metal-organic chemical vapor deposition of HfO2 thin films using Hf(dimethylaminoethoxide)4

Hf(OCH₂CH₂NMe₂)₄, [Hf(dmae)₄] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO₂). Hf(dmae)₄ is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO₂ film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO₂ film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO₂ thin film annealed at 800 °C was 2.2×10⁻⁶ A/cm² at 5 V.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

Physics of very thin ITO conducting films with high transparency prepared by DC magnetron sputtering

The preparation of very thin indium tin oxide (ITO) films with extremely high transparency and suitable resistivity, as well as resistivity stability for long term use, is described. In order to obtain these properties, amorphous suboxide films were first prepared and then annealed. Suboxide films with a thickness of 20 to 30 nm were prepared on PET film and glass substrates at a temperature of 60 °C using In₂O₃---SnO₂ targets with a SnO₂ content of 0 to 10 wt% by DC magnetron sputtering in a pure argon gas atmosphere. The films were annealed at a temperature of 150 °C for 1 to 100 h in air. The resistivity of films on PET films was, depending on the SnO₂ content, on the order of 10⁻³ ω cm. An average transmittance above 97% in the visible wavelength range and a resistivity of about 4 × 10⁻³ ω cm, as well as resistivity stability, were attained in ITO films with a SnO₂ content of about 1 wt% prepared on PET films by the low-temperature process. It is thought that these properties result from crystallization which occurred during the annealing, duration up to about 25 h.     

Highly conducting indium tin oxide (ITO) thin films deposited by pulsed laser ablation

Highly conducting and transparent indium tin oxide (ITO) thin films were prepared on SiO₂ glass and silicon substrates by pulsed laser ablation (PLA) from a 90 wt.% In₂O₃-10 wt.% SnO₂ sintered ceramic target. The growths of ITO films under different oxygen pressures (P_O2) ranging from 1×10⁻⁴–5×10⁻² Torr at low substrate temperatures (T_s) between room temperature (RT) and 200°C were investigated. The opto-electrical properties of the films were found to be strongly dependent on the P_O2 during the film deposition. Under a P_O2 of 1×10⁻² Torr, ITO films with low resistivity of 5.35×10⁻⁴ and 1.75×10⁻⁴ Ω cm were obtained at RT (25°C) and 200°C, respectively. The films exhibited high carrier density and reasonably high Hall mobility at the optimal P_O2 region of 1×10⁻² to 1.5×10⁻² Torr. Optical transmittance in excess of 87% in the visible region of the solar spectrum was displayed by the films deposited at Po₂≥1×10⁻² Torr and it was significantly reduced as the P_O2 decreases.     

Thermal reliability of n-GaAs/Ti/Pt/Au Schottky contacts with thin Ti films for reduced gate resistance

The thermal stability of Ti/Pt/Au Schottky contacts on n-GaAs with Ti films 0–60 nm is investigated. The contacts with Ti films as small as 10 nm remain thermally stable with annealing up to 400°C. The changes induced by thermal treatment in the electrical characteristics of the contacts are correlated with the Rutherford backscattering and microscopic analysis of the annealed samples. It shows profuse interdiffusion and interfacial reaction with 300°C anneal for the GaAs/Pt/Au system. It has been found that introducing the Ti film between GaAs and Pt/Au, the interdiffusion of Pt and Au is also prevented. These results are useful for reducing the gate metallisation resistance of metal semiconductor field effect transistors.     

Deep levels in GaInAs grown by molecular beam epitaxy and their concentration reduction with annealing treatment

X-ray diffraction (XRD), current–voltage (IV), capacitance–voltage (CV), deep-level transient Fourier spectroscopy (DLTFS) and isothermal transient spectroscopy (ITS) techniques are used to investigate the thermal annealing behaviour of three deep levels in Ga_0.986In_0.014As heavily doped with Si (6.8 × 10¹⁷ cm⁻³) grown by molecular beam epitaxy (MBE). The thermal annealing was performed at 625 °C, 650 °C, 675 °C, 700 °C and 750 °C for 5 min. XRD study shows good structural quality of the samples and yields an In composition of 1.4%. Two main electron traps are detected by DLTFS and ITS around 280 K, with activation energies of 0.58 eV and 0.57 eV, capture cross sections of 9 × 10⁻¹⁵ cm² and 8.6 × 10⁻¹⁴ cm² and densities of 2.8 × 10¹⁶ cm⁻³ and 9.6 × 10¹⁵ cm⁻³, respectively. They appear overlapped and as a single peak, which divides into two smaller peaks after annealing at 625 °C for 5 min.

Annealing at higher temperatures further reduces the trap concentrations. A secondary electron trap is found at 150 K with an activation energy of 0.274 eV, a capture cross section of 8.64 × 10⁻¹⁵ cm² and a density of 1.38 × 10¹⁵ cm⁻³. The concentration of this trap level is also decreased by thermal annealing.     

Precipitation of Cu in Fe–Cu alloys by high-speed deformation

The differences between defect structures in Fe–Cu alloys deformed at the high (4.3×10⁵ s⁻¹) and the low strain rate (67 s⁻¹) were studied. Positron lifetime and coincidence Doppler broadening (CDB) measurements were carried out to investigate the formation of vacancy clusters and Cu precipitates. Both the size of vacancy clusters and the total amount of vacancy-type defects were larger after high-speed deformation at room temperature. Cu precipitation in the specimen deformed at the high-speed stopped for 10 h after annealing at 400 °C, while that in the specimen deformed at the low-speed continued for 100 h. Transmission electron microscopy (TEM) observations showed a heterogeneous distribution of dislocations in the case of low-speed deformation but a homogeneous distribution in the case of high-speed deformation. These results suggested that the sink efficiency for defects was higher in the specimen deformed at the high-speed.     

Effect of dynamic strain ageing on the deformation behavior of Incoloy alloy MA956

Incoloy alloy MA956 is an oxide dispersion hardened ferritic stainless steel produced by powder metallurgy. It is used as a candidate material for the high temperature components of gas turbines. This material underwent dynamic strain ageing at 300–400°C and strain rate of 1.2 × 10⁻³ s⁻¹. The following features of dynamic strain aging were observed: serrated flow at 300 and 400°C, a peak in the ultimate tensile strength normalized by the elastic modules versus temperature curve at 400°C, a plateau in the 0.2% offset yield stress-temperature curve at 300–400°C, a peak in the deformation rate-temperature curve at 300°C and the elongation-temperature plot showed a minimum at 400°C associated with shear fracture and with a minimum in the reduction in area-temperature plot. These features of dynamic strain ageing were discussed in the view of the recent models of dynamic strain ageing. The effect of dynamic strain ageing on the deformation and fracture behavior of this material was discussed.     

The effect of rapid thermal annealing on structural and electrical properties of TiB2 thin films

This work reports on the effect of post-deposition rapid thermal annealing on the structural and electrical properties of deposited TiB₂ thin films. The TiB₂ thin films, thicknesses from 9 to 450 nm, were deposited by e-beam evaporation on high resistivity and thermally oxidized silicon wafers. The resistivity of as-deposited films varied from 1820 μΩ cm for the thinnest film to 267 μΩ cm for thicknesses greater than 100 nm. In the thickness range from 100 to 450 nm, the resistivity of TiB₂ films has a constant value of 267 μΩ cm.

A rapid thermal annealing (RTA) technique has been used to reduce the resistivity of deposited films. During vacuum annealing at 7 × 10⁻³ Pa, the film resistivity decreases from 267 μΩ cm at 200 °C to 16 μΩ cm at 1200 °C. Heating cycles during RTA were a sequence of 10 s. According to scanning tunneling microscopy analysis, the decrease in resistivity may be attributed to a grain growth through polycrystalline recrystallization, as well as to an increase in film density.

The grain size and mean surface roughness of annealed films increase with annealing temperature. At the same time, the conductivity of the annealed samples increases linearly with grain size. The obtained results show that RTA technique has a great potential for low resistivity TiB₂ formation.     

Chemical effect of CH4 implantation into iron, nickel and aluminum thin films

Polycrystalline thin films of iron, nickel and aluminium were bombarded with CH₄⁺ ions in the dose range from 1 × 10¹⁶ to 1.2 × 10¹⁸ ions cm⁻² at room temperature and with energies between 15 and 50 keV. The formation of carbides was indicated in the cases of both iron and nickel from high voltage transmission electron micrographs and selected area diffraction patterns. No such compound formation in the case of aluminium could be detected. The carbides of iron and nickel were found to be stable on annealing up to 350 °C for 2 h.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Atomic-layer doping in Si by alternately supplied PH3 and SiH4

Atomic-layer doping of P in Si epitaxial growth by alternately supplied PH₃ and SiH₄ was investigated using ultraclean low-pressure chemical vapor deposition. Three atomic layers of P adsorbed on Si(100) are formed by PH₃ exposure at a partial pressure of 0.26 Pa at 450°C. By subsequent SiH₄ exposure at 220 Pa at 450°C, Si is epitaxially grown on the P-adsorbed surface. Furthermore, by 12-cycles of exposure to PH₃ at 300–450°C and SiH₄ at 450°C followed by 20-nm thick capping Si deposition, the multi-layer P-doped epitaxial Si films of average P concentrations of 10²¹ cm⁻³ are formed. The resistivity of the film is as low as 2.4×10⁻⁴ Ω cm. By annealing the sample at 550°C and above, it is found that the resistivity increases and the surface may become rough, which may be due to formation of SiP precipitates at 550°C and above. These results suggest that the epitaxial growth of very low-resistive Si is achieved only at a very low-temperature such as 450°C.     

Preparation and characterization of Bi2Ti2O7 thin films by chemical solution deposition technique

Transparent and crack-free Bi₂Ti₂O₇ thin films with strong (111) orientation were successfully prepared on n-Si(100) by chemical solution deposition (CSD) using bismuth nitrate and titanium butoxide as starting materials. The structural properties were studied by X-ray diffraction. The dielectric constant at 100 kHz at room temperature was 118 and loss factor was 0.074, for a 0.4-μm-thick film annealed at 500°C for 30 min. The leakage current density was 4.06×10⁻⁷ A/cm² at an applied voltage of 15 V.     

Low temperature UV/ozone oxidation formation of HfSiON gate dielectric

Physical and electrical properties of hafnium silicon oxynitride (HfSi_xO_yN_z) dielectric films prepared by UV ozone oxidation of hafnium silicon nitride (HfSiN) followed by annealing to 450 °C are reported. Interfacial layer growth was minimized through room temperature deposition and subsequent ultraviolet/ozone oxidation. The capacitance–voltage (C–V) and current–voltage (I–V) characteristics of the as-deposited and annealed HfSi_xO_yN_z are presented. These 4 nm thick films have a dielectric constant of 8–9 with 12 at.% Hf composition, with a leakage current density of 3×10⁻⁵ A/cm² at V_fb+1 V. The films have a breakdown field strength >10 MV/cm.     

Dislocation structures introduced by high-speed deformation in bcc metals

Systematic experiments were carried out over a wide range of strain rate, 10⁰–10⁶ s⁻¹, so as to reveal the deformation mode in bcc crystals, especially at high strain rate. Dislocation structure showed heterogeneous distribution at low strain rates in all three bcc metals examined. At higher strain rates exceeding 10³ s⁻¹, distribution of dislocations was random, and the formation of small dislocation loops was observed in V and Nb. In Mo, small dislocation loops were not formed by deformation, even at high strain rates. However, post-deformation annealing of an Mo specimen that had been deformed by 20% at 5×10⁵ s⁻¹ produced dislocation loops. The inside–outside contrast method identified these loops to be of vacancy type. These results reveal that in Mo vacancy clusters are not formed directly from the interaction of dislocations, but by the aggregation of vacancies. In V and Nb, the same formation process is believed to occur at high strain rates. These results suggest that the different mode of plastic deformation at high strain rates accompanied by production of vacancies also occurred in bcc metals.     

Structural, electrical, and optical studies on rapid thermally processed ferroelectric BaTiO3 thin films prepared by metallo-organic solution deposition technique

Polycrystalline BaTiO₃ thin films having the perovskite structure were successfully produced on platinum coated silicon, bare silicon, and fused quartz substrate by the combination of the metallo-organic solution deposition technique and post-deposition rapid thermal annealing treatment. The films exhibited good structural, electrical, and optical properties. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) and metal-ferroelectric-semiconductor (MFS) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 255 and 0.025, respectively, and the remanent polarization and coercive field were 2.2 μC cm⁻² and 25 kV cm⁻¹, respectively. The resistivity was found to be in the range 10¹⁰–10¹² Ω·cm, up to an applied electric field of 100 kV cm⁻¹, for films annealed in the temperature range 550–700 °C. The films deposited on bare silicon substrates exhibited good film/substrate interface characteristics. The films deposited on fused quartz were highly transparent. An optical band gap of 3.5 eV and a refractive index of 2.05 (measured at 550 nm) was obtained for polycrystalline BaTiO₃ thin film on fused quartz substrate. The optical dispersion behavior of BaTiO₃ thin films was found to fit the Sellmeir dispersion formula well.