High-resistivity Films Research Articles

Location Of Residual Donors In GaN Epitaxial Layers

AbstractOptically-detected electron-nuclear double resonance (ODENDOR) studies at 24 GHz on high-resistivity GaN films grown on Al2O3 have been combined with x-ray diffraction measurements to obtain information on the location of the residual shallow donors. Strong ODENDOR assigned to 69,71Ga lattice nuclei was detected on the g=1.951 effective-mass donor resonance found on the 2.2 eV emission bands. The x-ray studies reveal that the layers are under biaxial compression with high values of strain (∼ 2–3 × 10−3). The quadrupole splittings for 69Ga are smaller than those reported for strain-free samples by 15–25 %. The dominant sources of the local electric field gradient (EFG) responsible for the splittings are attributed to the wurtzite crystal structure and the strain fields that arise from the lattice constant mismatch and the difference in thermal expansion coefficients. An EFG/strain relationship of 3 × 1022 Vm−2 per unit strain at the 69,71Ga nuclei is deduced. The ODENDOR can be described with asymmetry parameter η=0. This provides evidence that the donors are in the crystallites rather than near grain boundaries.

Ozone in reactive gas for producing tin-doped indium oxide films by DC reactive magnetron sputtering

We propose ozone (O 3) as a reactive gas for producing tin-doped indium oxide (ITO) films by DC reactive magnetron sputtering using a metallic alloy target for the first time. We show that incorporation of O 3 enhanced the reaction with the sputtered metal atoms on the substrate surface at room temperature due to its powerful oxidizing nature. The effect of O 3 in oxygen (O 2) gas on the properties of the ITO films was investigated. It is found that high transparency and low resistivity film can be fabricated at high deposition rates and low substrate temperatures by using ozone in oxygen gas.

Additive double gate analysis in photoinduced current transient spectroscopy: Application to cuprous oxide

AbstractPhotoinduced current transient spectroscopy, in its conventional doublegate version, has been used extensively in the characterization of deep levels in semiinsulating materials. The analysis of the digitally captured transient signals by the post capture double gate method is a parallel technique with much more advantages. One of the drawbacks of the latter is, of course, the excessive time needed to capture data with a high signal‐to‐noise ratio. We have shown that the capturing time can be chosen tobe relatively low and the signal‐to‐noise ratio can be improved by a post capture data analysis referred to as the additive double gate analysis. The usefulness of this approach is demonstrated by the results obtained, for the first time, on high resistivity films of cuprous oxide. Thetechnique leads to the identification and measurement of the parameters of a few deep levels. The apparent activation energies of these levels are 0.33, 0.47, 0.49, and 0.59 eV. The corresponding capture cross sections are 2 × 10−17, 7 × 10−12, 1 × 10−15 (7 × 10−13), and 4 × 10−15 cm2, respectively.

The capacitance of Pt/Pb0.65La0.28Ti0.96O3/Pt structures

The capacitance/voltage characteristics of thin paraelectric lead lanthanum titanate films are measured using platinum electrodes. The films have a maximum capacitance when either a small positive or negative bias voltage is applied. This characteristic is consistent with the electrode interfaces acting as Schottky-like barriers. The voltage at which the capacitance maxima occur increases linearly with film thickness indicating that the film is highly resistive. On the basis of the high apparent film resistance it is proposed that the voltage dependence of the capacitance of the electrode interfaces arises from the ionization of deep level traps within the film and not from depletion layers associated with shallow donor or acceptor states. Application of voltages larger than about 2–3 V results in the disappearance of the capacitance maxima indicating that irreversible changes in the electrode interfaces occur at higher electric fields.

無電解析出法による高比抵抗ＮｉＰ皮膜の作製とその特性

High-resistivity NiP films were prepared by electroless deposition while varying the complexing agent species. When complexing agents having -NH2 and=NH groups, e. g., amino acids or amines are used for the NiP bath, higher resistivity NiP films are obtained with electroless deposition. Complexing agents of β-alanine, diethylenetriamine, and sodium L-glutamate were most suitable making higher resistivity NiP films. The highest resistivity was obtained from a diethylenetriamine bath. The resistivity of NiP as-deposited film from a diethylenetriamine bath is 5, 400μΩcm, compared to 160μΩcm for usual NiP films. The most suitable NiP film from the diethylenetriamine bath shows resistivity stable against annealing at about 400°C. High specific resistivity films were found to contain a small amount of carbon. The NiP film from the diethylenetriamine bath contained ca. 3at% carbon, and exhibited a grain structure even at the amorphous state.

電子シャワー法によるＡＩＮ薄膜の作製

When AlN thin films are applied to surface acoustic wave (SAW) devices, c-axis oriented films and a-axis oriented films are necessary for the longitudinal wave and transversal wave, respectively. In general, when AlN thin films are prepared by sputtering and ion plating methods, the crystallographic orientation is dominantly c-axis; it is difficult to prepare films with an a-axis orientation.In this study, AlN thin films were prepared by a new PVD method: the electron shower. It was found that a-axis orientation films could be prepared readily. The crystallographic orientation varied from a-axis to c-axis when the substrate voltage was changed from +20V to -400V. A high hardness (Hv 2200), high electrical resistivity (1013Ωcm) film was obtained at -200V.

Magnetic Resonance Studies of High-Resistivity GaN Films Grown on Al2O3

ABSTRACTWe have made an attempt to obtain electronic and atomic structure information on the residual defects that exist in high-resitivity GaN epitaxial layers from optically-detected magnetic resonance (ODMR) experiments performed on the broad 3.0 and 2.2 eV photoluminescence (PL) bands observed from these films. The first observation of magnetic resonance on this 3.0 eV band reveals two ODMR signals. The first resonance is sharp (FWHM ∼ 3.5 mT) with g ∼ 1.950 and is assigned to effective-mass (EM) donors based on previous studies. The second feature is much broader (FWHM ∼18 mT) with a donor-like g-value of ∼ 1.977. This new resonance may be associated with partially EM-like donor states located ∼ 54 - 57 meV below the conduction band edge proposed recently to be involved in this 3.0 eV PL band.

Chemical vapor deposition TiN process for contact/via barrier applications

Chemical vapor deposition (CVD) TiN is an attractive replacement for PVD TiN as a barrier and glue layer for subhalf-micron contacts and vias. CVD TiN films have been deposited in a commercial reactor via the thermal decomposition of tetrakis-dimethyl-amino-titanium (TDMAT) precursor in an N2 ambient. The deposition can be characterized by a simple Arrhenius rate expression with a half-order dependence on TDMAT concentration and an activation energy of 0.53 eV. Designed experiments show that the deposition transitions from being kinetically limited at high TDMAT flow rates and low temperatures to transport limited at the other extreme. In the kinetically limited regime, the deposition rate increases with increasing TDMAT mole fraction and increasing temperature. Step coverage simulations have been performed by coupling SPEEDIE (a profile evolution program) with the Arrhenius rate expression. Experimental and simulated step coverages show good agreement over a wide range of process conditions. Step coverage improves with increasing deposition rate and decreasing temperature. Adequate deposition rates (≳400 Å/min) with good deposition uniformity and high step coverage (50%–85%) can be achieved. Film stress and roughness are mostly invariant with process conditions. These films are close to stoichiometric (i.e., 1:1 Ti:N ratio), but contain up to 30% carbon. Exposure of these films to air causes rapid oxidation with a steady state concentration of 15%–20% oxygen after 24 h of air exposure. The high carbon concentration results in high film resistivity (5000 μΩ cm), which doubles after 24 h of air exposure due to oxidation of the film. Film resistivity decreases and film stability improves with increasing N2 flow rate. Electrical characterization of two process variants have been performed. The first provides a film with 85% step coverage with a resistivity of 5600 μΩ cm, while the second process achieves a lower resistivity of 3700 μΩ cm and a lower step coverage of 50%. Electrical performance of both films is similar. Contact induced diode leakage is lower for CVD TiN compared to PVD TiN. Contact resistance for 100–200 Å CVD TiN is comparable or lower than 500 Å PVD TiN. A 100 Å CVD TiN barrier is adequate; 300 Å CVD TiN is too thick because of high film resistivity. An Al–Cu/100–300 Å CVD TiN/Si stack shows lower resistance increase after 450–500 °C, 30 min N2 anneal compared to a Al–Cu/200 Å PVD TiN/Si stack indicating that CVD TiN is a superior barrier and is more inert than PVD TiN.

DC operated thin filmelectroluminescent device

An improved version of a DC operated thin film electroluminescent device is proposed, which relies heavily on the nature of trapping states in a p--Si/ZnS:Mn heterodiode. Such a junction facilitates charge leakage from the inversion region of the silicon when films of ZnS are grown by sputtering in a sulphur-reduced environment. Alternatively, high resistivity films of ZnS are created by growth in a sulphur-enriched environment. Hence, the proposed structure is reverse biased p--Si/ZnS(grown in Ar/O)/Y2O3/ZnS:Mn(grown in Ar/H2S) and has a transparent electrode. The thin film of Y2O3 prevents diffusion of sulphur vacancies while facilitating electron tunnelling.

Low 1/f normal-state resistance noise in high-resistivity YBa2Cu3Oy films

We have measured 1/f resistance noise at room temperature in laser-ablated YBa2Cu3Oy (YBCO) thin films over a wide range of normal-state resistivities. Surprisingly, the high resistivity films exhibit lower normalized noise powers than the low resistivity films. The lowest normalized noise power is 100 times lower than any previously reported values for single crystals of YBCO and is comparable to the lowest noise levels found in other cuprates. Upon oxygen reduction, the noise power in the high resistivity films increases monotonically whereas it decreases in the low resistivity films. We conclude that the high noise level in YBCO is most likely intrinsic to the structure and due to conduction along the Cu-O chains. Therefore, the low noise power in high resistivity films appears to indicate a degraded chain conductivity.

Polymerization blending for compatible poly(ether sulfone)/aramid blends based on polycondensation of N-silylated m-phenylenediamine with isophthaloyl chloride in poly(ether sulfone) solution

Poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) (PES) and poly( m-phenyleneisophthalamide) (aramid PMIA) were blended readily by the polymerization blending method. That is, N,N′-bis(trimethylsilyl)-substituted m-phenylenediamine was reacted with isophthaloyl chloride in a PES solution in N,N-dimethylacetamide, and the resulting mixture was directly cast into films. The procedure afforded transparent films over the entire PES/PMIA composition range. Homogeneous mixing of the component polymers in the form of films was shown by a single glass transition temperature except for PES/PMIA 80/20, while a conventional solution blending method afforded less compatible blend films. This was also supported by the morphological studies. The tensile modulus and tensile strength of the blend films were improved over the entire PES/PMIA composition range by using the polymerization blending method. The polymerization-blended films had a high elongation at break over a relatively wide composition range from PES/PMIA 30/70 to PES/PMIA 60/40, leading to tough and ductile films. Annealing the blend films afforded high temperature resistant films with high tensile modulus and strength due to both crystallization and partial crosslinking of the aramid component.

Preparation and Characterization of Copper Films Deposited in Hydrogen Remote Plasma by Copper(II) Acetylacetonate

High purity and low resistive copper films are in high demand for ultralarge scale integrated process technology. By remote plasma‐enhanced chemical vapor deposition, high purity Cu films can be prepared using copper(II) acetylacetonate as a source material. Depositions were carried out with three types of flow tubes in order to study the reaction steps of the film formation. It is found that Cu films could be deposited only upon reaction of atomic hydrogen (H*), but not with ultraviolet radiation. Hydrogen remote plasma method makes Cu films damage free from ion impacts and free from contaminants of carbon, oxygen, and others. The resistivities of Cu film measured are about 1.8 μOHgr; cm which is close to the intrinsic value (1.72 μOHgr; cm) of bulk copper.

Excitonic Recombination Processes in Undoped and Doped Wurtzite GaN Films Deposited on Sapphire Substrates

ABSTRACTExcitonic recombination processes in GaN films grown by low pressure metalorganic chemical vapor deposition technique have been studied in the temperature range between 6K to 320K by photoluminescence spectroscopy. Low temperature photoluminescence spectra of high resistivity films show well-resolved spectral features associated with the excitonic interband transitions. A detailed spectral analysis allowed us to estimate the exciton binding energy and the energy gap. Spectral studies of Si-doped GaN films demonstrate that the high energy recombination processes in these films are dominated by excitons bound to neutral Si donors. Comparison between the recombination channels in high resistivity and in Si-doped films indicated that Si has a larger exciton binding energy than the unknown pervasive donor in undoped materials. These results confirm the excellent electronic properties of the undoped and doped films.

High resistivity Co and Ti silicide formation on silicon-on-insulator substrates

Under the condition of excess metal deposition, the formation of Co and Ti silicides on (001) silicon-on-insulator (SOI) substrates was investigated. In the Co silicide case, a high-resistivity Co silicide film was formed after a high temperature anneal (100 °C for 30 s). Transmission electron microscopy (TEM) revealed that the phase formed was CoSi. The phenomenon of CoSi being the most stable phase, instead of CoSi2, at high temperatures can be understood from both kinetics and thermodynamics. In the Ti silicide case, the most dominant phase was C49-TiSi2, therefore the film resistance was high even after high temperature annealing (900 °C for 20 s). The film morphology was thermally stable on further annealing and the resistance decreased gradually by means of partial transformation of C49-TiSi2 to the C54-TiSi2 phase. For device applications, high resistance silicide films are not desirable, therefore the metal thickness and consequent silicide thickness have to be controlled precisely.

Quantum liquid of vortices in superconductors at T=0.

We investigate the existence of a [ital T]=0 quantum melting transition in the vortex system of a type-II superconductor. We find that homogeneous high-resistance thin films are good candidates for the observation of this effect. We calculate both the continuous dislocation-mediated melting line [ital B][sub [ital m]][sup [ital d]]([ital T]) as well as the first-order melting line [ital B][sub [ital m]][sup [ital G]]([ital T]) driven by Gaussian fluctuations and present the resulting [ital H]-[ital T] phase diagram. At low temperatures the melting line [ital B][sub [ital m]][sup [ital G]] extrapolates to a value below the upper critical field, resulting in a quantum liquid state in the region [ital B][sub [ital m]][sup [ital G]][lt][ital B][lt][ital H][sub [ital c]2].

Dependence of material properties of radio-frequency magnetron-sputtered, Cu-doped, ZnTe thin films on deposition conditions

Because of its ability to be doped highly p type, and because its valence-band discontinuity with CdTe is small, ZnTe is believed to have an important use as an interface layer for electrical contacts to crystalline and thin-film CdTe devices. Although this and other potential uses have been identified, relatively little is known about the fundamental properties of ZnTe in its thin-film form, and even less is known about possible effects specific to sputter deposition. In this study, we investigate the effects of deposition conditions on the compositional, electrical, optical, and structural properties of thin-film ZnTe produced by rf-magnetron sputtering. Results indicate that, as is often observed when sputtering high-vapor-pressure compounds, rf-sputtered ZnTe films are slightly Zn deficient. Although this may be undesirable when producing high-resistivity undoped films, it may be advantageous when producing low-resistivity p-type films because it may encourage incorporation of substitutional Group I dopants, such as Cu. We have determined that the choice of deposition parameters can indeed affect the stoichiometry of the sputtered ZnTe film, and that Cu can be used effectively as a p-type dopant. Additionally, we have been able to produce Cu-doped ZnTe with carrier concentrations in excess of 1020 cm−3.

Transverse MIR fast response in PbSe films

Under lightening, anisotropic semiconductor or semimetal films can show large transverse voltage. PbSe and PbS films have a room temperature intense sub nsec response (∼ V/MW) in the 10µm region due to free carrier photon drag, but the effective direct matched response on a 50 Ω impedance is lower (∼ 0.1 V/MW for 1 cm2 film) because of the high film resistance (> KW). CO2 500ps mode locked pulses are easily detected in the scope limit.

Dependence of Photovoltages of Spray‐Deposited Indium Tin Oxide/Silicon Oxide/Silicon Junction Solar Cells on Spray Solvents

The photovoltages of spray‐deposited indium tin oxide/silicon oxide/n‐Si junction solar cells are found to depend strongly on the spray solvents such as methanol, ethanol, ethyl acetate, water, etc. It is also found that the work function of the indium tin oxide (ITO) films is dependent on the spray solvents, and the higher the work function of the ITO films, the larger the photovoltage. X‐ray photoelectron spectroscopy (XPS) measurements indicate that an In‐OH species, probably formed by reactions of the ITO film with the spray solvents, is present in the deposited film in cases where its work function is high. The resistivity of the ITO films produced using the organic spray solvents is in the range of , leading to high fill factors of the solar cells, while that of the films deposited using water as a spray solvent is as high as , resulting in low fill factors. On the basis of the XPS measurements, the high resistivity of the latter ITO films is attributed to a small amount of tin ions in the films. X‐ray diffraction measurements show that the crystal orientation of the ITO films also depends on the spray solvents, indicating that the film formation mechanism varies with the spray solvents. By use of a mixed solvent of , the photovoltage becomes the highest, and the conversion efficiency of 14% is achieved.

Compatibility and Mechanical Properties of Binary Blends Composed of Aromatic Poly(ether sulfone) and Poly(m-phenyleneisophthalamide) by Solution Blending

Poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) (PES) and poly(m-phenylene-isophthalamide) (aramid) were blended by a conventional solution blending method. The PES/aramid solution blended films, prepared by casting from the N,N-dimethylacetamide (DMAc) solution of the two polymer mixtures, exhibited two glass transition temperatures and gave phase-separated translucent or opaque films over the entire PES/aramid composition ranges. The morphology observed by scanning electron microscope also revealed that the blend films had two phase structure with the PES domain dispersed in the aramid matrix. The tensile modulus and tensile strength of the films were somewhat low because of the heterogeneous morphology compared with the component polymer films, while the elongation at break of the blend films increased remarkably, reaching to about 190%, indicative of the tough and ductile films. The annealing of the blend films afforded high temperature resistant films with high tensile modulus and strength due to both crystallization and partial cross-linking of the aramid component.

The photoresponse of high resistance anatase TiO 2 films prepared by the decomposition of titanium isopropoxide

High resistance films of the anatase phase of TiO 2 have been prepared by spray pyrolysis starting with titanium isopropoxide Ti(OPr i) 4. The films were deposited on glass substrates held at 590 K. The TiO 2 films were characterized structurally, optically, and electrically. The photoresponse of these films to prolonged UV radiation in a vacuum and subsequently subjected to O 2, H 2, water vapour, or air environments, has been investigated. When vacuum, O 2 or air is present, the electrical and optoelectronic properties observed can be explained by the induced variations in the oxygen deficiency at the surface of the TiO 2 film and the resulting formation or removal of an enhancement layer at the surface. An equivalent effect on the surface band bending can be induced by an absorbed species. For example, adsorbed water vapour can alter the surface conductance of the films and the result depends on the oxygen-to-titanium ratio present at the surface when the water vapour is introduced.