Total Impurity Content Research Articles

Impurities in silicon nitride raw materials and correlation with mechanical strength of the hot-pressed body.

Spark-source mass spectrometry was used in order to determine the impurity elements from Li to La in nine commercial samples of Si3N4 raw materials. Total contents of thirty three impurity elements detected from Si3N4 raw powders which were prepared by a reaction of Si and N2 were 1.0 to 2.2wt%. Otherwhile there were few kinds of impurities in samples which were prepared by reactions of pure SiCl4-NH3 and SiO2-C-N2, and total impurity contents was 0.07-0.14%. Three-point bending strength at 1200°C for the hot-pressed body from α-rich powder with 2wt% Al2O3 and 5wt% Y2O3 was decreased with the total impurity contents. Similar correlations were observed between the 1200°C-strengths and respective contents of Ca, Ti or Fe. However the room temperature strength was independent on the total impurity contents. Hot-pressed bodies from β-, α≅β- and amorphous powder showed lower strengths than those expected from the correlation curve for α-rich powder.

High purity GaAs prepared from trimethylgallium and arsine

A study of the sources and control of residual impurities in GaAs grown by metalorganic chemical vapor deposition (MOCVD) is presented. The effects of source purity, growth temperature, and reactor pressure upon residual impurities incorporation are detailed. Far infrared photoconductivity and photoluminescence indicate that C, Si and Zn are the dominant residual impurities in undoped material. It is demonstrated that GaAs with total impurity concentrations as low as 5 × 10 14 cm -3, μ(77 K) = 125,000 cm 2/V · s, can be grown by MOCVD. The conditions for growing such material are detailed.

On the formation of interstitial — Hydrogen clusters in iron

The results of a study of the interaction of H with C and N interstitial solutes in high purity Fe using the technique of magnetic disaccommodation are reported. This method, which is the magnetic analog of the better known internal friction methods, has the sensitivity to allow the study of these intersititial solutes at the ppm (atomic) concentration level. The Fe used in these experiments had a total impurity concentration of less than 100 ppm impurities (by spark source mass spectroscopic analysis) reduced by purification in wet and dry hydrogen atmospheres to less than one ppm as measured by the magnetic disaccommodation method. In these pure specimens, containing about 10 ppm H, only low temperature relaxations in the temperature range 4-40 K which were due to hydrogen clusters were observed. The addition of 50 ppm C solutes to these Fe-H specimens reduced the relaxation amplitudes of these H cluster relaxations and introduced a new low temperature relaxation which was identified as resulting from the tunneling of H around a C interstitial. The addition of 200 ppm of N interstitials to the solid solution completely removed the H cluster relaxations without introducing any new relaxations in the temperature range 4-300 K.more » These observations were interpreted as resulting from the trapping of H interstitials by C and N interstitaials.« less

Purification of Vanadium by External Gettering

Vanadium metal has been purified with respect to carbon, oxygen and nitrogen by allowing these impurities to diffuse to and react with a surface layer rich in titanium. The nitrogen concentration was reduced from 100 ppm to less than 1 ppm, the carbon concentration was reduced from 240 ppm to less than 2 ppm and the oxygen concentration was reduced from 290 ppm to 6 ppm. The resistance ratio was increased from 52 to more than 685, a value that would indicate a total interstitial impurity concentration of 11 ppm. The diamond pyramid hardness was between 44 and 50 after purification. The internal friction peaks due to these interstitial solutes had almost completely disappeared in the purified metal. The purification can be done at any temperature at which the interstitial solutes are able to diffuse rapidly enough. Both 1000 and 1200 °C were found to be satisfactory with somewhat higher purity obtained at 1000 °C. This method is quite versatile and can be applied to specimens more than one cm thick if sufficient time is allowed for diffusion.

Subsurface space charge and surface charge in AgBr microspheres

In contrast to previous studies on AgBr thin films, results are presented here on the effects of ionic space-charge layers in AgBr microcrystals. The method of calculating the space-charge potential is discussed for spheres 0.02 to 2.0 μm in diameter. Using spherical polar coordinates, minimization of the total free energy, and solution of Poisson's equation yield the potential and defect concentration profiles. The potential difference between the surface and the interior of the sphere, i.e., the force which repels electrons away from and drives holes toward the surface, increases with level of divalent-cation impurity and with increasing particle size. From the potential profile within a particle, the total concentration (defects/cm3) of excess positive charge within the sphere and the balancing negative surface charge (defects/cm2) can be calculated. The total concentration of interstitials and impurities is greater than the vacancy concentration. The concentration of interstitials decreases with increasing particle size, in agreement with the measured ionic conductivity. The surface charge increases with dopant level for any particular particle size and increases with size in the presence of dopants.

Net and total shallow impurity analysis of silicon by low temperature fourier transform infrared spectroscopy

A method for determining net and total shallow impurity concentrations in s silicon by low temperature IR measurements was developed. Calibration factors for quantitative analysis of boron, phosphorus and arsenic were experimentally determined, and estimates for the other shallow impurities were made. Detection sensitivities of better than 5 × 10 11 atoms cm -3 were demonstrated.

Growth of Ga 0.47 In 0.53 As on InP by low-pressure m.o. c.v.d.

The first heteroepitaxy is reported of Ga0.47In0.53As on InP by low-pressure metalorganic chemical vapour deposition (m.o. c.v.d.). Triethylindium (t.e.i.) and triethylgallium (t.e.g) were used as group III sources, and arsine as the group V source. These Ga0.47In0.53As epilayers exhibit high electron mobility (7.74 cm2 V- 1 s-1 for a total impurity concentration of 2.5 × 1016 cm-3 at 300 K) and a photoluminescence efficiency comparable to l.p.e. layers. The lattice mismatch is only Δa0/a0 ≃ 4 × 10-4. Our mobility measurements indicate that m.o. c.v.d. Ga0.47In0.53As is a promising material for microwave device applications.

Effect of titanium, copper and iron on silicon solar cells

The effect of Ti, Cu and Fe on silicon solar cells has been investigated. Ti severely degrades cell performance above a concentration of 10 11 cm −3. The presence of 2 × 10 14 cm −3 Ti results in a 63% loss in cell performance and more than an order of magnitude reduction in carrier lifetime. Ti gives rise to two deep levels in Si at Ev + 0.30 eV and Ec − 0.27 eV. Copper, at concentrations below 10 16 cm −3, has negligible effect on cell performance and carrier lifetime. Above 10 16 cm −3 copper occasionally produces a 10–15% loss in cell performance with a noticeable increase in junction excess current. No recombination centers were found due to Cu, instead considerable precipitation in the starting material was observed. Fe begins to hurt the cell performance above a concentration of 2 × 10 14 cm −3. Iron at 1.7 × 10 15 cm −3 results in 46% loss in cell efficiency and about an order of magnitude reduction in lifetime. Fe induces a deep level in silicon at Ev + 0.4 eV. The active center density, for both Ti and Fe, is only a very small fraction of the total impurity content in the starting silicon wafer.

The effect of strain rate on the tensile flow and fracture of α-uranium

Tensile stress-strain curves have been obtained for two grades of uranium (total impurity content 240 and 400 ppm) in the vacuum-annealed condition and one grade (total impurity content 240 ppm) in the as-received condition at strain rates from 10 −4 to > 10 +3/s. The effect of strain rate on the flow stress at constant strain has been determined and the results have been analysed in terms of the theory of thermally-activated flow. A ductility transition, decreasing ductility with increasing strain rate, was observed in the vacuum-annealed specimens but not in those of as-received material. Metallographic examinations of the deformed specimens were carried out using optical and scanning electron microscopy. Many voids were observed at intergranular sites, the number of such voids increasing with strain rate. The fracture mode, however, remained unaffected by strain rate.

Thermodynamics of polyaddition reactions of silicon and germanium dihydrides with bis(ethynyl) derivatives of silicon and germanium

Diphenyldiethynylsilane (DPS), diphenyldiethynylgermane (DPG), diphenylgermane (DG), e,~-dihydridopolyvinylenediphenylgermyl (PVG), and the copolymer (PVSG) consisting of regu- larly alternating vinylenedlphenylgermyl and vinylenediphenylsilyl units were prepared by the methods of (i, 3). The total impurity content (mole %) of these monomers, foundcalorimetri- cally from the melting point depression, was 1.00  0.01 in DPS, 0.236  0.003 in DPG, and 1.00  0.01 in DG. The elemental analyses of the monomers and polymers supported their for- mulas to within 0.5%. The number average molecular weights Mn, determined by ebulliometry, were 1400 for PVG and i0000 for PVSG. Heat Capacity and Thermodynamic Functions. We used an adiabatic vacuum calorimeter (4) for the measurements of the heat capacity (Cp ~ of DG; this provided an accuracy of 0.2% in Cp ~ in the solid and liquid states. We took the functions H~176 S~ and G~ - H~ in the 0-330~ range from published work for DPS (5), for DPG from (6), and for PVG and PVSG from (7). The calorimeter was charged with 5.3498,10 -3 kg of DG. In 22 series of measurements we got 113 experimental points of Cp~ their scatter about the averaging curve Cp ~ = f(T) did not exceed 0.2%. In this temperature range DG is in the crystalline and liquid states. Its melt- ing point Tm ~ = 239.78  0.01~ and its depression in the sample was AT = 0.341~ Three

Effects of indium on the electrical properties of n-type CdS

Indium doping of nominally pure n-type CdS containing excess Cd can raise the free-carrier concentration by an order of magnitude over the 77–300 °K temperature range even though this increase is only a small fraction of the total concentration of indium impurities included as dopants. At room temperature such doping does not significantly change the mobility from its value in undoped samples. As temperature is lowered toward 77 °K, neutral-impurity-like scattering in the indium-doped samples causes the mobility to become only weakly dependent on temperature. This is in contrast to undoped n-CdS which is dominated by longitudinal polar optical-phonon scattering and piezoelectric scattering that allow the mobility to rise an order of magnitude as temperature is lowered from 300 to 77 °K.

Brittleness of high-chromium ferritic stainless steels

1. Ferritic chromium steels with 10–30% Cr and grain size≥grade 8 with cleanness typical of openmelted steels undergo brittle fracture at room temperature. 2. The use of vacuum melting for high-chromium ferritic steels reduces the concentration of impurities (C+N+O) by an order (total concentration of interstitial impurities drops from tenths to hundredths of one percent), which lowers the transition temperature by 130–170° for steels of grade 8 and 220–295° for steels of grade 4. 3. Raising the chromium content from 10 to 30% in both open and vacuum heats raises the transition temperature additively, which is described by the equation T50=k·% Cr+b. 4. The transition temperature of high-chromium ferritic steels, both open and vacuum heats, increases with the grain size, which conforms with a relationship of the Hall-Petch type: T50=M+N·d−1/2.

High purity LPE InP

Typical LPE InP layers have previously been limited to liquid nitrogen mobilities of 25,000 cm2/ V-sec, which implies a total impurity concentration of 9 × 1015/cm3. Of the donor impurities identified in InP, Si is reported to have the highest segregation coefficient, with a value of 30 at typical growth temperatures of 650–700°C (1) . Because of this large segregation coefficient, and the fact that commercially available In has typical Si concentrations in the 0.1 ppm range, it is necessary to take additional purification steps on LPE starting materials to reproducibly obtain epitaxial layers with total impurity concentrations below the previously mentioned limit. This paper will discuss a novel approach to the problem by employing a baking scheme to reduce Si contamination. Thermodynamics of the SiO2 , H2, Si, H2O system will be considered which lead to a detailed schedule of time-temperature cycles for the removal of Si from an In based melt. Experimental data are presented which corroborates our thermodynamic, model, and which reproducibly yields epitaxial layers with 77°K mobilities in the range of 50,000–67,000 cm2/V-sec, and total impurity concentration below 2 × 1015/cm3 . Limiting factors in obtaining higher purity are discussed and suggestions are made for overcoming this problem.

Structure and morphology of chemical-sprayed CdS films

Chemical spray pyrolysis is a technique for film growth which is of interest because of its potential for very large-scale, inexpensive production of semiconductor materials such as CdS for photoconductor and photovoltaic applications. In this study, CdS films were prepared by spraying ∠0.1-M aqueous solutions of CdCl3 and NH2CSNH2 (thiourea) onto SnO2-coated glass substrates heated to 380°C. The films developed very intricate surface morphologies consisting of a variety of nodular and serpentine structures about 5–10 μm in size. Grain sizes were about 200 nm, with their c-axis generally normal to the local surface. The grain structure and morphology produce very large optical scattering and high effective absorption for wavelengths larger than the CdS band-gap wavelength of 500 nm. Films 3–4 μm thick typically have effective absorption constants of about 500 cm−1 at 1000-nm wavelength. The films were relatively impure, with total impurity contents of about 2 wt. % consisting of reaction products (principally chlorine), impurities picked up from the spray process (oxygen, iron, and others), and mobile glass species (such as sodium and potassium). These impurities may be an important factor in limiting grain size. Electrically, the carrier concentrations are on the order of 1016 cm−3, with mobilities of the order of 10 cm3/V s. Some of the effects of these properties on fabricated CdS/Cu2S photovoltaic devices are discussed.

Effect of trace impurities on hot ductility of as-cast cupronickel alloys

The effect of trace impurity elements on the hot-ductility behaviour of both simple and complex copper-nickel alloys has been investigated using a modified Gleeble apparatus. The elements studied were bismuth, lead, selenium, sulphur, and tellurium added singly and in combination at various levels in the range 1–750 ppm (wt). High strain-rate tensile tests (10S−1) were carried out on the alloys over a range of temperatures during the cooling part of a simulated TIG welding cycle. Ductility was found to decrease progressively as the amount of impurity increased, but recommended safe limits could be specifiedfor simple alloys. Bismuth and tellurium were particularly harmful whereas sulphur was relatively innocuous even at levels as high as 750 ppm. When such elements were present in combination, the ductility was significantly decreased and a simple relationship between ductility and the total trace impurity content of the alloy is produced. This gives reasonable agreement with experimentally determined ductilities of alloys containing two major impurities and of a commercial-purity Cu-10Ni alloy. With more complex alloys the relationship is able to rank alloys of various purities in order of increasing ductility. Significant improvements in ductility in commercial-purity alloys were achieved by using purer melting charges and better melting and casting procedures. Moreover, impurity-alloying-element reactions in such alloys resulted in more severe embrittlement than in simple alloys.

Hydrogen impurity in natural gem diamond

Five natural gem diamonds which included type IA, IB and IIA specimens, have been investigated by ion beam spectrochemical analysis (IBSCA) to determine the total hydrogen impurity concentration in the diamonds. These data were compared with that obtained from other “conventional” techniques such as infrared and ultraviolet absorption spectroscopy, electron spin resonance and transmission electron microscopy (TEM). IBSCA indicated that all the specimens appeared to contain ∼ 1 at. % of hydrogen contrary to the infrared evidence. The highest hydrogen concentration was recorded by a type IB specimen which contained small (∼ 3nm) bubbles. The hydrogen concentration did not correlate with any defect within the specimens, for example the {100} planar faults, and appeared to be a general impurity. No evidence was found to suggest that inclusions were responsible for the impurity.

The morphology of thick evaporated aluminium films and their purity as determined by proton-induced x-ray analysis

Aluminium films of thickness 7–65 μm were vacuum deposited using a 99.999% purity aluminium wire, a composite ceramic boat and a continuous wire feed source. The morphology and the purity of the films were studied at various deposition and wire feed rates. X-ray diffraction and scanning electron microscopy investigations showed that the films grew mostly in a one-dimensional {311} texture orientation and that the surface grain size first increased with deposition rates up to about 100 kÅ min -1 and then decreased. The purity of the aluminium films was studied mainly by proton-induced X-ray analysis with a 4 MeV Van de Graaff accelerator. A total impurity content of about 10 atomic ppm, composed mainly of iron, copper and zinc and in some cases lead, was observed at low and medium wire feed rates. In addition, of the light elements, magnesium was qualitatively detected.

NMR method for quantitative analysis of dilute alloys

The nuclear magnetic resonance (NMR) method is employed for the first time for quantitative analysis of dilute metallic alloys, thereby allowing the non-destructive determination of the concentration of foreign atoms present in a dissolved state in the metal matrix. Valuable information can be obtained on the real structure of given alloys by comparing the dissolved impurity content obtained by NMR measurements and total impurity content determined chemically. The method is based on the measurement of the NMR intensity as a function of dissolved foreign atoms, the NMR signal intensity being measured through the derivative signal amplitude (D) with logD expressed as a linear function of the foreign atom concentration.The slope of the curve depends on the nature of the foreign atom. Sample preparation, apparatus and procedure are described.

Optimization of a tunable far-infrared InSb source

Recombination radiation from Landau states in impact ionized n-InSb provides a magnetically tunable far i.r. source. Investigations in order to optimize the emission intensity and linewidth are performed. The radiation is studied in dependence of the electric and magnetic field the total impurity concentration and the sample geometry. Donor spectroscopy on high purity n-GaAs is demonstrated with a resolution of 3 cm −1.

An analysis of the distribution of defects in a two-stage tight binding model for Al-In alloys

It has been shown previously that the isochronal recovery of dilute binary alloys of In in Al is consistent with the concept of a two-stage tight binding model which, in its simplest form, assumes the existence of single vacancies, isolated impurity atoms, bound mixed pairs, and triplets consisting of two vacancies and one impurity atom. The expressions relating the equilibrium concentrations of these defects are solved, and the two measured binding energies are used to calculate the distributions of defects as a function of total impurity and vacancy content of the alloy and of temperature. Comparison of the form of these calculated distributions with the pertinent isochronal recovery stages observed in dilute alloys of In in Al is quite satisfactory and, hence, is taken as supporting evidence that the model is a valid representation of dilute alloys of this and similar systems in which there is a strong interaction between vacancies and impurity atoms.