Showing papers in "Journal of Electronic Materials in 1977"

The effects of CO, water vapor and surface temperature on the conductivity of a SnO2 gas sensor

Abstract: It is shown that the conductivity of a SnO2 gas sensor depends on the concentration of CO and H2O in the atmosphere n which it is placed The experimental data can be explained in a consistent manner by hypothesizing that 1) adsorbed oxygen depletes the surface electron concentration and therefore decreases the conductivity; 2) adsorbed water causes electrons to accumulate at the surface and therefore increases the conductivity; 3) CO increases the conductivity by removing adsorbed oxygen by reacting with it to form CO2; and 4) adsorbed water catalyzes the CO to CO2 reaction

Effect of electron trapping on IGFET characteristics

Abstract: At large applied voltages, electrons flowing from the source to the drain of a n-channel insulated-gate field-effect transistor (IGFET) may gain sufficient energy from the high-field region near the drain to be emitted into the gate insulator layer near the drain junction. The trapping of these hot electrons in the gate insulator results in transconductance degradation and/or threshold voltage shift. There is also evidence of surface-state generation resulting from hot-electron emission into the SiO2 layer. The extent of the resultant transconductance degradation and/or threshold shift depends strongly on the electron trapping characteristics of the gate insulator. For devices having SiO2/Si3N4 as gate insulator, electron trapping is completely dominated by the Si3N4 layer. In this case, channel hot-electron effect results in threshold shift alone. For devices having SiO2 as gate insulator, the trapping characteristics depend on its positive oxide-charge concentration. In this case, channel hot-electron effect results in a combination of transconductance degradation and threshold shift.

Debye temperature and standard entropies and enthalpies of compound semiconductors of the type I-III-VI 2

Abstract: The heat capacities at constant pressure have been measured for CuInSe2, CuInTe2 and AgGaTe2 in the temperature range 1K ≤T≤40K and for CuInS2 and AgInTe2 between 1 K and room temperature. From the low temperature data we derive the following Debye temperatures θD in the limit T → O K: θD(CuInS2) = 273 K, θD(CuInSe2) = 222 K, θD(CuInTe2) = 191 K, θD(AgGaTe2) = 182 K and θD(AgInTe2) = 156 K. A plot of the average atomic heat capacity at constant volume Cv shows that the data scale to one general curve for all 5 compounds considered in this paper. This is, also, true for a plot Cv, i.e., all I-III-VI2 compounds measured thus far deviate similarly from the Debye approximation. By integration of the general curves Cv(T/θD) and θD x Cv(T/θD) we derive tne standard entropies S 0 298 and energies E 0 298 -E 0 0 of 11 compounds of the type I-III-VI2, for which the Debye temperatures are known. The difference between the energies E 0 298 -E 0 0 and enthalpies H 0 298 -H 0 0 is within the error limits of the experimental data (< 1%). The molar S 0 298 and H 0 298 -H 0 0 values for the I-III-VI2 compounds are approximately twice the corresponding molar values for their II-VI isoelectronic analogs. The thermodynamic functions at standard state obtained by integration of the experimental data are all < 10% smaller than the corresponding values estimated on the basis of the Debye approximation.

Heterojunction solar cells of SnO2/Si

Abstract: Heterojunction solar cells (HJSC’s), fabricated by electron beam evaportaion of SnO2 films onto monocrystalline and polycrystalline Si substrates, show conversion efficiencies as high as 9.9%, fill factors of 0.64, and open circuit voltages of 525 mV under AMI simulated irradiation. The SnO2, an n-type semiconductor, acts as a transparent window to solar irradiation and as an antireflection coating of the Si, and it provides the band bending in the Si necessary for photovoltaic conversion. The SnO2 films, nominally 50 nm thick, have conductivities of the order of 103(Ω-cm)−1 so that the film makes a good electrical contact between the junction and the metallic front contacts. Measurements of C−2-V and I-V characteristics are consistent with heterojunction theory, and the data imply an electron affinity of the SnO2 of approximately 0.8 eV greater than the electron affinity of Si. This value limits the open circuit voltage of HJSC’s made on p-type substrates to values too small for useful photovoltaic conversion. The predominant dark current mechanism of units of n-type substrates at room temperature and forward bias in the range of 0.3−0.5 V is electron-hole recombination in the transition region. The experimentally determined activation energy is 0.51 eV, approximately Eg/2. At forward voltages below 0.3 V, multistep tunneling via interband states predominates. The photocurrent apparently depends on interface states through which the photogenerated holes in the Si recombine with electrons in the SnO2.

Solar cells using discharge-produced amorphous silicon

Abstract: Thin film solar cells, ≲ 1 μm thick, have been fabricated in p-i-n and Schottky barrier structures using d.c. and r.f. glow discharges in silane. Conversion efficiencies in the range of 2.5 to 4.0% have been obtained with both structures. The p-i-n cells exhibit built-in potentials of ∼ 1.1 V while the Pt Schottky barrier cells have barrier heights of ∼ 1.1 eV. The dark currents in the p-i-n cells appear to be recombination-limited while the Schottky barrier cells exhibit near-ideal diode characteristics with diode quality factors near unity.

SnSe single crystals: Sublimation growth, deviation from stoichiometry and electrical properties

Abstract: Large SnSe single crystals of high metallurgical quality have been grown by a closed tube vapor phase technique. Hall measurements on annealed and quenched samples were performed to establish the stability range of the compound. The crystals are p-type with hole concentrations between 3 × 1015 and 2 × 1018 cm−3 and mobilities up to 7 × 103 cm /Vs at 77 K.

III-V alloys for optoelectronic applications

Abstract: The energy bandgap values of the 9 binary compounds, 18 ternary alloys and 15 quaternary alloys comprising the family of practical III-V materials can, in principle, provide sources, detectors, and optoelectronic components over a wavelength range between 0.51 and 7.3 μm. The material and metallurgical properties essential to the selection of III-V compounds and alloys for epitaxial opto-electronic devices are reviewed. Emphasis is given to the effects of lattice mismatch between ad joining heteroepitaxial layers, with techniques illustrated for minimizing mismatch effects in practical ternary and quaternary device structures. The most promising applications for III-V heteroepitaxial structures in the emerging fields of fiber optics, integrated optics, and photodetectors are cited.

Doping properties of selected impurities in Hg1−x Cdx Te

Abstract: The doping properties of selected impurities in Hg1-x Cdx Te have been determined. Primary emphasis is on elements from Groups IB and IIIA, expected to substitute on the metal sublattice, and on elements from Groups VA and VIIA, expected to substitute on the Te sublattice. In addition, the behavior of some elements from Group IV as well as behavior of Li has been determined. Impurities were introduced into Hg1-x Cdx Te either by diffusion or during crystal growth. Cu, Ag and Li are fast diffusing acceptors, Ga is a fast diffusing donor, Al and Si are donors which require high diffusion temperature to effect diffusion, P and As are slowly diffusing acceptors and Br is a slowly diffusing donor. Sn appears to be inactive. In general, impurities substituted on the metal sublattice are rapid diffusers while those substituted on Te sites are slow diffueers.

Some prospective applications of silicon electrodeposition from molten fluorides to solar cell fabrication

Abstract: Electrodeposition of both epitaxial and polycrystalline continuous films of dense, coherent, and well-adherent silicon coatings was achieved from molten fluorides. A dissolving Si anode and an operating temperature of about 750 C were utilized. Silicon electrocrystallization epitaxy (ECE) produced films with the (111) orientation on Si substrates of the same orientation. The unintentionally doped films were of p-type character with a resistivity in the range 0.05 - 0.10 Ω-cm. Polycrystalline Si films were similarly electroplated onto various polycrystalline metal substrates. Uniform coherent, and well-adherent coatings with grain diameters as large as 40 – 50 µm were obtained. The useful rate of electrodeposition of Si could be significantly increased by the application of an alternating square wave pulse (ASWP)2technique. Cathodic current pulses as high as 300 mA/cm2 (growth rate of about 5 µm/min) were demonstrated. The cathodic current efficiencies, for all modes of growth, were about 70 – 100%. The effects of the various operating parameters, and some prospective applications to the fabrication of solar cells, are discussed.

Analysis of the solidus lines for PbTe and SnTe

Abstract: Experimental values of p-n, PTe 2, and T along the solidus lines of PbTe and SnTe, and for compositions within the homogeneity range of SnTe are fit using the simple model of a nondegenerate semiconductor compound containing fully-ionized native defects. As a result values for the intrinsic material parameters of these compounds at high temperature are obtained as well as some indication of the uncertainty in these.

Application of thermal analysis

Abstract: The evaluation of molding compounds is generally based on the performance of encapsulated semiconductor devices under specific sets of environmental conditions. Testing under these conditions may require several months. To reduce the evaluation time to a few days, tools and techniques which enable some prediction of encapsulation material’s behavior on the basis of certain characteristics, have been developed by thermal analysts techniques. The instrumentation consists of a DuPont 990 Analyzer equipped with a Differential Scanning Calorimeter (DSC) and a Thermo-gravimetric Analyzer coupled to a Gas Chromatograph. Other commercial equipment is available for this testing. Thermo-gravimetric analysis was used to evaluate the thermal stability of four (4) types of epoxy molding compounds. The types and relative amounts of organic constituents are determined by gas chromatography analysis of the degradation products. Differential scanning calorimeter thermograms are used to characterize the behavior of molding compounds during polymerization. The first exotherm, which is characteristic of cross polymerization, is used for determining shelf life, pelietizing, preheating, and molding process conditions. The second major exotherm reaction, which is characteristic of the degradation mechanism, is used to evaluate the effect of post curing conditions and, in addition, is used to identify the type of resin used in the formation of the moldings compounds.

Electric current controlled liquid phase epitaxy of GaAs on N+ and semi-insulating substrates

Abstract: Electric current controlled liquid phase epitaxy (LPE) of GaAs has been performed on both n+ and semi-insulating substrates. Growth is induced by current flow across the substrate-melt interface. The furnace temperature is held constant during growth so that direct electrical control of the growth process is achieved. The dependence of the growth rate on both the electric current density across the substrate-melt interface and the ambient furnace temperature was determined. Current densities from 5 to 20 A/cm2 were employed and furnace temperatures ranging from 680 to 800°C were used. Sustained steady state growth rates as small as 0.022μm/min and as large as 1.4μm/min were obtained. For a given furnace temperature and current density, the measured growth rates on semi-insulating substrates range from 48% to 77% of the rates obtained on n+ n substrates. The surface morphology of the epitaxial layers is observed to depend on the electric current density employed during growth. Electric current controlled doping modulation was studied in epitaxial layers grown from unintentionally doped melts. The degree of doping modulation achieved is approximately proportional to the change in applied current density. Approximately a 40% increase in the net electron concentration is obtained by changing the current density from 10 to 30 A/cm2 during growth. Preliminary experiments with tin doped epitaxial layers indicate that similar changes in the amount of tin incorporation can be achieved.

Temperature-gradient lpe growth of Pbl-x Snx Te

Abstract: An apparatus has been constructed for liquid-phase epitaxy that permits the application of a strong temperature gradient normal to the substrate-solution interface with minimal, unwanted gradients in other directions. A morphology problem with growth of Pbl-xSnxTe alloys on PbTe substrates slightly misorientated from the (100) plane has been used to test the induced temperature gradient growth. No improvement is found over growth with a conventional LPE slider, and very large gradients cause a deterioration in morphology and growth stability. A small systematic variation of the Sn/Pb ratio in the grown layers with rate of cooling is found, but no variation with temperature gradient can be detected. Thus, contrary to our conjecture made before this study, the presence or absence of an induced temperature gradient cannot be used to explain the systematic differences between the data of different workers for the liquid-solid tie-line behavior of the Pb-Sn-Te system.

Effect of externally applied pressure on zinc oxide varistors

Abstract: A study of the effect of uniaxial pressure on the I-V response of zinc oxide varistors has shown a pressure sensitivity in both prebreakdown and breakdown regions. The general observation is that the conductivity increases with pressure, the effect being more pronounced in the prebreakdown region. Data are in general agreement with the phenomenological model given by Schwertz and Mazenko. Data are also treated on the basis of Schottky barrier and tunneling theories. According to this analysis, the barrier height is found to decrease with pressure.

Tellurium-rich growth and laser fabrication of lead-tin-telluride (Pb 1-x Sn x Te: 0.06<x<0.08)

Abstract: Single crystals of Pb1−x Snx Te (0.06

Liquid phase epitaxial growth of InAsxSbyPl-x-y layers on InAs

Abstract: High quality InAsxSbyPl-x-y quaternary layers, which are lattice matched to InAs, have been grown successfully on InAs substrates by liquid phase epitaxy. Both Graded and constant composition InAsxSbyPl-x-y layers have been grown. In addition, the graded InAsxSbyPl-x-y layer has been used as a buffer layer for the growth of InAsl-xSbx on an InAs substrate.

Proton bombarded double heterostructure LED’s

Abstract: In this paper we report the first experimental results for double heterostructure (DH) Burrus LED’s in which current confinement is achieved by proton bombardment techniques. Both p-type and n-type active layers with carrier concentrations ranging from 1016 cm−3 to 2 × 1018 cm−3 were investigated. Devices with shallow surface bombardments (at 100 keV) were compared to devices with deep bombardments (at 390 keV), which penetrate past the p-n junction. Measurements were made of the shape of the light emitting area, device capacitance, 3 dB bandwidth, external efficiency, and operating reliability. These results have been compared with those obtained from LED’s fabricated from the same crystals with conventional oxide-masking techniques. It has been found that deep proton bombardment provides precise control of the. light emitting area as well as the largest 3 dB bandwidths through reductions in the device capacitance. Comparisons of the output power for the various devices established that the overall device efficiency improved in going from deep to shallow bombardment conditions. However, in all cases, the highest efficiencies were achieved with conventional oxide confinement as a result of enhanced reflection at the SiO2-metal interface. These observations have led to the fabrication of an innovative LED structure which incorporates both oxide-masking for improved efficiency and proton bombardment for improved 3 dB bandwidth. Under operation at 100°C and junction current densities of approximately 3 kA/cm2, the reliability of LED’s with proton bombardment confinement was found to be equal to or better than LED’s with conventional oxide confinement.

Recent advances in the production

Abstract: Emphasis has been directed toward consistent and reproducible fiber characteristics, among them optical attenuation, dispersion, dimensional tolerances, numerical aperture and strength.

Effect of edges on the reliability of GaAs and (AlGa) as heterojunction leds

Abstract: The effect of various diode geometries on the degradation rate of heterojunction diodes with either GaAs or (AlGa)As in the recombination region has been studied. It is shown that GaAs diodes are particularly sensitive to edge-related degradation which varies with the current density J as J3/2. The addition of Al to the recombination region considerably reduces the degradation rate of diodes both with and without exposed edges, and data are reported for Al0.1Ga0.9As stripe-contact edge-emitting structures operating for over 20,000 hours with no change in output at 1000 A/cm2.

The electron trapping behavior of silicon dioxide with ion implanted aluminum

Abstract: The electron trapping behavior of SiO2 films implanted with Al has been studied by Johnson, Johnson, and Lampert1 and they conclude that the trapping is occuring in damage sites resulting from the implantation. They used annealing temperatures up to 600C. We find that the trapping is reduced further as we increase the annealing temperature up to 1050C. We have characterized the traps and find that the predominate traps have cross sections of 1.26 × 10−16 and 1.4 × 10−17cm2. The trapping is proportional to the fluence and is not a strong function of the measuring temperature. The centroid of the trapped charge is close to the centroid of the implanted Al as predicted by the LSS theory6.

Degradation of GaP:N LEDs

Abstract: The degradation of light output with operating time has been studied for nitrogen doped GaP light emitting diodes fabricated from vapor phase epitaxial material. The degradation is found to saturate at a non-zero value of efficiency. The process is characterized in terms of a degradation rate constant and the saturation value of efficiency. The rate is found to be a strong function of current density during operation and to a lesser degree materials parameters such as dislocation density. The saturation value appears to be independent of these parameters.

Formation of secondary phases during crystal growth of Pb 5 Ge 3 O 11

Abstract: Studies of secondary phases formed during the Czochralski growth of lead germanate crystals (Pb5Ge3O11) show that these phases form inclusions in the crystal, thereby reducing its optical quality, and can also cause twinning and cracking. Results of differential thermal analysis, energy dispersive X-ray fluorescence analysis, and X-ray diffraction studies of secondary phases are presented. The narrow stability range for Pb5Ge3O11 shown in the phase diagram, the thermal instability of this compound, and its pronounced supercooling during crystallization suggest that equilibrium conditions are difficult to sustain and that other compounds of the PbO-GeO2 family may form, although Pb5Ge3O11 is melting congruently. It is shown that Pb3GeO5 and PbGeO3, which are both reported to melt congruently, can crystallize during the growth of Pb5Ge3O11 forming inclusions in the crystal. The successful synthesis of these three compounds is reported. The compound Pb3Ge2O7, reported in the literature, is identified as a mixture of Pb5Ge3O11 and PbGeO3. Experimental conditions are presented for growing single phase Pb5Ge3O11 crystals of uniform composition and high optical quality.

Characterization of GaN epitaxial layers using

Abstract: Cathodo luminescence (CL) properties of GaN heteroepitaxial layers, both undoped and Mg-doped, were studied by scanning electron microscopy. The GaN samples examined were grown on single crystal sapphire substrates by vapor phase epitaxy and contained different amounts of Mg. It was found that the CL intensity of a GaN specimen depends on its Mg concentration. As the amount of Mg in the GaN lattice increases, the spectral maximum shifts to longer wavelengths; as the full compensation level is approached, as indicated by an abrupt increase in resistivity, the overall CL intensity decreases to complete extinction. These effects are presumably due to the increased density of recombination centers, predominantly nonradiative, generated by the incorporation of Mg deep level impurities. These results established a basis for the qualitative characterization of the Mg distribution in GaN layers. This technique was applied to GaN metal-insulator (GaN:Mg)-n-type semi conductor (GaN) electroluminescent diodes in order to determine the nonuni formity of Mg distribution in the insulating layer. Relevant CL micrographs indicate that, in some cases, isolated conducting grains are embed-ded in an otherwise insulating matrix. This observation was correlated with specific device characteristics to provide a basis for rationalizing device performance.

Transient phenomena in the sublimation of cadmium sulfide

Abstract: New results on transient effects in basal-surface sublimation of cadmium sulfide and on sublimation morphologies of its basal surfaces are presented and discussed in terms of the terrace-ledge-kink theory of sublimation. In this context, various mechanisms for the stepwise sublimation of II-VI compounds are reviewed. The results are shown to be consistent with activation control of sublimation at the kink sites as influenced by surface charge.

Use of photocurrent-voltage characteristics of mos structures to determine insulator bulk trapped charge densities and centroids

Abstract: A new technique is described for determining the density and centroid of trapped space charge in the oxide layer of metal-oxide-semiconductor (MOS) structures. Photo-current-voltage (photo I-V) characteristics for both the metal-oxide and Si-oxide interfaces are used to determine the internal fields due to bulk trapped charge, and hence its density and centroid. Experimental examples for locating both positive and negative charge are presented. For negative charge, an Al-Si02-W-SiO2-Si structure (MOWOS) with a layer of approximately 1014 W atoms/cm2 deposited 80 A from the Si-SiO2 interface and charged by electronic internal photoemission is investigated. For positive charge, the location of trapped holes generated by 16.85 eV photons or x-rays in the SiO2 layer of an MOS structure under a voltage bias is discussed. The photo I-V technique is compared to others in terms of its direct, rapid, minimally perturbing, low current, and low field characteristics.

Silicon carbide technology for blue-emitting diodes

Abstract: Silicon carbide light-emitting diodes with emission in the blue range of the spectrum have been produced by vapor growth and liquid-phase epitaxy. The technology of devices with a p-type (Al-doped) luminescent layer is described. Emission spectra and efficiency data are presented for two types of diodes.

SOME BULK AND THIN FILM PROPERTIES OF ZrPt3 AND HfPt3

Abstract: Bulk and thin films of ZrPt3 and HfPt3 specimens were prepared and evaluated with respect to their physical and electrical properties. Both thin and bulk specimens showed excellent corrosion resistance and electrical conductivity. In order to evaluate both properties simultaneously a relay contact test in which one pole of a double pole single throw relay was coated with HfPt3 was conducted. Under a resistive load of 7 amps at 110 volts the uncoated pole failed after ∿ 105 cycles. After the same number of cycles the coated pole had not failed and had a contact resistance of approximately one quarter that of the failed contact.

Phase diagram and crystal growth of pseudobinary HgSe-CdSe alloys

Abstract: The liquidus and solidus curves for the pseudobinary HgSe-CdSe system have been determined by differential thermal-arrest measurements, which also show the presence of a peritectic reaction with an invariant temperature of 947.5 ± 4.0°C and a peritectic composition corresponding to a CdSe mole fraction of 0.57. The measured heat of transformation is small and has negligible effect on the shape of the solidus line. The data have been corrected for vapor-pressure effects and analyzed by a thermodynamic non-ideal solution theory that assumes completely miscible solid solutions. The experimental liquidus and solidus data points can be fit with free-energy-of-mixing values of BL = 27570 − 3.09RT and BS = 30930 − 2.93RT for the liquid and solid phases, respectively, where R is the ideal gas constant and T is the absolute temperature. The phase diagram data have been applied to analyze the growth of HgSe-CdSe pseudobinary alloy crystals by the Bridgman and quench-anneal methods, and the crystalline properties of ingots grown by both methods are discussed.

Thermally stimulated discharge in fractional component and moisture effect studies of epoxy encapsulants

Abstract: Thermally stimulated discharge (TSD) is used to characterize fractional components of epoxy encapsulation systems used on semiconductor devices. Previous work is reviewed. Present results based on individual components and component interactions are detailed. Various resin/hardener systems are examined and are not found to be major contributors to TSD structure when balanced by epoxy equivalent weight. Catalyst additions reveal increased TSD structure, especially for low levels. TSD is suggested as a cure indicator for epoxy systems. Moisture is found to resolve thermogram structure, and TSD is found to be a viable method of studying moisture effects.

Charge distribution in the nitride of MNOS memory devices

Abstract: The steady state charge distribution for weakly occupied traps is a universal function of position over most of the nitride, with dielectric constant and Frenkel-Poole coefficient α being the only material parameters. The transient charge distribution for constant current pulses is approximated by truncating the steady state distribution and the resulting relation between charge content and its centroid is used to fit experimental data which provides α-values of a reasonable magnitude. A diffusive component of charge motion during application of alternating polarity voltage pulses is identified, and its diffusion coefficient is related to the Frenkel-Poole emission rate from traps.