Showing papers in "Journal of Electronic Materials in 1975"

A study of deep levels in GaAs by capacitance spectroscopy

Abstract: We show how the DLTS capacitance spectroscopy technique can be used to detect small amounts of deep level impurities in GaAs p-n junctions The DLTS spectra associated with Cu, Fe, Cr, 0, and two unidentified but commonly occurring deep levels in GaAs are shown The LPE distribution coefficients are obtained for Cu, Fe, and Cr The carrier capture cross sections for six levels are measured and give evidence for capture by multiphonon emission

Excited state polarization, bulk photovoltaic effect and the photorefractive effect in electrically polarized media

Abstract: Optical absorption in pyroelectric crystals is accompanied by electrical effects (in addition to the well-known pyroelectric effect) which are not present in other materials. Optical excitation between localized states gives rise to an instantaneous macroscopic polarization change due to the change of dipole moment at the absorbing center. Excitation of free carriers from localized states will in general result in a bulk photovoltaic effect due to asymmetric charge transfer. Thus spatially non-uniform illumination gives rise to internal fields, resulting in refractive index variations. Studies of these effects for fast detection, optical logic, memories, and microwave generation will be described.

Bonding and thermal stability of implanted hydrogen in silicon

Abstract: The behavior of implanted hydrogen in Si has been investigated by differential infrared transmittance measurements using multiple-internal-reflection (MIR) plates. Si-H bonding of implanted hydrogen is detected by seven absorption bands between 4.5 and 5.5 µm after implantation with 1016 H+/cm2 at ion energies between 70 and 400 keV. The absorption bands are close in frequency to those for SiH stretching modes for silane, and they are produced only by hydrogen implantation. Implantation with deuterium gave absorption bands shifted to lower frequencies in accord with the square root of the reduced mass ratio for Si-H relative to Si-D.

Mechanism for the high voltage photovoltaic effect in ceramic ferroelectrics

Abstract: The high-voltage photo-emf seen in poled ferroelectric ceramics is explained as the result of light-induced carriers screening an internal field within the bulk of individual grains. The internal field itself is explained as the result of the shielding by equilibrium carriers of the potential produced by the spontaneous polarization. Less-than-band-gap emf’s are produced across individual grains; these emf’s add in ceramics to produce the high-voltage photo-emf. A model yields the polarity and magnitude of the photo-emf, the dependence on temperature, remanent and spontaneous polarization, dielectric constant and grain size. The calculated and experimental results are in general agreement.

Te and Ge — doping studies in Ga1−xAlxAs

Abstract: The temperature dependence in the range 77–400 K of the carrier concentration, resistivity and mobility of a series of n and p-type single crystal, liquid-phase epitaxial layers of Ga1−xAlxAs are presented. These layers were doped, n-type with tellurium, and p-type with germanium to yield carrier concentrations in the range 1017 – 1018cm−3 at 295 K. Donor and acceptor ionization energies, eD and eA, are derived from the data. The dependence of eD on alloy composition is interpreted in terms of the known band structure variation in the alloy system.

Rare-earth-modified Sr 0.5 Ba 0.5 Nb 2 O 6 , ferroelectric crystals and their applications as infrared detectors

Abstract: Rare-earth-modified ferroelectric crystals with the formula (Sr1−xBax)1− 3y/2 RyNb22O6, where R = La, Nd, Sm, Gd, and Lu, have Been prepared and studied. When R = La, Nd, x ≃ .5 and y = 0.02, the modified material, at room temperature, exhibited twice the pyroelectric coefficient and four times the dielectric constant of the unmodified Sr1−xBaxNb2O6 (x ≃ .5). Curie temperatures decreased, dielectric constants increased, while loss factor and detector signal-to-noise ratios remained nearly the same with the addition of rare earth doping. The calculated response based on the measured properties agree with the measured response of actual detectors. These properties suggested that the modified SBN are good materials for small element or array pyroelectric infrared detector applications.

The EFG process applied to the growth of silicon ribbons

Abstract: The development of edge-defined, film-fed growth (EFG) techniques for silicon ribbons has prompted analyses of appropriate die materials, die shapes, meniscus shapes and thermal gradients. The requirement for high electronic quality of the ribbons, in conjunction with the high effective solute distribution coefficients expected for EFG, narrows the choice of die materials primarily to graphite and fused silica. The shape of the meniscus between crystal and die has been calculated. This shape, together with contact angle information, is used to determine design criteria for both graphite and silica dies. The effect of crystal growth on the temperature gradient ahead of the growth interface has been calculated in terms of the ribbon thickness and an empirical parameter characterizing the radiating environment of the growth apparatus. Numerous 25 mm wide × 0.3 mm thick ribbons from carbon dies and a few small ribbons from silica dies have so far been grown. The ribbon quality is discussed.

Microstructure-critical current relationships in hard superconductors

Abstract: The pinning of the flux line lattice (FLL) by crystal lattice defects gives rise to a critical current density Jc for hard superconductors. The volume pinning force density Fp = ‖BXJc‖ however, depends both on the elementary interaction force fp between a single defect and the FLL and on the nature of the summation of these many fp’s. The latter will depend on the spatial arrangement of defects and on the elastic and plastic deformation properties of the FLL. For localized defects the fp is a strong function of defect “size”, reaching a maximum when the size is approximately the coherence length, and is approximately proportional to Hc 2(T) (1−h) where Hc is the thermodynamic critical field and h is the reduced magnetic field H/Hc2. The summation model must give a Fp which obeys the following empirical rules: 1) Fp has a maximum at a reduced field hp which decreases with increasing defect density ρ and f . 2) Fp at h > hp is structure insensitive while Fp at h < hp is structure sensitive. 3) A scaling law is obeyed if T is changed, i.e., Fp = Hc2(T)m .f(h), where m is ∿2.5 andf(h) is only a function of reduced field and microstructure. Experimental evidence for these generalizations is presented and a model which predicts these results is outlined and quantitatively tested.

Laser window materials — An overview

Abstract: The laser window problem is reviewed with emphasis on failure mechanisms, absorption processes, and material evaluation. Failure by thermal fracture and by optical distortion is discussed and the material parameters needed to calculate figures of merit for these failure modes are tabulated for a variety of materials. The exponential dependence of absorption coefficient on wavenumber for intrinsic multi-phonon processes is discussed and its use in discriminating extrinsic from intrinsic absorption emphasized. Laser calorimeter absorption measurements at 10. 6 Μm and 5. 25 Μm are described and the measured values tabulated. The use of internal reflection spectroscopy to examine the effect of various surface treatments on

The application of heterojunction structures to optical devices

Abstract: Basic factors are reviewed that enter into the successful operation of single crystal heterojunction devices, with an emphasis on the role of defects. The devices discussed include laser diodes, solar cells and electron emitters using negative electron affinity surfaces.

Liquid encapsulated czochralski pulling of InP crystals

Abstract: The growth of bulk indium phosphide crystals via liquid encapsulated Czochralski pulling from both stoichiometric and nonstoichiometric melts is described. Nominally un-doped crystals with carrier concentration ND-NA = 6 × 1015 cm−3 and Hall mobilities of 4510 cm2/Vsec at room temperature were grown. Also, we prepared Zn-or Cd-doped p-type crystals in the range 1016 ≤ NA-ND ≤ 1018 cm−3 with Hall mobilities ≤ 130 cm2/Vsec and Sn-doped n-type crystals in the range 4 × 1017 ≤ NA-ND ≤ 1018 cm-3 with Hall mobilities ≤ 2400 cm2/Vsec. The dislocation density of LEC pulled InP crystals is typically ~ 104 cm−2.

Growth and properties of VPE GaP for green LEDs

Abstract: The PH3-HCl-Ga-H2 technique for VPE growth of GaP is described. The influence of various growth parameters, including substrate temperature, orientation, and PH3 flow rate on morphology and growth rate are described. For both VPE and LPE nitrogen doping is known to be a major factor in obtaining high green luminescence efficiency. The major emphasis of this paper is an examination of the effect of nitrogen concentration in the range less than 1019 cm−3 (using the Lightowlers correction factor) on the growth process and materials properties, such as defect structure, photoluminescence spectra (at 300 and 77K) and photoluminescence intensity and lifetime. The LED device performance (B/J and efficiency) is used as the final test of material quality. Nitrogen is found to be incorporated far in excess of the solubility limit, and the solid gas distribution coefficient for nitrogen is found to increase rapidly with decreasing temperature below 840°C . The optimum nitrogen concentration for high diode efficacy, photoluminescence intensity, and lifetime is found to be approximately 5 × 1018 cm−3, where diodes fabricated by Zn diffusion into the VPE GaP have efficiencies at a current density of 10 A/cm2 of 0.1%, comparable to the state-of-the-art in the more widely used grown p-n junctions using LPE.

The gold-silicon phase diagram

Abstract: The temperature and composition of the eutectic reaction in the gold-silicon system have been redetermined. The eutectic temperature was determined by equilibrating specimens containing 2, 4, 6, 8 and 10 at. % silicon at temperatures above and below the eutectic and then quenching them into iced brine. Each one was then examined metallographi-cally, and the phases in it were determined using X-ray diffractometry. The eutectic temperature was found to be 363 ±2° C. The eutectic composition was determined by equilibrating specimens on either side of the eutectic above the liquidus line, permitting them to solidify at various rates, and then examining them metallographically and by X-ray diffraction. The eutectic composition was found to be 19.0 ±0.5 at. % silicon. The liquidus line for composition up to 12 at. % silicon was redetermined by equilibrating specimens containing 2, 6, 10 and 12 at. % silicon above and below the liquidus line and then quenching them into iced brine.

Infrared transmission in GE-SB-SE glasses

Abstract: The infrared transmission properties of GeSbSe glasses have been investigated in order to determine the extrinsic and intrinsic absorption effects which limit their performance in avionic infrared systems and as CO2 laser windows. Extrinsic effects were found to include oxide and carbonaceous contamination. These detrimental contaminants were negated by preparation techniques such as distillation through quartz frits and addition of a gettering agent such as Al. Removal of the large extrinsic absorptions revealed the lower level intrinsic absorptions. The long wavelength infrared cutoff appears to be determined by higher order excitations of several fundamental vibrational modes, near 245 cm−1 for Ge-Se and 180 cm−1 for Sb-Se. Variation of the composition resulted in changes in the absorption coefficient in the 8–12 micron atmospheric window. These changes are due to the formation of distorted molecular units and to mixtures in the types of bonds formed among Ge, Sb, and Se. At 10.6 microns the absorption coefficients were found to very from a high of 0.024 cm−1 to a low of 0.008 cm−1.

Metallurgical amd electroluminescence characteristics of vapor-phase and liquid-phase epitaxial junction structures of In x Ga 1−x As

Abstract: InxGa1−xAs (x = 0.05 to 0.32) p-n junction structures have been grown on GaAs substrates by vapor-phase epitaxy (VPE) and liquid-phase epitaxy (LPE). It is shown that by step-grading the VPE material, lattice-mismatch strain can be absorbed by dislocations at the grading interfaces, leaving the final constant-composition device layers relatively dislocation free. In contrast, the dislocation density for LPE InxGa1−xAs increases with increasing InAs concentration. For both materials, diffusion lengths, electroluminescence efficiencies, and 77°K laser-diode parameters (threshold and efficiency) can be correlated with their dislocation densities. The VPE materials have electrical and luminescence properties that are independent of InAs concentration, and match those of their GaAs counterparts. The LPE materials exhibit properties that degrade with increasing InAs concentration.

The carrier lifetime of heat-treated silicon crystals

Abstract: Carrier lifetime measurements were performed on crucible-grown, float-zoned, and swirl-free float-zoned silicon single crystals after annealing up to about 1000°C. In dislocation-free, crucible-grown silicon one pronounced maximum of the carrier lifetime can be found after annealing at 450°C . This gettering effect is correlated to the appearence of numerous IR-absorption bands at 80 K. The absorption coefficients of these bands depend on the oxygen concentration of the crystals and on the annealing duration. A differing number of maxima of the carrier lifetime after annealing at various temperatures can be found in dislocation-free, float-zoned silicon. These maxima are correlated to still remaining lattice defects in the crystals such as vacancy clusters of A-and B-type. Models are presented to explain the experimental findings.

Temperature dependence of carrier ionization rates and saturated velocities in silicon

Abstract: The temperature dependencies of the carrier ionization rates and saturated drift velocities in silicon have been extracted from microwave admittance and breakdown voltage data of avalanche diodes. The avalanche voltage and broadband (2–8 GHz) microwave small-signal admittance were measured for junction temperatures in the range 280 to 590 K. An accurate model of the diode was used to calculate the admittance characteristic and voltage for each junction temperature. Subsequently, the values of ionization coefficients and saturated velocities were determined at each temperature by a numerical minimization routine to obtain the best fit between the calculated values and measured data.

Nonstoichiometry and nonradiative recombination in GaP

Abstract: models which have been successful in explaining observations of other defect phenomena are used to identify the native nonradiative recombination center in GaP. It is concluded to be the complex VGa − PGa +2VGa − acting via the configuration coordinate mechanism. It is believed to form during the cooling of the crystals from the quasi-equilibrium distribution of defects present during growth. Recent direct lattice-imaging experiments in GaAs have observed the corresponding defect complex in a concentration close to that predicted. It is predicted that the defect in GaP will exhibit recombination-enhanced diffusion.

Structure study of a metallic glass using positron annihilation methods

Abstract: The effects of vitrification and cold rolling on the structure in a metallic glass of Pd.775Cu.06Si.165 alloy and crystalline Pd have been investigated using positron lifetime and angular correlation measurements. It is concluded that: A) the metallic glass contains a negligible concentration of vacancy-like defects and the crystallite model may be excluded as a possible structure of metallic glasses, B) the glass-crystalline boundaries contain a very small fraction of vacancy-like defects and exhibit a smooth transition structure from glassy to crystalline regions, C) the cold rolling of the metallic glass induces no vacancy or dislocation-like defects and plastic flow in metallic glasses is accompanied by cooperative atomic regroupings somewhat analogous to the visco flow of glasses near the glass transition temperature, D) the electronic structure of the Pd-Cu-Si alloy alters little upon disordering from a crystalline to glassy state, but exhibits a large change from that of crystalline Pd. This is attributed to the valence electrons transferred from Si to the d-shell of Pd in the Pd-Cu-Si alloy.

Pb1-xSnxTe epitaxial layers prepared by the hot-wall technique

Abstract: Epitaxial layers of Pb1-xSnxTe were grown on polished-etched KCl substrates using the modified hot-wall technique. Four layers, each 5-30 μm thick, of area 5.5 × 5.5 mm2 were simultaneously grown at growth rates of 0.3–4.8 µm/hr. A typical substrate temperature of 325°C , and baffle and source temperatures of 450-560°C were used. P-and n-type layers were obtained from stoichio-metric and metal-rich sources of (Pb1-xSnx)1+δ Te1-δ, 0.01≤δ ≤0.02, respectively. From metal-rich sources with 0<δ<0.01, the layers obtained were n-type at 300K but p-type at 77K. The layers became intrinsic between approximately 250K and 295K. Carrier concentrations of as-grown layers with 0≤x ≤0.26 were in the range of 1016-1017 /cm3 and mobilities were of the order of 104 cm2 /V-sec at 77K. Both n-and p-type layers were also obtained from metal-rich sources of δ = 0.01 by controlling the Te vapor pressure from a separate reservoir. With Te temperatures higher than the n-p turnover point of 240°C , p-type characteristics were obtained. Layers that were p-type at 77K grown with the Te temperatures near the n-p turnover point had the best mirror-like surfaces.

Some properties of chemically vapor deposited films of AlxOyNz on silicon

Abstract: Transmission electron microscopy (TEM) studies of films prepared in the AlN-Al2O3 pseudobinary system by chemical vapor deposition (as described in a companion paper entitled, “Chemical Vapor Deposition of AlxOyNz Films”) indicates that four different phases can be obtained by altering the NH3/CO2 gas ratio and preparation temperature. Films prepared at 900°C yield three polycrystalline phases and an amorphous composition. From zero to 25 at. percent O an AlN phase is observed. Amorphous material is observed from 25 to 47 at. percent O. From 47 to 59 at. percent O an AlxOyNz spinel is observed. At 60 at. percent O (pure Al2O3) an alumina phase is observed (KI phase). For 770°C films the AlN phase is observed from zero to 8 at. percent 0; from 8 to 23 at. percent O the zeta-alumina phase is seen; and at 60 at. percent O the KI alumina phase is again observed. For both the 770 and 900°C films, the grain size of the AlN phase was found to decrease with increasing oxygen content.

The structural and piezoelectric properties of epitaxial AℓN on Aℓ 2 O 3

Abstract: The piezoelectric properties of epitaxial AlN films grown by the method of chemical vapor deposition utilizing trimethylaluminum and ammonia as chemical reactants were investigated. Large variations of the measured electromechanical coupling coefficient, k2, were found in different regions of the same sample and on different samples having approximately the same h/λ value. Electron microscope observations of replicated as-grown and etched surfaces of epitaxial AlN were used to show a relationship between surface facet ordering and the magnitude of k2. A plot of k2 measured at various h/λ values shows k2 as large as 0.6% for films grown at a rate of ˜0.2 µm/min and measured at ˜400 MHz.

Charge transfer properties of mnos structures as influenced by processing parameters

Abstract: The charge transfer and retention characteristics of MNOS structures have been studied as a function of specified processing parameters utilized when fabricating the tunneling silicon oxide and charge storage silicon nitride layers. A grid array of n+ junctions fabricated on 2 ohm-cm “p” type silicon substrates allowed simulation of the transient characteristics of FET’s. Electrical measurements included switching speed, static and dynamic charge storage windows, and stored charge retention with time. The switching speed and window width were influenced by some processing parameters. Some shortcomings with recent discharge models are noted, based upon the data obtained. Limited (multiple cycling) “fatigue” studies have indicated improved window behavior with increased write-erase voltages, and pulse widths below one microsecond, for MNOS structures with the tunneling oxide prepared within an NO plus H2 ambient.

Electrical properties and luminescence of CuInSe2

Abstract: We have studied the electrical properties and luminescence spectra of melt-grown CuInSe2 single crystals and the doping of the crystals with intrinsic defects and extrinsic impurities. The preparation and the properties of p-n junctions are also discussed. We find that the low temperature photoluminescence spectra of crystals as-grown or annealed between 400 and 700 C are characteristic of the conductivity type. At 77 K, p-type crystals emit in a band peaked at 1.00 eV (type A spectrum) whereas the emission of n-type crystals peaks at 0.93 eV (type B spectrum). Type A and type B spectra can be interchanged by alternate anneals in minimum or maximum Se pressure. Type B emission dominates the electroluminescence spectrum of p-n junctions. These features are explained by the appearing and disappearing of a donor level as a consequence of annealing in vacuum or in Se atmosphere. We find that Zn and Cd act as donors. Crystals doped with these impurities have electron concentrations above 1018 cm−3. Zn-dopped samples exhibit a very broad recombination band below the bandgap in photoluminescence both at 77 and 300 K.

Effects of Mg additions on the electromigration behavior of Al thin film conductors

Abstract: Aluminum thin film conductors containing Mg alloying additions have been tested for electromigration failure by formation of electrically open circuits. The test conditions were either 2 × 106 A/cm2 or 4 × 106 A/cm2 for the current density, and either 175 or 225°C for the temperature. The median lifetimes were found to increase with increasing Mg concentrations up to the highest concentration tested, about 6%. With polycrystalline films the maximum increase in lifetime resulting from Mg additions corresponds to a factor of about 100, as compared to pure Al films. This is about equal to previously reported results obtained with Cu additions. The increase in lifetime has been shown to result from a decrease in the rate of grain boundary diffusion for the Al atoms. Magnesium atoms diffuse at approximately the same rate as Al atoms. Thus the mechanism of failure formation in Al films containing Mg is thought to be different than in Al-Cu films, where Cu atoms diffuse faster than Al atoms and failure ensues upon local Cu depletion.

Formation of lithium niobate-tantalate waveguides

Abstract: Low loss diffused lithium niobate-tantalate waveguides exhibiting strong electrooptic coefficients have been made by a simple processing procedure. The formation of these waveguides takes place by the conversion of a Nb metal film to Nb oxide at a low temperature, followed by diffusion of Nb into the LiTaO3 substrate at about 1100°C. The diffused layer has a Gaussxan composition profile. Its measured refractive index is consistent with that calculated by interpolation between the indices of LiNbO3, and LiTaO3.

Tl 3 VS 4 as an acousto-optic and surface wave material

Abstract: Single crystals of thallium vanadium sulphide (Tl3VS4) up to 2 cm in length were grown from melts using the Stockbarger technique. This material has acoustic velocities as low as 8.73 × 104 cm/sec for bulk shear waves and 8.7 × 104 cm/sec for surface (Rayleigh) waves. In a sample oriented (001)Λ(110), k2 was found to be 1.39%, and the temperature coefficient of delay −54 ppm for surface waves. The optical transmission is from 0.75 to 10.5 µm, and the indices of refraction range from 3.156 at 0.749 µm to 2.808 at 5.26 µm. These properties make it an attractive candidate for use in acousto-optic and acoustic surface-wave devices.

Chemical vapor deposition of AlxOyNz films

Abstract: A chemical vapor deposition process for depositing dielectric films of aluminum oxynitride is described. AlCl3, CO2 and NH3 were employed as the reactive gases in a nitrogen carrier. Films were grown from the mixed gases at 770 and 900°C in a resistively heated fused silica enclosure. The composition of the films could be varied over the entire range of the pseudobinary AlN-Al2O3 system by controlling the NH3/CO2 gas ratio with an appropriate flow of gaseous AlCl3. Growth rate and index of refraction for the films were obtained using ellipsometric techniques. The film compositions reported were determined by electron microprobe analysis. Film structure, evaluated using transmission electron microscopy, and the electrical properties of the dielectric films have been correlated and are discussed separately in a companion paper entitled, “Some Properties of CVD Films of AlxOyNz on Silicon”.

Void initiation, growth, and coalescence in ductile fracture of metals

Abstract: Ductile fracture in metals and alloys occurs through the coalescence of voids in the necked region of the specimen. While considerable information exists on the propagation of cracks, the mechanism of their initiation is still unclear. This paper reports onin situ electron microscope investigations aimed at an elucidation of crack initiation and the enlargement of crack nuclei to final rupture. Single crystal ribbons of silver 0.5 − 7.0 μm thick were pulled to fracture inside of a high voltage electron microscope (HVEM). After considerable necking, cracks initiated at the edges; their propagation occurred by the formation of microcracks ahead of the macrocrack, followed by the growth of the microcracks and finally their coalescence. Thesein situ experiments were complemented by stress-strain data obtained from fractured austenitic 304 stainless steel foils; subsequent examination of fracture surfaces in a scanning electron microscope allowed the accurate measurement of intervoid spaclngs. Inter-particle spacings were determined by HVEM. It was found that the average void density is 100 times larger than the average particle density. The combination and analysis of all experimental data led to a detailed model of void initiation and growth, which is based on a dislocation-vacancy mechanism and crystal plasticity.

Deep level spectroscopy, low temperature defect motion and nonradiative recombination in GaAs and GaP

Abstract: Recent developments in junction capacitance measurements allow deep levels in semiconductors to be conveniently studied for the first time. Experiments carried out on deep levels in GaP and GaAs show that the levels are often strongly coupled to the lattice. This coupling can cause rapid nonradiative recombination in which the released electronic energy causes violent vibrations of the lattice near the defect. The vibrations can promote low temperature defect motion. These two phenomena, nonradiative recombination and defect motion, are fundamental to the understanding of how defects limit the efficiency of light emitting devices and cause junction devices to degrade when forward biased. The recent work of Lang on deep level spectroscopy, Lang and Kimerling on defect motion and Henry and Lang on nonradiative recombination by multiphonon emission will be reviewed.