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15 Dec 1988

Volume 64, Issue 12, pp. R93-6870

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Atom diffusion and impurity‐induced layer disordering in quantum well III‐V semiconductor heterostructures

D. G. Deppe and N. Holonyak

J. Appl. Phys. 64, R93 (1988); http://dx.doi.org/10.1063/1.341981 (21 pages) | Cited 95 times

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The process of impurity‐induced layer disordering (IILD) or layer intermixing, in AlxGa1−xAs‐GaAs quantum well heterostructures (QWHs) and superlattices (SLs), and in related III‐V quantum well heterostructures, has developed extensively and is reviewed. A large variety of experimental data on IILD are discussed and provide newer information and further perspective on crystal self‐diffusion, impurity diffusion, and also the important defect mechanisms that control diffusion in AlxGa1−xAs‐GaAs, and in related III‐V semiconductors. Based on the behavior of Column III vacancies and Column III interstitials, models for the crystal self‐diffusion and impurity diffusion that describe IILD are reviewed and discussed. Because impurity‐induced layer disordering has proved to be an important method for III‐V quantum well heterostructure device fabrication, we also review the application of IILD to several different laser diode structures, as well as to passive waveguides. We mention that it may be possible to realize even more advanced device structures using IILD, for example, quantum well wires or quantum well boxes. These will require an even greater understanding of the mechanisms (crystal processes) that control IILD, as well as require more refined methods of pattern definition, masking procedures, and crystal processing.
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68.35.Fx Diffusion; interface formation
66.30.J- Diffusion of impurities
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.30.De Semiconductor-device characterization, design, and modeling

Nd:LNA laser optical pumping of 4He: Application to space magnetometers

R. E. Slocum, L. D. Schearer, P. Tin, and R. Marquedant

J. Appl. Phys. 64, 6615 (1988); http://dx.doi.org/10.1063/1.342042 (3 pages) | Cited 9 times

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We have observed Hanle signals and n=0, p=1 parametric resonances of 23S1 metastable helium atoms in a discharge cell by optically pumping the helium atoms with a tunable Nd:LNA laser. These resonances were used to construct a sensitive magnetometer for the measurement of very small magnetic fields. Since magnetometer sensitivity is proportional to the slope of the parametric resonance signal (signal amplitude divided by linewidth), the slopes for single‐line laser pumping were compared with similar quantities obtained from conventional helium lamp pumping. Laser pumping yielded 45 times greater slopes with comparable power requirements, thus establishing the potential for developing ultrasensitive resonance magnetometers using single‐line laser pumping.
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32.80.Xx Level crossing and optical pumping
32.30.Bv Radio-frequency, microwave, and infrared spectra
07.55.-w Magnetic instruments and components

High gain metal grating free‐electron laser

E. Garate, R. Cherry, A. Fisher, and P. Phillips

J. Appl. Phys. 64, 6618 (1988); http://dx.doi.org/10.1063/1.342043 (8 pages) | Cited 3 times

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The small signal gain is calculated for a metal grating free‐electron laser consisting of a planar metallic grating and an opposing planar metal boundary. The TM01 mode of the metal grating waveguide interacts with a cold, dense, mildly relativistic electron beam which is constrained to move along the axis of the waveguide. Since the interaction fields evanesce away from the slow wave supporting structure, a beam‐grating gap is included in the analysis. Results indicate appreciable gain at lower mm wavelengths over a 30‐cm interaction length at electron accelerating voltages as low as 20 kV. Interaction between the forward wave region of the n=0 space harmonic and the electron beam slow‐space‐charge wave could result in output wavelengths as low as 400‐μm at 250‐kV accelerating voltages.
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41.60.Cr Free-electron lasers
41.75.Ht Relativistic electron and positron beams
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers

Current multiplication during relativistic electron‐beam propagation in a subTorr‐pressure gas

G. P. Gupta and V. K. Rohatgi

J. Appl. Phys. 64, 6626 (1988); http://dx.doi.org/10.1063/1.342044 (5 pages) | Cited 3 times

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The current multiplication observed when a relativistic electron beam is propagated in an initially neutral gas at subTorr pressures (0.1–0.3 Torr) is generally attributed to the two‐stream instability. A general expression for this current gain is derived for a scattered beam propagating in a neutral gas, which takes into account a quasihydrodynamic expression for the beam energy loss. Moreover, the beam‐to‐plasma density ratio is obtained as a function of time for a given beam pulse by numerically solving the electron energy and continuity equations. It is found that at a given beam‐to‐plasma density ratio, the current gain increases with increasing the beam energy, with the increase being most rapid for the small scattering angles. A finite average scattering angle is seen to reduce the current multiplication. The experimentally observed peak current gains are in good agreement with the predicted peak gains obtained by taking into account the time‐evolved beam‐to‐plasma density ratio.
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41.75.Ht Relativistic electron and positron beams
52.40.Mj Particle beam interactions in plasmas

Effects of stress on threshold, wavelength, and polarization of the output of InGaAsP semiconductor diode lasers

Charles S. Adams and Daniel T. Cassidy

J. Appl. Phys. 64, 6631 (1988); http://dx.doi.org/10.1063/1.342045 (8 pages) | Cited 22 times

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The effects of tension and compression applied to unbonded InGaAsP semiconductor diode lasers have been studied. The observed dependence of threshold, wavelength, and polarization of the laser output on the applied stress is explained in terms of the strain dependence of the valence‐band wave functions. The polarization behavior is found to be related to thermal stress and the structure of the device. A technique has been developed to measure the thermal stress induced by current heating at the 105‐dyn/cm2 level.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

A method to calculate the laser heating of layered structures

Roger J. Anderson

J. Appl. Phys. 64, 6639 (1988); http://dx.doi.org/10.1063/1.342046 (7 pages) | Cited 12 times

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This work describes a method to calculate the heating that occurs when a Gaussian laser beam is scanned across the surface of a flat object which may be coated with one or more layers of differing materials. The laser beam is characterized by its power, radius, and scan velocity. Each layer of the object is characterized by its thickness, density, heat capacity, and thermal conductivity. Absorption of laser light is assumed to vary linearly across any one layer, and this absorption is characterized by two dimensionless constants. Temperature rise versus time is calculated as a function of position within the multilayer stack. Use of the technique is illustrated by considering the case of an optically opaque organic dye/polymeric binder coated onto a polymeric substrate. Such a construction may be used in optical data storage applications.
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44.30.+v Heat flow in porous media
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.79.Vb Optical storage systems, optical disks
65.40.Ba Heat capacity

Investigation of collisional effects in the plasma erosion opening switch

J. M. Grossmann, R. Kulsrud, J. M. Neri, and P. F. Ottinger

J. Appl. Phys. 64, 6646 (1988); http://dx.doi.org/10.1063/1.342050 (8 pages) | Cited 12 times

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During the conduction phase of the plasma erosion opening switch (PEOS), magnetic field has been observed experimentally to penetrate completely through plasmas up to 30 cm long. Current channels in the main body of the plasma have been observed that are more than 10 cm (or more than about 60 collisionless skin depths) wide. In addition, the maximum current carried by the switch before opening (the conduction current) seems to scale roughly linearly with plasma density n and switch length l. Collisionless pic code simulations of the plasma switch show current conducted in skin‐depth‐like channels, with the conduction current scaling close to l 2/5 and n1/4. In this paper, the effect of collisions on the behavior of the PEOS is investigated and is shown to bring the pic simulations and experimental results in closer agreement. In collisional simulations, current channels as wide as those in experiments are observed, and the conduction current scales linearly with l and as n1/2 in the anode‐dominated case. In the cathode‐dominated case, linear scaling with both length and density can be inferred from the cathode penetration distance versus time.
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52.75.Kq Plasma switches (e.g., spark gaps)
52.65.-y Plasma simulation
52.20.Fs Electron collisions
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Characterization of layer‐tilted state in ferroelectric liquid‐crystal cells by electro‐optical switchings

T. C. Chieu, K. H. Yang, and A. Lien

J. Appl. Phys. 64, 6654 (1988); http://dx.doi.org/10.1063/1.342019 (8 pages) | Cited 5 times

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Using an electro‐optical method, we have determined the director tilt angle, the layer‐tilt angle, and the quiescent‐state azimuthal angles of a surface‐stabilized ferroelectric liquid‐crystal (SSFLC) cell as a function of temperature in the smectic C phase. The method is based on a collective switching of the director’s conical motion due to the interaction of the external field with the spontaneous polarization and the dielectric anisotropy of the liquid‐crystal medium, together with a one‐elastic constant free‐energy model. Using the equation of total free energy, we have proved that only splayed states could be stabilized in layer‐tilted geometry, but bistable cells could still be obtained. When the surface interactions at both substrate surfaces are nonidentical, the SSFLC cell will exhibit two distinct quiescent states: one stable and the other quasistable. The twist angles of the director from top to bottom substrates at quiescent states and the ratio of the surface polar to nonpolar interaction are deduced. The experimental observation and calculation on an overshoot in the rising part of the optical response upon bipolar switching are also presented.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.80.Dj Domain structure; hysteresis
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
78.20.Jq Electro-optical effects

An investigation of magnesium in indium phosphide grown by molecular‐beam epitaxy

T. S. Cheng, V. M. Airaksinen, and C. R. Stanley

J. Appl. Phys. 64, 6662 (1988); http://dx.doi.org/10.1063/1.342020 (6 pages) | Cited 7 times

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The role of magnesium as a p‐type dopant in the growth of InP by molecular‐beam epitaxy (MBE) has been investigated. The growth was performed at substrate temperatures of ≊500 °C under conditions which produced high‐quality unintentionally doped InP with 77 K residual electron concentrations of ND−NA ≊2×1015 cm−3 and mobilities up to 42 500 cm2 V−1 s−1. InP grown in an elemental Mg flux under such ‘‘optimum’’ conditions has electrical properties which are comparable to those of the undoped material. Using low‐temperature photoluminescence, the presence of electrically active shallow acceptors due to Mg and C has been detected in the ‘‘Mg‐doped’’ samples, with Mg being the dominant impurity. Mg is also found to be the principal, electrically active shallow acceptor in undoped InP. The activation energies for Mg and C are 40.9 and 44.4±0.3 meV, respectively, in excellent agreement with previously published data for low‐dose ion‐implanted InP. Secondary electron microscopy studies on the Mg‐doped InP show that the concentration of morphological defects increases as the Mg flux is increased, suggesting Mg is responsible for assisting the formation of defects. However, the increase in defect density does not appear to affect either the electrical or the optical properties of the semiconductor. The small concentration of Mg incorporated into InP from an elemental source makes it unsuitable as a p‐type dopant in MBE growth under the condition discussed here.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Structure and properties of diamondlike carbon coatings deposited in rf plasma from benzene and monosubstituted benzenes

Asawari Joshi, S. A. Gangal, and S. K. Kulkarni

J. Appl. Phys. 64, 6668 (1988); http://dx.doi.org/10.1063/1.342021 (5 pages) | Cited 9 times

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Properties of diamondlike coatings deposited in a modified design of the plasma reactor system are reported. Benzene and monosubstituted benzenes are used as the source gases. The films have been analyzed using scanning electron microscopy, glancing angle x‐ray diffraction, Fourier transform infrared spectroscopy, and x‐ray photoelectron spectroscopy techniques. Large crystallites (∼30 μm) are observed. The x‐ray diffraction and x‐ray photoelectron spectroscopy have been utilized to identify the physicochemical nature of the deposited films. Fourier transform infrared spectroscopy results suggest sp3 type of bonding in the films. Films are colorless, electrically insulating (≥109 Ω cm), and corrosion resistant.
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68.55.-a Thin film structure and morphology
81.15.Rs Spray coating techniques
78.66.-w Optical properties of specific thin films
73.61.Ng Insulators

The effects of gas ambients on the formation of surface and bulk defects in silicon

J. S. Kang and D. K. Schroder

J. Appl. Phys. 64, 6673 (1988); http://dx.doi.org/10.1063/1.342022 (6 pages) | Cited 4 times

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The effects of gas ambients on the density of oxide precipitates and stacking faults have been studied in samples annealed in various gas ambients. It is found that the densities of oxide precipitates and bulk and surface stacking faults in oxynitrided samples are higher than those of samples annealed in oxygen, nitrogen, trichloroethane plus oxygen, and pure ammonia. Also, stacking faults have been observed at the surface of the samples annealed in an ammonia ambient. These observations are contrary to our expectations, and several models are proposed to explain the phenomena.
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61.72.Bb Theories and models of crystal defects
61.72.Nn Stacking faults and other planar or extended defects
61.72.jd Vacancies
61.72.jj Interstitials
68.35.Dv Composition, segregation; defects and impurities

Copper passivation of dislocations in silicon

Jae‐Gwang Lee and S. Roy Morrison

J. Appl. Phys. 64, 6679 (1988); http://dx.doi.org/10.1063/1.342023 (5 pages) | Cited 9 times

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The J‐V characteristics of metal‐insulator‐semiconductor solar cells fabricated on Si samples which are damaged (lapped) with 1‐μm grit size of Al2O3 are substantially degraded. The introduction of copper at 250–400 °C passivates the dislocations. The copper is diffused in from the surface. Anodic oxidation followed by etching in aqua regia and 48% HF was used to remove excess copper remaining on the damaged surface and to etch away controlled amounts of the silicon wafers. The experimental results are compared to the model of Divigalpitiya and Morrison [J. Appl. Phys. 60, 406 (1986)]. It is concluded using the model that copper passivation reduces the product of the density of hole traps and the capture cross section of hole traps and may also increase the specific conductance of the dislocations. Results for samples lapped with finer‐grit alumina (0.3 μm) seem qualitatively different from those with 1‐μm alumina. The variation in dislocation density as a function of depth into the surface is used to explain the difference qualitatively. The dislocation density decreases rapidly with distance from the damaged surface.
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84.60.Jt Photoelectric conversion
61.72.uf Ge and Si
81.65.-b Surface treatments
72.40.+w Photoconduction and photovoltaic effects

Photorefractive measurement of photoionization and recombination cross sections in InP:Fe

George C. Valley, Stephen W. McCahon, and Marvin B. Klein

J. Appl. Phys. 64, 6684 (1988); http://dx.doi.org/10.1063/1.342024 (6 pages) | Cited 28 times

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The photorefractive effect combined with standard Hall measurements is used to determine photoionization and recombination cross sections and deep‐level number densities in a crystal of iron‐doped InP. The results are well fit by iron densities [Fe2+]=6×1016 cm−3 and [Fe3+]=2.5×1015 cm−3, photoionization cross sections at 1.06 μm, se= 4×10−18 cm2, and sh= 3.1×10−16 cm2, and recombination cross sections σe= 10−14 cm2 and σh= 3×10−16 cm2. The sign of the photorefractive beam coupling gain implies that holes dominate this process even though the dark conductivity and photoconductivity are dominated by electrons.
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78.20.Jq Electro-optical effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.My Galvanomagnetic and other magnetotransport effects
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors

Stress relaxation during thermal cycling in metal/polyimide layered films

S. T. Chen, C. H. Yang, F. Faupel, and P. S. Ho

J. Appl. Phys. 64, 6690 (1988); http://dx.doi.org/10.1063/1.341999 (9 pages) | Cited 22 times

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The stress relaxation behavior during thermal cycling of metal/quartz and metal/polyimide/quartz layered structures has been investigated using a cantilever bending beam technique. The metals chosen for this study include Cu and Cr, two materials with contrasting mechanical and interfacial bonding properties. A finite element analysis, as well as an analytical calculation, has been carried out to deduce the stress distribution in the layered structures. Results indicate that the extent of stress relaxation strongly depends on the intrinsic mechanical property of the metal film with significantly higher stresses residing in the Cr film than in the Cu film. The interfacial polyimide layer has been found to serve as an effective buffering layer to reduce the residual stress in metal films. Observations from transmission electron microscopy suggest that the stress is partially released through the deformation of the polyimide near the metal/polyimide interface.
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62.20.Hg Creep
68.35.Gy Mechanical properties; surface strains
46.80.+j Measurement methods and techniques in continuum mechanics of solids
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Tensile plasticity and ductile fracture

J. N. Johnson and F. L. Addessio

J. Appl. Phys. 64, 6699 (1988); http://dx.doi.org/10.1063/1.342000 (14 pages) | Cited 27 times

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A mathematical model of tensile plasticity and void growth based on the Gurson flow surface and associated flow law is developed and applied to the problem of ductile fracture under general tensile loading conditions. The flow surface defines the plastic strain components in the tensile region; conditions of fracture are defined in terms of the plastic deformational strain, porosity, and the ratio of mean stress to shear stress, p/τ. This model reduces to the Carroll and Holt [J. Appl. Phys. 43, 759 (1972)] tensile threshold pressure for void growth, and to the Rice and Tracey [J. Mech. Phys. Solids 17, 201 (1969)] expression relating the fractional change in void radius to the incremental plastic deformational strain and p/τ in a triaxial tensile stress field. The model has sufficient generality to represent plastic flow and fracture in notched and smooth tensile bars as well as in uniaxial‐strain spallation tests. One‐ and two‐dimensional finite‐difference calculations demonstrate this capability.
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62.20.F- Deformation and plasticity
46.25.Cc Theoretical studies
62.50.-p High-pressure effects in solids and liquids
62.20.M- Structural failure of materials

Resolution of thermal wave imaging methods for periodic structures

A. Lörincz

J. Appl. Phys. 64, 6713 (1988); http://dx.doi.org/10.1063/1.342001 (3 pages) | Cited 3 times

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A model computation was conducted in two dimensions to determine the spatial resolution of thermal wave methods for periodic structures. The model is appropriate for line heating systems used for improving speed limits of thermal wave methods. The results may be considered as approximate for problems requiring three‐dimensional treatment. Numerical computations of the response of a thermal wave imaging system for periodic variations of material parameters along the surface show resonancelike behavior around the thermal diffusion length. The resolution of the system determined according to the Rayleigh criterion is about two thirds of the thermal diffusion length. Below that value the amplitude of the temperature signal decreases with increasing periodic variation wave vector with a slope of about 9.5 dB/octave. A formula is given for the determination of resolution for structures other than periodic.
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46.80.+j Measurement methods and techniques in continuum mechanics of solids
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
65.90.+i Other topics in thermal properties of condensed matter (restricted to new topics in section 65)

The contrastive behavior of Fe and Cr during the intrinsic gettering of silicon

M. S. Goorsky, J. Lagowski, and H. C. Gatos

J. Appl. Phys. 64, 6716 (1988); http://dx.doi.org/10.1063/1.342002 (5 pages) | Cited 2 times

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We found that Fe and Cr exhibit significantly different characteristics in being gettered during a high (1150 °C), low (750 °C), and medium (1000 °C) temperature cycle in Czochralski silicon. The behavior of Fe and Cr was monitored using deep level transient spectroscopy. Although Si was highly supersaturated with respect to both species throughout the low temperature step, Fe was gettered but Cr was not. This behavior indicated that a barrier to bulk silicide formation on oxide precipitates existed for Cr, but not for Fe at this temperature. We attribute the gettering of Cr at 1000 °C to the production of strain and Si interstitials during oxide precipitate growth. Since the differences in gettering behavior cannot be explained in terms of diffusivity and supersaturation, we propose a model which considers additional physical and chemical interactions.
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66.30.J- Diffusion of impurities
81.30.Mh Solid-phase precipitation
61.72.Bb Theories and models of crystal defects
61.72.jd Vacancies
61.72.jj Interstitials

The high‐temperature stability of chemically vapor‐deposited tungsten‐silicon couples rapid thermal annealed in ammonia and argon

E. K. Broadbent, A. E. Morgan, J. M. Flanner, B. Coulman, D. K. Sadana, B. J. Burrow, and R. C. Ellwanger

J. Appl. Phys. 64, 6721 (1988); http://dx.doi.org/10.1063/1.342003 (6 pages) | Cited 1 time

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A rapid thermal anneal (RTA) in an NH3 ambient has been found to increase the thermal stability of W films chemically vapor deposited (CVD) on Si. W films deposited onto single‐crystal Si by low‐pressure CVD were rapid thermal annealed at temperatures between 500 and 1100 °C in NH3 and Ar ambients. The reactions were studied using Rutherford backscattering spectrometry, x‐ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and four‐point resistivity probe. High‐temperature (≥1000 °C) RTA in Ar completely converted W into the low resistivity (31 μΩ cm) tetragonal WSi2 phase. In contrast, after a prior 900 °C RTA in NH3, N inclusion within the W film and at the W/Si interface almost completely suppressed the W‐Si reaction. Detailed examination, however, revealed some patches of WSi2 formed at the interface accompanied by long tunnels extending into the substrate, and some crystalline precipitates in the substrate close to the interface. The associated interfacial contact resistance was only slightly altered by the 900 °C NH3 anneal. The NH3‐treated W film acted as a diffusion barrier in an Al/W/Si contact metallurgy up to at least 550 °C, at which point some increase in contact resistance was measured.
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68.60.Dv Thermal stability; thermal effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
73.40.Ns Metal-nonmetal contacts

Effects of misfit dislocations and thermally induced strain on the film properties of heteroepitaxial GaAs on Si

R. M. Lum, J. K. Klingert, R. B. Bylsma, A. M. Glass, A.T. Macrander, T. D. Harris, and M. G. Lamont

J. Appl. Phys. 64, 6727 (1988); http://dx.doi.org/10.1063/1.342004 (6 pages) | Cited 20 times

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GaAs hereroepitaxial films on Si contain a high number of misfit dislocations and large internal stresses due to the lattice and thermal mismatch of the two materials. These greatly affect the structural, optical, and electrical properties of the films. We report a study of these effects in films grown by metalorganic chemical vapor deposition using x‐ray diffraction, sample curvature, photoluminescence, and carrier concentration measurements. The x‐ray data indicate that the lattice misfit strain is almost entirely relieved by the generation of dislocations, but that the difference in thermal expansion between the film and substrate causes significant tetragonal distortion of the GaAs lattice which results in wafer bowing and, for thicker GaAs layers, film cracking. Wafer bowing was successfully eliminated by growth of GaAs films on both sides of the Si substrate. Photoluminescence spectra of crack‐free GaAs layers indicated that the thermally induced strain was distributed in a nonuniform but continuous manner throughout the film. The magnitude of the strain, as determined from x‐ray diffraction, wafer curvature, and photoluminescence spectroscopy, was consistently 10% lower than the value calculated from simple thermal relaxation. Finally, for large numbers of misfit defects (>108 cm−2) the electrical properties of the sample were found to be correlated to the mean dislocation density of the GaAs film.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
73.61.Ey III-V semiconductors
68.60.Bs Mechanical and acoustical properties

X‐ray and Raman characterization of AlSb/GaSb strained layer superlattices and quasiperiodic Fibonacci lattices

A. T. Macrander, G. P. Schwartz, and G. J. Gualtieri

J. Appl. Phys. 64, 6733 (1988); http://dx.doi.org/10.1063/1.342005 (13 pages) | Cited 27 times

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Double‐crystal rocking curves of samples grown on (001)‐oriented GaSb substrates by molecular‐beam epitaxy have been analyzed by fitting computer simulations to data for the symmetric (004) and (002) reflections and for asymmetric (115) reflections. Rocking curves revealed a multiplicity of superlattice diffraction peaks. Dynamical diffraction theory using Abeles matrix method [D. W. Berreman, Phys. Rev. B 14, 4313 (1976)] was applied for the symmetrical reflections. We compare our results to standard kinematical simulations, and we find that there are significant differences. For the asymmetric reflections a new dynamical computer simulation code [D. W. Berreman and A. T. Macrander, Phys. Rev. B 37, 6030 (1988)] involving an 8×8 matrix solution of Maxwell’s equations was used. Lattice incoherency was determined from measurements of the in‐plane mismatch. Dramatic diffraction peak broadening was observed for incoherent superlattices, and this broadening was attributed to a mosaic structure formed by misfit dislocations. Peak broadening was used to infer both a growth direction as well as an in‐plane coherence length. The in‐plane coherence length was found to be somewhat less than the mean distance between misfit dislocation lines. Mosaic broadening of diffraction peaks of a quasiperiodic lattice was found to be qualitatively similar to that observed for the periodic superlattices. Raman measurements of zone‐folded acoustic phonon spectra yielded superlattice periods that agreed with the x‐ray measurements within a few percent. Analysis of Raman peak intensities to yield individual layer widths was not found to be quantitative within the confines of current analytic models.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
78.30.Fs III-V and II-VI semiconductors

Thickness‐dependent formation of Gd‐silicide compounds

G. Molnár, I. Geröcs, G. Petö, E. Zsoldos, E. Jároli, and J. Gyulai

J. Appl. Phys. 64, 6746 (1988); http://dx.doi.org/10.1063/1.342006 (4 pages) | Cited 20 times

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Gd‐silicide phases were investigated by x‐ray diffraction. The results showed that not only one phase exists in a Gd thin‐film and silicon substrate reactions. The first phase formed was hexagonal GdSi≊1.7, the second orthorhombic GdSi2. The ratio of the two phases depends on temperature of the heat treatment, and at a given temperature and time of annealing, a dependence of the thickness of the evaporated Gd layer was found. At ∼100‐nm Gd thickness the dominant phase was orthorhombic GdSi2, at ∼250 nm hexagonal GdSi≊1.7. In the 300–1000‐nm interval orthorhombic GdSi2 was the main component again. Rutherford backscattering analysis showed that the phases were found mixed within the layer. This thickness‐dependent formation could be described with a simple model proposed by Gösele and Tu [J. Appl. Phys. 53, 3252 (1982)].
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68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology

Homoepitaxial growth of ZnTe by low‐pressure metalorganic vapor phase epitaxy

Hiroshi Ogawa and Mitsuhiro Nishio

J. Appl. Phys. 64, 6750 (1988); http://dx.doi.org/10.1063/1.342007 (4 pages) | Cited 6 times

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Zinc telluride homoepitaxial layers have been grown on the substrates with different orientations by metalorganic vapor phase epitaxy method. Dimethylzinc and diethyltelluride were used as source materials. The substrate temperature was in the range of 385–470 °C. Relatively flat and smooth surface of the epitaxial layer was obtained only on the (100)ZnTe substrate. The in situ gas analysis using the quadrupole mass spectrometer was carried out during the growth.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase

Substituting low‐energy (<30 eV) ion bombardment for elevated temperature in silicon epitaxy

G. K. Wehner, R. M. Warner, P. D. Wang, and Y. H. Kim

J. Appl. Phys. 64, 6754 (1988); http://dx.doi.org/10.1063/1.342008 (7 pages) | Cited 16 times

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Normally required high substrate temperature for achieving epitaxial film growth can be replaced by low‐energy (<30 eV), high‐current‐density (∼1 mA/cm2) ion bombardment during film deposition. For this a Si substrate wafer was immersed like a large negative Langmuir probe in a low‐pressure (5×10−4 Torr) mercury vapor plasma while receiving Si atoms sputtered from a Si wafer target. The Hg plasma was created by extracting a 4‐A discharge current at 25‐V discharge voltage from a Hg cathode spot on a liquid‐Hg pool. Electron channeling patterns proved that uniform Si spitaxial films can be obtained over the whole substrate wafer area at temperatures not exceeding 300 °C. The best epitaxial films were obtained when the substrate is bombarded (by biasing) during deposition with 23‐eV Hg ions. The electrical properties of the coatings indicated that the films were close, but not yet of device quality because of the impurities inherent in our non‐ultrahigh‐vacuum nonbakable Pyrex chamber pumped only with a 12‐l/s Hg diffusion pump.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Cd Deposition by sputtering
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Excited states of the Mg acceptor in GaAs

J. R. Cavins, Y. K. Yeo, and R. L. Hengehold

J. Appl. Phys. 64, 6761 (1988); http://dx.doi.org/10.1063/1.342009 (6 pages) | Cited 3 times

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Selective pair luminescence (SPL) has been used to measure the excited states of shallow acceptors in undoped vapor‐phase epitaxial (VPE) grown GaAs and Mg‐implanted VPE GaAs. A set of experimental data for Mg excited states in GaAs is presented here. The results show that the 2P3/2 ‐, 2S3/2 ‐, and 2P5/2 ‐1S3/2 energy differences are 17.0, 20.0, and 21.0 meV, respectively. The value of the 2S3/2 state agrees very well with the previously reported two‐hole transition luminescence result, and the other two values for the excited states agree very well with those reported for far‐infrared Fourier transform spectroscopy. This assignment was further confirmed by making SPL measurements on Mg‐implanted GaAs.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
61.72.U- Doping and impurity implantation

Stoichiometry related deep levels in undoped, semi‐insulating GaAs

P. Dobrilla

J. Appl. Phys. 64, 6767 (1988); http://dx.doi.org/10.1063/1.342010 (3 pages) | Cited 4 times

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The influence of stoichiometry on the deep levels found in undoped, semi‐insulating GaAs has been investigated by photoinduced transient spectroscopy. Traps shallower than the main midgap donor EL2 have been found to be unambiguously related to the melt stoichiometry.
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71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
72.80.Ey III-V and II-VI semiconductors
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