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15 Dec 1993

Volume 74, Issue 12, pp. R111-7627

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Novel magnetic applications of high‐Tc bulk superconductors: Lenses for electron beams

Hidenori Matsuzawa

J. Appl. Phys. 74, R111 (1993); http://dx.doi.org/10.1063/1.354944 (21 pages) | Cited 6 times

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This paper presents a review on the latest state of the novel bulk devices, with an emphasis on lenses for electron beams. As one application of high critical‐temperature (Tc) bulk superconductors, the author proposed the lenses (Supertrons) and his group has developed them. The principle of the lenses is simple: When one injects electron beams into narrow superconducting tubes, the tubes confine the self‐magnetic field of the beams to the bore of the tubes because of the Meissner effect. The enhanced field accordingly focuses the beams into thinner ones. The first two sections outline high‐Tc superconducting materials and fundamental characteristics of electron beams. In the body of this article, the lenses are evaluated according to the focusing of intense electron beams (∼340 keV, ∼1 kA, ∼10 ns) and assigned a figure of merit. Lenses were made from powder‐pressed yttrium‐ (Tc=∼90 K), bismuth‐ (∼105 K), thallium‐ (∼120 K), and melt‐processed yttrium‐based superconductors. From the experimental results, one can say that powder‐pressed lenses are suitable for short pulsed, low repetition‐rate electron beams (a ferrite‐core model) and that melt‐processed lenses are, on the other hand, probably appropriate for continuous or slowly time‐varying electron beams. In addition to the temperature‐dependent focusing of the electron beams, a criterion for design of the lenses is discussed. To show the potential of the lenses, two applications of the lenses are described: a wiggler for free‐electron lasers and an electron‐beam guide for induction linear accelerators. Finally, other novel applications (current leads, magnets, and bearings) indicate the interest in bulk materials which are rapidly being developed. The review will provide fundamentals for potential applications of bulk superconductors.
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85.25.-j Superconducting devices
74.72.-h Cuprate superconductors
41.85.-p Beam optics

The Talbot effect (a self‐imaging phenomenon) in holography

A. Maripov and Y. Ismanov

J. Appl. Phys. 74, 7039 (1993); http://dx.doi.org/10.1063/1.355041 (5 pages)

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The Talbot effect in holography has been studied. The study has shown that in monochromatic illumination of a bleached off‐axis hologram of a periodic grating, self‐images of the grating are reconstructed in the real image region. These self‐images of the reconstructed grating appear not only in the rays of the ±1st orders but also in the zeroth diffraction order.
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42.40.-i Holography

Shock wave analysis of laser assisted particle removal

S. J. Lee, K. Imen, and S. D. Allen

J. Appl. Phys. 74, 7044 (1993); http://dx.doi.org/10.1063/1.355017 (4 pages) | Cited 18 times

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Laser assisted particle removal (LAPR) is an innovative laser cleaning technique which can remove various particles from solid surfaces via laser induced explosive evaporation of a chosen energy transfer medium, e.g., water. An Ar+ ion continuous‐wave laser (488 nm) was used to study the CO2 laser pumped explosive evaporation of water adsorbed on a Si substrate. The probe laser beam was parallel to the sample surface at different displacements and interacted with the ejected material upon pulsed CO2 laser irradiation in analogy with the time resolved laser beam deflection experiments on laser induced vaporization of copper by Guo et al. [Opt. Commun. 77, 381 (1990)]. Using CO2 laser energies which are much greater than the LAPR thresholds, we observed the generation and propagation of a shock wave at supersonic speeds followed by a water vapor/aerosol/particle cloud at a much slower speed. From the evolution of the shock wave, the total conversion efficiency of the incident laser beam into the shock wave has been determined using a self‐similar approximation.
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42.62.-b Laser applications
81.65.-b Surface treatments
79.20.Ds Laser-beam impact phenomena

High‐quality focused‐ion‐beam‐made mirrors for InGaP/InGaAlP visible‐laser diodes

M. H. F. Overwijk and J. A. de Poorter

J. Appl. Phys. 74, 7048 (1993); http://dx.doi.org/10.1063/1.355018 (6 pages)

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We employed a focused ion beam (FIB) to sputter the end mirrors on InGaP/InGaAlP laser diodes. This particular diode operates at a wavelength of about 670 nm. For this wavelength the quality of the sputtered mirrors is far more critical than for longer wavelength devices. The present lasers do, in fact, show a relatively large increase in their threshold current after FIB micromachining. In this article, we investigate the origins of this increase and how to prevent it. After optimization, the lasers with a FIB‐made end mirror have a threshold current comparable to that of cleaved‐facet devices. We have seen that the polycrystalline structure of the device metallization on top of the laser diode causes roughening of the mirror during sputtering, which results in severe scatter losses of the laser light. A method to decrease the surface roughness is given. A further reason for the increase in threshold current is optical absorption at the mirror, presumably by a Ga‐rich layer. This can be circumvented by chemical etching after FIB treatment to remove the absorbing layer. Finally, to demonstrate the quality and the applicability of the FIB‐made mirrors, the influence of the tilt angle of the end mirror on the threshold current of the laser has been investigated. This dependency can be excellently described by theory.
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42.55.Px Semiconductor lasers; laser diodes
81.40.Tv Optical and dielectric properties related to treatment conditions

Mirror temperature of a semiconductor diode laser studied with a photothermal deflection method

M. Bertolotti, G. Liakhou, R. Li Voti, Ruo Peng Wang, C. Sibilia, and V. P. Yakovlev

J. Appl. Phys. 74, 7054 (1993); http://dx.doi.org/10.1063/1.355019 (7 pages) | Cited 7 times

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The mirror temperature response of a diode laser to injection current is studied through the photodeflection method. A theoretical model is presented together with some experimental measurements. Theoretical results are compared with experimental measurements for an AlGaAs quantum well laser diode.
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42.55.Px Semiconductor lasers; laser diodes
85.60.Jb Light-emitting devices
05.70.Ce Thermodynamic functions and equations of state

Zero chirp quantum well asymmetric Fabry–Perot reflection modulators operating beyond the matching condition

J. A. Trezza, M. C. Larson, and J. S. Harris

J. Appl. Phys. 74, 7061 (1993); http://dx.doi.org/10.1063/1.355020 (6 pages) | Cited 4 times

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We demonstrate asymmetric Fabry–Perot reflection modulators using both InGaAs and GaAs quantum wells which operate beyond the matching condition and exhibit zero phase change (zero chirp) when switched. These devices are structurally similar to devices which can operate before the matching condition, and with incorporation of only a small etch step enable planar realization of zero phase change modulators operating before and beyond the matching condition which reflect 180° out of phase. We also show how observation of the reflectivity spectrum can provide quick information about the voltage necessary to obtain this zero chirp behavior. These structures provide a basis for low chirp optical switching, beam steering, and spatial light modulation.
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42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

In‐plane acceleration sensitivity of contoured quartz resonators stiffened by quartz cover plates supported by clips

Y. S. Zhou and H. F. Tiersten

J. Appl. Phys. 74, 7067 (1993); http://dx.doi.org/10.1063/1.355021 (11 pages)

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It has been shown that the resultant acceleration sensitivity of contoured quartz resonators vanishes for perfect symmetry of the resonator with respect to the support system. It has further been shown that any loss of symmetry in the combined resonator plus support configuration results in a linear increase in the acceleration sensitivity. Since it is impossible to construct a perfectly symmetric resonator plus support configuration in practice, a stiffened structure is investigated. The structure consists of the active biconvex quartz resonator attached to identical top and bottom quartz cover plates by means of small sidewalls around the periphery. The mounting clips are attached to the top and bottom cover plates without touching the active plate. An analysis of the linear increase in the in‐plane acceleration sensitivity of the stiffened configuration is performed. Results are presented which show the influence on the in‐plane and resultant acceleration sensitivities of differences in the properties of the clips and a mispositioning of either a clip or the mode shape for a range of thickness of the cover plates relative to the active plate.  
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77.65.Fs Electromechanical resonance; quartz resonators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Method for thermal diffusivity measurements based on photothermal deflection

M. Bertolotti, G. Liakhou, R. Li Voti, F. Michelotti, and C. Sibilia

J. Appl. Phys. 74, 7078 (1993); http://dx.doi.org/10.1063/1.355334 (7 pages) | Cited 10 times

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The thermal diffusivity measurement through pulsed photodeflection in a modified collinear configuration is presented and discussed; comparison between theory and experiment is also shown.  
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05.70.Ce Thermodynamic functions and equations of state
81.70.-q Methods of materials testing and analysis
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

General solution to the hygrothermoelastic interface problem with discontinuity between dissimilar anisotropic media

R. C. Chang and C. K. Chao

J. Appl. Phys. 74, 7085 (1993); http://dx.doi.org/10.1063/1.355022 (9 pages)

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A general solution to the hygrothermoelastic problem associated with an interface discontinuity between dissimilar anisotropic media is presented. The complex variable representation of Lekhnitskii [Theory of Elasticity of an Anisotropic Elastic Body (Holden‐Day, San Francisco, CA, 1963)] is extended into the hygrothermoelastic problem by means of five complex functions including three stress functions, one temperature function, and one moisture function. A special technique of analytical continuation is used to deal with the continuous conditions of dissimilar media. Based on the Hilbert problem formulation, the linear relation between the boundaries of discontinuity can be derived into a type of Cauchy integral, which makes the solution in a compact version. The result shows that the heat or moisture flux exhibits an inverse square‐root singularity at the tips of discontinuity while the nature of singularity of the hygrothermal stresses possess the same trig‐log character as those obtained for the elastic problem.  
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46.25.Cc Theoretical studies
44.30.+v Heat flow in porous media
62.20.D- Elasticity

Expansion and electron emission characteristics of a hollow‐cathode plasma contactor

Donald E. Parks, Ira Katz, Brett Buchholtz, and Paul Wilbur

J. Appl. Phys. 74, 7094 (1993); http://dx.doi.org/10.1063/1.355023 (7 pages) | Cited 6 times

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A theory is presented to explain the observed electron emission characteristics of a hollow‐cathode‐based plasma source. The theory is compared with measurements made in a laboratory vacuum facility and is used to predict emission characteristics when the source plasma expands into an ambient space plasma. Crucial to understanding the observed emission current‐voltage characteristic of hollow‐cathode‐type devices is the recognition of the role of emission current, not just the current in the main discharge circuit, in ionization of the neutral gas flowing through the device. This ionization can lead to breakdown of the sort that is familiar in many gas discharge devices. Equally crucial to understanding the low impedance capability of the device in coupling spacecraft to an ambient space plasma is recognition of the role of escaping as well as trapped source electrons in the formation of the space potential profile. The presence of these electrons, according to the theory, results in space electron emission current‐voltage characteristics which are well approximated by those observed in laboratory chambers.
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52.80.Tn Other gas discharges
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.-b Plasma properties

Argon incorporation in Si(100) by ion bombardment at 15–100 eV

W. M. Lau, I. Bello, L. J. Huang, X. Feng, M. Vos, and I. V. Mitchell

J. Appl. Phys. 74, 7101 (1993); http://dx.doi.org/10.1063/1.355024 (6 pages) | Cited 19 times

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Argon incorporation in Si(100) by low energy ion bombardment has been studied by polar angle dependent x‐ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The bombardment was performed at 15, 20, and 100 eV in an ultrahigh vacuum chamber where a mass‐separated argon ion beam with an energy spread of less than 1 eV was directed to the target. Both the argon penetration depth and incorporation probability were found to increase with bombardment energy. With a fluence of 2×1017/cm2, most of the incorporated argon was located within 20 Å of the target surface for the 100 eV bombardment and within 10 Å for the 15 eV bombardment. In all cases, the argon depth distribution reached a maximum and then declined. At this fluence, the incorporation probabilities were 0.0015 and 0.0004 for the 100 and 15 eV bombardment, respectively. When the amount of incorporated argon was measured as a function of fluence, it increased with fluence at low fluences, reached a quasisaturation at about 1×1016/cm2, but became fluence dependent again above 1×1018/cm2. The retained argon was stable at room temperature but showed at least two stages of thermal desorption in the temperature range 25–500 °C.
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61.80.Jh Ion radiation effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Density changes and viscous flow during structural relaxation of amorphous silicon

C. A. Volkert

J. Appl. Phys. 74, 7107 (1993); http://dx.doi.org/10.1063/1.355025 (7 pages) | Cited 36 times

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Structural relaxation of amorphous silicon (a‐Si) surface layers made by ion irradiation has been studied during heating using wafer curvature measurements. These measurements, which determine the stress in the amorphous layer, are sensitive to both plastic deformation and density changes. The amorphous layer first expands (0.1%) on heating from room temperature to 250 °C and then densifies (0.1%) on heating further to 500 °C. A larger expansion (≥0.3%) is observed on heating liquid‐nitrogen‐temperature irradiated a‐Si to room temperature. This behavior reveals the existence of two distinct relaxation regimes, and is explained in terms of the annihilation of complementary features of the amorphous covalent network. In addition to density changes, shear deformation was observed during heating the a‐Si layers. This deformation was characterized by a Newtonian shear viscosity of roughly 3×1012 N s/m2. The thermal‐expansion coefficient of the a‐Si was determined to be roughly 6.5% smaller than that of crystalline Si. Stress changes due to crystallization by epitaxial regrowth were observed between 600 and 700 °C and revealed evidence for the existence of large compressive stresses at the amorphous‐crystalline interface.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity

Implantation temperature effect on polycrystalline silicon by ion shower doping

Y. Mishima, M. Takei, N. Matsumoto, and T. Uematsu

J. Appl. Phys. 74, 7114 (1993); http://dx.doi.org/10.1063/1.355026 (4 pages) | Cited 3 times

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We present a new doping technique using an ion shower doping system with a bucket ion source. Phosphorus atoms were implanted in polycrystalline silicon from room temperature to 300 °C. Sheet resistances were significantly reduced by raising the implantation temperature. With a crystal fraction of 85%, sheet resistance was 5×102 S−1/☒ as implanted. These effects were not due to pure thermal annealing by ion beam heating. A significant improvement was found in sheet resistance as a result of averaging the impurity profile by radiation enhanced diffusion and low temperature recrystallization of the implanted region by collision of atoms.  
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61.72.uf Ge and Si
72.80.Cw Elemental semiconductors

The effect of coimplantation on the electrical activity of implanted carbon in GaAs

A. J. Moll, J. W. Ager, Kin Man Yu, W. Walukiewicz, and E. E. Haller

J. Appl. Phys. 74, 7118 (1993); http://dx.doi.org/10.1063/1.355027 (6 pages) | Cited 5 times

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The effects of radiation damage and stoichiometry on the electrical activity of carbon implanted in GaAs are studied. Damage due to implantation of an ion heavier than C increases the number of C atoms which substitute for As (CAs). Creation of an amorphous layer by implantation and the subsequent solid phase epitaxy during annealing further enhances the concentration of CAs. However, the free carrier concentration does not increase linearly with increasing concentration of CAs due to compensating defects. Activation of implanted C is maximized by maintaining the stoichiometry of the substrate which reduces the number of compensating defects in the crystal. Under optimum conditions for carbon implanted at a dose of 5×1014 cm−2, the carbon acceptor activity can be increased from 2% to 65% of the total implanted carbon.
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61.72.uj III-V and II-VI semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Synchrotron x‐ray topography study of Er‐doped LaP5O14 crystal

Z. W. Hu, P. Q. Huang, S. S. Jiang, J. Y. Wang, J. H. Jiang, and J. Y. Zhao

J. Appl. Phys. 74, 7124 (1993); http://dx.doi.org/10.1063/1.355028 (5 pages) | Cited 3 times

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An Er‐doped LaP5O14 ferroelastic crystal has been studied by synchrotron radiation white beam x‐ray topography. A set of normal ferroelastic domains is revealed in topographs by the intense contrast at the domain walls and the temperature dependence of the wall contrast is shown to be in good agreement with that expected from the structural consideration. In addition to growth bands and growth sector boundaries, a type of abnormal boundary is observed, and the contrast varies with the occurrence of phase transitions. A detailed discussion on experimental results is given in terms of structural and symmetry analyses.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Microstructural studies of epitaxial CoSi2 layers on silicon produced by ion beam synthesis and rapid thermal annealing

C. D. Meekison, G. R. Booker, K. J. Reeson, R. S. Spraggs, R. M. Gwilliam, and B. J. Sealy

J. Appl. Phys. 74, 7129 (1993); http://dx.doi.org/10.1063/1.355029 (5 pages) | Cited 8 times

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Structures of cobalt disilicide layers fabricated by ion beam synthesis on (001) silicon wafers have been studied by cross‐sectional transmission electron microscopy. Implantation at 350 °C with doses of 5 and 7×1017 cm−2 of 200 keV Co+ ions was used, followed by rapid thermal annealing. For the as‐implanted wafer with the lower dose, a CoSi2 layer in a parallel (A‐type) epitaxial orientation was formed, and below this there were CoSi2 precipitates, some in twinned (B‐type) orientations, and {113} defects. With the higher dose, polycrystalline CoSi was also present at the surface and there was substantial surface roughening. For the annealed wafers, as the annealing temperature increased from 700 to 1100 °C, the CoSi2 layer progressively increased in thickness, and the CoSi at the surface of the CoSi2 layer was eliminated. In the silicon beneath the silicide layer, the CoSi2 precipitates were greatly reduced in number and the {113} defects were eliminated.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.72.uf Ge and Si

Theory of the electron fracture mode in solids

Genady P. Cherepanov and Andrew A. Borzykh

J. Appl. Phys. 74, 7134 (1993); http://dx.doi.org/10.1063/1.355030 (20 pages)

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The theoretical model serving to explain and describe the phenomenon of the electron fracture mode (EFM) discovered experimentally nearly 20 years ago is advanced. EFM is characterized by the brittle cleavage of common plastic crystals proceeding with supersonic velocities independently of initial cracks when subjected to high‐intensity electron beams. Using the invariant Γ integral of an electromagnetic deformable medium, it is proven that two electrons moving faster than the phase speed of light attract one another, as distinct from the common Coulomb’s law. Self‐packing of such relativistic electron beams is studied using a periodic chain model. It is suggested that during irradiation of a solid by a high‐intensity electron beam, some electron clusters are formed, which act as wedges cutting the crystalline specimen. The dynamic problem of supersonic cutting by a thin wedge is studied, and the drag is calculated. The length of the resulting crack is computed. The theoretical results are confirmed by available experimental data.
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61.80.Az Theory and models of radiation effects
62.20.M- Structural failure of materials

Viscosity and elastic constants of amorphous Si and Ge

Ann Witvrouw and Frans Spaepen

J. Appl. Phys. 74, 7154 (1993); http://dx.doi.org/10.1063/1.355031 (8 pages) | Cited 52 times

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The biaxial modulus and coefficient of thermal expansion of ion‐beam‐sputtered amorphous Si and Ge thin films were determined from curvature changes induced by differential thermal expansion. Viscous flow was measured by stress relaxation and was found to be Newtonian. The viscosity increased linearly with time as a result of structural relaxation, and its isoconfigurational activation enthalpy was 1.8±0.3 and 2.6±1.3 eV for amorphous Si and Ge, respectively. An atomistic model, based on a chain reaction of broken bond rearrangements, is proposed to describe the observation.  
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68.60.Bs Mechanical and acoustical properties
61.43.Dq Amorphous semiconductors, metals, and alloys
62.20.D- Elasticity

Spall strength of molybdenum single crystals

G. I. Kanel, S. V. Razorenov, A. V. Utkin, V. E. Fortov, K. Baumung, H. U. Karow, D. Rusch, and V. Licht

J. Appl. Phys. 74, 7162 (1993); http://dx.doi.org/10.1063/1.355032 (4 pages) | Cited 33 times

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Spall strength measurements for commerical grade molybdenum and molybdenum single crystals were made in a wide range of load durations (∼10−9 s – 10−6 s) and intensities (∼5 – 100 GPa). Resistance to fracture of pure single crystals was found to exceed two times the spall strength of polycrystalline molybdenum and to increase with shorter load duration. The value of the shock wave amplitude does not influence the spall strength of single crystals. The largest spall strength obtained under nanosecond load duration amounts to 30% of the ultimate theoretical strength.
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62.20.M- Structural failure of materials
62.50.-p High-pressure effects in solids and liquids

Evidence of silicon interdiffusion in selectively doped GaAs‐AlAs superlattices by Hall measurements

P. Sellitto, P. Jeanjean, J. Sicart, J. L. Robert, and R. Planel

J. Appl. Phys. 74, 7166 (1993); http://dx.doi.org/10.1063/1.355033 (7 pages) | Cited 8 times

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Hall and photo‐Hall measurements have been performed on GaAs‐AlAs short‐period superlattices selectively doped with silicon. The dopant was introduced selectively in either the GaAs or AlAs layers or at the interface. A superlattice doped uniformly in both layers was investigated for comparison. The electrical properties were controlled by DX deep donors lying in the gap of the superlattice. Hall data are interpreted with a model taking into account the existence of two DX deep donors and a shallow donor both related to the silicon impurity. It is found that the silicon donor state in AlAs lies 60 meV below the silicon donor state in GaAs. The ionization energies of the DX states in GaAs and AlAs are computed to account for the experimental results. Interpretation of Hall data in selectively doped samples needs to assume segregation of silicon atoms during epitaxy.    
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Transmission‐line‐matrix modeling of grain‐boundary diffusion in thin films

Xiang Gui, Steven K. Dew, Michael J. Brett, and Donard de Cogan

J. Appl. Phys. 74, 7173 (1993); http://dx.doi.org/10.1063/1.355034 (8 pages) | Cited 16 times

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The use of the transmission‐line‐matrix (TLM) method for analyzing the grain boundary and interfacial diffusion problems in thin films is demonstrated. The method employed has a variable mesh and automatic time‐stepping capability, and is highly versatile in treating complex structures and incorporating various boundary conditions. The present model takes account of separate diffusion coefficients in grain boundaries, grains, interfaces, and the substrate. The combined diffusion problems are solved as a function of position and time, and the concentration distributions are presented as clearly visible isometric projections and contour plots. The results are compared with those of semi‐infinite samples (Whipple’s analysis [Philos. Mag. 45, 1225 (1954)]) and idealized thin‐film systems (Gilmer and Farrell’s analysis [J. Appl. Phys. 47, 3792 (1976)]), with the emphasis being placed on the differences due to the treatment of concentration flux along the interface between the film and the substrate and into the substrate. The TLM method is shown to have considerable potential in practical applications for diffusion processes in thin films.
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66.30.-h Diffusion in solids
68.60.Wm Other nonelectronic physical properties

Stabilization and growth interruption effects at ZnSxSe1−x/ZnSe quantum‐well interfaces grown by metalorganic vapor‐phase epitaxy

A. Schneider, K. P. Geyzers, J. Söllner, and M. Heuken

J. Appl. Phys. 74, 7181 (1993); http://dx.doi.org/10.1063/1.355035 (7 pages) | Cited 2 times

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ZnSxSe1−x/ZnSe quantum wells (QW) with and without growth interruption at the interface were grown using atmospheric pressure metalorganic vapor‐phase epitaxy. It has been shown that growth interruptions have a major influence on the optical properties of the QW. An interruption of growth in ternary ZnSSe layers causes a quasi‐QW photoluminescence (PL), explained by sulfur depletion of the layer. A stabilization is necessary to avoid a quasi‐QW. High‐quality ZnSSe/ZnSe QWs were achieved by suitable stabilization with H2S and DESe during the growth interruption at the interface, so a sulfur diffusion out of the barrier can be avoided. The QW thicknesses grown under these conditions were in agreement with the nominal well thicknesses, and for stabilized 1‐nm QWs we obtain a PL blueshift of 158 meV for x=0.68 and 60 meV for x=0.4 compared to the ZnSe band‐edge emission. Characteristic QW‐PL transitions at room temperature were observed for unstabilized QW grown with a long interruption time, tp=90 s. The thermal activation energies of the QW excitons investigated by temperature‐dependent PL show that with decreasing interruption time an increased binding energy is obtained. The binding energy shows no dependence on the stabilization so that other effects (e.g., interface roughness and sulfur diffusion) may play a role. For QW with a low sulfur content (x=0.4) in the barrier material, we find binding energies which fit to theoretical models. This was not achieved for QWs with x=0.68.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.55.Et II-VI semiconductors

Investigation of InAs submonolayer and monolayer structures on GaAs(100) and (311) substrates

Matthias Ilg, M. Isabel Alonso, Arno Lehmann, Klaus H. Ploog, and Matthias Hohenstein

J. Appl. Phys. 74, 7188 (1993); http://dx.doi.org/10.1063/1.355036 (10 pages) | Cited 13 times

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We demonstrate a new route to the synthesis of InAs monolayer structures in GaAs by bridging the fundamental gap between the requirement of the lowest possible substrate temperatures to suppress In segregation and the necessity to maintain sufficiently high temperatures for the growth of low‐defect density material. This mediation between opposing aspects of the molecular beam epitaxy of these InAs structures is achieved by a modulation of the substrate temperature and by a minimization of the amount of GaAs cap material grown at low temperature. High‐resolution x‐ray diffraction and high‐resolution electron microscopy combined with photoluminescence (PL) and PL excitation spectroscopies reveal excellent structural properties for our series of (311) and (100) oriented submonolayer and monolayer structures. A comparison of our PL results with already published data proves our In concentration profiles to be very sharp and from a numerical analysis we deduce an upper limit of 0.2 for the In segregation probability in these structures. In addition we obtain as upper limits for the conduction band offsets Q(100)c≤0.4 and Q(311)c≤0.55 for (100) and (311) orientations, respectively.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.C- X-ray diffraction and scattering
78.55.Cr III-V semiconductors

On spinodal decomposition in elastically anisotropic epitaxial films of III‐V semiconductor alloys

I. P. Ipatova, V. G. Malyshkin, and V. A. Shchukin

J. Appl. Phys. 74, 7198 (1993); http://dx.doi.org/10.1063/1.355037 (13 pages) | Cited 64 times

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The elastic energy associated with alloy composition modulation in the epitaxial film of a III‐V semiconductor alloy on the [001]‐substrate is calculated in the analytic form. Composition modulation both in the directions parallel to the substrate surface and in the growth direction are taken into account. It is shown that the minimum of the elastic energy corresponds to the modulation along the [100]‐ (and/or [010]‐) direction, the period of the modulation d being small compared to the film thickness h (d≪h). The ‘‘soft mode’’ of composition modulation is exponentially localized near the free surface, the localization length l being l=d/2π. The elastic energy caused by this modulation is less by the factor 1/2c11/(c11+c12) than the elastic energy corresponding to spinodal decomposition in the bulk sample. This factor is ≊1/3 for III‐V alloys. Critical temperatures of spinodal decomposition Tc are calculated for a number of epitaxial ternary III‐V alloys. The diffusion which occurs only in the very thin subsurface layer (nearly monolayer) is shown to provide exponential amplification of the composition modulation amplitude δc(0)∼exp(Δh/l) at early stages of the subsequent layer‐by‐layer growth.
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68.60.-p Physical properties of thin films, nonelectronic
81.30.Mh Solid-phase precipitation
64.75.-g Phase equilibria

Growth and characterization of GaSe and GaAs/GaSe on As‐passivated Si(111) substrates

J. E. Palmer, T. Saitoh, T. Yodo, and M. Tamura

J. Appl. Phys. 74, 7211 (1993); http://dx.doi.org/10.1063/1.355038 (12 pages) | Cited 16 times

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We have grown and characterized epitaxial layered structure GaSe on As‐passivated Si(111) and GaAs on GaSe on As‐passivated Si(111) for the ultimate purpose of using the layered structure GaSe as a lattice mismatch/thermal expansion mismatch buffer layer in the GaAs on Si system. Films were grown on nominally (111) oriented Si substrates by molecular beam epitaxy and characterized by in situ reflection high energy electron diffraction, as well as by ex situ scanning electron microscopy and both plan‐view and cross‐sectional TEM (transmission electron microscopy). In this study, GaSe was grown epitaxially on As‐passivated Si(111) substrates at 500 °C with Se/Ga BEP (beam equivalent pressure) ratios of ∼10 and ∼20. Small droplets were observed on the surface after GaSe growth. These are thought to be droplets of unreacted Ga. The density and size of the droplets decreases with the increasing Se/Ga BEP ratio. When the GaSe surface is exposed to As, the droplets become GaAs islands. Subsequent GaAs growth was carried out at 400 and 500 °C, giving the following results for 300‐Å‐thick films: as grown GaAs films were highly twinned, and some polycrystalline GaAs was present in the film grown at 400 °C. In situ annealing at 650 °C for 10 min reduced the density of twins in both cases. In plan‐view TEM, Moiré fringes from both GaAs and GaSe are observed and show conclusively that the GaAs grew epitaxially on the GaSe without contacting the Si substrate. Cross‐sectional TEM shows the interface between the Si and GaSe is not smooth on the atomic scale. In spite of this, the GaSe becomes smooth with about 2 monolayers of growth and the GaAs/GaSe interface appears to be very smooth.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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