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Si1-xGex films were grown from SiH2Ci2/GeH4 precursors.

A study was conducted to determine the kinetics of the As/P exchange reaction at an epitaxially grown InP surface exposed to As flux using a two-step mechanism. The transient and steady-state profiles of As composition and the maximum depth of As/P exchange reaction were analytically obtained. Results indicated the effectivity of the two-step mechanism in analyzing superlattice growth supporting different group V atoms.

A study was conducted to characterize a technique for solving the time-dependent Schrodinger equation for double-barrier quantum wells supporting the presence of incident waves. Time-independent basis functions were also considered for the solution. Results indicated that the method can be utilized to determine precise tunneling lifetime. Findings also showed that the technique can be used in systems where numerical methods fail.

Studies of the superlattice systems of Si-Si(x)Ge(1-x) indicate that the band gap of materials containing Ge correspond with the maximum attainable band gaps. The superlattice period controls the directness of the energy bands while the thickness of Si and Si(x)Ge(1-x) controls the energy extrema of the valence and conduction bands, respectively. Analysis of the band structure of Si-Si(x)Ge(1-x) superlattices on the substrates of type Si-Si(1-x)Ge(x) gives the strain effect on these bands.

Computation of the optical matrix elements of different types of Si-Si(x)G(1-x) for transitions from valence-band maximum to conduction band minimum enables the evaluation of the applicability of the direct-gap superlattice configuration. The method is identical to the k.p vector method that is used for indirect band-gap constituent materials, and is more accurate than the envelope-function method. The optical matrices obtained are more reliable than the other parameters obtained from the envelope-function method.

The output intensity of a semiconductor laser increases by an order of magnitude consequent to a decrease in stripe width, but the maximal increase is by a factor of about two. The laser with a smaller stripe width can operate at a higher temperature at the same output power in comparison to a laser with a larger width.

The effects of external electric fields on the electronic band structure and absorption coefficient forintersubband transitions in a Si/Si1-xGex superlattice are studied. A transfer-matrix technique is used to analyze the Wannier-Stark ladders or discrete energy levels generated by electric fields applied along the growth axis of a Si/Si1-xGex superlattice. Results reveal that Wannier-Stark ladders shift to the shorter photon wavelength for intersubband transitions as the electric field increases.

A physical model for estimating the surface recombination velocity and lifetime of semiconductor lasers are discussed. The model, which is based on reactions involving oxidation, takes into account the chemical and physical parameters that control the degradation process and lifetime of semiconductor lasers. Aging tests performed on several laser structures show that the proposed model is very useful for estimating the laser lifetime.

Intersubband optical absorption in Si/Si1-xGex superlattices was investigatedusing multicomponent envelope functions. The results showed that the results obtained using multicomponent envelope functions markedly differed from those obtained using single wave function approximation. In the latter method, much lower absorption coefficient values were obtained and most of the transition peaks were absent.

The expression for electron energy distribution function was derived from the Boltzmann transport equation. Nonpolar and polar optical phonon scattering were characterized and differentiated as well as all other scattering mechanisms. Computations for impact ionization coefficients for electrons and holes in Ge, Si and GaAs compare favorably with experimental results. Intervalley scattering was found to dominate particular GaAs in polar semiconductors.

Effective-mass approximation is the basis for an alternative to the infinite boundary condition for free-standing quantum films.

A study was conducted to examine the variables that influence surface morphology in the heteroepitaxial growth of Si1-xGex layers on silicon. These include pressure, temperature, deposition and composition. Phase boundary lines that define the regions for planar and island growth in terms of composition-pressure and composition-temperature were derived. Similarly, the influence of temperature, pressure and characteristic time on the roughening characteristic length was also determined.

An evolving mechanism of the ripple structure in Si/Ge heteroepitaxy is proposed while an expression for the phase boundary between the ripple and hut structures is derived. A criterion is obtained that can provide the conditions under which one of the two intermediate steps is favored. A relationship is derived by energy minimization which indicates that the ratio of the amplitude to the square of the period of the ripple structure is constant in the evolving stage.

We demonstrate that the separated polymer strips of micro- and sub-micro-length-scales rupture anisotropically along the strip direction, resulting in the formation of distinctly observable, regularly spaced polymer drops. The wavelength of the polymer drops and the surface tension dependence of the rupture behavior are found to be well represented by a relationship derived on the basis of Rayleigh instability. The period is proportional to the square root of the cross-sectional area of the strip and the proportionality constant depends on the contact angle. The rupture of polymer strips into polymer blocks instead of drops, which result when annealed with physically confining walls in place, is found to be well described by the same relationship. [ABSTRACT FROM AUTHOR]

We observed the formation of regular nanoscale undulations on a polystyrene film when imprinted by a soft poly(dimethylsiloxane) mold above the polymer’s glass transition temperature. The shape of the wave was reminiscent of a buckling wave frequently observed for a metal film supported on an elastomeric substrate. We derived a simple theoretical model based on an anisotropic buckling of the polymer film rigidly bound to a substrate, which agrees well with the experiment. [ABSTRACT FROM AUTHOR]

Theoretical analysis based on a nondegenerate perturbation method is presented for two-dimensional buckling patterns of a thin metal-capped polymer bilayer on a rigid substrate. The analysis reveals that isotropic one-dimensional buckling mode has the lowest free energy, which contrasts previous work on the buckling of a thin metal film on the semi-infinitely thick polymer layer studied by Chen and Hutchinson [J. Appl. Mech. 71, 597 (2004)]. In the low stress region, however, checkerboard buckling mode has the lowest energy. Herringbone buckling mode is shown to be represented by a linear combination of the checkerboard mode and the isotropic one-dimensional mode. Disorder parameter values are given for these various two-dimensional buckling modes on the basis of an envelope function. [ABSTRACT FROM AUTHOR]

An experimental method suitable for reproducible results has been used to investigate dewetting behavior of thin films of solvent-laden polymer. This solvent-driven dewetting enables one to change spreading coefficient by an order of magnitude that is not readily realizable in thermal dewetting and to study polar interactions that have not been fully exploited experimentally. While the film instability is similar to that found in thermal dewetting, the rim instability is quite different. Two different types of the rim instability have been found. With a polar solvent, the rim instability changes from one type to another with increasing film thickness whereas the unstable rim becomes stable for an apolar solvent. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A unique experimental system is devised that reveals the interplay among capillary force and alternating intermolecular forces. As a consequence of the interplay, untrathin (<10 nm) liquid films, which invariably experience dewetting, can be made stable, leading to a smooth and dropless minimum-potential surface. Theory and experiment show that the film thickness is < 1 nm when the film recedes in spite of the capillarity and it is <3 nm when it rises into a cavity. [ABSTRACT FROM AUTHOR]

We report ordering of polymer drops that takes place when a thin polystyrene film confined by polydimethylsiloxane walls dewets on a silicon substrate. When annealed above the glass transition temperature, the thin polymer film dewets, resulting in the formation of a regular structure inside and outside the confinement. It is found that the ordering becomes strongly suppressed as the film thickness increases and the pattern size decreases due to the physical confinement of the mold. As a result, the ordering can take place only when the wavelength of the capillary wave is smaller than the characteristic length of the physical confinement. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report dewetting behavior of thermally annealed thin polymer strips of poly (styrene-b-butadiene-b-styrene) and polystyrene films that are laterally confined by polydimethylsiloxane walls on silicon substrate. Regularly spaced holes are initially nucleated on the polymer surface and then grow with the aid of the confining walls, resulting in the formation of distinctly observable, regularly spaced blocks of the strip. It is observed that the dependence of hole density on the film thickness severely deviates from the conventional capillary wave model. This anomaly may be related to the viscoleastic properties of the polymer film. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Aging behavior of red, green, and blue photoluminescence from porous silicon formed by electrochemical etching aided with zinc has been studied over a 3 month time span. Time-resolved photoluminescence spectra and decay dynamics have revealed that there are two radiating states in Zn-aided porous silicon. One is the quantum confinement and the other is the oxygen-related defect. For green emission, the wavelength shifts from 520 to 420 nm and its photoluminescence spectra and decay behavior become very similar to those of blue emission. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A study of the conduction band characteristics of Si/Si(1-x)Ge(x) superlattices revealed that the most prominent feature of such double well-and-barrier superlattices was the merging of two adjacent state minibands that had islands in the center. Far infrared range photodetection uses optical transitions that occur across the miniband islands.

Direct optical transition can be achieved between the two lowest conduction subbands of a Si/GexSi1-x superlattice in the infrared subrange. The resulting optical-absorption strength of the direct intersubband transition is two orders of magnitude smaller than that of gallium arsenide. If a well is inserted into the barrier part of an n by n superlattice, then the absorption strength will increase by almost an order og magnitude.

Presents a study which developed a theoretical model for the composition dependence of the activation energy in solid phase epitaxial growth of Si[sub1-x]Ge[subx] alloys. Description of the proposed models for the solid phase epitaxy mechanism (SPE); Requirements for the recrystallization in SPE; Comparison between the regrowth rate of stressed and stress-relaxed alloys.

Presents a study which used an approximate solution of the Boltzmann transport equation to arrive at an expression for the electron energy distribution function in polar and nonpolar semiconductors. Development of the Boltzmann transport equation; Impact of ionization coefficients on polar and nonpolar semiconductors; Comparisons and discussion.

Presents a framework for the kinetics of thin film growth under simultaneous doping conditions. Importance of the codeposition of a dopant on the growth of semiconductor crystals and thin films; Examination of codeposition and growth; Discussion on the results of the study.

Presents a necessary and sufficient condition for no thermal runaway in carrier wave double heterostructure (DH) semiconductor lasers. Characteristics of DH semiconductor laser; Factor which limits the lifetime of a laser and the output power for rapidly pulsed operation; Limitations of the thermal model for the criterion.

The features of the blue emission from the in situ copper-doped porous silicon (PS) mediated by carbon contamination are presented. The formation of the carbonyl group, which is catalyzed by Cu on the surface of the porous silicon, is revealed by Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy.