摘要:

The two limits for modeling vibrating thin films, viz as a plate or as a membrane, are discussed. In terms of these limits the sources of experimental uncertanties are identified and the advantages of using films which can be modeled as membranes are explained. The mathematical formalism for treating films as vibrating membranes is developed and relations for self‐consistency checks are presented. The drive mechanisms used to generate vibrations in the films are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.350804

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Effects of In, Zn, and Si impurities on the mechanical behavior of GaAs are investigated. Experimental results are interpreted in terms of the impurity effect on the dislocation velocity and of dislocation locking due to impurities which have been clarified by previous experiments. It is shown that in the temperature range lower than about 600 °C the impurity effect on the dislocation mobility in glide motion plays a dominant role in determining the mechanical strength, while in the higher temperature range dislocation locking by impurities controls the strength. Thus, Si impurity is the most effective in enhancing the strength in the low‐temperature range while In impurity is so in the high‐temperature range. The dislocation processes which take place during plastic deformation of any impurity‐doped GaAs crystals in the low‐temperature range are essentially the same as those taking place in highly pure crystals of other kinds of semiconductors such as Ge and Si.

ISSN:0021-8979    

DOI:10.1063/1.350805

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The thermal conductivity of heavily doped,n‐type Si‐Ge alloys has been studied from 300 to 1200 K. The scattering rate of several phonon scattering mechanisms has been calculated, including intrinsic scattering, mass defect and distortion scattering, phonon‐electron scattering, and scattering by inclusions. These rates were then used to calculate the lattice thermal conductivity. The electronic component of the thermal conductivity was calculated from the calculated Lorenz ratio and measured values of the electrical conductivity. The total thermal conductivity was then compared to measured values for a specimen studied by Viningetal. [J. Appl. Phys.69, 15 (1991)].

ISSN:0021-8979    

DOI:10.1063/1.350806

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Time‐dependent vacancy concentration profiles are calculated numerically as solutions to the electromigration transport equation under dc and pulsed dc current stress conditions. An electromigration failure model based on the time to reach a critical vacancy supersaturation to initiate void formation agrees well with several reported experimental observations. In a line of finite lengthlcarrying a constant current densityjthe electromigration‐induced vacancy concentration buildup at a blocking boundary saturates with time which implies a threshold value ofjlis required to initiate failure. The vacancy buildup as a function of time has aj−2current density dependence below saturation. Under pulsed dc stress the level at which vacancy concentration saturates depends on duty ratior; hence, there is a threshold value ofrrequired to initiate failure as well. The vacancy buildup with time is found to be proportional tor−2below saturation.

ISSN:0021-8979    

DOI:10.1063/1.350807

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The formation mechanisms and properties of TiSi2on Si are investigated. The particular emphasis is in relating the nucleation, morphology, and phase stability of the films. TiSi2films were prepared by deposition of Ti on atomically clean silicon substrates in ultrahigh vacuum. The silicide formation was initiated either byinsituannealing or deposition onto heated substrates. The island formation of TiSi2and surface and interface morphologies of TiSi2were examined by scanning electron microscopy and transmission electron microscopy. The TiSi2formation process was monitored withinsituAuger electron spectroscopy and low‐energy electron diffraction to analyze the surface concentration and the surface structures, respectively. Raman spectroscopy was used for phase identification of the TiSi2. Titanium film thicknesses from 50 to 400 A˚ were examined. For all thicknesses studied, the C49 TiSi2phase is observed to nucleate. Immediately after low‐temperature deposition, the interface morphology was smooth, but after reaction and nucleation of the C49 TiSi2phase a rough interface was observed. After higher‐temperature annealing the transition to the C54 TiSi2phase was observed. For TiSi2on Si(111), the interface becomes smooth and flat. The temperature of the C49‐to‐C54 transition was observed to vary as a function of film thickness and substrate orientation. The films exhibited island formation after high‐temperature annealing. For similar Ti thicknesses and annealing temperature, different areal coverages and island morphologies of TiSi2on Si(100) and Si(111) were observed. The island morphologies are modeled and analyzed based on a liquid‐liquid model, and the surface and interface energies for different TiSi2island structures are deduced from contact angle measurements. The C49 nucleation, interface morphologies, surface morphologies, and the C49‐to‐C54 structural phase transition are discussed in terms of surface and bulk free‐energy considerations.

ISSN:0021-8979    

DOI:10.1063/1.350808

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The growth process in the initial deposition stage of Ge films on an Si(001) surface where tellurium is adsorbed was investigated. The growth mode of these films was found to change to layered growth on a Te/Si(001) surface, i.e., Te atoms were observed on the surface of the Ge films as a result of successive site exchanges between the Te and Ge atoms. Thus, Te is believed to act as a surfactant to grow Ge in a layer‐by‐layer mode on a Si substrate. The growth process was observedin situby reflection high‐energy electron diffraction and low‐energy electron diffraction, with the microstructure of Ge films being examined in detail using a transmission electron microscope.

ISSN:0021-8979    

DOI:10.1063/1.350809

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A quantitative theory of the nonspecular scattering of x rays from multilayer structures having rough interfaces is presented. The results are valid for arbitrary polarization and angles of incidence (measured from the normal) less than the critical angle for total external reflection. A structural model is adopted wherein each interface is assumed to be described by a surface having statistically random roughness with a well‐behaved power spectrum. In addition, the model accounts for arbitrary correlation of the roughness between different interfaces. Calculations are presented for a variety of roughness configurations to investigate the dependence of the nonspecular scattering on the fundamental structural parameters. In particular, it is shown that the scattering from correlated roughness exhibits characteristic resonance behavior (quasi‐Bragg diffraction).

ISSN:0021-8979    

DOI:10.1063/1.350810

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have systematically examined the transition from two‐dimensional nucleation to step‐flow growth on variously misoriented vicinal GaAs (001) surfaces during molecular beam epitaxy using reflection high‐energy electron diffraction (RHEED). The time to the first maximum of the RHEED intensity oscillations is gradually delayed as the growth mode transition temperature is approached from below as the result of an increasing number of adatoms being incorporated at steps. Detailed analysis of this delay has shown that the incorporation rate is independent of the Ga flux, but it is strongly dependent on the direction of misorientation. This means that step edges do not act as perfect sinks for adatoms, but that detachment can occur relatively easily. The energy barrier for incorporation is considerably higher for Ga‐ than As‐terminated steps, which strongly suggests that the anisotropic growth mode transition on GaAs (001) stems mainly from the different step structures rather than anisotropic Ga adatom migration.

ISSN:0021-8979    

DOI:10.1063/1.350811

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

SimGenstrained layer superlattice (SLS) structures were grown by molecular beam epitaxy on GexSi1−xbuffer layers on ⟨100⟩ Si substrates to determine the effects of buffer layer composition, SLS thickness ratio, and superlattice periodicity, on the overall quality of these structures. X‐ray diffraction methods were used to determine how closely actual periodicities and compositions met targeted values, and to evaluate the quality of these samples. In most instances the as‐grown structures matched the targeted values to within 10%, though in some instances deviations of 20–25% in either the period or composition were observed. The quality of the SLS structures was greatly dependent on the composition of the buffer layer on which it was grown. SimGenSLS structures grown on Si‐ and Ge‐rich buffer layers were of much higher quality than SimGemSLSs grown on Ge0.50Si0.50layers, but the x‐ray rocking curves of the SimGensamples indicated that they were far from perfect and contained moderate levels of defects. These results were confirmed by cross sectional transmission electron microscopy, which showed that the SimGemstructures contained significant numbers of dislocations and that the layers were nonuniform in thickness and wavy in appearance. SimGenstructures, however, displayed fewer defects but some dislocations and nonparallelism of layers were still observed.

ISSN:0021-8979    

DOI:10.1063/1.350812

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A simple method, which uses numerical calculations to estimate diffusion fluxes into reactive interfaces during silicide formation processes, has been developed. Based on analysis of calculated diffusion fluxes from experiments from five different published papers, a model has been proposed to explain the unique kinetic behavior associated with thin‐film metal‐silicon diffusion couples. The reactive interface in a metal‐silicon diffusion couple is considered to be a reaction region, and the reaction process is divided into three steps. Several physical quantities have been defined to describe each of these steps, i.e., the diffusion flux of moving reactant to the reaction regionJm, the release rate of nonmoving reactantrn, and the formation rate of the growing phaseF. The relationship between these quantities has been demonstrated by means of a reaction process plot, which is also developed in this study.

ISSN:0021-8979    

DOI:10.1063/1.350813

出版商:AIP    

年代:1992

数据来源: AIP