摘要:

Single crystals ofn‐Hg1−xCdxTe (x=0.18) were grown by the Bridgman technique. The bulk single crystals were irradiated with laser pulses of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53‐&mgr;m wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the van der Pauw technique in the temperature range 77–300 K, for both as‐grown and laser‐irradiated samples. Also, transmission measurements of the samples were taken at room temperature. Both electrical and optical studies showed that laser irradiation introduces additional defects in mercury cadmium telluride (MCT), and its quality deteriorates instead of improving as observed in many other semiconductor materials. We found that laser irradiation increases free‐carrier concentration and decreases the band gap of MCT.

ISSN:0021-8979    

DOI:10.1063/1.348440

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A detailed theoretical and experimental study of laser‐induced density and temperature changes, and flow‐reorientation effects in the nematic and smectic phases of liquid crystals is presented. Using picosecond lasers, the initial nanosecond dynamics of the photoinduced density waves, temperature buildup, and relaxations are temporally resolved. The experimentally observed relaxation phenomena and time scales are in good agreement with the theoretical expressions obtained by analytical solutions of the coupled hydrodynamical equations describing these fundamental mechanisms. Our new measurement and theory provide a quantitative account of the relative contribution from the electrostrictive and thermoelastic contributions that had not been presented in previous studies. Our study of the smectic phase has conclusively established the mechanism for the formation of erasable and permanent grating effects under short‐laser‐pulse excitation as laser‐induced electrostrictive and thermoelastic effects.

ISSN:0021-8979    

DOI:10.1063/1.348441

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The conditions for the preparation of nominally undoped semi‐insulating (SI) InP wafers by annealing under controlled phosphorus pressure are described. It is demonstrated by the results of electrical profile measurements (differential Hall effect) and by photoluminescence that diffusion effects in a thin peripheral layer (≊20 &mgr;m) can be correlated to a phosphorus in‐ and indium out‐diffusion. But diffusion of these species is correlated to a donor behavior and relatively slow. It can, therefore, not be used to explain the SI bulk property which seems not to depend on the phosphorus overpressure during annealing.

ISSN:0021-8979    

DOI:10.1063/1.348442

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A systematic theory is presented for the prediction of oxygen migration near a 60° dislocation and for the resulting retardation of dislocation motion. Quantitative predictions are based on the solution of the macroscopic equation for transport of oxygen in the elastic stress field created by the dislocation. The link between the microscopic dynamics of interstitial oxygen within the diamond lattice and macroscopic transport is established by a constitutive model for the dependence of the drift velocity band diffusivity of oxygen on the elastic interaction of oxygen atoms and dislocations and on temperature. The transport equation is solved numerically assuming that the dislocation core is fully saturated with oxygen. The drag force on the gliding dislocation caused by the surrounding oxygen is computed from linear elasticity theory, combined with the phenomenological model of Alexander and Haasen [Solid State Phys.22, 27 (1968)] for the dependence on the applied stress of the velocity of a dislocation in pure silicon. The predicted dependence of the dislocation velocity on the applied stress at specific temperatures and oxygen concentrations is in qualitative agreement with the experimental data of Imai and Sumino [Philos. Mag. A47, 599 (1983)].

ISSN:0021-8979    

DOI:10.1063/1.348443

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report on the results of a study of the influence of rapid thermal annealing (RTA) on the diffusivity and solubility limit of titanium and chromium in silicon. It is shown that RTA has no influence on the diffusion of the metal atoms as long as the treatment is performed with the metal silicide as the boundary phase, but that the diffusivity is decreased if silicidation occurs during RTA. On the other hand, a strong solubility enhancement is found to occur during RTA.

ISSN:0021-8979    

DOI:10.1063/1.348444

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Low‐power annealing by a pulsed laser is used to recover the structure of low‐dose implanted (100) GaAs crystals. Reflection high‐energy electron diffraction with variable glancing incidence is employed to detect the structural changes at different depths in the specimens. The depth dependence of the damage is studied in more detail by Rutherford backscattering analysis. The annealing results depend on the irradiation conditions. A laser energy window below the melting threshold is found within which the structure can be restored to about as high degree of crystallinity as the virgin one, without any visible surface damage. A simple theoretical estimate shows that the temperature rise of the material is far below the melting threshold. This rise is too short in time to cause substantial dopant diffusion; however, it can enhance well the point‐defect mobility.

ISSN:0021-8979    

DOI:10.1063/1.348445

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Problems in the practical fabrication of high‐efficiency x‐ray diffractors are discussed and a diffractor with a stepped surface is proposed to overcome these problems. The effects of the diffracting materials’ rocking curve width and x‐ray penetration on the performance of diffractors with simple geometry are evaluated to determine when diffractor geometries involving doubly curved surface and planes are more advantageous than simple geometries. An example calculation of the performance of a stepped diffractor approximating the Wittry geometry (J. Appl. Phys.68, 387, 1990) is given and experimental results are presented for the performance of a six‐step diffractor using mica as the diffracting material and the fifth‐order reflection of CuK&agr; radiation produced by a microfocus x‐ray source. It is concluded that the stepped diffractor geometry is a viable solution to the problem of fabricating high‐efficiency x‐ray diffractors.

ISSN:0021-8979    

DOI:10.1063/1.348446

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The simple fluid constituents of the reaction products of an aluminized nitromethane explosive are described by a perturbation technique based on their intermolecular interactions. Liquid metal constituents are treated with a Grover scaling model. Standard solid‐state approaches are applied to the solid components of the reaction products. Calculated detonation velocities compared favorably with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.348447

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of dopant‐dopant interaction on diffusion in silicon for a specific set of impurities is modeled. The first step in the modeling process involved quantum chemical calculations. The connection between the atomic scale results and macroscopic behavior was made through the medium for transmission of interactions between dopants. The molecular orbitals of the lattice system comprise that medium; consequently, interactions can be transmitted, with minimal reduction in magnitude, over separations of hundreds of lattice spacings. Macroscopically, additional flux components are generated that modify the conventional expression of Fick’s second law. Detailed simulation of boron and phosphorous diffusion in germanium‐rich regions of silicon illustrate the power of this approach to successfully model and predict the complex behavior exhibited by a particular set of interacting dopant species.

ISSN:0021-8979    

DOI:10.1063/1.348448

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The thermal stability and the interfacial reactions in the metallization system of Al/Ti‐Ta/Si forT≤550 °C were studied by x‐ray diffraction, transmission electron microscopy, and Auger electron spectroscopy. The analysis of this complex system was made possible by a systematic study of its subsystems. Bilayers of Al/Ti and Al/Ta, tri‐layers of Al/Ti/Ta and Al/Ta/Ti, and finally Al on alloy films of Ti‐Ta were deposited on Si(100) and studied. The refractory metals interactions with Al started at much lower temperatures than those with Si. In the case of the bilayer systems, Al/Ti/Si and Al/Ta/Si, the onset of interaction with Al was at 300 and 350 °C for Ti and Ta, respectively, resulting in the formation of Al3Ti and Al3Ta. The corresponding temperatures for silicide formation were 500 and 700 °C. For the tri‐layer systems the Al overlayer reacted with the top refractory metal at 300–350 °C, while the lower metal reacted with the Si substrate at the corresponding temperature for silicide formation. For the alloy samples, reactions at the Al/refractory alloy interface at 300–350 °C resulted in a mixture of Al3Ti and Al3Ta. The majority of the Ti‐Ta film, and especially its interface with Si, remained intact at annealing temperatures lower than 500 °C. For the Ta‐rich compositions studied (Ti20Ta80and Ti50Ta50) at 500 °C Si diffused through the Ti‐Ta alloy to the outer region of the contact forming Ti and Ta disilicides, while Al penetrated deeply into the Si substrate. Most of the Ti‐rich alloy, Ti80Ta20, however, remained essentially intact even after 500 °C 30‐min anneal. At this stage a shallow contact was obtained by the formation of a very thin silicide layer at the substrate interface, while penetration of Al to the substrate was prevented by a limited interaction of Al with Ti and Ta to form the corresponding aluminides.

ISSN:0021-8979    

DOI:10.1063/1.348449

出版商:AIP    

年代:1991

数据来源: AIP