摘要:

The contributions of nonlocal mechanisms to nonlinear transport in semiconductors, with special emphasis on hot‐electron emission at heterojunctions and its variations which are now commonly termed real‐space transfer effects, are reviewed. The goal is to equitably account for and bring together the body of literature that has developed, often independently, in the U.S. and the former Soviet Union as well as in Europe and Japan. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358947

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The reliability of a phenomenological model in describing the profile of a spatially extended complex system is analyzed. An assessment is essential because an observed image of a two‐dimensional object is sensitive to increases in sampling intervals. The range of interval values wherein the fractal dimension of the image remains invariant is determined for various kinds of object boundaries. Data sets of the same object that are obtained using sampling intervals that belong within the range contain the same amount of fractal information, and therefore adhere to one phenomenological model. This reliability range is determined for both coherent and incoherent measurement processes. Numerical experiments show that the range is the same for all fractal objects considered, and depends only on the type of measurement process. However, the measurement errors introduced when sampling at intervals beyond the reliability range are highly dependent on the type of fractal structures. Boundaries described by larger fractal dimensions are less sensitive. The existence of a nonzero reliability range implies that object fractal information can be recovered at sampling rates lower than the minimum value imposed by the Nyquist sampling criterion. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358948

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Spectrally narrow outputs of about 10 MHz (full width at half‐maximum) are obtained from an optically pumped high‐power (100 kW) D2O laser system by using the oscillator‐amplifier configuration, in which a low‐power single‐mode output from a compact D2O laser with a short cavity length is amplified by a large D2O laser amplifier. In order to obtain spectrally narrow outputs from the amplifier, the following three conditions need to be satisfied: (1) the D2O gas pressure of the amplifier is adjusted in the range from 4 to 6 Torr; (2) the oscillation frequency of the compact laser is tuned in the range about 15–35 MHz lower than the Raman resonance frequency; and (3) the intensity of the compact laser beam injected into the amplifier is larger than about 50 W/cm2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358949

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Passive chemical‐vapor‐deposited diamond layers have the potential to improve thermal conduction in electronic microstructures because of their high thermal conductivities. The thermal resistances for conduction normal to the boundaries of diamond layers, which must be small in order to realize this potential, have not been measured. This research develops two independent experimental methods that measure the total thermal resistance for conduction normal to diamond layers thinner than 5 &mgr;m on silicon substrates, yielding an upper bound for the thermal resistance of the diamond‐silicon boundary. The data for layers as thin as 0.2 &mgr;m agree with predictions that account for phonon scattering on layer boundaries and couple the local scattering rate in the diamond to the grain size. The agreement lends support to the conclusion that the effective diamond‐silicon boundary resistance is dominated by a highly localized volume resistance in the diamond near the interface. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358950

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A Monte Carlo simulation of radiation transport is used to determine the angular distribution of resonance radiation emanating from a positive column discharge. With the specification of the oscillator strength, absorption/emission profile, gas density, spatial distribution of radiating atoms, and boundary geometry, the angular distribution of photons arriving at the wall of the discharge is obtained. The ratio of the integral of the angular distribution to that for a diffuse, Lambertian surface is on the order of one‐half for the parameter space studied here. When combined with a measurement of the absolute intensity at one angle, this distribution provides a means of determining the radiant emittance of the source when measurement of the actual distribution is problematic. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358951

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The study of the formation of Sulfur Hexafluoride (SF6) dissociation products under point to plane corona discharges was carried out atPSF6=300 kPa using different discharges production conditions (50 Hz ac voltage, dc negative polarity voltage, mean discharge current intensityI¯ varying between 2 and 45 &mgr;A for dc negative polarity voltage), for two plane electrode materials (aluminum and stainless steel), and moisture levels (200 and 2000 ppmvH2O). The stable gaseous by‐products formed (SO2F2, SOF4, SOF2, and S2F10) were assayed by gas‐phase chromatography. The results indicate an important effect of the metal constituting the plane electrode and of the moisture conditions whatever the SF6pressure (100–300 kPa), discharges intensity (I¯) and voltage type studied. An effect of the increase of SF6pressure up to 300 kPa was mainly observed for S2F10and corresponds to a greater formation of this compound withPSF6. The influence of the mean discharge current intensity on SF6by‐product formation carried out for a transported charge of 1 C showed that forI¯≤10 &mgr;A, the effect varies according to the compound considered and depends on the water content of the SF6and/or on the plane electrode material, whereas forI¯≳10 &mgr;A, the levels of the four compound studied hardly vary with the current. Comparison of results obtained under ac and dc voltage for a cumulated charge of between 0.5 and 11 C showed that (SO2F2+SOF4) and SOF2were formed in larger quantities with ac than with dc, unlike S2F10for which the opposite effect was observed. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358952

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

For defects or impurities with deep energy levels, such as the commonly observed EL2, EL3, and EL6 in GaAs, it is very important to take account of the so‐called &lgr; effect in order to deduce the correct concentrations of these centers when using capacitance techniques. By measuring capacitance at several forward bias voltages for a given reverse bias voltage it is possible to determine concentrationNTand energyETwithout requiring the usual emission rate analysis. Convenient formulas forNTandETare given, although onlyNTcan be determined with a high degree of precision. The results for ann‐type horizontal Bridgman wafer (n&bartil;2.8×1016cm−3) are:NEL2=(1.14±0.02)×1016cm−3,EEL2(377 K)=0.71±0.06 eV;NEL6=(8.0±0.5)×1015cm−3,EEL6(167 K)=0.42±0.09 eV. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358953

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Si(001) structures, implanted with Sn at energy of 50 keV and with doses in the range 2–9×1015cm−2, were investigated by multicrystal x‐ray diffraction, reciprocal space mapping (RSM), high‐resolution transmission electron microscopy, and secondary‐ion‐mass spectrometry (SIMS). For Sn doses up to 3.30×1015cm−2, annealing at 600 °C for 30 min under dry N2atmosphere resulted in recrystallization by solid‐phase epitaxy (SPE) to a layer thickness of more than 50 nm. These SPE‐grown layers were shown to be free of extended defects and Sn redistribution was negligible. As measured by x‐ray diffraction, the Sn‐induced strain in Si increased with the implant dose. From RSM measurements, this strain was shown to be tetragonal with negligible in‐plane relaxation. Mosaicity and defect‐related effects were shown to be negligible. Instead, limited thickness effects and strain variation due to the implantation profile appeared to be the major sources of the observed broadening in the diffraction peaks. The lattice expansion coefficient for Sn in Si was estimated from the measurements to be 2.5×10−24cm3/atom. For Sn doses above 3.3×1015cm−2, a reduction in the Sn‐induced strain in Si was observed despite the fact that Sn concentrations were higher. In this high‐dose regime, the SPE growth under the same annealing conditions was limited to ∼10 nm. The remainder of the structure showed a succession of layers dominated by twinned Si(001), polycrystalline Si, nanocrystalline Si:Sn, and an untransformed amorphous top layer. In addition, Sn redistribution was detected in the SIMS measurements at levels much higher than expected from trace‐diffusivity values at the employed annealing conditions. The observed SPE retardation was related to the high concentrations of Sn in these structures. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358954

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Amplitude‐division electron holography achieved in a nonbiprism transmission electron microscope is presented. A single‐crystal thin film is used to divide the amplitude of the incident electron beam. The lattice fringes of the crystal film are used to form off‐axis holograms. The relation between the spatial coherence of the illuminating beam and the resolution of the reconstructed image is derived and compared with that of the conventional wave‐front‐division holography achieved with a biprism. It is shown that using a low‐coherence illuminating beam will reduce the resolution of the reconstructed images in the amplitude‐division holography, whereas it will reduce sensitivity in conventional wave‐front‐division holography. Experimental results obtained using a gold crystal thin film as the beam splitter show that the amplitude‐division electron holography permits any coherent or incoherent illumination when high resolution is not strongly required. Advantages over the wave‐front‐division electron holography achieved with a biprism system have been pointed out. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358955

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

As‐grown Czochralski silicon samples with different oxygen concentrations have been heated at temperatures in the range 350–500 °C. Oxygen loss during anneals at low temperatures (T≤400 °C) is shown to follow second‐order kinetics and measurements led to values of oxygen diffusivity that were larger than normal by a factor of ∼3, assuming the capture radius for dimer formation was 5 A˚. Variations in the rate of [Oi] loss during more extended anneals could be explained if oxygen diffusion was initially enhanced but tended to its normal value as the anneals progressed. Much greater initial enhancements were derived from similar measurements for samples which had been hydrogenated by a heat treatment in H2gas at 1300 °C for 30 min followed by a rapid quench to room temperature, and the enhancements were consistent with values derived from measurements of the relaxation of stress‐induced dichroism. At higher temperatures (T≥450 °C) the measured rates of [Oi] loss were less than the expected rate of Oi‐Oiinteraction and tended to vary with increasingly high powers of [Oi]. Modeling of the clustering process demonstrated that the reductions could be explained if the oxygen dimers were present in a quasiequilibrium concentration throughout the anneals. The establishment of this equilibrium appears to require that oxygen dimers diffuse much more rapidly than isolated Oiatoms. The kinetics of oxygen loss over the whole range of temperatures can then be explained if dimer clustering leads mainly to increases in concentrations of agglomorates containing large numbers (≥8) of oxygen atoms. It is therefore possible to account for thermal donor (TD) formation based on the formation of different sizes of oxygen clusters, although the possibility that self‐interstitials are involved in TD formation is not excluded. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358890

出版商:AIP    

年代:1995

数据来源: AIP