摘要:

The epitaxial nature of the CoSi2formed on the (100)Si substrate as a result of annealing a Co/Ta bilayer at 500–1000 °C for 20 s in N2atmosphere is described. At the early stage of annealing, diffusion of Co and Si occurs across the interlayed Ta layer, first forming a CoSi layer on the Si substrate. After that, CoSi2grains nucleate at the CoSi/Si interface and grow laterally parallel to the surface. Due to a difference in mobility the CoSi2grains at the interface of the CoSi/Si impede the interface movement, leading the facet formation. Even after annealing below 600 °C, the epitaxial CoSi2grains are nucleated at the limited area of the nonepitaxial CoSi/Si interface and the faceted corner, and grow laterally along the Si surface. By increasing the annealing temperature, the epitaxiality of CoSi2improves due to the increased lateral growth rate of the CoSi2. However, annealing above 900 °C impairs the CoSi2crystallinity because the interlayered Ta loses its function as a diffusion barrier due to the formation of the TaSi2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360201

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A series of chlorine‐doped epitaxial layers of ZnSe have been grown by molecular‐beam epitaxy. Measurements have been made of the relative intensity of the blue photoluminescence at room temperature, of the decay time of this emission, and of the concentrations of deep levels determined by photocapacitance techniques. A GaAs buffer layer improves the light emission and decreases the deep‐level concentrations. Over the uncompensated donor concentration range 2×1016to 3×1018cm−3the photoluminescence intensity, decay rate, and deep‐level concentrations only vary by one order of magnitude. The results are consistent with the room‐temperature blue emission resulting in recombination of a free hole with electrons on relatively isolated donors, this radiative recombination competing with a strong nonradiative Hall–Shockley–Read recombination via deep levels in the lower half of the energy gap. The significance of these results for the making of light‐emitting diodes and lasers is discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360202

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effective response of a class of weakly nonlinear conducting composite media is investigated. We combine the previously developed perturbation expansion method for solving electrostatic boundary‐value problems with the well‐known Rayleigh method for treating periodic composite media to compute the effective conductivities. We derive general expressions for the effective nonlinear response functions and show that the results agree with the generalized Landau’s formula at low inclusion concentrations. Numerical calculations are also obtained for a square array of cylindrical inclusions suspended in a host medium in two dimensions. Possible applications and extensions of the method to more complicated problems are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360203

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The Ag content in Ag–As–S glasses can be spatially modified by illumination of visible light. Optical and thermal studies demonstrate that the Ag‐content modification is caused by Ag+ionic migration from the dark to the illuminated region in a sample. The migration can be reversed by changing the illuminated region. The magnitude of the Ag‐content modification is maximal (∼7 at. %) at a composition of Ag25As25S50. The migration mechanism can be accounted for by assuming diffusion of photoexcited holes, and the composition dependence can be understood on the basis of the Owens’ thermodynamic model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360204

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thin films of different thicknesses in the range 400–1600 A˚ have been vacuum deposited on clean glass substrates held at room temperature by very fast evaporation of the Se10Sb10Te80bulk alloy. The thermoelectric power of these films has been measured as a function of temperature during heating and cooling cycles by the integral method. It is found that the thermoelectric power of these films is slightly different during the heating and the cooling cycles which is ascribed to slight reorientation of microcrystallites as also evidenced by x‐ray diffraction. It is further found that the thermoelectric power (at a constant temperature) is a function of film thickness; it varies nearly linearly with reciprocal thickness. From these data, the nature of carrier scattering in the films has been ascertained. From the energy‐dispersive x‐ray analysis patterns of the films the semiquantitative content of the constituent elements Sb, Se, and Te has been determined. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360719

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The ac electrical behavior of the polycrystalline yttria was evaluated in the temperature range of 800–1300 °C in air as a function of frequency (5 Hz≤f≤13 MHz). Resistance‐temperature and resistance‐time (aging) characteristics were examined using immittance measurements and electron microscopy to establish microstructure‐property relationships. The ac electrical data indicated two distinct relaxations when analyzed in the impedance plane. These relaxations are attributed to the lumped grain and grain‐boundary contributions in conjunction with a polarization effect at the electrode/sample interface. The admittance plane analysis revealed a semicircular relaxation in the low‐frequency region, indicative of a trapping effect associated with grain‐boundaries and the electrode/sample interface. The variation in the total electrical resistance with time is found to be dependent on the starting microstructure of the sample. A sample with a larger grain size shows a smaller degree of aging at elevated temperatures. Immittance measurements suggest that the major contribution to the aging behavior comes from the evolution in the microstructure. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360205

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Theory and measurements of the conductivity and the (transient) photoconductivity in the microwave frequency range are presented. The theory is tested on noninvasive measurements of semiconductors with known properties, i.e., Si wafers, in a simple apparatus. Quantitative agreement between theory and experiment is found without the use of adjustable parameters. A contactless and accurate determination of the conductivity of Si wafers in a restricted conductivity range is proposed. The quantitative evaluation of photoconductivity measurements makes a detailed discussion of nonuniform photoconductivity possible. The requirements for reliable measurements of nonhomogeneous charge carrier kinetics are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360206

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Previous perturbed angular correlation (PAC) spectroscopy measurements on the donor indium in CdTe and its alloys have revealed several defect complexes. One defect characterized by two sets of quadrupole interaction parameters, &ngr;Q=83 MHz, &eegr;=0.08 and &ngr;Q=92 MHz, &eegr;=0.08, was observed in Hg0.8Cd0.2Te (x=0.2 MCT) and attributed to the substitutional indium–metal vacancy complex InM2+3+VM2+. A defect characterized by &ngr;Q=61±1 MHz and asymmetry parameter &eegr; between 0 and 0.19 was seen in CdTe and widely attributed to the same complex. Both of these assignments were based mainly on an observed relationship between complex formation and the loss of metal ions. In this article we present PAC measurements on111In‐dopedx=0.45 MCT (Hg0.55Cd0.45Te). These measurements reveal defects having quadrupole interactions very similar to those seen previously in CdTe and inx=0.2 MCT. Two unique defect fractionsf1andf2, characterized by &ngr;Q1=60±3 MHz, &eegr;1≊0–0.2, and &ngr;Q2=87±4 MHz, &eegr;2≊0–0.15, were seen inx=0.45 MCT, in some cases simultaneously. The observation of both of these interactions in the same material—if they correspond to the defects seen in CdTe andx=0.21 MCT—precludes the possibility that they both correspond to precisely the same defect. We also observed a change in the relative fractions of these two defects with time at room temperature; the fractionf2vanished over a period of a day, whilef1andf0(the fraction of indium atoms in sites having cubic or higher symmetry) increased. While we cannot rule out the possibility of a slow electronic transition, at present we favor a model in which one of the interactions (probably the one near 60 MHz) corresponds to a complex in which indium is paired to a fast‐diffusing monovalent metal ion like Ag+, Cu+, or Li+. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360207

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The linear response of a novel AlxGa1−xAs superlattice electron‐wave interference diode (EWID) is numerically investigated using the time‐dependent Schro¨dinger equation. This device is based on analogies between electromagnetic waves in dielectrics and quantum mechanical electron waves in semiconductors. These analogies provide a basis for a new class of highly functional devices which use above‐band transport. Recent experimental results and theoretical models showed that the EWID has direct current characteristics similar to the resonant tunneling diode. This first quantum mechanical calculation for the EWID alternating current characteristics shows that the device negative differential resistance (NDR) persists up to about 10 THz. By examining three different EWID designs, it is shown that device parameters, such as the number of layers, have a strong effect on high‐frequency performance. The important property of NDR, combined with expected high current densities and possible integration with optoelectronic devices, makes the EWID a good candidate for high speed applications. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360208

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects of the presence of charged centers of different sign on the electron mobility inn‐channel metal‐oxide‐semiconductor transistors are studied by a Monte Carlo simulation. By solving the Poisson equation for the potential fluctuations, an expression for the Coulomb‐scattering rate when there are charged centers of different sign is provided. In addition, it is shown that, when charges of different sign exist in the structure, local band‐bending fluctuations are greater, thus resulting in lower electron mobility. In contrast, since in this case the potential mean value is lower, the influence of the charged centers on the threshold voltage is lesser. The electron mobility in compensated substrates is also analyzed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360209

出版商:AIP    

年代:1995

数据来源: AIP