摘要:

For GaAs VPE layers grown on Ge substrates, it is found that a one‐dimensional misfit‐dislocation density 1/pis proportional to lattice constant mismatch, just as for compositionally graded GaAs1−xPxlayers grown on GaAs substrates. On the basis of these experimental results, lattice constant variation due to compositional change is given in a form explicitly including a compositional step. The compositional step width, calculated from this relationship and observed dislocation density, is about 500 atomic layers. Regular compositional steps, which are unintentionally formed, are actually observed onA‐Betched cleavage planes of the graded layers. The observed width of this step is about 0.3 &mgr;m. This value roughly agrees with the calculated one. Presumably, the discontinuous change in composition is caused by competition between the following two processes which alternately dominate GaAs1−xPxepitaxial growth: a free‐energy increase due to a decrease in arsenic supersaturation in vapor phase and a free‐energy increase due to an increase in formation enthalpy of the crystal. Furthermore, in final compositional layers equidistant striae about 3.5 &mgr;m wide are observed onA‐Betched cleavage planes. The origin of these striae is considered to be misfit dislocations which are generated in graded layers and climb as a result of association with Ga vacancies. Some of the striae are regularly bent in the direction perpendicular to the growth axis by shear stress due to sample bending.

ISSN:0021-8979    

DOI:10.1063/1.328275

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

In the quest for an electroplated selective black coating stable to 500 °C in air, black cobalts have been prepared by three techniques to yield (a) plated cobalt sulphides, (b) plated cobalt oxide‐hydroxide, and (c) cobalt oxide prepared by thermal oxidation of electropolated cobalt metal. The optical properties of the various coatings are analyzed before and after exposure to air for extended periods of time at temperatures in the 300 °–500 °C range. The sulfide black cobalt is not acceptable as a high‐temperature selective absorber due to severe thermal degradation. The plated oxide is a good selective absorber to about 400 °C, and the thermally oxidized black to a slightly higher temperature, but degrades at 500 °C. Structure studies via scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and x‐ray photoemission spectroscopy (XPS) are reported which yield a full account of the coating chemistry before and after heating. The studies reveal that the high solar absorptance of the acceptable black cobalt coatings is due to a continuation of a porous outer layer grading into nondense oxides of cobalt; either CoO or Co3O4, depending on the film. Absorption is intrinsic but not due to metal particles as in black chrome. A limited amount of optical degradation occurs upon heating the oxide black cobalt in air due to oxidation of hydroxide. However, the major degradation problem is shown to be substrate oxidation in contrast to black chrome where film oxidation is the principal problem.

ISSN:0021-8979    

DOI:10.1063/1.328276

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Thermal stresses in chemical vapor deposited (CVD) vitreous silicate and phosphosilicate glass (PSG) films on Si substrates are measuredinsitufrom room temperature (RT) to 900 °C. As‐deposited films grown at one atmospheric (APCVD) and lower pressures (LPCVD) are found to be inherently under a tensile and compressive stress at RT, respectively. On heating to 500 °C, the tensile component of the stress develops in both CVD films. Tensile stress increases with time at a given temperature. In the range 500–900 °C, the tensile component is reduced with temperature and time. During the cooling process from a temperature between 700 and 900 °C, the stress component of APCVD and LPCVD films changes from tension to compression. With APCVD film, the temperature dependence of the stress in the range RT–500 °C can be represented as a function of phosphorous concentration in mol % P2O5. Temperature and time dependence, and thermal hysteresis are attributable to water content, sintering, and viscoelastic properties of CVD film. These are explained from the viewpoint of glass annealing and softening temperature points.

ISSN:0021-8979    

DOI:10.1063/1.328277

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The influence of oxygen on the resistivity of dislocation‐free silicon wafers was studied after annealing at various temperatures under a nitrogen ambient. Significant resistivity shifts were observed in the temperature range 600–900 °C and related to oxygen precipitation. This phenomenon is independent of the well‐known donor generation observed around 450 °C and is more difficult to cure.

ISSN:0021-8979    

DOI:10.1063/1.328278

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The electronic properties of two dominant sulfur‐related deep donor levels in silicon have been investigated using capacitance and dark current transient techniques. One of the centers, theBcenter, has an enthalpy &Dgr;Hnof 0.32 eV and an electron‐capture cross section &sgr;tnBof 2×10−15cm2at 100 K. &sgr;tnBvaries with temperature asT−3.3. A plot of log etnAvs 1/Tfor the other center, theAcenter, shows a ’’thermal activation energy’’ of 0.59 eV. &sgr;tnAis estimated to be larger than 10−14cm2. The nature of theAandBcenters is discussed.

ISSN:0021-8979    

DOI:10.1063/1.328279

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Systematic studies of the magnetic and the transport properties are lacking in Metglas 2826 MB (Fe40Ni38Mo4B18). Low‐field magnetic susceptibility between 300 and 1000 K givesTc=(591±2) K in the amorphous state. A thermal cycling up to 1000 K yields two crystalline magnetic phases withTc=(760±10) K and (545±5) K. Differential thermal analysis shows that the crystallization temperature is about 810 K. The ferromagnetic anisotropy of resistivity (FAR) is very small and positive with a typical value of 0.1%. The average slope of magnetoresistivity changes from −(1.1×10−8) G−1to −(0.55×10−8) G−1from 300 K to 77 K. The transverse and the longitudinal magnetoresistances could be related to the tangent of the Hall angle for a number of Metglas alloys including 2826 MB by considering the normal anisotropic magnetoresistance as well as the reduction in resistance due to the removal of domain walls in a uniaxial ferromagnet.

ISSN:0021-8979    

DOI:10.1063/1.328280

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A dc method is described for measuring the magnetoconductivity tensor of an anisotropic crystal when the magnetic field is along a crystallographic symmetry axis. The method is particularly suited for compounds with large anisotropies, for which conventional techniques are not practical. The sample to be measured is a rectangular parallelepiped, each of whose faces is either free or on a highly conducting substrate. The electrodes are arbitrarily located point contacts. Special attention is given to self‐consistency checks for verifying that the conditions required to apply the method are satisfied. A convenient alternative to the usual procedure of separating resistive and Hall voltages by magnetic field reversal is presented.This new procedure is based on a reciprocity theorem in a magnetic field, proved here apparently for the first time.

ISSN:0021-8979    

DOI:10.1063/1.328281

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Inhomogeneous current systems in bismuth specimens under longitudinal and transverse magnetic fields have been investigated by solving a boundary‐value problem of a rectangular parallelepiped medium to which current electrodes are attached with a finite contact area. The main results are as follows. In a longitudinal field, the current inhomogeneity governed by specimen geometry grows, extending toward the middle part of the specimen, and at the same time the current is condensed around the specimen axis parallel to the magnetic field. This current condensation increases the total resistance and decreases the potential difference measured on a side surface. In a transverse field, conversely, the current inhomogeneity degenerates to be confined in a narrow region near the end surface. Influences of specimen dimensions and electrode contact area are quantitatively discussed.

ISSN:0021-8979    

DOI:10.1063/1.328236

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The influence of electron‐electron scattering processes on high‐field transport properties of electrons in GaAs, and the usefulness of a drifted Maxwellian approximation to the distribution function in analysis of devices in which these effects are important, have been studied. Monte Carlo simulations of transport both with and without electron‐electron scattering included are compared with drifted Maxwellian distribution functions over a range of doping and electric field values typical of submicron‐scale devices. Electron‐electron scattering is found to have a significant effect on the shape of the distribution function derived by MC simulation, but little effect on the average electron velocity. The degree of approximation involved in device analyses when the drifted Maxwellian is used instead of the correct distribution function is discussed.

ISSN:0021-8979    

DOI:10.1063/1.328237

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The thermionic emission enhanced by barrier lowering and the Zener tunnelling in ZnO varistors are discussed. Capacitance versus voltage, reverse current versus temperature, and 1/fnoise measurements have been performed on commercial varistors. A model is proposed from which follows a diffusion voltageVDwhich is consistent both with the 1/C2vsVplot and with the thermal activation energy obtained from the reverse current versus 1/T. The empirical law &bgr;=d logV/dlogI= constant, is explained by Zener breakdown. The 1/fcurrent noise is proportional to the square of the current and independent of the conduction mechanism across reversely biased barriers.

ISSN:0021-8979    

DOI:10.1063/1.328238

出版商:AIP    

年代:1980

数据来源: AIP