摘要:

We have used the methods of picosecond time‐resolved reflectivity to measure the carrier lifetime in fine grain polycrystalline silicon films grown by low pressure chemical vapor deposition at 625 °C. After monatomic hydrogen diffusion or implantation with phosphorus ions followed by high temperature annealing (1150 °C), the trapping time &tgr; increased from 40 to 150 ps, consistent with passivation of the grain boundaries or an increase in grain size, respectively. If implantation was not followed by annealing, &tgr; decreased to less than 10 ps, while if it was followed by low temperature annealing (900 °C), which approximately restored the original grain size, &tgr; recovered to 50 ps, very close to the trapping time measured in the as‐grown samples. In all cases, we found indications that trapping of carriers was much faster than their subsequent recombination.

ISSN:0021-8979    

DOI:10.1063/1.341047

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Monte Carlo methods have been used to obtain the electron energy distributions, transport parameters, and rate coefficients for electrons in a three‐valley model of GaAs with nonparabolic energy bands in the presence of an external electric field. A technique has been developed which reduces the computation time when using self‐scattering algorithm. Consequently, for a given computation time, more test particles can be used in the simulation. This results in a reduction in the fluctuation of the calculated quantities. In this paper, the Monte Carlo technique is presented for two generic time variations of the applied field: (a) dc and (b) a step change. The results shown are for the steady‐state behavior of electrons in GaAs, for dc electric fields with values up to 70 kV/cm.

ISSN:0021-8979    

DOI:10.1063/1.341048

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The Seebeck coefficient and electrical resistivity have been measured for the La3−xMxS4alloys with the Th3P4‐type structure forM=Sm, Eu, Yb, andx=0.1 to 0.9 in order to determine their potential as high‐temperature thermoelectric energy conversion materials. An analysis of the lattice parameters of these alloys suggests that Sm has a valence of 2.2 over the entire composition range. Furthermore, the variation of the Seebeck coefficient and electrical resistivity as a function of electron concentration is different for the Sm‐doped alloys than for the Eu‐ and Yb‐doped alloys, which are all different from that of the pure binary LaSyalloys. A maximum in the electrical power factor at 1000 °C is found to occur atx&bartil; 0.3, but when a reasonable estimate is made of the thermal conductivity the maximum in the figure‐of‐merit at 1000 °C shifts to largerxvalues (∼0.7) in all alloy systems. The long term stability of the Sm and Eu ternaries is also reported.

ISSN:0021-8979    

DOI:10.1063/1.341049

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The origin of the frequency‐dependent Mott–Schottky behavior observed in a wide range of ZnO‐Bi2O3varistor systems has been investigated. Lumped parameter/complex plane analysis of two‐probe ac electrical data indicates that several trapping relaxations contribute to the measured MOV grain‐boundary admittance in the frequency range, 10−2Hz≤f≤107Hz. Furthermore, this approach allows the development of an equivalent circuit representation which incorporates these trapping phenomena in a systematic manner.

ISSN:0021-8979    

DOI:10.1063/1.341176

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The subgap absorption spectra for hydrogenated amorphous silicon carbide/silicon (a‐Si1−xCx:H/a‐Si:H) and silicon nitride/silicon (a‐SiN:H/a‐Si:H) alternatively multilayered films were measured by photothermal deflection spectroscopy and the defect density at the heterojunction was evaluated from the increase in absorption shoulder with the number of layering periods. The defect density at thea‐Si0.66C0.34:H/a‐Si:H heterojunction increased with increasinga‐SiC:H layer thickness, while that at thea‐Si0.50N0.50@B:H/a‐Si@B:H heterojunction showed no dependence on thea‐SiN:H layer thickness and was 1.4×1011cm−2. The defect density at thea‐Si1−xCx:H/a‐Si:H heterojunction increased to 1×1011cm−2with increasing carbon content in the 0.1–0.5 range. Hydrogen dilution of the starting gases of thea‐SiC:H layer was effective to decrease the interface defect density to less than 2×1010cm−2. A graded composition layer at thea‐SiC:H/a‐Si:H interface did not decrease the defect density.

ISSN:0021-8979    

DOI:10.1063/1.341050

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Niobium‐stress influence on Nb/Al‐oxide/Nb trilayer Josephson‐junction characteristics is studied. Different junction fabrication techniques are examined such as conventional etching and new lift‐off processes. Nb‐film stress, relaxed during trilayer etching, can deteriorate junction quality in etching‐processed junctions smaller than a few micrometers square. Such deterioration does not occur in lift‐off processed junctions even when they are 1 &mgr;m square because stress relaxation occurs during trilayer deposition through lift‐off stencils. This new all‐Nb Josephson‐junction fabrication technique produces high‐quality junctions withRsg/Rnn=24 (RsgandRnnare tunnel resistances at 2 and 4 mV, respectively) and a current uniformity of 1.5% for 100 1‐&mgr;m‐square junctions connected in series.

ISSN:0021-8979    

DOI:10.1063/1.341051

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The damping behavior of zone‐refined iron was investigated at low temperatures as a function of strain amplitude of oscillation, magnetic field, frequency, and temperature. Observations of increased damping at relatively low temperatures are correlated with reports of other investigators. These features appear to be associated with the hysteretic breakaway of domain walls from pinning points. As temperature increases the hysteretic process becomes thermally assisted and diminishes. The parameters for this process are an attempt at frequency of the order of 106Hz, or somewhat more, and an activation energy of the order of 0.02 eV or more. It appears that the interaction of moving dislocations with domain walls can also assist depinning from the unspecified pins.

ISSN:0021-8979    

DOI:10.1063/1.341052

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The thermomagnetic switching process in amorphous Tb‐FeCo alloys has been investigated theoretically for typical compositions with a Curie temperature of 500 K and compensation temperatures ranging from 360 to 420 K. The temperature and radial dependence of the relevant magnetic parameters such as the saturation magnetization, the exchange constant, the uniaxial anisotropy, and the domain wall energy have been calculated in terms of the respective sublattice magnetizations inferred from the mean field theory and data obtained experimentally. The condition for domain stability has been derived and the radial dependence of the forces controlling the domain wall position is calculated yielding domain diameters for writing and erasure as a function of the applied field, the wall energy, and the laser‐induced temperature. Heating above the Curie temperature is shown to offer an alternative possibility to control the domain diameter and to achieve high domain regularity at low applied magnetic fields.

ISSN:0021-8979    

DOI:10.1063/1.341053

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Parallel field ferromagnetic resonance spectra of an yttrium iron garnet film in the vicinity of a metallic ground plane are presented. The evolution of the spectra with changing film‐ground distance is traced continuously over a wide range. The following effects are found to occur at distances of less than about 500 &mgr;m: Large shifts of the resonance fields, disappearance and subsequent reappearance of lines, appearance of ‘‘forbidden’’ lines, and crossing of lines. All of these effects are confirmed by a theoretical calculation which relies on the mechanism of excitation of waves which are circulating around the sample.

ISSN:0021-8979    

DOI:10.1063/1.341054

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The photoluminescence characteristics of undoped and TbCl3‐doped zinc oxide films deposited by the spray pyrolysis technique are reported. Undoped films present the characteristic blue‐green emission peak at ∼508 nm observed in single‐crystal and powder ZnO. The TbCl3‐doped films present a luminescence peak at ∼540 nm. The light emission of the doped films decreases with time of exposure of the sample to the excitation light. The phenomenon is interpreted in terms of a simple model in which a competitive process of hole trapping and phototrapping occurs at a radiative recombination center generated by the TbCl3.

ISSN:0021-8979    

DOI:10.1063/1.341055

出版商:AIP    

年代:1988

数据来源: AIP