摘要:

Diode properties of structures containing a porous silicon layer have been investigated. The structures have been fabricated by depositing metal or indium‐tin‐oxide layers either directly on the ‘‘as‐anodized’’ silicon wafer or on the wafers with upper, nanocrystalline part of the porous layer removed. Different behavior was observed in both cases: (1) The photovoltaic effect is absent in diodes from as‐anodized wafers but appears in diodes from the cleaned wafers; (2) the diode ideality factor is close to 2 for ‘‘cleaned’’ diodes and increases in diodes containing an upper porous silicon layer. Energy‐band diagrams for the structures are proposed and it is concluded that the electrical transport in those structures is limited by the carrier recombination in the depletion layer. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358779

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dependence of giant magnetoresistance on the composition of ferromagnetic face‐centered cubic precipitates in an Ag matrix grown epitaxially on MgO {100} is described. These compositions were chosen from the alloy ranges Ni0.6Cu0.4→Ni→NixCo1−x→ Co→Fe0.2Co0.8to give a number of valence electrons per atom,n=n3d+n4s, in the ferromagnetic precipitates that ranged from 8.8 to 10.4. This corresponds to a decrease of the saturation magnetization from ∼1500 emu/cm3to approximately zero. To reduce the influence of other variables the concentration of the precipitates was kept constant (at 23.5 vol %) and their size approximately so. Corrections are applied to adjust for some remaining variation in precipitate size. With other factors held constant, there is a steady increase in both the magnetoresistance ratio and the magnetic‐field‐dependent resistivity with increase in the saturation magnetization of the alloys, i.e., with increase in the spontaneous magnetization of the single‐domain precipitates. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359542

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The crystallographic, electronic, and optical properties of thin ReSi2films (∼20–300 A˚) have been investigatedinsituby low energy electron diffraction (LEED) and photoelectron spectroscopy (XPS and UPS),exsituby glancing incidence x‐ray diffraction (GIXD), and optical absorption measurements. Thin Re layers were evaporated under ultrahigh vacuum on Si(111) (7×7) surfaces, maintained at room temperature, or heated at 650 °C. The films were subsequently annealed at increasing high temperature and the silicide formation was followed byinsitusurface techniques. For very thin films (≲35 A˚) LEED shows a faint (1×1) pattern after annealing at 750 °C, which improves slightly up to ∼900 °C. For thick films (∼50–300 A˚) only a bright background is observed. XPS indicates that the ReSi2composition is attained upon annealing at 600 °C. In the Re‐Si bonding the charge transfer is negligible: the energy positions of the corelevels (Si 2pand Re 4f) are the same in the compound and in the elements. As the energy shift of the SiKLLAuger is negligible also, the extra‐atomic relaxation energy for Si atoms is the same in silicide as in silicon, indicating that ReSi2has a semiconducting character. UPS results confirm this assumption: the density of states nearEFdecreases strongly upon ReSi2formation and at the same time the valence band edge shifts fromEFto lower binding energy. GIXD gives sharp diffraction peaks, characteristic of ReSi2(110) in epitaxy on Si(111). This technique also reveals that the films present an additional orientation near the interface. Optical absorption measurements performed on ReSi2films of ∼300 A˚ thick indicate that this silicide is a semiconductor with an indirect energy gap of 0.15 eV, in agreement with previous studies. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358780

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In experiments on single electron devices, the electromagnetic noise from parts of the apparatus at temperatures higher than that of the device can dramatically increase the tunnel rates out of the Coulomb‐blocked state and therefore increase the device error rate. The electrical lines must therefore be filtered adequately. We derive simple expressions for calculating the required attenuation coefficient. We describe a wide‐band miniature dissipative filter functioning at cryogenic temperatures. The effective thermalization of an experiment at 30 mK can be obtained by placing four of these filters in series at temperatures ranging from 4 K to 30 mK. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358781

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A detailed investigation of the electrical transport in (100) CoSi2/Si contacts is presented. The transport properties of epitaxial CoSi2films, obtained both by ion‐beam synthesis and by solid‐state reaction of a Ti/Co bimetallic layer, are compared with the transport properties of conventional polycrystalline CoSi2layers. The electrical resistivity, the magnetoresistance, and the Hall effect are measured on Hall bars for temperatures ranging from 1.2 to 300 K and magnetic fields up to 5 T. Very high values of the order parameterkFL0are observed, indicating that the investigated samples are of very high purity and crystalline order. In addition, the electric transport at the CoSi2/Si interface is studied by current‐voltage and capacitance‐voltage measurements on Schottky diode structures for temperatures ranging from 173 to 333 K. Ideality factors close to unity are observed for the highest temperatures, for the lower temperatures the ideality factors are found to increase with decreasing temperatures. The observed temperature dependence of the ideality factor and the Schottky barrier height can be attributed to Schottky barrier inhomogeneities. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358782

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on experimental and theoretical investigations of the dark current behavior inn‐type GaAs/AlAs/Al0.3Ga0.7As double‐barrier quantum wells (DBQW). The dark current perpendicular to the 50‐period DBQW structures shows evidence of tunneling through the 2‐nm‐wide AlAs tunnel barriers and thermionic emission across the 25‐nm‐wide AlGaAs layers. The temperature dependence is in good agreement with our numerical simulations, using an effective escape rate of 2.2×1014s−1. The dark current is further modified by internal electric fields caused by an asymmetric dopant distribution, which partially arises from a dopant segregation during epitaxial growth. We also present a theoretical simulation showing how the dark current versus voltage dependence is influenced by these space‐charge fields. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358783

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The parameter known as the modified sheet resistanceRskhas been used in the modeling of ohmic contacts to define the region of alloying/reaction immediately below the metallization. In this study, the value ofRskhas been measured for Pd/Zn/Pd/Au, Pd/Au, Zn/Pd/Au, Au/Zn/Au, Ni/Zn/Ni/Au, Cr/Au, and Pd/Mn/Sb/Pd/Au contacts to In0.47Ga0.53As/InP as a function of the annealing temperature to 500 °C. In the as‐deposited contacts, the measured value ofRskwas lower than the sheet resistance outside of the contact,Rsh, by a factor of ∼2 to 3. This reduction inRskfromRshhas been attributed to (a) the formation of low‐resistivity phases at the interface and (b) the creation of a doped region by indiffusion of the Zn. In addition, in the Pd/Zn/Pd/Au contacts, the effect of varying the thickness of the layer of Zn between 0 and 400 A˚ onRskwas examined. A thickness of Zn≥50 A˚ was required in order to produce a significant reduction inRskfrom the value for the Pd/Au (Zn=0 A˚) contacts. This effect was enhanced by annealing at 500 °C, which produced a value ofRsklower thanRshby a factor of ∼10. The reduction inRskby annealing treatment was consistent with an enhanced formation of the interfacial phases and an increase in the rate of indiffusion of the Zn. The exceptions to these trends were in the Pd/Mn/Sb/Pd/Au contacts which showed an approximately constant value ofRskand Pd/Au which showed a minor reduction inRskwith increase in annealing temperature. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358784

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The electromechanical and dielectric responses of ferroelectric materials near paraelectric–ferroelectric (PF) phase transitions are examined both experimentally and theoretically. It is shown that the type of PF transition, i.e., first order and continuous transitions, and diffused phase transition found in relaxor ferroelectrics, has marked effect on the electromechanical and dielectric response behavior for materials under electric field bias. It is demonstrated that an exceptionally large piezoelectric and electromechanical response can be achieved in materials with a first order PF transition. For example, in Ba1−xSrxTiO3(x∼0.35) ceramics at room temperature, a piezoelectricd33larger than 1500 pm/V with very little frequency dispersion can be obtained. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358785

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We reportabinitiostudies on the electronic structures of strained‐layer superlattices (SLSs) (InAs)n(InP)n(001), (n=1–5) under three different strain conditions via a linearized muffin‐tin‐orbital method with two treatments fordstates. The effects of In 4dorbitals on the band structure and the valence band offset (VBO) are investigated. The hydrostatic pressure behavior and the &Ggr;–Xmixture in these SLS systems are also discussed. It is found that the band gap of the InP/InAs system is insensitive to its layer thickness. The VBO values at the SLS’s under the three strain conditions are determined by a frozen potential approach. Our results demonstrate that for the InP/InAs system the bulklike property is almost recovered in the molecular layer next to the interface. This behavior may be due to the common cation on both sides of the interface. This makes the frozen‐potential approach converge very fast with the layer thickness. Our results of band structure for the (1+1) SLS under a free‐standing mode are consistent with those given by a more elaborate full‐potential linearized augmented‐plane‐wave (FLAPW) calculation. The present results of VBO are about 0.07–0.09 eV larger than the data from an x‐ray photoelectron spectroscopy measurement and the FLAPW method, while in good agreement with the results given by the model solid theory. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358717

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

By use of the mode‐matching technique the quantum bound states in a double‐bend quantum channel of finite length connecting to two 2D electron gas reservoirs have been investigated in detail. The conductanceGof the quantum system is calculated as a function of Fermi energy and the electron density associated with bound states. It is found that there exists one resonant peak inGcorresponding to resonant tunneling via one quasibound state below the first conductance plateau for the quantum channel with double‐bend continuity and two resonant peaks inGcorresponding to resonant tunneling via two quasibound states which are symmetric and antisymmetric superposition of two local bound states localized at two right‐angle bends below the first conductance plateau for the quantum channel with double‐bend discontinuity. At finite temperature the results are compared with experimental results and are found to explain them well. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358718

出版商:AIP    

年代:1995

数据来源: AIP