摘要:

Schottky barrier heights (SBH’s) of a variety of metals (In, Cd, Nb, Ti, W, Cu, Ag, Au, Ni, Pt, and Se) contacting top-ZnSe grown by a molecular beam epitaxy method were measured by an internal photoemission, capacitance–voltage(C–V),and/or current density–voltage(J–V)method. The internal photoemission method could not measure accurately the SBH’s of these metals due to a strong interference of the monochromatic incident light in thep-ZnSe epilayer. TheC–Vmethod measured a SBH value of 1.23 eV for the Au contact and 1.13 eV for the Ni contact, but did not measure the SBH’s of other metals due to strong hysteresis of theC–Vcurves. The SBH’s of these metals were successfully measured by theJ–Vmethod to be 1.2±0.1 eV. The present experiment showed that the SBH values were independent of the work functions of the contact metals, indicating that the Fermi-level could be pinned at thep-ZnSe/metal interface. In addition, turn-on voltages conventionally used to evaluate the electrical properties of the contact metals were found to be very sensitive to the SBH values. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366049

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

GaAs and related materials, grown by molecular beam epitaxy at 200–300 °C under normal, group V-rich conditions are highly nonstoichiometric, with excess group V concentrations of up to1021 cm−3,and the material properties are defect controlled. Here we report on comparative studies of low temperature growth of GaAs on (100) substrates and on (111)A, (111)B, (311)A, and (311)B surfaces. We show that material grown on both the (111) faces, under As-rich conditions, becomes polycrystalline almost immediately after commencement of growth. We attribute this to faceting of the surface creating regions of excessive As incorporation and either directly nucleating misorientated growth or producing areas of extreme localized strain resulting in the breakdown of crystallinity. Layers grown on (311)A and (311)B surfaces are of good crystalline quality but are highly nonstoichiometric in both cases, contrary to the anticipation that the (311)A surface, having fewer available forward Ga bonds than the (100) or (311)B surfaces might have a lower affinity for As incorporation. We also describe the reduction of excess As incorporation into layers grown on both (311) surfaces in the presence of Si or Be doping concentrations of1×1019 cm−3or greater, as we previously reported for layers grown on (100) substrates. This is evidenced by the reduced lattice parameter and lower absorption in the near-band-edge infrared region due to As antisite defects, compared to undoped material. Also, little or no hopping conduction is seen in Be doped layers although they are totally compensated. A proportion of donors are active in the Si doped layers and the conduction mechanism seems to be normal band conductivity. Electrical activation of the Si donors and Be acceptors can be increased, however, only after high temperature annealing. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366050

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this work, the electrical properties ofPb1−xSnxTeepitaxial layers with Sn composition covering the whole range were investigated. The samples were grown on(111)BaF2substrates in a molecular beam epitaxy system using PbTe, SnTe, and Te solid sources. As the alloy composition varies from PbTe to SnTe, the hole concentration increases exponentially from1017to1020 cm−3for Te-rich sources and from1017to1019 cm−3for stoichiometric ones. The resistivity of the samples, which depends mainly on their hole concentrations, shows an exponential dependence on the temperature with a slope which decreases asxgoes from 0 to 1. For allPb1−xSnxTesamples withxin the range of 0.35–0.7, the resistivity curve shows a very well defined minimum at low temperatures. This anomalous behavior is supposed to be related to the band crossing, where the energy gap temperature coefficient changes sign. The temperatures where the minimum in the resistivity occurs only agree with the ones predicted by the band inversion model aroundx=0.4,exhibiting a large deviation to lower temperatures asxincreases. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366051

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of humidity on the electronic structure of Na-containing polycrystallineCu(In,Ga)Se2thin films on soda-lime glass substrates has been investigated by x-ray and UV photoemission as well as by Auger electron spectroscopy. Different interactions between coadsorbed Na,H2O, and the Cu(In,Ga)Se2surface are revealed at low temperatures and upon annealing at room temperature. Both, reversible and irreversible interactions such as aH2O-induced reduction of the Na surface content and the formation of a Na–O–Cu(In,Ga)Se2complex are observed. Our findings can be correlated with the influence of ambient conditions on Cu(In,Ga)Se2solar cell adsorbers and demonstrate the importance of adequate encapsulation of Na-containing Cu(In,Ga)Se2-based thin-film solar cells. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366096

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a model and results of self-consistent calculation of current–voltage(I–V) characteristics of the InAs/AlSb/InAs, InAs/AlSb/GaSb resonant tunneling structures with type II heterojunctions. The different current components, charge accumulation in the quantum well and quasi-Fermi level variation in contacts and spacers due to the drift-diffusion processes, are taken into account. Thekpband model is used to describe the interband and intraband tunneling processes. The transfer Hamiltonian approach is employed to obtain the resonant tunneling current density and charge density in the quantum well. A good quantitative agreement with the experiment is obtained for both structures including the agreement for the values of peak-to-valley(P/V) current ratio. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366261

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the measurement and analysis of critical current(Ic)modulation and microwave response in magnetic field for a set ofYBa2Cu3O7-YBa2Co0.15Cu2.85O7-YBa2Cu3O7ramp-edge Josephson junctions. These junctions have been fabricated with various widthswto span the transition from the moderately small(w<2&lgr;J)to the moderately large(w>2&lgr;J)junction limit at 77 K. Aswincreases, both theIcmodulation and microwave absorption behavior independently suggest a growing contribution from edge supercurrents. The addition of a superconducting ground plane was shown to reduce the edge supercurrent effects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365765

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Bulk Fe/Ag multilayers with layer thickness of about 10 nm have been successfully fabricated by repeated press-rolling directly from a macroscopic stack of metal sheets. The press-rolled multilayers exhibited giant magnetoresistance of 13&percent; in the current perpendicular to the plane geometry and 4&percent; in the current in the plane geometry at 5 K. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366052

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magnetization patterns and remanence states of thin films with a surface anisotropy normal to the film plane are analyzed. The total film energy integral is expanded to second order to find both equilibrium and nucleation. It is shown that for a given film and applied field a critical surface anisotropy is required for the magnetizations to deviate from initial saturation. Analytic expressions are given for these critical conditions for both in-plane and normal applied field. Remanent state magnetization distributions are shown. For small thickness where the exchange energy keeps the magnetization approximately uniform throughout the film, the out-of-plane component increases monotonically with the magnitude of the surface anisotropy. For larger thicknesses, only a layer near the film surfaces rotates into the normal direction. In this case the nucleation condition for formation of these quasiwalls is independent of the film thickness. For large thicknesses the nucleation field varies quadratically with the surface anisotropy. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366053

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magnetic induction maps from a sputter-deposited Co/Cr/Co trilayer have been obtained at different points of the hysteresis cycle, using a conventional transmission electron microscope. The sample shows hysteresis, with nearly parallel alignment of the magnetization in the two Co layers at remanence, but areas of antiparallel alignment developing in reverse fields. Such areas occur in similar positions at opposite points of the hysteresis loop. The strongly correlated domain patterns seen in opposite field directions suggest that the interlayer exchange coupling varies spatially. The parallel alignment observed at remanence suggests the presence of an energy barrier that needs to be overcome before antiparallel alignment can be formed. This conclusion is supported by observations of the film in a demagnetized state. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366054

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The change in the magnetic properties of melt-spunSm2+&dgr;Fe15Ga2C2permanent magnets with variation of the Sm content &dgr; has been investigated in the range of −0.05⩽&dgr;⩽0.20. A drastic increase in the coercive field&mgr;0HCfrom 1.5 to 2.2 T at room temperature has been observed for &dgr;⩾0.1. This can be understood as an influence of the Sm-rich nonmagnetic intergranular phase, occurring due to the Sm excess. Room temperature values of the maximum energy density up to(BH)max=64.2 kJ/m3(&dgr;=0.03) can be obtained. The samples with higher Sm contents exhibit larger values of the maximum energy density at elevated temperatures(T⩾450 K).For &dgr;=0.13, a value of(BH)max=31.4 kJ/m3has been observed at 500 K. The microstructural parameters&agr;KandNeffdescribing the influence of the nonideal microstructure on the coercive field in the framework of the nucleation model were determined from the temperature dependence of the coercive field. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366055

出版商:AIP    

年代:1997

数据来源: AIP