摘要:

We report the first direct demonstration of a strain‐generated built‐in electric field in a (111) oriented strained‐layer heterostructure. We present a model which describes the accommodation of the misfit strain in a lattice‐mismatched quantum well, and the resulting generation of a longitudinal electric field via the piezoelectric effect. On a (111)BGaAs substrate, we grew the quantum well in the intrinsic region of ap‐i‐ndiode such that the strain‐generated electric field in the quantum well opposes the weaker built‐in electric field of the diode. Under reverse bias operation, photoconductivity measurements show a quadratic blue shift of the quantum well electroabsorption peaks, in contrast to the red shifts normally observed in the quantum‐confined Stark effect. The measured blue shifts demonstrate an electric field strength of 1.7×105V/cm, which agrees with theory to within the accuracy of the measured sample characteristics.

ISSN:0003-6951    

DOI:10.1063/1.102729

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Either spontaneous or artificial ordering of semiconductor alloys into CuAu‐like, chalcopyrite, or CuPt‐like structures is predicted to be accompanied by a reduction in the direct band gaps relative to the average over the binaries. In this letter calculated results are presented for seven III‐V and II‐VI alloys. We identify the mechanism for this band‐gap narrowing as band folding followed by repulsion between the folded states. The latter is coupled by the non‐zinc‐blende component of the superlattice potential. The same physical mechanism (but to a different extent) is responsible for gap bowing indisorderedalloys.

ISSN:0003-6951    

DOI:10.1063/1.103307

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

ISSN:0003-6951    

DOI:10.1063/1.102730

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Molecular beam epitaxial GaAs layers of electron concentration 1.69×1017cm−3, and various thicknessesd=0.25, 0.50, 1.00, and 2.00 &mgr;m, have been grown on semi‐insulating GaAs substrates and characterized by the Hall effect and capacitance‐voltage (C‐V) techniques. A plot of sheet Hall concentrationnsvsdgives accurate values of (ND−NA) and (ws+wi), the sum of the surface and interface free‐carrier depletion widths, respectively. TheC‐Vmeasurements verify the value ofND−NA, and also give a good estimate ofwi. By comparing the value ofwiwith depletion theory, it is shown unambiguously that the interface depletion is mainly due to interface states, of concentration 1.2×1012cm−2(below midgap). This result has important technological implications.

ISSN:0003-6951    

DOI:10.1063/1.102731

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Metal/single‐crystal‐silicide interface evolution has been examined for Ti/MoSi2 (001) using high‐resolution synchrotron radiation and x‐ray photoemission. Reaction between Ti and Si was observed for temperatures 300≤T≤873 K. At 300 K, it was limited to Ti interaction with the single Si layer terminating the cleaved MoSi2 (001) surface. Analysis of the Si 2pcore level line shape showed two different interfacial reaction products with bonding characteristics of TiSi and a disordered solution of Si in Ti. Interfacial development was dominated by Si outdiffusion at higher temperatures with Si enrichment of the overlayer but not conversion to a silicide.

ISSN:0003-6951    

DOI:10.1063/1.103308

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Multiple quantum well structures consisting of alternating layers of two crystalline organic semiconductors, namely, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) and 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA), have been grown by organic molecular beam deposition. The individual layer thicknesses in the multilayer samples were varied from 10 to 200 A˚. X‐ray diffraction and birefringence data show that there is a strong structural ordering in all layers, as well as across large spatial distances along the sample surface. Thus, the growth is ‘‘quasi‐epitaxial’’ even though the PTCDA and NTCDA crystal structures are incommensurate. From the optical absorption spectra, it was found that the lowest energy PTCDA singlet exciton line shifts to higher energy with decreasing layer thickness. Comparison of these results with a quantum mechanical model based on exciton confinement in the PTCDA layers is proposed to describe the energy shift.

ISSN:0003-6951    

DOI:10.1063/1.102733

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superconducting Nd‐Ce‐Cu‐O thin films were epitaxially grown on SrTiO3 (100) by activated reactive evaporation. As‐grown films showed the metallic temperature dependence of the resistivity and superconducting transition at 12.5 K (R=0). The remarkable parallel shift of the onset temperature of the resistive transition in the magnetic fields was observed. Ginzburg–Landau coherence lengths along thecaxis and in the basal plane are 7 and 96 A˚, respectively.

ISSN:0003-6951    

DOI:10.1063/1.103309

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We describe the voltage‐current characteristics of YBa2Cu3O7−&dgr;epitaxial films within the flux creep model in a manner consistent with the resistive transition behavior. The magnitude of the activation energy, and its temperature and magnetic field dependences, are readily derived from the experimentally observed power law characteristics and show a (1−T/Tc)3/2type of behavior nearTc. The activation energy is a nonlinear function of the current density and it enables the determination of the shape of the flux line potential well.

ISSN:0003-6951    

DOI:10.1063/1.103310

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have, for the first time, made quasi‐particle tunneling measurements on a YBa2Cu3O7−x(001)/Y2O3(001)/YBa2Cu3O7−x(001)junction, which was epitaxially grown on a MgO(100) substrate in anin‐situprocess. Both layers of YBa2Cu3O7−xshowed the same superconducting transition ofTc end=86 K with &Dgr;T(R=10–90%)=1.5 K. Quasi‐particle tunneling in the direction perpendicular to the Cu‐O planes was measured. A gap parameter &Dgr;(4.5 K) of 9.0±0.2 meV and a value of 2&Dgr;/kTcof 3.5+0.4−0.6were obtained.

ISSN:0003-6951    

DOI:10.1063/1.103311

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present the first observations of superconducting quantum interference in multilevel, all highTc, lithographically patterned edge junction structures. The current‐voltage characteristics are nonhysteretic and have well‐defined critical currents. The dynamic resistance is independent of current above the critical current. These devices show periodic sensitivity to magnetic fields and low levels of magnetic hysteresis up to temperatures around 60 K.

ISSN:0003-6951    

DOI:10.1063/1.102706

出版商:AIP    

年代:1990

数据来源: AIP