摘要:

Interface morphology of strained In0.5Ga0.5As/GaAs wells grown by molecular beam epitaxy from 470 to 570 °C has been examined by photoluminescence at 77 K. Transition from the two‐dimensional to three‐dimensional (3D) growth was observed after a critical layer thickness, which largely depended on the growth temperature and was far ahead of the formation of misfit dislocations. Luminescence from the layer after the start of 3D growth had a high quantum efficiency but was rather broad or even split. The 3D growth started at nine monolayers for 470 °C and four monolayers for 540 °C. The reason for the onset of 3D growth is discussed in terms of In segregation.

ISSN:0003-6951    

DOI:10.1063/1.106111

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

With attention to total energy loss of injected electrons through Fowler–Nordheim (F–N) tunneling, time‐dependent dielectric breakdown (TDDB) of 5‐nm‐thick silicon oxide films was investigated. Metal‐oxide‐semiconductor (MOS) diodes with four combinations of gate electrode and substrate type were fabricated. This produced different energy losses of injected electrons at a constant F–N tunneling current stress in spite of the same oxide thickness. TDDB lifetime was strongly affected by this energy loss difference. Since other electrical changes caused by trapping of stress‐induced positive charges in oxide also exhibited the similar energy loss dependence to the lifetime, TDDB for ultrathin oxide films is probably dominated by the trapping of positive charges, which are mainly generated near anode‐side oxide interfaces through the surface plasmon mechanism.

ISSN:0003-6951    

DOI:10.1063/1.106114

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of valence‐band discontinuity at the collector base heterojunction on the current gain and base charge storage is modeled. It is shown that the onset of the Kirk effect is accompanied by a sharp drop in the current gain andftdue to the formation of a potential barrier. The variation of barrier height with collector current density is determined and its effect on current gain and base transit time described. The results discussed here are applicable to Si/SiGe double‐heterojunction bipolar transistors.

ISSN:0003-6951    

DOI:10.1063/1.106115

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The distribution of electrons in two parallel two‐dimensional electron sheets in close proximity at low temperatures is investigated. We find that due to the exchange interaction a symmetric structure may have a ground state in which all electrons are transferred to one of the sheets. This occurs if the separation between the two systems is sufficiently small and the two‐dimensional electron gas density is sufficiently low. The exchange interaction consequently leads to a bistability with respect to electron population in the two‐sheet system which may be useful for future electronic devices, such as memory elements.

ISSN:0003-6951    

DOI:10.1063/1.106116

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Vertical transport in GaAs/AlGaAs superlattices is probed in structures with graded composition. Such structures allow both to impose a quasi electric field to the carriers and to evidence the carrier movement by the temporal changes in the luminescence line shape. The fit of this line shape by a drift‐diffusion model gives the transport properties of electrons. High mobility of the electrons is evidenced for the shortest period superlattices, in agreement with previous optical measurements. The importance of the transfer to the satellite valleys and of the finite capture time in the large well included as a marker are evidenced.

ISSN:0003-6951    

DOI:10.1063/1.106117

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The low internal damping of micromachined monolithic silicon levers with integrated probe tip has been exploited to detect nonconservative components in the interaction forces between the probe tip and sample. This is accomplished by monitoring the mechanicalQwhile scanning the surface. The gap width was controlled by keeping the lever’s resonance frequency detuning, caused by the gradient of the force between tip and surface, fixed to a preset value. Nonconservative components are present even in Coulomb attraction since, whenever a voltage is applied between tip and substrate, currents are induced by the lever’s oscillation leading to Joule dissipation of energy at a rate that depends on the local conductivity. Strong damping contrast was observed in layered GaAs/AlGaAs semiconductor heterostructures. It depended on the type of material, dopant concentration, illumination, and the applied voltage. Damping variations were resolved over distances of less than 20 nm.

ISSN:0003-6951    

DOI:10.1063/1.106088

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is shown that LiF(100) films with the electronic properties of cleaved bulk LiF crystals can be grown epitaxially on Ge(100). These include an exceptionally large, negative electron affinity of −2.7 eV, which leads to intense photoemission at zero kinetic energy. The valence band offset ranges from 7.3–7.6 eV.

ISSN:0003-6951    

DOI:10.1063/1.106091

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report an extension of the bi‐epitaxial Josephson junction process that permits the use of a variety of substrate materials and allows junctions to be placed at any level of a multilayer structure. The new materials, SrTiO3, MgO, and CeO2, serve as a base layer, a seed layer, and a buffer layer, respectively, and replace Al2O3, MgO, and SrTiO3in the original bi‐epitaxial process. This new process offers much more flexibility in designing a circuit. Bi‐epitaxial junctions made with the new set of materials show much improved electrical properties, especially at 77 K. We attribute the improved electrical characteristics to a better thermal expansion match between the substrate and the thin‐film layers. Important junction properties such as critical currents and junction resistances are compared to other types of grain boundary junctions.

ISSN:0003-6951    

DOI:10.1063/1.106411

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High‐quality epitaxial Y1B2Cu3Oxthin films (Tc,o≥ (R18) 90 K,jc(77 K)≥ (R18)3 ×106A/cm2) wereinsitugrown on MgO by KrF excimer laser ablation. The combination ofinsituresistance measurements, x‐ray diffraction experiments,Tcmeasurements, scanning electron microscopy and scanning tunneling microscopy gives clear indications for an island growth on these substrates and shows growth steps and spirals at the film surface.   

ISSN:0003-6951    

DOI:10.1063/1.106066

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We observed that the superconducting critical temperatureTc(x) of the oxides (R1−xPrx)Ba2Cu3O7−y(R=Er, Y, Dy, Gd, Eu) decreases monotonically with increasing Pr concentrationx. Using the reduced parametersTc/Tc(0) andx/xcrall the experimental data for five studied systems fall onto the theoretical universal curve of Abrikosov and Gor’kov over the reduced Pr concentration regime,x/xcr<0.6, wherexcris the critical concentration of Pr for the complete suppression of superconductivity andTc(0) is theTcfor undoped material. The consistency of these results suggests a pair‐breaking mechanism which plays a role in depressing superconductivity in these highTcoxides.

ISSN:0003-6951    

DOI:10.1063/1.106067

出版商:AIP    

年代:1991

数据来源: AIP