摘要:

AlGaAs/GaAs tunneling emitter bipolar transistors (TEBT’s), grown by molecular beam epitaxy, have been fabricated. Device structures with two different tunneling barrier Al mole fractions and each for two different barrier thicknesses were characterized at room temperature. A differential current gain of 410 was achieved using a single 50 A˚ AlAs tunneling barrier. Devices with either thinner barriers (20 A˚) or Al0.38Ga0.62As barriers had lower gains. Al0.24Ga0.76As/GaAs heterojunction bipolar transistors and GaAs homojunction bipolar transistors without tunneling barriers were also fabricated and characterized, for comparison. The performance of the homojunction devices was improved in all cases by inserting the tunneling barrier. The variations of the base and collector currents were measured for all devices and, for the TEBT’s they showed a functional dependence on the interfacial barrier Al mole fraction and thickness, which was attributed to carrier tunneling through the barrier. Furthermore, the above characteristics exhibit a clear electron‐to‐hole preferential tunneling.

ISSN:0003-6951    

DOI:10.1063/1.97685

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have investigated the crystallography and microstructure of Y1Ba2Cu3O9−xwith transmission electron microscopy and x‐ray diffraction. Y1Ba2Cu3O9−xis a distorted, oxygen‐defect perovskite with ordering of the yttrium and barium ions. Its unit cell is orthorhombic with space groupPmm2 and lattice parametersa=3.893 A˚,b=11.688 A˚, andc=3.820 A˚. The structure is heavily twinned on {101} type planes, possibly due to a tetragonal‐to‐orthorhombic transition above room temperature.

ISSN:0003-6951    

DOI:10.1063/1.97686

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A unique scanning tunneling microscope (STM) system has been developed for spectroscopy of the superconducting energy gap. High‐resolution control of tunnel current and voltage allows for measurement of superconducting properties at tunnel resistance levels 102–103greater than that achieved in prior work. The previously used STM methods for superconductor spectroscopy are compared to those developed for the work reported here. Superconducting energy‐gap spectra are reported for three superconductors, Pb, PbBi, and NbN, over a range of tunnel resistance. The measured spectra are compared directly to theory.

ISSN:0003-6951    

DOI:10.1063/1.97687

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Laser‐induced gratings are produced in thin films of mixtures of nematic and cholesteric liquid crystals doped with a dye. A transient grating regime is found which decays on the order of seconds; additionally, a ‘‘persistent’’ grating with lifetimes up to 16 h has been found. Mechanisms for creation and decay are discussed.

ISSN:0003-6951    

DOI:10.1063/1.97688

出版商:AIP    

年代:1987

数据来源: AIP