摘要:

The atomically ultrasmooth surfaces with atomic steps of sapphire substrates were obtained by annealing in air at temperatures between 1000 and 1400 °C. The terrace width and atomic step height of the ultrasmooth surfaces were controlled on an atomic scale by changing the annealing conditions and the crystallographic surface of substrates. The obtained ultrasmooth surface was stable in air. The topmost atomic structure of the terrace was examined quantitatively by atomic force microscopy and ion scattering spectroscopy as well as a theoretical approach using molecular dynamics simulations. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114313

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A behavior of plastic deformations of C60single crystals was examined using the microindentation technique. Not only slip lines but also dislocation etch pits were observed around the indentation on the crystal surface. It is confirmed that the slip systems in C60single crystals are {111}⟨110⟩ in a temperature range of 240 K to 450 K. This means that, even in a simple cubic phase below a phase transition temperature of ∼260 K, the slip systems are the same as a face‐centered‐cubic phase. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114314

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the interface formation of Ca with an alkanethiol CH3(CH3)17SH monolayer self‐assembled onto gold‐coated silicon. Deposited Ca neither diffused into nor interacted chemically with the monolayer. Core‐level shift and work function changes were observed in the monolayer as soon as Ca was deposited and they were stabilized after 8 A˚ of Ca coverage. The shifts are interpreted in terms of charge transfer from Ca to the monolayer, creating a dipole layer at the interface. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114315

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Microwave attenuation of coplanar waveguides fabricated on high–resistivity silicon substrates with SiO2insulation layer is investigated from 10 GHz up to 600 GHz by optoelectronic time–domain measurements. They are performed directly on the wafer employing a freely positionable photoconductive switch for picosecond–electric–pulse injection and an electro–optic crystal for pulse detection. The attenuation is significantly altered over the whole frequency range by free–carrier absorption resulting from inversion and accumulation effects at the Si/SiO2interface. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114316

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied the avalanche dynamics in shallow junction avalanche diodes designed for detection and timing of single photons. Space charge effects have been correctly taken into account, and both electron and hole transport were considered. Based on the results of the detailed computer simulation we have developed a simplified model of the detector which can be used for studying the avalanche transient in these devices and for optimizing the detector structure for the best timing performance. The results are in good agreement with the experiments. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114317

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe the molecular beam epitaxy growth of superlattices where silicon layers with a thickness between 3 and 10 nm alternate with very thin carbon layers. High resolution x‐ray diffraction reveals that the superlattices are of excellent crystalline quality and are pseudomorphic with respect to the silicon substrate. From a dynamical simulation of the diffraction spectra we conclude that the nominal carbon layers are in fact silicon–carbon alloys with a carbon content up to 50%. Given the large lattice mismatch of more than 10% of such an alloy to the silicon substrate, astonishingly thick superlattices with up to 100 periods can be grown without lattice relaxation. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114318

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have calculated the effect of alloy interdiffusion on the one‐dimensional energy confinement of (Al,Ga)As/GaAs crescent shaped quantum wire structures. We show that the energy splitting between excited states may be greatly enhanced by the interdiffusion mechanism. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114319

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report an improved camel‐gate field effect transistor using a high‐medium‐low doped channel. A 1000‐A˚‐thickn=1×1017cm−3GaAs layer is employed to form the camel gate, which prevents the planar‐doped barrier from being dropped abruptly. In addition to transition channel, a thin (200 A˚) heavily doped (n=5×1017cm−3) GaAs layer works as the main active channel to enhance the current drivability and transconductance. For our 1.5×100 &mgr;m2device, the maximum current density of over 850 mA/mm was obtained. Moreover, an enhanced voltage‐independent transconductance was also observed. Generally, the device exhibits a transconductance of 220 mS/mm which is compatible to that of MESFETs and is two‐ or threefold to that of reported camel‐gate FETs. In addition, the proposed device demonstrates a large gate voltage swing for high transconductance operation. Due to the excellent device performance, our devices do hold promise for both large signal and digital circuits application, simultaneously. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114320

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have realized a (GaAs1−xSbx‐InyGa 1−yAs)/GaAs bilayer‐quantum well (BQW), which consists of two adjacent pseudomorphic layers of GaAs1−xSbxand InyGa1−yAs sandwiched between GaAs barriers. Photoluminescence was observed at longer wavelengths than those found for corresponding InyGa1−yAs/GaAs and GaAs1−xSbx/GaAs single quantum wells (SQW), which indicates a type‐II band alignment in the BQW. The longest 300 K emission wavelength achieved so far was 1.332 &mgr;m. For an accurate determination of the band offset between GaAs1−xSbxand GaAs, required for a theoretical modeling of the interband transition energies of these BQWs, a large set of GaAs1−xSbx/GaAs SQWs was prepared from which a type‐II band alignment was deduced, with the valence band discontinuity ratioQvfound to depend on the Sb concentrationx(Qv=1.76+1.34x). With this parameter it was possible to calculate the expected interband transition energies in a BQW structure without any adjustable parameters. The calculations are in agreement with experimental data within a range of ±4%. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114321

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We experimentally study the effect of perpendicular electric field on the exciton binding energy using a specially designed step quantum well. From photoluminescence spectra at the temperature of 77 K, we have directly observed remarkable blueshift of the exciton peak due to the transition from spatially direct to spatially indirect excitons induced by electric field. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114322

出版商:AIP    

年代:1995

数据来源: AIP