摘要:

We calculate the dispersion curves of surface acoustic waves of shear horizontal polarization propagating perpendicular to the grooves of a lamellar grating ruled on the surface of a cubic elastic medium. The calculation is based on a formulation of the problem that employs a coordinate‐dependent elastic modulus tensor and mass density, and is valid for an arbitrary ratio of the height of the ridges to the period of the grating. It is found that as this ratio increases the dispersion curve acquires additional, high‐frequency branches in addition to the one already known from earlier studies of this problem. An explanation for this result is proposed.

ISSN:0003-6951    

DOI:10.1063/1.106189

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The growth and properties of thin films of InN on (00.1) sapphire and (00.1) sapphire nucleated by a 400 A˚ layer of AlN have been found to be radically different. The unnucleated InN films exhibit a mixed morphology (largely textured with lesser amounts of epitaxial grains), a monofunctional thickness dependence on sputtering time, uniformly low mobility and carrier concentration, and high resistivity. In contrast, the AlN‐nucleated overlayers show only heteroepitaxial grains, a bifunctional dependence for the film thickness and surface roughness on sputtering time, higher mobility and carrier concentration, and lower resistivity−even in the limit of an InN overlayer on the order of 20–40 A˚.

ISSN:0003-6951    

DOI:10.1063/1.106190

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report here the first investigation on the quench aging of a low‐carbon steel under the influence of an electric charge produced by 6.7 kV dc voltage between the specimen and a parallel electrode separated by 5 mm. This arrangement produced the following effects: (a) retarded the aging kinetics and (b) reduced the peak hardness. Fitting the results to a thermally activated rate equation indicated that the activation energy was increased from 0.65 to 0.85 eV. TEM observations revealed significant changes in precipitate size, morphology, and distribution near the grain boundaries and in the grain interior. It is proposed that the existing electrical conditions enhanced the migration of quenched‐in vacancies from the grain interior to the grain boundaries.

ISSN:0003-6951    

DOI:10.1063/1.106191

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The gate turn off capability of a trench insulated gate metal/amorphous silicon (a‐Si:H)/crystalline silicon (c‐Si) (p‐n) heterojunction switching device is studied. Using a negative gate voltage to modulate the depletion width in thea‐Si:H region, and hence lowering the field for the multiplication of carriers, the heterojunction switching device can be gate turned off or even gate locked. Thus the device can be developed as a gate controllable light switch or light sensor.

ISSN:0003-6951    

DOI:10.1063/1.106192

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Then2ieDpproduct (wheren2ieis thenpproduct andDpis the minority hole mobility) in heavily dopedn‐GaAs has been measured by electrical characterization ofp‐n‐pGaAs homojunction transistors with base dopings ranging from approximately 1×1017to 9×1018cm−3. The measuredn2ieDpproduct decreases as the doping density increases. These results suggest thatnieis roughly constant with doping density, in sharp contrast to the large increase observed forp‐type GaAs. This work shows that when designing GaAs bipolar devices, it is important to consider the large difference in effective band gap betweenn+andp+regions.

ISSN:0003-6951    

DOI:10.1063/1.106416

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is shown that finite‐potential heterostructure wells, homostructure voltage‐induced wells, and heterostructure barriers can act as waveguides for ballistic electrons and that waveguiding is described by a single dispersion relation and can occur at energies above all band edges. The guided mode cutoffs, electron velocity, effective mass, density of states, and ballistic current density (applicable to 2D electron gases) are presented. The maximum ballistic guided current flowing in a given direction for a 10 monolayer Ga0.75Al0.25As/GaAs/Ga0.9Al0.1As waveguide is found to be 2.3 mA per &mgr;m of waveguide width–allowing considerably greater currents than in single‐mode quantum wires.

ISSN:0003-6951    

DOI:10.1063/1.106193

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A novel Bragg confining structure is proposed and analyzed. The combination of a shallow quantum well with superlattice‐Bragg reflectors makes it possible to tailor separately the eigen‐energy, and the wave function of the Bragg confined state. Longer lifetimes and higher effective barriers than in previously proposed Bragg confining structures is possible with the present scheme. Photoluminescence at energies close to the highest direct bandgap of the material system in use is expected from the proposed structure.

ISSN:0003-6951    

DOI:10.1063/1.106168

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

To separate the majority and minority carriers in the deep level transient spectroscopy (DLTS), the transient is usually measured in the dark. However, under some circumstances, the transient measurement should be performed under illumination. In these cases, the effects introduced by the illumination become a concern. In this letter, effects of secondary laser illumination on samples of hydrogenated amorphous silicon (a‐Si:H) during the transient measurement in optical and electrical DLTS are reported. The experimental results show that background illumination decreases the time constant of the transient but it is unlikely to create new gap states during the short time period.

ISSN:0003-6951    

DOI:10.1063/1.106169

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The first long wavelength quantum well infrared photodetector based on valence band intersubband absorption holes is demonstrated. Anormalincidencequantum efficiency of &eegr;=28% and detectivity ofD*&lgr;=3.1×1010cm &sqrt;Hz/W atT=77 K, for a cutoff wavelength &lgr;c=7.9 &mgr;m, have been achieved.

ISSN:0003-6951    

DOI:10.1063/1.106170

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We demonstrate the first waveguide intensity modulator for visible wavelengths based on the quantum‐confined Stark effect. The active waveguide core is composed of 58 Cd0.42Zn0.58Te/ZnTe quantum wells surrounded by Cd0.12Zn0.88Te cladding layers. We obtain ≳10 dB modulation depth at 640 nm with 4 V bias in a 500‐&mgr;m‐long waveguide.

ISSN:0003-6951    

DOI:10.1063/1.106171

出版商:AIP    

年代:1991

数据来源: AIP