摘要:

We report on the characterization of selectively doped GaAs/AlGaAs heterostructures, grown by an extremely clean molecular beam epitaxy system, which exhibit a Hall mobility of a two dimensional electron gas exceeding10×106 cm2/Vsfor a wide range of undoped spacer layer thickness (50–100 nm). A maximum electron mobility of14.4×106 cm2/Vswas measured at 0.1 K in a structure with a 68 nm spacer thickness and an areal carrier density of2.4×1011cm−2. This is the highest electron mobility ever reported, leading to a momentum relaxation mean-free path of∼120&mgr;m. We present experiments that enable us to distinguish between the main scattering mechanisms. We find that scattering due to background impurities limits electron mobility in our best samples, suggesting that further improvement in structure quality is possible. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119829

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An aluminum-wire grid polarizer fabricated directly on a gallium–arsenide photodiode is used to realize a polarization-selective photodetector. Since all of the light transmitted through the wire grid, including higher-order diffraction components, can be detected at the photodiode and since a resonance of incident electromagnetic waves is utilized, the required grid period can be significantly larger. With a grid period of 600 nm and normal incident light at 715 nm, an extinction ratio of 16 can be obtained both for light detected at the photodiode and light reflected from the surface. If light detected at the photodiode is to be optimized, a higher extinction ratio of 30 and a loss of 30&percent; have been experimentally obtained as well. These experimental results are in good agreement with our theoretical simulation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119830

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We formed ideal Ti Ohmic contacts on ann-type 6H-SiC epitaxial layer by reducing Schottky barrier heights. The ideal contacts were realized by utilizing ideal SiC surfaces formed under processes that intend to lower the density of surface states. As the first process to form the ideal surfaces, SiC surfaces were flattened by oxidation followed by HF etching. Further, the ideal SiC surfaces in terms of passivation of surface states were formed by immersing the flat SiC surfaces in boiling water. Ti electrodes thus formed had Ohmic properties with excellentI–Vcharacteristic linearity without the use of heavy doping and high-temperature annealing. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119831

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The creation of Hg interstitials during ion implantation of mercury cadmium telluride is found to strongly depend on the preferred lattice position of the element implanted. Elements that substitute onto the cation sublattice create significantly more interstitials than elements that sit interstitially or on the anion sublattice. In particular, implants of column II elements Mg and Zn produced much larger interstitial concentrations than implants of column VI elements S and Se. Implants of B, which resides mostly as an interstitial, produced Hg interstitial concentrations intermediate between the column II and column VI ions. Recoils from implant damage also contributed to Hg interstitial formation in heavier mass implants (Zn and Se), but appear to have negligible influence on interstitial generation in implants of lighter ions. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119832

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of surface reconstructions on the surface morphology duringin situlayer-by-layer etching of GaAs(001) has been studied based on the observation of reflection high-energy electron-diffraction measurements. For the etching,AsBr3is used as a reactive source etchant under solid source molecular beam epitaxy conditions, focusing on a high temperature region in which the etching rate is limited by a supply rate ofAsBr3resulting in a constant value. Despite the fact that the etching starts on a layer-by-layer basis, an initially smooth surface turns considerably rougher depending on the stoichiometry associated with the surface reconstruction. The best morphology after a removal of 250 nm is obtained in the Ga-rich (3×1) reconstruction region close to the phase transition boundary to the As-rich (2×4). This is also verified by the measurement of scanning electron microscopy and atomic force microscopy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119921

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Three photoluminescence (PL) bands at 340–370, 400–430, and 740 nm were observed at room temperature ina-Si:H:O films fabricated by plasma enhanced chemical vapor deposition without any postprocessing. The violet-blue emission is very strong and stable, and its intensity is closely related to the oxygen content in the films, which can be controlled by the applied dc biases on the sample substrates during deposition. The first two PL peaks are ascribed to Si–O related species, and the last one to the quantum size effect of the nanocrystallites embedded in thea-Si:H:O matrix. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119833

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Initial stage of lattice relaxation of GaAs islands grown on Si(100) substrate were investigated by combination of reflection high-energy electron diffraction and molecular beam epitaxy. In addition to the lattice constants in horizontal direction(a∥)to the substrate surface, we first measured directly those in vertical one(a⊥).At the beginning of the growth, the rapid increase ofa∥and the larger Poisson’s ratios than that of bulk were observed. Atomic bond flexibility and extension induced by surface effects might cause this rapid increase ofa∥and large Poisson’s ratios. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119834

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed a novel coplanar resonator serving as a tank circuit for radio frequency washer superconducting quantum interference devices (SQUIDs). Two coplanar lines surrounded the circular flux concentrator washer, 13.4 mm in diameter. The SQUID, 3.5 mm in diameter, was coupled to the concentrator in the flip-chip configuration. All parts were fabricated from single-layer epitaxialYBa2Cu3O7films onLaAlO3substrates. In this layout, the resonant frequency could be set between 600 and 850 MHz. With SQUID loops of100×100 &mgr;m2(SQUID) inductanceLs=150 pHor10×500 &mgr;m2(Ls=260 pH),we determined at 77 K white flux noise levelsS&fgr;1/2of1.0×10−5and1.5×10−5&fgr;0/Hz,respectively. Both figures corresponded to the field resolution of about30 fT/Hz.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119835

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using high-TcJosephson junctions made ofYBa2Cu3O7−&dgr;deposited across MgO bicrystal boundary, at terahertz (THz) frequency band, we demonstrated both fundamental and harmonic mixing. Radiation from a far-infrared laser was coupled to the junction, which was integrated with a planar bow-tie antenna, via an extended hyperhemispherical silicon lens. Fundamental mixing manifested itself in the junction’s dc current–voltage (I–V) curve as a third Shapiro step in addition to those two induced by the THz laser lines from a slightly misaligned resonator. In harmonic mixing between a THz laser line and a microwave local oscillator, the highest harmonic number we could get was 490 with a signal-to-noise ratio of 9 dB at the intermediate frequency. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119836

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Major challenges concerning the use of chemical beam epitaxy deposition techniques are posed by the lack of reliablein situcomposition control and well-behaved metal–organic precursors. To circumvent these shortcomings, we propose the use of a different type of metal–organic precursors, namely molecules resistant to high temperatures, for the growth of thin films. As these molecules cannot be decomposed by the substrate temperature, they are subjected to a chemical reaction with a beam of activated species. The major advantages of this novel deposition process are listed and illustrated by the growth of CuO and YBa2Cu3O7thin films. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119837

出版商:AIP    

年代:1997

数据来源: AIP