摘要:

A high performance, bias tunable,p-GaAs homojunction interfacial workfunction internal photoemission far-infrared detector is demonstrated. A responsivity of3.10±0.05 A/W,a quantum efficiency of 12.5&percent;, and a detectivityD*of5.9×1010 cmHz/Wwere obtained at 4.2 K for cutoff wavelengths from 80 to 100 &mgr;m. The bias dependences of the quantum efficiency, detectivity, and cutoff wavelength were measured and are well explained by the theoretical model. The effect of the layer number on detector performance and the uniformity of the detectors are discussed. A comparison with Ge:Ga photoconductive detectors suggests that similar or even better performance may be obtainable with a far-infrared detector. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120176

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Proton irradiation followed by rapid thermal annealing was used to selectively induce layer intermixing and thus shift the emission wavelengths of GaAs–AlGaAs graded-index separate-confinement-heterostructure quantum well lasers. Up to 40 nm shifts were observed in 4 &mgr;m ridge waveguide devices irradiated to a dose of1.5×1016 cm−2.Although the wavelength shifts were accompanied by some degradation in the lasing threshold current and differential quantum efficiency, they were still quite acceptable at moderate wavelength shifts. This technique provides a simple and promising postgrowth process of integrating lasers of different wavelengths for wavelength-division-multiplexing applications. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120177

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We study the critical behavior of 1.3&mgr;mInP-based strained-layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures. We show that, under the critical injection condition where the carrier density in the quantum wells reaches the maximum possible without causing any extra pile-up of carriers in the separate heterostructure confinement regions, an InP-based SL-MQW system exhibits an absorption-to-gain phase transition at some critical temperature(Tc). The characteristic feature of this phase transition shows excellent agreement with Landau theory of second-order phase transitions. It is demonstrated thatTcis a significant and meaningful quantity not only for laser design but also for characterizing the nature of an InP-based SL-MQW system in terms of condensed matter physics. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120178

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The charge carrier transport in poly(p-phenylenevinylene) (PPV) is investigated by the time-of-flight technique. Mobilities of positive carriers in PPV are determined and the dispersive character of transport is established. The dispersion parameters are analyzed in the frame of a multiple trapping model. The drift mobility of the positive carriers is in the range of 10−5cm2/V s at room temperature for an electric field of105V/cm and increases with increasing field and temperature. The mobility shows thermally activated behavior with an activation energy of about 0.75 eV at zero field. It is shown that the experimental results can be interpreted by polaron transport. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120179

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the experimental realization of a quantum point contact in a semiconductor heterostructure by lithography with an atomic force microscope (AFM). A thin, homogeneous titanium film on top of the chip surface was patterned by local anodic oxidation, induced by a current applied to ann-doped AFM tip. We demonstrate that self-aligned gate structures in the sub-micron regime can be fabricated with this technique. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120137

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present anab initiocalculation of the infrared vibrational spectrum of amorphous silicon. The electron polarization, which is the main ingredient to obtain the infrared spectra, is evaluated using the recent formulation in terms of Berry’s phase, while the time evolution of the system is studied using Car–Parrinello molecular dynamics. Our results are in quantitative agreement with experimental data and also with the results of empirical calculations based on a bond-dipole model. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120188

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Self-field ac losses were measured by the conventional ac four-probe method in biaxially aligned Y–Ba–Cu–O tapes using polycrystalline Hastelloy tapes with textured yttria-stabilized-zirconia buffer layers. The ac losses increased in proportion to the fourth power of transport current in the highJcsample, and agreed well with Norris’ equation for thin strip conductors. However, the lowJcsample had rather higher losses than Norris’ prediction, suggesting excessive magnetic flux penetration caused by percolated current paths. The results confirmed Norris’ prediction of the low ac losses for thin strip conductors, and indicated the importance of removing percolated structures of current paths to avoid higher ac losses than the theoretical predictions based on uniform conductors. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120180

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Faraday rotation spectrum has been measured at room temperature in a magnetic nanocomposite of&ggr;-Fe2O3/SiO2.The material consists of isolated&ggr;-Fe2O3nanoparticles dispersed in a silica matrix, and it was prepared through a sol-gel method. The composite contains 18&percent; of&ggr;-Fe2O3in weight with an average particle size of 20 nm. It has a coercitivity of 30 Oe and anMSof 6 emu/g. The specific Faraday rotation spectrum exhibits a narrow peak centered around 765 nm, reaching a value of 110°/cm and an absorption coefficient of64 cm−1.Faraday rotation versus applied field has also been measured, and a cycle similar to the one described by the magnetization has been found. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120181

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An optimal composition ofLa0.67Cd0.33MnO3was synthesized by ceramic route. The compound crystallized in a rhombohedral structure with lattice parametersa=5.473(4) Åand&agr;=60°37′.Resistivity measurement showed an insulator-to-metal transition coupled with a ferromagnetic transition of around 255 K. Epitaxial thin films were fabricated on theLaAlO3(100) substrate by a pulsed laser deposition technique. The psuedocubic lattice parameteraof the film is 3.873(4) Å. The insulator-to-metal transition of the film was observed at 250 K which is comparable with the bulk value. The film was ferromagnetic below this temperature. Magnetoresistance defined as&Dgr;R/R0=(RH−R0)/R0was over−86&percent;near the insulator-to-metal transition temperature of 240 K at 6 T magnetic field and over-30&percent; at relatively low fields of 1 T. No magnetoresistance was observed at low temperatures in the film unlike in the polycrystalline sample, where about a 40&percent; decrease in resistance was observed on applying 6 T magnetic field due to the spin dependent scattering at the grain boundaries. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120182

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electron emission characteristics of sulfur (S)-doped boron nitride (BN) films synthesized by plasma-assisted chemical vapor deposition (PACVD) are investigated. The BN film consists of hexagonal grains of 3 nm in size. The energy gap is estimated to be as wide as 6.0 eV from ultraviolet-visible optical transmission measurement. The electrical resistivity is reduced to4.9×102 &OHgr; cm.Si tip field emitters coated with the BN film are fabricated. The electron emission occurs at an electric field as low as 6 V/&mgr;m, while a high electric field of 20 V/&mgr;m is needed to emit electrons from the Si tip array without BN coating. It is deduced that the tunneling barrier height of 0.1 eV exists at the surface of the BN film. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120183

出版商:AIP    

年代:1997

数据来源: AIP