摘要:

Two different approaches, a photoconductive response technique and a correlation of lasing thresholds with theoretical threshold carrier concentrations have been used to determine Auger lifetimes in InAs/GaInSb quantum wells. For energy gaps corresponding to 3.1–4.8 &mgr;m, the room-temperature Auger coefficients for seven different samples are found to be nearly an order-of-magnitude lower than typical type-I results for the same wavelength. The data imply that at this temperature, the Auger rate is relatively insensitive to details of the band structure. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122609

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate single-mode laser emission at 490 nm from a stable cavity based on a methyl-substituted poly-(para-phenylene)-type ladder polymer. The laser emission is characterized by a well-defined excitation fluence threshold, a high directionality, and a drastic spectral narrowing. The laser generates picosecond pulses of excellent amplitude stability. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122610

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The influence of the carrier confinement on the output characteristics of GaInAs/AlGaAs lasers was investigated. To improve the carrier confinement, AlGaAs/GaAs short-period superlattices were used as quantum well barriers. In comparison to lasers with GaAs barriers the structures with the modified barriers show improved temperature properties at low threshold current densities without deterioration of the internal quantum efficiency (>95&percent;). High characteristic temperatures(T0)well above 300 K were measured between 20 and 75&hthinsp;°C and laser operation up to 238&hthinsp;°C could be achieved. The large improvement inT0is mainly attributed to the reduced thermionic emission of carriers out of the quantum well due to the increased barrier height and the carrier reflection above the barrier by the short-period superlattice. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122611

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Bright organic electroluminescent devices were developed using a metal-doped organic layer as an electron-injecting layer at the interface between the cathode and the emitter layer. The typical device structure is a glass substrate/indium-tin oxide/arylamine/tris(8-quinolinolato)Al (Alq)/metal-doped Alq/Al. Dopant metals are highly reactive metals such as Li, Sr, and Sm. A device with Li-doped Alq layer showed high luminance of over 30&hthinsp;000cd/m2,while a device without the metal-doped Alq layer exhibited only 3400cd/m2.These results suggest that the Li doping to the Alq layer generates the radical anions of Alq serving as intrinsic electron carriers, which result in low barrier height for electron injection and high electron conductivity of the Li-doped Alq layer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122612

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Compressively strained InGaAsP quantum well (QW) active (&lgr;=732 nm) diode lasers achieve 2.9 W continuous wave (cw) power from facet-coated (4&percent;/95&percent;) 100-&mgr;m-wide apertures, with reliable operation demonstrated at 0.5 W cw power. A broad waveguide structure is used to obtain a large transverse spot size(d/&Ggr;=0.433&mgr;m), resulting in a low internal loss(&agr;i∼2&hthinsp;cm−1)and narrow transverse far-field beam width(&thgr;1/2=38°).Record-high characteristic temperatures for the threshold current and the differential quantum efficiency(T0=115K andT1=285K) are obtained by growing on misoriented substrates. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122613

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The electron injection from the composite cathode consisting of a very thin LiF layer and an Al layer (LiF/Al) into Al–hydroxyquinoline (ALQ) layers showed the voltage and temperature dependence, which is characteristic to the Schottky emission mechanism. The barrier formed at the interface is lower than that formed at the interfaces between the conventional cathodes and the ALQ layer. The current–voltage characteristics of the light emitting diodes having the LiF/Al cathode and the ALQ/diamine junction were well explained on the basis of the properties of the electron injection into the ALQ layer and the hole injection into the diamine layer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122614

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

TheCaS:Sm3+ nanocrystallites are synthesized by the modified sol-gel technique. The grain size of the nanocrystallites is approximately 60 nm, which is determined by transmission electron microscopy, x-ray diffraction and UV-vis absorption spectrum. Compared to theCaS:Sm3+macrocrystallites, the absorption and emission of the nanocrystallites have a blueshift in their spectra, and the emission spectrum of the host CaS appears in the region of 400–500 nm. It was also found that the efficiencies of both photoluminescence and upconversion in the nanocrystallites are higher than those in the macrocrystallites. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122615

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using picosecond pulsed laser excitation, we investigate the optical emission characteristics of poly(2,5-dioctyloxy-p-phenylenevinylene), (DOO-PPV), thin films at high excitation intensities (∼1–90 MW/cm2). We observe the presence of amplified resonance Raman scattering in the emission spectra of conducting polymer films. The effect results in sharp Raman lines (widths smaller than 3 Å) superimposed on a significantly broader, well known, spectrally narrowed emission band (width ∼10 nm) caused by the amplified spontaneous emission in the waveguided polymer film. At the highest used excitation intensities, Raman scattering dominates the DOO-PPV emission spectrum resulting in a highly monochromatic, single-line emission spectrum. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122616

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have fabricated a nematic liquid crystal cell associated with a homogeneously aligned to twisted transition of a liquid crystal director. In the absence of an electric field, the liquid crystal molecule is homogeneously aligned under the crossed polarizers, and thus the cell appears to be black. When a fringe field induced by interdigital electrodes is applied, liquid crystal molecules rotate in plane even above electrodes and thus the cell transmits light. The device exhibits a high transmittance ratio as well as a wide viewing angle, which solves a long standing problem of low transmittance existing in the conventional in-plane switching mode. We show that the distance between electrodes smaller than the width of an electrode and cell gap is required for generating fringe field with applied voltage and rotating molecules above electrodes. We also investigate the mechanism of fringe-field switching and dependence of electro-optic effect on different cell conditions and dielectric anisotropy of liquid crystal. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122617

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Extending our scanning second harmonic microscopy (SSHM) technique for the detection of lateral orientational inhomogeneities in high field poled polymer films, we present results with considerably improved lateral resolution by using optical fiber technology. Two experimental setups for measuring the&khgr;(2)susceptibility of thin films are introduced. The first setup uses a standard monomode infrared-fiber with 10 &mgr;m core that carries the coherent fundamental infrared wave to the surface of a poled polymer film (illumination mode). The generated doubled frequency wave behind the nonlinear optical sample is detected by a photomultiplier tube. In the second setup a lens focuses the fundamental wave into the poled film. The resulting second harmonic wave is coupled into a 2.5 &mgr;m single mode fiber. SSHM micrographs of high field poled nonlinear optical polymer films were obtained with lateral resolutions of <3.5 &mgr;m. SSHM was also realized with a scanning near field optical microscopy fiber in pick up mode. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122618

出版商:AIP    

年代:1998

数据来源: AIP