摘要:

Thick (225 nm)InxGa1−xNlayers, grown on 5 &mgr;m thick GaN, were found by x-ray diffraction (XRD) measurements to be pseudomorphic up tox=0.114.Transmission electron microscopy showed that no misfit or additional threading dislocations were created at theInxGa1−xN/GaNinterface. Composition of the overlayers was determined by Rutherford backscattering spectrometry and correlated to both theaandclattice constants from XRD. It was found that Vegard’s law is applicable at these compositions, if the biaxial strain is included. Biaxial strain must also be considered to accurately determine the bowing parameter as shown by optical transmission measurements. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122272

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report an investigation, performed in the full composition rangex=0–1,of the change in infrared reflectivity spectra ofAlxGa1−xNlayers deposited on 6H–SiC substrates. We have found two different transverseE1(TO)phonon frequencies that can be assigned to AlN-like and GaN-like modes. The composition dependences of these frequencies can be well approximated by linear functions and the oscillator strengths scale like the corresponding Al and Ga mole fractions, respectively. On a purely experimental basis, this establishes evidence of a two-mode behavior for this controversial alloy system. The frequencies of the impurity mode of Ga in AlN (622 cm−1) and of the impurity mode of Al in GaN (643 cm−1) were determined. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122273

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on a novel phenomenon in calcium aluminosilicate glasses doped withCe3+,Tb3+,andPr3+.After irradiation by an 800 nm femtosecond pulsed laser, the focused part of the laser in the glasses emits bright and long-lasting phosphorescence able to be clearly seen with the naked eye in the dark even one hour after the removal of the activating laser. Moreover, by selecting appropriate glass compositions and species of rare earth ions, optional three-dimensional image patterns emitting long-lasting phosphorescence in various colors, including blue, green, and red, can be formed within glass samples by moving the focal point of the laser. Based on absorption spectra, the long-lasting phosphorescence is considered to be due to the thermostimulated recombination of holes and electrons at traps induced by the laser irradiation, which leave holes or electrons in a metastable excited state at room temperature. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122274

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe the use of low cost printing and molding techniques to fabricate distributed feedback and Bragg reflector resonators for photoexcited plastic lasers that have narrow emission profiles in the visible range. The good performance of the lasers demonstrates the suitability of these techniques for fabricating certain types of functional optoelectronic devices that require submicron features patterned over macroscopic areas. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122275

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The combination of pulsed-mode excitation multifocal multiphoton microscopy with a high-repetition, time-gated intensified CCD camera enables efficient three-dimensional (3D) fluorescence lifetime imaging. With a 200-ps gate opening at 76 MHz repetition rate, fluorescence decay can be traced in a sequence of images with varying delays between pulse and gate. Fluorophore lifetimes are measured with a precision of a few picoseconds. As an application we show that, upon two-photon excitation at 800 nm, certain pollen samples feature a multiexponential fluorescence relaxation. Our results indicate that efficient four-dimensional microscopy with hundreds of nanometer spatial and tens of picoseconds temporal resolution is within reach. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122276

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Mg-dopedp-GaNfilms have been grown on sapphire substrate with a multilayered buffer (MLB) by metalorganic chemical vapor deposition and characterized by photoluminescence spectroscopy. The MLB consists ofGaN/AlxGa1−xN (0<x⩽1)superlattice-like layer structures although the material combination as well as the periodicity and uniformity in layer thickness and composition are not essential issues for constituting a MLB. It was found that thep-GaNfilms grown on MLBs gave much stronger optical emission than those grown on conventional GaN orAlxGa1−xN (0<x⩽1)single-layer buffer orGaN/AlxGa1−xNdouble-layer buffer under identical reactor configuration. This fact indicates that, by using the newly-developed MLB, the crystalline quality of group-III nitride-based-semiconductor epitaxial layers can be significantly improved. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122277

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have demonstrated that fluorescent dyes may be introduced into previously fabricated polymer thin films by local application of a dye-containing droplet. The UV fluorescence spectra of the films and the spectra of organic light-emitting diodes made from these films can be successfully tuned by this method. The technique has been implemented by ink-jet printing of the dye droplet. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122278

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Two identical diode-pumped bulk Er–Yb:glass lasers, operating at 1534-nm wavelength, have been independently locked to the P(15) rovibrational line of the acetylene molecule by the FM sideband technique. Measurements of the beat note between the two lasers show a long-term frequency stability of 170 kHz over a 1-h period and a short-term laser linewidth below 50 kHz over 1 ms. The Allan standard deviation of the beat frequency was measured yielding values below10−10for integration times between 10 ms and 1 s, reaching the4×10−11level at 0.1 s. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122279

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Here we present experimental evidence of the strong modification of the CdS photoluminescence when it is embedded in aSiO2colloidal photonic crystal. When the emitted light matches a forbidden photonic band in the matrix, inhibition of the semiconductor photoluminescence is achieved. In this work we prove the effective control of this effect by means of the photonic lattice parameter of the host. CdS was grown by chemical bath deposition and its quality has been checked employing Raman spectroscopy and x-ray diffraction. Scanning electron microscopy is used to study the morphology of the composite. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122280

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Red-light-emitting quantum dot injection lasers have been prepared by solid-source molecular beam epitaxy. The separate confinement heterostructure contains densely stacked layers of self-assembled InP quantum dots embedded inGa0.51In0.49Pwaveguide and Si/Be-dopedAl0.53In0.47Pcladding layers. Edge-emitting laser diodes are processed, which show quantum dot lasing at 90 K. Thereby, the threshold current density is 172 A/cm2. The energy of the laser line is at 1.757 eV, which is very close to the peak energy of subthreshold electroluminescence. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122281

出版商:AIP    

年代:1998

数据来源: AIP