摘要:

The modulation of the electric field within the intrinsic layer of surface-intrinsic-doped structures by means of a chopped pump beam and in the presence of a constant probe beam is calculated by considering the modulation of the surface voltage by the photoactivated majority carrier flow. The analysis is focused as to determine the dependency on the probe and pump photocurrents and on the chopping frequency of the observed rise and fall transient time constants of the time resolved photoreflectance signal. The non linear features of the carrier dynamics are worked out in detail. A rescaling of the time constants by the power of the probe beam is predicted. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366380

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Temperature dependences of time-resolved picosecond beam coupling gains and losses in semi-insulating undoped GaAs and CdTe:Ga are investigated experimentally at a wavelength of 1.064 &mgr;m. In the temperature range of283–363 Ka weak temperature dependence of the free-carrier energy transfer gain is observed at high fluence excitation, while photorefractive beam coupling gains and nonlinear absorption losses are found to exhibit no clear temperature dependence. A numerical simulation of the dynamics of photoexcited carriers and space-charge fields is also performed in order to examine the experimental results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366381

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Transient surface displacement of gold under femtosecond laser irradiation is studied using a probe beam deflection technique. A surface thermal expansion rise time of about 100 ps is explained in terms of nonequilibrium diffusion and thermalization of photoexcited electrons. Transient displacement provides direct information on the lattice temperature profile established once the electron-lattice relaxation is completed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366382

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The refractive indices ofCd1−xMnxTeandCd1−yMgyTe(0<x<0.28and0<y<0.70) were determined by analyzing interference fringes in reflectivity spectra of thin films grown by molecular beam epitaxy. It is shown that their dispersions in the transparent region at 4 K are well described by a Sellmeier relation. These results have been applied to grow CdMnTe/CdMgTe Bragg mirrors incorporated in a II–VI microcavity operating in the strong exciton-photon coupling regime. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366383

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the dependence of the absorption edge and the refractive index of wurtziteAlxGa1−xNfilms on temperature and composition using transmission and photothermal deflection spectroscopy. The Al molar fraction of theAlxGa1−xNfilms grown by plasma induced molecular beam epitaxy was varied through the entire range of composition(0⩽x⩽1).We determined the absorption edges ofAlxGa1−xNfilms and a bowing parameter of1.3±0.2 eV.The refractive index in the photon energy range between 1 and 5.5 eV and temperatures between 7 and 295 K was deduced from the interference fringes. The static refractive indexn(0)changed from 2.29 for GaN to 1.96 for AlN at room temperature. A variation of temperature from 295 to 7 K resulted in a decrease of refractive index (at photon energies close to the band gap) by0.05±0.01and in an energy shift of the absorption edge of about64±5 meVindependent of the Al content of the films. Using the Kramers–Kronig dispersion relation and an approximation for the dispersion coefficient for photon energies near the band gap, the refractive index could be described as a function of photon energy, Al content, and temperature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366309

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of biaxial strain on optical phonons in high-quality GaN epitaxial layers grown on 6H–SiC substrates by metal organic chemical vapor deposition has been studied. The deformation potential constants for theE2(1),A1(TO),E1(TO),andE2(2)optical phonon modes in hexagonal GaN have been obtained. A method for calculating strain in hexagonal GaN layers from Raman data alone is suggested. A comparative analysis of the strain measured by x-ray diffraction and Raman spectroscopy shows that these data agree well. It is found that the biaxial stress of 1 GPa results in a shift of the excitonic photoluminescence lines of 20±3 meV. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366310

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Heteroepitaxial GaAs layers were grown on Si (001) substrates by metalorganic chemical vapor deposition. The tetragonal distortion induced by the lattice and the thermal expansion coefficient mismatches gives substantial effects on the acceptor energy level as well as the valence band structure. The biaxial tensile strain in GaAs layers is investigated using low-temperature photoluminescence. The origins of intrinsic exciton lines and carbon-related extrinsic lines observed in the photoluminescence spectra are identified by the two-band model. It is also found that the binding energy of the carbon acceptor is reduced as biaxial tensile strain increases. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366311

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies are employed to investigate single heterostructures based on twoGaInP2layers that have the same composition but different degrees of order on the cation sublattice. Four sample configurations are studied: two complementary single heterostructures, a more ordered layer grown on a less ordered layer and vice versa, and two single layers nominally equivalent to the constituent layers of the heterostructures. The degree of order of the two layers was controlled via the V/III ratio used during organometallic vapor phase epitaxial growth. From our measurements, the difference between the band gaps of the two layers is 20–30 meV. The PLE spectra show clearly that the emission comes from both layers of the heterostructures and that the PL is excited by direct absorption of the exciting light into each layer as well as the injection of carriers from the less ordered (higher band gap) layer into the more ordered (lower band gap) layer. The data clearly show that the heterostructures contain two layers, each very similar to the corresponding single layer sample. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366312

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Hole burning spectroscopy has been carried out for glasses with compositions of(75−x)SiO2⋅xAlO3/2⋅25NaO1/2⋅1.0EuO3/2with several aluminum oxide contents. Persistent hole was burned in the5D0−7F0transition ofEu3+at temperatures between 4.2 and 20 K in aluminosilicate glasses, while the hole burning was not observed above 4.2 K in silicate glass. In other words, an introduction ofAl3+ions in silicate glass promotes the formation of a stable hole. Hole spectra without any antiholes suggest that the holes are burned by an optically induced rearrangement of local structure around theEu3+ion. The homogeneous linewidth shows a linear dependence withTbetween 4.2 and 8 K and a nearly quadratic dependence forT>8 K.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366313

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The optical properties ofNi2+dopedRb1−xCsxCaF3andRbCa1−xCdxF3solid solutions were studied. The1T2g(1D)→3A2g(3F)and1T2g(1D)→3T2g(3F)emission bands and the lifetime of the1T2glevel were measured as a function of the crystal composition. Both the band positions and the lifetime show a monotonic change withxbetween the values corresponding to the pure crystals. InRb1−xCsxCaF3crystals the contributions of differentNi2+centers in the emission bands were resolved. The shift of emissions is due to theRb+–Cs+substitution as next nearest neighbors ofNi2+ions as well as to a change of the lattice parameter with the composition of solid solutions. Both contributions were separated for some of theNi2+centers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366314

出版商:AIP    

年代:1997

数据来源: AIP