摘要:

The photoluminescence properties of metal-organic chemical vapor deposition GaAs:Er were investigated as a function of temperature and applied hydrostatic pressure. The4I13/2→4I15/2Er3+emission energy was largely independent of pressures up to 56 kbar and temperatures between 12 and 300 K. Furthermore, no significant change in the low temperature emission intensity was observed at pressures up to and beyond the&Ggr;-Xcrossover at ∼41 kbar. In contrast,AlxGa1−xAs:Eralloying studies have shown a strong increase in intensity near the &Ggr;-Xcrossover atx∼0.4.These results suggest that the enhancement is most likely due to a chemical effect related to the presence of Al, such as residual oxygen incorporation, rather than a band structure effect related to the indirect band gap or larger band gap energy. Modeling the temperature dependence of the 1.54 &mgr;mEr3+emission intensity and lifetime at ambient pressure suggested two dominant quenching mechanisms. At temperatures below approximately 150 K, thermal quenching is dominated by a ∼13 meV activation energy process which preventsEr3+excitation, reducing the intensity, but does not affect theEr3+ion once it is excited, leaving the lifetime unchanged. At higher temperatures, thermal quenching is governed by a ∼115 meV activation energy process which deactivates the excitedEr3+ion, quenching both the intensity and lifetime. At 42 kbar, the low activation energy process was largely unaffected, whereas the higher activation energy process was significantly reduced. These processes are proposed to be thermal dissociation of the Er-bound exciton, and energy back transfer, respectively. A model is presented in which the Er-related electron trap shifts up in energy at higher pressure, increasing the activation energy to back transfer, but not affecting thermal dissociation of the bound exciton through hole emission. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365821

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on photoluminescence and photoreflectance studies of metalorganic chemical vapor deposition grown InGaAs/InGaAlAs quantum well structures on lattice matched InGaAs substrates. The optical characteristics of the substrates are also discussed. The quantum wells exhibit a high degree of relaxation, despite their thickness being below the critical values, which may be related to the growth conditions. A correlation was found between the optical characteristics and the quality of the layer structures grown on the InGaAs substrates. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365822

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Three-dimensional arrays of structurally confined InP wire-like nanostructures were grown in channels (nanotubes) of a chrysotile asbestos matrix by metalorganic chemical vapor deposition. The formation of the InP compound was confirmed by absorption spectroscopy, X-ray diffraction and Raman scattering. It is shown that the density of states around the band edge increases with the InP loading of the matrix. Photoluminescence spectra of the asbestos filled in with InP consist mainly of two bands: a high energy band which is interpreted to be associated with charge transfer from InP to defect states of the asbestos and a low energy band which is associated with energy relaxation in the InP deposit itself. We show that the optical properties of this material are dominated by the size and dimensionality of the pore system of the matrix for heavy loading and by the semiconductor-to-matrix interface for light loading of the matrix with InP. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365823

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Strain effects on optical gain in hexagonal bulk GaN are calculated and explained in terms of the change in the effective hexagonal crystal field component. Qualitatively, even unstrained wurtzite structures correspond to cubic crystals with a proper biaxial stress applied. Such biaxial stress results in effective tensile deformation along thecaxis ([111] direction in cubic crystals) and compressive strain in the perpendicular plane. Therefore, the light mode with a polarization vector parallel to thecaxis is suppressed, while the mode with a perpendicular polarization is enhanced in wurtzite structures. Thus, compared to cubic structures with similar material parameters, a strong optical anisotropy of wurtzites results in enhanced gain for certain light polarizations, which make wurtzite structures superior for lower-threshold lasing. These qualitative arguments are illustrated by numerical calculations of optical gain in biaxially strained wurtzite GaN, based on a6×6envelope-function Hamiltonian. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365824

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence (PL) properties ofSi1−xGex/Sidisordered superlattices (d-SLs) are investigated. Two types ofd-SLs with various Ge compositions(x<0.55)and various averaged superlattice periods are grown for experiments. The PL intensity ratioI(d-SL)/I(o-SL),the redshift energy, and the characteristic temperatureT0are strongly affected with Ge composition variation but not with averaged superlattice period variation. Small improvement of the ratio of no-phonon (NP)/TO-phonon assisted PL intensities by theSi1−xGex/Sidisordered structure suggests that the disorder effect on the increase in NP recombination probability is not as large as expected by other disordered superlattices. The reasons are (1) the weak electron localization and (2) the difference in the directions between momentum ambiguity caused by the localization and the momentum required for recombination. Thus, improved PL properties for SiGe/Sid-SLare mainly owing to the strong hole localization by increased valence-band offset. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365825

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two kinds of porous silicon layers (fresh and oxidized) were impregnated with laser dyes solutions before drying. An original technique of diffuse reflectance allowed us to give an estimation of the concentration of the dye molecules in the pores, which appears to be higher for oxidized samples than for fresh ones. Selective excitation of the red photoluminescence of the silicon crystallites with a pulsed ultraviolet laser was performed and it showed a rapid luminescence of the laser dye. This emission is more important for fresh samples than for oxidized ones, although the dye concentration is lower in fresh samples. This indicates that the luminescence of the dye molecules does not come from direct excitation of the laser but that it is provided by an energy transfer from the porous silicon crystallites. In as far as the coupling between the crystallite and the dye molecule theoretically decreases when the distance between them increases, a lowering of the transfer on oxidized samples for whom the distance is larger is expected and is experimentally observed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365826

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two experiments are reported which demonstrate the means to stabilize the photoluminescence from an electrochemically etched (100) Si surface (porous silicon). The strong stabilizing influence of small quantities of water on a nonaqueous [2 mol/lHF in methylcyanide (MeCN)] etching process and the stabilizing effect of hydrochloric acid on a porous silicon surface photoluminescing in solution are described. Mechanisms consistent with these observations are considered as they are commensurate with a silicon oxyhydride emitting species. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365827

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The microstructure of the SCS-6 SiC fiber, a fiber widely studied as a reinforcement in metal matrix and ceramic matrix composites, was characterized by spatially resolved Raman spectroscopy. Cross sections of as-received fibers and fibers annealed at 1640 °C were characterized in the backscattering geometry with the 514.5 nm line of an Ar+laser. Characteristic graphitic peaks were observed in the several regions of the SCS-6 fiber, including the inner SiC region. The SiC transverse optical phonon mode was observed in the outer SiC region as a double peak, suggesting the presence of multiple polytypes in this region. Spectra of the outer SiC layer of this fiber in the zircon-matrix composite also showed a distinct Si peak. Silicon in this fiber is believed to be responsible for the observed anomalous thermal expansion behavior of the fiber between 1300 and 1400 °C. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365828

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The optical properties of amorphous-diamond films prepared by a mass-separated ion beam are studied and compared with the shape of the corresponding Raman spectra. The Raman measurements with moderate spatial resolution indicate that the films possess thesp3fraction distributed along the film surface, the thinner edges being less diamondlike than the thicker center. The optical parameters of the film material, such as the refractive index and absorption coefficient, follow the spatial changes of thesp3fraction, and the amorphous-diamond center is characterized by a relatively high refractive index(n∼2.50)and quite low absorption(&agr;∼0.2×104 cm−1at 633 nm). Numerical correlation between the Raman spectra and optical parameters proposes a common origin for their spatial distribution, namely, impurities perturbing the three-dimensional diamondlike network and causingsp2-coordinated carbon areas. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365830

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Luminescence studies have been performed on phosphorous-doped diamond films deposited by hot-filament chemical vapor deposition. A broad luminescence band, centered around 1.9 eV is revealed, in the cathodo luminescence spectra of homoepitaxial and polycrystalline films, whereas the blue band-Aluminescence, which is characteristic for undoped diamond, is quenched in the presence of phosphorus. The 1.9 eV luminescence band could not be excited byAr+laser light (2.54 eV) and did not show a zero-phonon line in the spectrum. Therefore, we suggest that this band is a red form of band-Aluminescence, related to electron-hole recombination at substitutional phosphorous and a phosphorus-vacancy complex. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365831

出版商:AIP    

年代:1997

数据来源: AIP