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ABSTRACT: Off-axis implantation of 80 keV Eu ions into epitaxial c -plane InAlN/GaN bilayers confines rare-earth (RE) doping largely to the InAlN layer. Rutherford backscattering spectrometry and x-ray diffraction show good correlations between the Eu <sup>3+</sup> emission linewidth and key structural parameters of In <sub>x</sub> Al <sub>1-x</sub> N films on GaN in the composition range near lattice matching (x∼0.17) . In contrast to GaN:Eu, selectively excited photoluminescence (PL) and PL excitation spectra reveal the presence of a single dominant optical center in InAlN. Eu <sup>3+</sup> emission from In <sub>0.13</sub> Al <sub>0.87</sub> N : Eu also shows significantly less thermal quenching than GaN:Eu. InAlN films are therefore superior to GaN for RE optical doping.
Journal of Applied Physics 11/2009; · 2.17 Impact Factor
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ABSTRACT: Eu was implanted into high quality cubic (zincblende) GaN (ZB-GaN) layers grown by molecular beam epitaxy. Detailed structural characterization before and after implantation was performed by x-ray diffraction (XRD) and Rutherford backscattering/channeling spectrometry. A low concentration (≪10%) of wurtzite phase inclusions was observed by XRD analysis in as-grown samples with their (0001) planes aligned with the {111} planes of the cubic lattice. Implantation of Eu causes an expansion of the lattice parameter in the implanted region similar to that observed for the c -lattice parameter of wurtzite GaN (W-GaN). For ZB-GaN:Eu, a large fraction of Eu ions is found on a high symmetry interstitial site aligned with the <110> direction, while a Ga substitutional site is observed for W-GaN:Eu. The implantation damage in ZB-GaN:Eu could partly be removed by thermal annealing, but an increase in the wurtzite phase fraction was observed at the same time. Cathodoluminescence, photoluminescence (PL), and PL excitation spectroscopy revealed several emission lines which can be attributed to distinct Eu-related optical centers in ZB-GaN and W-GaN inclusions.
Journal of Applied Physics 07/2009; · 2.17 Impact Factor
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ABSTRACT: Simple II–VI laser cavities were formed by cleaving epitaxial ZnSe samples containing a single CdSe quantum well of mean thickness about 1 monolayer. Time‐integrated stimulated emission spectra of these lasers show little evidence of mode structure. A video camera enables temporal resolution of the stimulated emission spectra. Mode structure appears on the time‐resolved spectra. In addition, however, video spectroscopy reveals spatial variations of wavelength and intensity in the laser output which are not well understood. © 1995 American Institute of Physics.
Applied Physics Letters 04/1995; · 3.84 Impact Factor
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ABSTRACT: Time‐resolved luminescence of transiently excited porous silicon reveals the dynamics of the excitation‐luminescence cycle in which localized excitons efficiently generate orange‐red luminescence from this material at room temperature. Upon transient excitation with nanosecond pulses, both blue and orange luminescence bands appear coincidently. At long time delays, the orange luminescence dominates. We show here that the time‐delayed orange luminescence is thermally activated by hopping‐related processes. The activation energy for a 500 ns delay is 36 meV. Our observations are in principle capable of resolving outstanding contradictions in the porous silicon luminescence literature. Quantum confinement on a wire fluctuating width provides the strong energy disorder which facilitates exciton localization. © 1995 American Institute of Physics.
Journal of Applied Physics 02/1995; · 2.17 Impact Factor
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ABSTRACT: The luminescence decay of excitons in disordered low‐dimensional semiconductors with quantum confinement is shown experimentally to be characterized by a nonexponential profile and an absence of spectral diffusion. We are able to describe this luminescence as a hopping‐assisted recombination using the correlation function approach to nondispersive transport developed by H. Scher, M. F. Shlesinger, and J. T. Bendler [Phys. Today 41, 26 (1991)]. We suggest a simple derivation of analytical functions which accurately describe the anomalous luminescence decays of disordered II‐VI superlattices and of porous silicon, and show that this model includes exponential and Kohlrausch [Pogg. Ann. Phys. 119, 352 (1863)] (stretched‐exponential) relaxations as special cases.
Applied Physics Letters 06/1992; · 3.84 Impact Factor
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ABSTRACT: A study of the absorption spectra of excitons in ZnSe‐ZnS strained layer superlattices (SLS) with well widths ranging from 0.6 to 7.6 nm is reported. The n=1 heavy hole (hh) and light hole (1h) exciton absorptions are clearly resolved for all samples even near room temperature. A theoretical estimation of the n=1 hh exciton peak energy, which takes account of strain, quantum confinement of free carriers, and exciton binding energy enhancement by reduced dimensionality, is in excellent agreement with the experimental results. The variations in absorption linewidth and energy shift between absorption and emission band peaks, as a function of quantum well width, have also been measured: the experimental results provide evidence that the origin of the so‐called ‘‘Stokes’ shift’’ lies in Anderson localization due to monolayer fluctuations in the well width. The temperature dependence of the exciton peak energy and its linewidth are interpreted in terms of electron‐phonon and exciton‐phonon interactions.
Applied Physics Letters 11/1991; · 3.84 Impact Factor
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ABSTRACT: The application of a simple three‐parameter fit to the temperature dependence of semiconductor band gaps is justified on both practical and theoretical grounds. In all trials the fit is numerically better than that obtained using the widely quoted Varshni equation. The formula is shown to be compatible with reasonable assumptions about the influence of phonons on the band‐gap energy. Approximate analytical expressions are derived for the entropy and enthalpy of formation of electron‐hole pairs in semiconductors.
Applied Physics Letters 07/1991; · 3.84 Impact Factor
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