Passivation of an isoelectronic impurity by atomic hydrogen: The case of ZnTe:O
Marco FeliciA. PolimeniM. CapizziY. NabetaniT. OkunoKagari AokiT. KatoTakashi MatsumotoTakayuki Hirai
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We investigated the optical properties of ZnTe:O∕GaAs before and after atomic hydrogen irradiation. Oxygen incorporation gives rise to energy levels associated with single O atoms, O–O pairs, and O clusters, and to a blueshift of the energy gap of the material with respect to that of pure ZnTe∕GaAs. All of these effects disappear progressively after irradiation with H, which also leads to an increase in the tensile strain of the epilayer. These observations provide experimental evidence of H-induced passivation of an isoelectronic impurity in II–VI alloys.Keywords:
Passivation
Blueshift
Effects of large copper deficiency and surface modification on the photoluminescence of CuInS2 nanocrystals were explored. The large copper deficiency improved PL intensity due to the enhanced internal defect-related emission. Surface modification of copper deficient nanocrystals by simply refluxing with zinc acetate and fatty acid resulted in more than 10 times improvement in the photoluminescence intensity and a large blueshift of the photoluminescence spectra. The uniformity in size/shape distribution after surface modification was attributed to the origin of shrinkage in Stokes shift from ∼600 meV to ∼300 meV in Cu0.2InS2/ZnS nanocrystals. Furthermore, the contribution of lattice strain to this large blueshift in emission wavelength in Cu0.2InS2/ZnS nanocrystals was proposed and tested with the CdS shell layers. The electronic process underlying the large enhancement of PL intensity was studied with time-resolved and temperature-dependent photoluminescence. This drastically enhanced photoluminescence after surface modification was attributed to the efficient reduction of non-radiative recombination originated from surface trap states, the activation energy of which was estimated to be 85 meV.
Blueshift
Stokes shift
Stoichiometry
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Surface States
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The photoluminescence properties of hollow ZnS microspheres with different sizes and shell thickness were studied. There exist two emission bands situated in blue and green regions in the photoluminescence spectra of the microspheres: the green band has a red shift with increasing the excitation power at different temperatures, while the blue band has a blue shift at room temperature and without any changes excited at 83 K. The green emission has a normal red shift while the blue emission shows an abnormal red-blue shift with increasing temperature. The origins of anomalous photoluminescence properties were analysed and discussed in terms of the carrier localisation at the defect levels.
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Stokes shift
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An analytic model addressing the energy bandgap of nanoporous (NPs) structures with aligned cylindrical pores has been established from the perspective of nanothermodynamic considerations. It is found that the bandgap energies of NPs structures are unambiguously blueshifted as compared with those of nanowires with the same sizes and the bulk counterparts. The anomalous surface energies in the inner and outer surfaces of NPs structures seem the physical origin of the bandgap shifts. Agreement between the theoretical predictions and the evidence from experimental measurements and calculations suggested that the proposed method could be expected to be applicable to NPs structural materials.
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Nanoporous
Wide-bandgap semiconductor
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It is found that the lateral etching rate increases with increasing intensities of photo-irradiation during electrochemical etching of porous silicon until its bandgap becomes larger than the photon energies. The corresponding photoluminescence peak energies blueshift then saturate. These suggest that the photoluminescence spectra of the as fabricated samples are controlled by the quantum size effect. On the other hand, It is shown that the transitions between the oxide levels produce the photoluminescence with the peak position at about 1.7 eV, because the photoluminescence peak energies of the as fabricated samples ranging from 1.45 to 1.92 eV shift toward 1.7 eV after the samples axe oxidized in air for a period of time. Both the quantum size effect and the oxide related transitions should be attributed to the photoluminescence mechanisms.
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Porous Silicon
Photoluminescence excitation
Silicon oxide
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Gate-voltage effects on photoluminescence spectra of suspended single-walled carbon nanotubes are investigated. Photoluminescence microscopy and excitation spectroscopy are used to identify individual nanotubes and to determine their chiralities. Under an application of gate voltage, we observe slight blueshifts in the emission energy and strong quenching of photoluminescence. The blueshifts are similar for different chiralities investigated, suggesting extrinsic mechanisms. In addition, we find that the photoluminescence intensity quenches exponentially with gate voltage.
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Photoluminescence excitation
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We have established an analytical model to address the bandgap shift in SnO2 nanostructures in self-equilibrium state on the basis of bond length and bond energy correlations. Based on these analyses of the relationship among the bonding identities, single bond energy, and bandgap shifts derived from the energy perturbation, we found that the deformation potentials relationship of SnO2 nanodots and nanowires are different, while both bandgap energies exhibit a pronounced blueshift as comparable to those of the bulk counterparts. This bandgap shift is attributed to the lattice strain and coordination imperfection in the surfaces of nanostructures.
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Nanodot
Wide-bandgap semiconductor
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ZnTe quantum dots embedded in ZnS were grown successfully by controlling the flow duration in a metalorganic chemical vapor deposition system. Blueshift as large as 250 meV was observed in photoluminescence measurement, and the emission persists up to room temperature. The amount of blueshift decreases with increasing quantum dot size and for large quantum dots, no photoluminescence could be detected. From studying the temperature-dependent integrated intensity of the emission spectra, it is found that the activation energy for the quenching of photoluminescence increases with decreasing quantum dot size, and is identified as the binding energy of exciton in ZnTe quantum dot.
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The effect of the growth temperature (Tg) on photoluminescence of Ge(Si) self-assembled islands embedded between tensile-strained Si layers was studied. The observed redshift of the photoluminescence peak of the dome islands with a decrease of Tg from 700to630°C is associated with an increase of Ge content in the islands and with the suppression of smearing of the strained Si layers. The blueshift of the photoluminescence peak with a decrease of Tg from 630to600°C is associated with a change of the type of islands on surface, which is accompanied by a decrease in islands’ height.
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Dome (geology)
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Crystalline ZnO nanoparticles with nearly uniform size were studied using photoluminescence and Raman spectroscopy. The main spectral feature of ultraviolet photoluminescence is attributed to the recombination of free exciton (FX) and the first surface phonon replica of FX emission. The energy of FX emission shows a clear blueshift as the size of nanoparticles decreases, indicating that the quantum confinement effect exists in the electronic structure of nano-ZnO, although no confinement effect on the vibrational modes has been found in the same series of samples.
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Potential well
Ultraviolet
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A new method was used to fabricate nanometer-scale structures in Si for photoluminescence studies. Helium ions were implanted to form a dense subsurface layer of small cavities (1–16 nm diameter). Implanted specimens subjected to annealing in a variety of atmospheres yielded no detectable photoluminescence. However, implantation combined with electrochemical anodization produced a substantial blueshift relative to anodization alone. This blueshift is consistent with the quantum confinement model of photoluminescence in porous silicon.
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Passivation
Anodizing
Porous Silicon
Photoluminescence excitation
Nanometre
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