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Structural disorder and in-gap states of Mg-implanted GaN films evaluated by photothermal deflection spectroscopy
摘要： Both structure of the valence band maximum (VBM) and deep-level defects for box-pro?le Mg-ion implanted (4 × 10^19 cm^-3) GaN samples are characterized by photothermal de?ection spectroscopy (PDS). Compared with the results evaluated by positron annihilation spectroscopy, the variations caused by the thermal annealing is discussed with respect to Urbach energy, defect levels in the band gap, and photoluminescence. Forming Urbach tail gradually at the VBM at the 1000 °C annealing, vacancy-type defects clusters without drastic decrease of deep-level defects. Green and yellow luminescence emits slightly as the PDS signal at the deep-level is decreased by the annealing at 1100 °C due to the decrease of non-radiative recombination centers. The Urbach energy is improved by the further annealing so that the luminescence becomes intense due to the energy transfer through the phonon from Urbach region. The shift of Fermi level towards the valence band at the 1300 °C annealing, the sign of p-conduction, is con?rmed from the valence band spectra. Compared to the Mg-doped GaN with p-conduction, it is considered that the improvement of Urbach energy is crucial for p-type activation.
关键词： B1. Gallium compounds,B1. Nitrides,A1. Defects
更新于2025-09-19 17:15:36
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Influence of trimethylaluminum predoses on the growth morphology, film-substrate interface, and microstructure of MOCVD-grown AlN on (111)Si
摘要： Aluminum nitride (AlN) was deposited on (111) silicon by metalorganic chemical vapor deposition after varied trimethylaluminum predoses. Growth morphologies, film-substrate interfaces, and film microstructures were examined using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. In samples grown with predoses, lateral growth was observed over faceted "patches" formed during the predose. Three-dimensional growth was observed to seed from small islands on the surface of these patches and eventually overgrow them. The three-dimensional growth mode was similar to that observed when AlN was grown without a predose, resulting in similar morphologies in all films, regardless of predose, after the islands coalesced. The AlN-silicon interface was found to be predominantly amorphous when no predose was used. However, narrow regions were observed over which the film was in atomic registry with the substrate. This indicates AlN nucleates in epitaxy with the substrate and amorphous silicon nitride forms between nucleation sites due to ammonia exposure. Films grown with predoses had structurally abrupt interfaces, suggesting aluminum within the observed patch features inhibits the reaction between ammonia and silicon at the onset of growth. A structure distinct from both wurtzite AlN and diamond cubic silicon was observed at the substrate interface in films grown with a predose, consistent with either zinc blende AlN or a strained Si/Al alloy. A mosaic microstructure was observed in all films, grown with or without predoses, which consisted of sub-boundaries formed by clusters of threading dislocations. Threading dislocations, separated by hundreds of nanometers, were found to be tilted along common directions, providing evidence for a dislocation bending mechanism possibly enhanced by the predose.
关键词： Defects,Crystal morphology,Metalorganic chemical vapor deposition,Semiconducting aluminum compounds,Nucleation,Nitrides
更新于2025-09-19 17:15:36
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Surface passivation and point-defect control in Cu(In,Ga)Se <sub/>2</sub> films with a Na <sub/>2</sub> S post deposition treatment for higher than 19% CIGS cell performance
摘要： Na2S as a new alkaline source was employed to passivate the surface of CIGS film. Na2S has less formation enthalpy compared to alkali fluoride compounds leading to the more effective dissolution at the surface. An efficiency of 19.2% was obtained by post deposition treatment (PDT) with Na2S source for cell with anti-reflective coating and active area of a 0.43cm2. The remarkable performance enhancement compared to the efficiency of 16.64% of the cell without the PDT was due to the increase of Voc and FF. With the Na2S PDT, Na distribution in CIGS film was much shallower and the valence band lowering was smaller compared to that with NaF PDT. The emission intensity of low-temperature photoluminescence at 1.04 eV, which corresponds to electron transition from In-in-Cu (InCu) antisite to the valence band maximum, was greatly reduced by Na2S PDT compared to NaF PDT. The result suggests that in addition to lowering the Cu vacancy concentration, the concentration of InCu defects significantly decreased at the CIGS surface by Na2S PDT compared to NaF PDT. Our results indicated that the surface passivation by Na2S PDT was more effective than NaF PDT.
关键词： point defects,Na2S source,CIGS solar cells,surface passivation,post-deposition treatment (PDT)
更新于2025-09-19 17:15:36
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Calibration of galvanometric scan heads for additive manufacturing with machine assembly defects consideration
摘要： The calibration of additive manufacturing machines using scanning heads in processes such as Laser Powder Bed Fusion (LPBF) and vat photopolymerization is an iterative and time-consuming process often based on limited physical models. Indeed, the relationship between the laser spot position in the work plane and the actuators position (galvanometers) is achieved by interpolating correction tables experimentally determined. In this paper, representative geometrical models of the real system are established in order to reduce the time required to obtain the final correction tables. For this purpose, a geometrical model is developed with assembly defects consideration. This model is used in a process of defects identification to obtain a virtual machine representative of the real system and thus directly generates the final correction tables. The geometrical model thereby developed is used to quantify the impact of assembly defects on the laser spot position, to compensate them and to reduce the calibration time of an additive manufacturing machine.
关键词： Assembly defects,Additive manufacturing,Geometrical model,Virtual machine,Calibration
更新于2025-09-19 17:15:36
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Interplay between Composition, Electronic Structure, Disorder, and Doping due to Dual Sublattice Mixing in Nonequilibrium Synthesis of ZnSnN <sub/>2</sub> :O
摘要： The opportunity for enhanced functional properties in semiconductor solid solutions has attracted vast scientific interest for a variety of novel applications. However, the functional versatility originating from the additional degrees of freedom due to atomic composition and ordering comes along with new challenges in characterization and modeling. Developing predictive synthesis–structure–property relationships is prerequisite for effective materials design strategies. Here, a first-principles based model for property prediction in such complex semiconductor materials is presented. This framework incorporates nonequilibrium synthesis, dopants and defects, and the change of the electronic structure with composition and short range order. This approach is applied to ZnSnN2 (ZTN) which has attracted recent interest for photovoltaics. The unintentional oxygen incorporation and its correlation with the cation stoichiometry leads to the formation of a solid solution with dual sublattice mixing. A nonmonotonic doping behavior as a function of the composition is uncovered. The degenerate doping of near-stoichiometric ZTN, which is detrimental for potential applications, can be lowered into the 1017 cm?3 range in highly off-stoichiometric material, in quantitative agreement with experiments.
关键词： multinary material,computational materials design,disorder,semiconductor solid solution,electronic structure,nonequilibrium synthesis,defects
更新于2025-09-19 17:15:36
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Intrinsic Defect-Assisted UV-Visible Energy Conversion in Gd <sub/>2</sub> O <sub/>3</sub> :Er Nanoparticles
摘要： The correlations between defectiveness and optical properties of Er-doped Gd2O3 nanoparticles coupled into cubic and monoclinic crystal structures were studied employing XPS and PL spectroscopies. The main focus of this research is paid to the cubic Gd2O3 phase, which is more suitable for light-emitting purposes. It is shown that oxygen-related point defects are the precursors for the formation of cationic irregulars – “defective” Gd3+ ions with local energy levels in the energy band gap of Gd2O3. Energy transfer from Gd3+ intrinsic defects to Er3+ dopants provides an additional channel for UV–visible radiation conversion. These Er3+ ions have bimodal distribution due to the non-equivalent lattice sites of “defective” Gd3+ ions. An increase of Er3+ concentration leads to the giant phonon softening effect, which opens up a new prospective way to enhance energy conversion efficiency.
关键词： UV conversion,photoluminescence,gadolinium oxide,erbium,defects
更新于2025-09-19 17:15:36
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Interaction between Bi Dopants and Intrinsic Defects in LiNbO <sub/>3</sub> from Local and Hybrid Density Functional Theory Calculations
摘要： The interactions between Bi dopants including Bi-substituting Li (BiLi) and Bi-substituting Nb (BiNb) and the intrinsic antisite defects (NbLi) and Li vacancies (VLi) in LiNbO3 are investigated using local and hybrid density functional theories. Three charge-compensated defect clusters, BiLi4+ + NbLi4+ + 8VLi-, BiLi4+ + 4VLi-, and BiLi0 + 4VLi- + BiNb4+, are modeled in this work to investigate the effects of the Bi concentration. The most stable cluster configurations, the Bi-doping stability in the clusters, and the electronic state interaction between Bi and intrinsic defects have been studied in detail. It is found that BiLi4+ has a stronger electron-capturing ability than NbLi4+ in Bi-doped congruent LiNbO3. The BiLi-doping-induced local lattice distortion and the electron-trapping behavior remain unchanged with increasing Bi-doping concentration. However, the position of the Bi defect states in the band gap is found to be shifted in congruent LiNbO3. This is mainly attributed to the large lattice relaxation induced by the large number of Li vacancies instead of the ionic level redistribution caused by the direct interaction between Bi and intrinsic defects.
关键词： LiNbO3,Bi dopants,lattice distortion,defect clusters,intrinsic defects,density functional theory,electron trapping
更新于2025-09-19 17:15:36
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Methodical engineering of defects in MnXZn1-X O(x?=?0.03, and 0.05) nanostructures by electron beam for nonlinear optical applications: A new insight
摘要： A series of MnxZn1-xO (x = 0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in e-beam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra reveals the quenching of defect centers, implying the role of electron beam irradiation regulating luminescence and defect centers in the nanostructures. Irradiation induced spatial confinement and phonon localization effects have been observed in the films via micro Raman studies. The later are evident from spectral peak shifts and broadening. Detailed investigations on the effect of electron beam irradiation on third order nonlinear optical properties under continuous and pulsed mode of laser operation regimes are deliberated. Third order absorptive nonlinearity of the nanostructures evaluated using the open aperture Z-scan technique in both continuous and pulsed laser regimes shows strong nonlinear absorption coefficient β eff of the order 10-4 cm/W confirming their suitability for passive optical limiting applications under intense radiation environments. Laser induced third harmonic generation (LITHG) experiment results supports the significant variation in nonlinearities upon electron beam irradiation, and the effect can be utilized for frequency conversion mechanisms in high power laser sources and UV light emitters.
关键词： Mn:ZnO nanostructures,8MeV e-beam,Spatial confinement effects,Defects quenching,Third harmonic generation
更新于2025-09-19 17:15:36
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Photoluminescence and phosphorescence of Mn2+ ion activated green phosphor Na2ZnSiO4:Mn2+ synthesized by self-reduction
摘要： Mn2+ activated phosphors are vital for lighting and displays, whereas the multivalent states characteristics of Mn made that reducing atmosphere (such as H2, CO, H2/N2) is generally required in the synthesis processes. Herein, a Mn2+ doped silicate green phosphor Na2ZnSiO4:Mn2+ was synthesized by an unconventional self-reduction of Mn7+/Mn4+/Mn3+ to Mn2+ under air atmosphere. Upon 260 nm excitation, an intense green photoluminescence band centered at 515 nm and the phosphorescence after stoppage of the excitation source can be observed in this phosphor. The photoluminescence and phosphorescence properties, self-reduction processes and mechanism in Na2ZnSiO4:Mn, as well as the phase transformations of the different Mn sources (MnCO3, Mn2O3, MnO2) at various temperatures were investigated systematically. Based on these investigations, together with the density functional theory (DFT) calculations, a self-reduction mechanism of Mn7+/Mn4+/Mn3+ to Mn2+ based on zinc vacancies VZn'' has been proposed. This work provides not only a new luminescent material, but also new insights into the Mn valence states controlling and luminescence tuning.
关键词： Mn2+,redox reactions,self-reduction,defects
更新于2025-09-19 17:15:36
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Defects creation in the undoped Gd3(Ga,Al)5O12 single crystals and Ce3+ - doped Gd3(Ga,Al)5O12 single crystals and epitaxial films under irradiation in the Gd3+ - related absorption bands
摘要： For the ?rst time, an e?ective photostimulated creation of defects is observed under selective irradiation of the undoped Gd3Ga3Al2O12 single crystal and the Ce - doped Gd3(Ga,Al)5O12 single crystal and epitaxial ?lm in the Gd3+ - related 8S7/2 → 6IJ and 8S7/2 → 6PJ absorption bands. Defects creation processes are investigated by the thermally stimulated luminescence (TSL) method in the 4.2–500 K temperature range. The dependences of the TSL glow curve peak intensity on the irradiation photon energy, irradiation temperature, and irradiation duration are measured and analyzed. The activation energy of the TSL glow curve peaks creation is found to be about 0.02 eV. Possible mechanisms of defects creation under irradiation in the absorption bands of Gd3+ in Gd3Ga3Al2O12 and Gd3(Ga,Al)5O12:Ce are discussed.
关键词： Defects,Gd3(Ga,Al)5O12:Ce,Gd3Ga3Al2O12,Crystals,Luminescence,Epitaxial ?lms
更新于2025-09-19 17:15:36