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Electron-phonon interactions in subband excited photoluminescence of hexagonal boron nitride
摘要： The h-BN microcrystalline powder with carbon and oxygen impurities have been studied at 83 and 296 K using Raman and photoluminescence (PL) spectroscopies. The observed blue shift of Raman peaks with temperature decreasing have been discussed allowing for the enhanced role of the optical vibrational modes. Two series of phonon replicas in PL emission spectra with a zero-phonon line at 4.08 eV have been registered under 4.28 eV excitation. The energy levels model of the impurity (CN-ON)-complex responsible for observe luminescence was proposed. It was shown that the optically active center retains its electroneutrality in the processes of radiative recombination under subband (in 4.28 eV) or band-to-band excitation. Possible mechanisms of electron-phonon scattering and phonon replicas forming under subband excitation of (CN-ON)-complex were analyzed. It was substantiated that the longitudinal optical (?ωLO = 174 meV) and transverse acoustic (?ωTA = 60 meV) phonons at the middle points of high symmetry in the first Brillouin zone participate in the processes of intravalley (M- and Κ-scattering) and intervalley (Κ → Μ)-scattering, respectively.
关键词： ultraviolet luminescence,intravalley scattering,point defect,intervalley scattering,phonon replicas,h-BN,carbon-oxygen complex
更新于2025-09-23 15:23:52
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Effects of Co Doping and Point Defect on the Ferromagnetism of ZnO
摘要： The effects of different doping proportions of Co doping and oxygen vacancies (VO) on the ferromagnetism of zinc oxide (ZnO) are controversial. To solve this problem, we investigated the effects of Co doping and point defects (VO, VZn, Hi, and Zni) on the ferromagnetism of ZnO through first-principle calculations by using generalized gradient approximation + U (GGA + U) under density functional theory. Results show that the closer the distance between Co and vacancies (VO or VZn), the lower the formation energy and the more stable the system will be. Co-doped ZnO with VO or VZn exhibits long-range ordered ferromagnetism and Curie temperature above the room temperature. Especially, Co-doped ZnO with VZn shows a half-metallic behavior, resulting in 100% conduction hole polarizability, which is highly beneficial for dilute magnetic semiconductors (DMSs) as a hole injection source. The ferromagnetism of Zn14CoO16 is caused by the double exchange effects among the electrons of the O–2p, Co–3d, and Zn–3d orbits mediated by the hole carriers after complexes were formed by the Co doping and Zn vacancy. Similarly, the origin of ferromagnetism in Zn15CoO15 is derived from the double exchange effects among the electrons of O–2p, Co–3d, and Zn–4s states mediated by the electron carriers after complexes were formed by the Co doping and O vacancy. In addition, the result shows that Co-doped ZnO with interstitial H (Hi) or Zn (Zni) is unfavorable for ferromagnetism and should be avoided experimentally.
关键词： First-principle,Co doping and point defect,Ferromagnetism,ZnO
更新于2025-09-23 15:22:29
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Simulation and Measurement of Properties of Metallic Photonic Crystal Point-Defect-Cavities with a Centrally-Loaded Rod
摘要： Properties of a class of M-PhC (metallic-photonic-crystal) point-defect-cavities (PDCs) with a centrally-loaded rod are theoretically and experimentally investigated. After the computation of the resonant frequencies and Q-factors of the resonant modes, the PDCs are fabricated and experimentally measured to validate the simulation results.
关键词： resonant frequency,M-PhC,Q-value,bandgap,point-defect cavity
更新于2025-09-23 15:21:21
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Extrinsic Defects in Crystalline MoO <sub/>3</sub> : Solubility and Effect on the Electronic Structure
摘要： The effect of six potential contaminants (Cu, In, Ga, Se, Sn and Zn) and five potential dopants (Ti, Mn, Sc, V and Y) on the electronic and optical properties of molybdenum oxide (MoO3) contact layers for solar cells was investigated using point defect analysis informed by density functional theory simulations. Of the contaminants investigated, Sn, In and Ga were found to be highly insoluble at all relevant temperatures and pressures, and therefore not a concern for solar cell manufacturing. Zn, Cu and Se exhibit some solubility, with the latter two appearing to introduce detrimental defect states near the valence band. This contamination can be avoided by increasing the O2 partial pressure during MoO3 deposition. Out of five potential aliovalent dopants, Sc, Ti and Y were disregarded due to their limited solubility in MoO3, while V was found to be highly soluble and Mn somewhat soluble. The effect of Mn and V doping was shown to be strongly dependent on the O2 partial pressure during deposition with a high pO2 favoring the formation of substitutional defects (potentially beneficial in the case of Mn doping due to the addition of defects states near the conduction band) while low pO2 favors interstitial defects.
关键词： electronic structure,solubility,solar cells,molybdenum oxide,extrinsic defects,point defect analysis,density functional theory,MoO3
更新于2025-09-23 15:21:21
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Intrinsic Defect Limit to the Electrical Conductivity and a Two‐Step p‐Type Doping Strategy for Overcoming the Efficiency Bottleneck of Sb <sub/>2</sub> S <sub/>3</sub> ‐Based Solar Cells
摘要： The photovoltaic efficiency increase of Sb2S3-based solar cells has stagnated for five years since the highest efficiency 7.5% was achieved in 2014 [Adv. Funct. Mater. 24, 3587]. One important bottleneck is the high electrical resistivity of Sb2S3. Our first-principles calculations reveal that the high resistivity results from the compensation between the intrinsic donor VS and acceptors VSb, SbS, SSb which have comparably high concentration (low formation energy). The compensation also limits the improvement of conductivity through direct extrinsic doping. Further calculations of O dopants show that OS has a low formation energy, so the dominant intrinsic donor VS can be passivated by O and thus the p-type doping limit imposed by VS can be overcame. Meanwhile, other p-type limiting and recombination-center donor defects can be suppressed under the S-rich condition, which explains why the highest efficiency was achieved in O-doped Sb2S3 after sulfurization. Given the unexpected beneficial effects of O doping and sulfurization, a two-step doping strategy is proposed for overcoming the efficiency bottleneck: (i) use O to passivate the VS and S-rich condition to suppress other detrimental defects, making p-type doping feasible and minority carrier lifetime long; (ii) introduce other p-type dopants to increase hole carrier concentration.
关键词： first-principles,photovoltaic,O doping,Sb2S3 solar cell,point defect
更新于2025-09-12 10:27:22
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Emergence of point defect states in a plasmonic crystal
摘要： Plasmonic crystals are well known to have band structure including a band gap, enabling the control of surface plasmon propagation and con?nement. The band dispersion relation of bulk crystals has been generally measured by momentum-resolved spectroscopy using far ?eld optical techniques while the defects introduced in the crystals have separately been investigated by near ?eld imaging techniques so far. Particularly, defect related energy levels introduced in the plasmonic band gap have not been observed experimentally. In order to investigate such a localized mode, we performed electron energy-loss spectroscopy (EELS) on a point defect introduced in a plasmonic crystal made up of ?at cylinders protruding out of a metal ?lm and arranged on a triangular lattice. The energy level of the defect mode was observed to lie within the full band-gap energy range. This was con?rmed by a momentum-resolved EELS measurement of the band gap performed on the same plasmonic crystal. Furthermore, we experimentally and theoretically investigated the emergence of the defect states by starting with a corral of ?at cylinders protrusions and adding sequentially additional shells of those in order to eventually form a plasmonic band-gap crystal encompassing a single point defect. It is demonstrated that a defectlike state already forms with a crystal made up of only two shells.
关键词： point defect,band gap,Plasmonic crystals,momentum-resolved spectroscopy,electron energy-loss spectroscopy
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - Crystal Growth and Optical Property of GaN Nanowire Cores and GaInN/GaN Multi-Quantum Shells Grown by Metalorganic Vapor Phase Epitaxy
摘要： An n-GaN nanowire and a GaInN/GaN multi-quantum shell (MQS) were uniformly grown by the continuous flow mode MOVPE with the optimal growth condition. Although the extended defect-free crystal was successfully grown, the MQS may contain point defects acting as the nonradiative recombination centers. The AlGaN underlying shell was found to be effective point defect trap to improve the optical property of the MQS.
关键词： AlGaN,optical property,point defect,multi-quantum shell,nanowire
更新于2025-09-11 14:15:04
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Effects of Ag Doping and Point Defect on the Magnetism of ZnO
摘要： The magnetism sources and magnetic mechanism of Ag doping and point defect, which coexist in the presence of ZnO, are frequently controversial. To solve these problems, the effects of Ag doping and Zn or O vacancy on the magnetism of ZnO were investigated using geometry optimization and energy calculation according to the first-principles generalized gradient approximation + U (GGA+U) method of density functional theory. Results revealed that the system which Ag doping and Zn vacancy coexists in ZnO could achieve room-temperature ferromagnetism. This system had an extremely high spin polarization, which was advantageous for the spin electron injection sources applied in dilute magnetic semiconductors. Result also revealed that the magnetism of Zn14AgO16 was caused by the electron hybrid coupling effects among the O-2p, Ag-4d, Ag-5s, and Zn-4s orbits. And these effects were produced by the hole carriers after complexes were formed by the Ag doping and Zn vacancy. With regard to the most stable structure of the ground state, all doping systems which Ag replacing Zn and O vacancy coexisted in ZnO and those which Ag replacing Zn, interstitial Ag, and O vacancy coexisted in ZnO were all non-magnetic. Thus, these doping systems were unsuitable for dilute magnetic semiconductors. By contrast, the doping systems of interstitial Ag and Zn vacancy were magnetic, although the magnetism was relatively weak, thus rendering such systems inapplicable as well.
关键词： Point defect,Ag doping,ZnO,Magnetism,First-principles,Vacancy
更新于2025-09-10 09:29:36
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Enhanced thermoelectric properties of InSb: Studies on In/Ga doped GaSb/InSb crystals
摘要： In/Ga elements were doped in GaSb/InSb crystals respectively, and their thermoelectric performances were studied. The crystals had cubic zinc blende structure with change in lattice parameters. The charge transfer occurred between all the three (In, Ga and Sb) elements when In was doped with GaSb. Whereas in Ga doped InSb crystals, the charge transfer occurred only among Ga and Sb elements. In/Ga doped GaSb/InSb crystals exhibited degenerate and non-degenerate electrical properties, respectively. Optical modes of phonon vibrations were present, and their transverse mode was dominant over longitudinal mode in all the samples. The thermoelectric ?gure of merit (ZT) of In doped GaSb crystals were low because of their low power factor and high thermal conductivity. The highest power factor (59.5 μW/cmK2) and ZT (0.56) at 573 K were achieved by Ga doped (1 × 1021/cm3) InSb crystal. The ZT 0.56 at 573 K is thus far the highest among other reported values of InSb crystals.
关键词： D. Point defect,B. Thermoelectric properties,A. Intermetallics,C. Crystal growth,G. Thermoelectric power generation
更新于2025-09-10 09:29:36
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Nitrogen Trapping Ability of Hydrogen-Induced Vacancy and the Effect on the Formation of AlN in Aluminum
摘要： This paper presents the ternary interaction of N, H, and vacancy point defects and the nitrogen trapping ability of aluminum vacancies induced by hydrogen by means of DFT methods employed in VASP (Vienna Ab initio Simulation Package) and Abinit packages. The obtained vacancy formation energy of 0.65 eV is close to experimental values. Although the N–vacancy complex is unstable with the negative binding energy of ?0.51 eV, the stability of H–vacancy–N is proved by the positive binding energy of 0.59 eV and the appearance of the orbital hybridization in the density of state (DOS) of atoms connecting to this complex. Moreover, Al vacancies can trap more than 4 N atoms, which prevents the formation of aluminum nitride and subsequently affects not only the hardness of the Al surface but also many practical applications of AlN coating.
关键词： ternary point-defect interaction,first-principles calculations,alpha aluminum,superabundant vacancy
更新于2025-09-09 09:28:46