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Rare Earth Doping of Topological Insulators: A Brief Review of Thin Film and Heterostructure Systems
摘要： Magnetic topological insulators (MTIs) are a novel materials class in which a topologically nontrivial electronic band structure coexists with long-range ferromagnetic order. The ferromagnetic ground state can break time-reversal symmetry, opening a gap in the topological surface states whose size is dependent on the magnitude of the magnetic moment. Doping with rare earth ions is one way to introduce higher magnetic moments into a material, however, in Bi2Te3 bulk crystals, the solubility limit is only a few percent. Using molecular beam epitaxy for the growth of doped (Sb,Bi)2(Se,Te)3 TI thin films, high doping concentrations can be achieved while preserving their high crystalline quality. The growth, structural, electronic, and magnetic properties of Dy, Ho, and Gd doped TI thin films will be reviewed. Indeed, high magnetic moments can be introduced into the TIs, which are, however, not ferromagnetically ordered. By making use of interfacial effects, magnetic long-range order in Dy doped Bi2Te3, proximity-coupled to the MTI Cr:Sb2Te3, has been achieved. Clearly, engineered MTI heterostructures offer new possibilities that combine the advantageous properties of different layers, and thus provide an ideal materials platform enabling the observation new quantum effects at higher temperatures.
关键词： rare earth doping,MBE,topological insulators,heterostructure,bismuth telluride,antimony telluride
更新于2025-09-23 15:22:29
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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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Wavelength conversion characteristics of Y1–– Er Yb BaZn3AlO7
摘要： For future energy conversion applications, Y1–x–yErxYbyBaZn3AlO7 were synthesized using a flux method and their wavelength conversion characteristics were investigated. The emission intensities of down-shifting under 365 nm excitation, which was observed in the range of 400–800 nm, were significantly changed by doping with rare-earth ions. Up-conversion emission peaks under 980 nm excitation were observed at 535, 550, and 661 nm; two or three photon processes are involved. The maximum emission intensity of bidirectional wavelength conversion under 365 nm and 980 nm irradiation was observed for x = 0.10 and y = 0.20. For simultaneous excitation under irradiation at 365 and 980 nm, an additive effect with very little alteration of energy transfer mechanisms was observed compared with that of each single excitation.
关键词： Up-conversion,Multi-component oxide,Co-doping,Bidirectional wavelength conversion,Down-shifting
更新于2025-09-23 15:22:29
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Acceleration of tungsten doping on vanadium dioxide (VO2) by alkali species
摘要： The monoclinic vanadium dioxide, VO2(M), undergoes reversible phase transition from monoclinic (semiconductor) to tetragonal (metal), which exhibits a good thermochromic property. VOSO4, as a vanadium source, is easy to handle produces VO2(M) under mild condition in the presence of alkali species. In this study, the effects of the additions of NH4HCO3, NH3·H2O, and NaOH on the VO2 crystal formation with/without tungsten doping for thermochromicity were investigated. NaOH, the strongest base of the three, provided the strongest and narrowest x-ray diffraction peak, while NH4HCO3, the weakest base, provided the opposite. Interestingly, for the tungsten doping to adjust the transition temperature, the use of NH4HCO3 was more suitable due to the possibility of a slow crystal frame formation as compared to the use of NaOH.
关键词： Sodium hydroxide,Vanadium dioxide,Ammonium hydrogen carbonate,Ammonium hydroxide,Tungsten doping
更新于2025-09-23 15:22:29
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Effects of Mg incorporation in cubic GaN films grown by PAMBE near Ga rich conditions
摘要： The structural and electrical properties of Mg-doped cubic GaN epi-layers grown by plasma-assisted molecular beam epitaxy (PAMBE) near Ga rich conditions are investigated. The diffraction of high-energy reflected electrons (RHEED) in situ, in addition to structural studies of X-ray diffraction, show that the fraction of hexagonal and crystal twinning inclusions decreases when the Mg flux increases. The condition for the higher incorporation of Mg where the electrical properties are optimized is highly sensitive to the flow ratio Mg/Ga. The p-doping level steadily increases with increasing Mg flux. The Mg concentration obtained by secondary ion mass spectroscopy (SIMS) from samples grown at Mg temperatures from 200 °C to 700 °C are in a range between 2 × 10^19 to 2 × 10^20 atoms/cm^3. The highest mobility and p-type doping level achieved, determined from Hall measurements, were 28.2 cm^2/V-s and 2 × 10^19 cm^-3, respectively. We corroborate that the Mg doped c-GaN films are suitable for the construction of optoelectronic devices based on cubic III-Nitrides.
关键词： Plasma-assisted molecular beam epitaxy,Cubic GaN diode,Mg p-type doping
更新于2025-09-23 15:22:29
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The influence of Ag doping and annealing on phase, structural and carrier transport characteristics of CIS thin films
摘要： The un-doped and Ag-CIS thin films were deposited on quartz glass substrates by single source thermal evaporation method. Then, some CIS films were annealed in vacuum or N2 atmosphere from 350 °C to 550 °C. The results of XRD patterns showed the phase compositions of CIS thin films were changed with the increase of annealing temperature. Meanwhile, the results of Raman measurement confirmed a dramatic transition from CA phase to CH phase. Furthermore, the Ag atoms could promote the recrystallization process and the transition from CA phase to CH phase, which might result in the improvement of optical-electrical properties of CIS film. The transient photocurrent of the CIS-3 sample annealed at 450 °C was higher than those of other samples, which might be related to the good crystal quality. The results of I-V curves confirmed the N-type conduction of CIS-3 films, which was consistent with the results of EDS measurement. The C-V results of CIS-2 films also were the same as the results of EDS measurement. Furthermore, for the CIS-2 samples, with increase of annealing temperature, the change of conduction type may be related to the S element volatilization under vacuum situation and the decomposition of the substitutional defects AgIn.
关键词： Doping,CIS,Optical-electrical Properties,Photocurrent,Annealing
更新于2025-09-23 15:22:29
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Effect of Magnesium on Structural and Optical Properties of CaTiO3: A DFT Study
摘要： The electronic bandstructure, optical and structural properties of pure and Mg-doped CaTiO3 are calculated by using first-principle calculation which is based on the density functional theory. The effect of Mg-dopant on the properties of CaTiO3 perovskite explored by using ultra soft pseudo-potential (USP) and generalized gradient approximation (GGA). The incorporation of Mg at Ca site affected the electronic band structure of CaTiO3 meaningfully by introducing new gamma point. The incorporation of Mg increases the band gap from 1.84 eV to 1.92 eV. The partial density of states of pure CaTiO3 changed after doping cleared the effect of dopant on pure system. Optical properties of both the systems are examined which reveals that the absorption edge shifting from 2.1 eV to 2.5 eV indicates a blue shift whereas the refractive index also increases from 2 to 2.4 after doping. Thus Mg-doped CaTiO3 not only affect the optical properties of the system but also make it and appealing candidate for optical devices.
关键词： Refractive index,Doping,Density of states,Oxide Based Perovskite,Optical Properties,Band Gap
更新于2025-09-23 15:22:29
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Doping-induced giant rectification and negative differential conductance (NDC) behaviors in zigzag graphene nano-ribbon junction
摘要： By p-type and n-type doping on the electrode edges of V-notched zigzag graphene nano-ribbons (ZGNRs), four V-notched ZGNR-based PN-junctions are designed theoretically. The electronic transport properties of the doped and un-doped V-notched ZGNRs are studied applying non-equilibrium Green’s function method combined with the density functional theory. The numerical results show that, the doped systems are less conductive than the un-doped system, because after doping the transition states become localized. To our surprise, the ZGNR-based PN-junctions do not show obvious rectification by purely doping the boron atoms and nitrogen atoms on the edges of two ZGNR electrodes respectively. However, after hydrogenated the doped boron atoms and nitrogen atoms, the ZGNR systems present giant rectifications with the maximum rectification ratios up to 106 ～ 107, which attributed to the vanishing of overlap between left-electrode sub-band and right-electrode sub-band in the negative bias regime after the doped boron and nitrogen atoms being hydrogenated. Due to the same reason, the hydrogenated doping systems also show large negative differential conductance behaviors.
关键词： Giant rectification,Negative differential conductance,Graphene nano-ribbon junction,Boron and nitrogen doping
更新于2025-09-23 15:22:29
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Doping of Monolayer Transition Metal Dichalcogenides via Physisorption of Aromatic Solvent Molecules
摘要： Two-dimensional (2D) transition metal dichalcogenides (TMDs) recently emerged as novel materials displaying a wide variety of physico-chemical properties that render them unique scaffolds for high-performance (opto)electronics. The controlled physisorption of molecules on the TMD surface is a viable approach to tune their optical and electronic properties. Solvents, made of small aromatic molecules, are frequently employed for the cleaning of the 2D materials or as 'dispersant' for their chemical functionalization with larger (macro)molecules, without considering their potential key effect in locally modifying the characteristics of 2D materials. In this work, we demonstrate how the electronic and optical properties of mechanically exfoliated monolayer of MoS2 and WSe2 are modified when physically interacting with small aromatic molecules of common solvents. Low-temperature photoluminescence (PL) spectra recorded at 78 K revealed that physisorbed benzene derivatives could modulate the charge carrier density in monolayer TMDs, hence affecting the switching between neutral exciton and trion (charged exciton). By combining experimental evidences with DFT calculations, we confirm that charge transfer doping on TMDs depends not only on difference in chemical potential between molecules and 2D materials, but also on the thermodynamic stability of physisorption. Our results provide unambiguous evidence of the great potential of optical and electrical tuning of monolayer MoS2 and WSe2 by physisorption of small aromatic solvent molecules, which is highly relevant both for fundamental studies and more device applied purposes.
关键词： transition metal dichalcogenides,aromatic molecules,Density Functional Theory,doping,photoluminescence
更新于2025-09-23 15:22:29
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Control of Structural and Electrical Properties of Indium Tin Oxide (ITO)/Cu(In,Ga)Se <sub/>2</sub> Interface for Transparent Back-Contact Applications
摘要： Development of transparent-conducting oxide (TCO) back contact for Cu(In,Ga)Se2 (CIGS) absorber is crucial for bifacial CIGS photovoltaics. However, GaOx formation at the TCO/CIGS interface has hampered the photocarrier extraction. Here, by controlling the Na doping scheme, we show that the hole transporting properties at the indium?tin oxide (ITO)/CIGS back contact can be substantially improved, regardless of the GaOx formation. Na incorporation from the glass substrate during the GaOx forming phase created defective states at the interface, which allowed efficient hole extraction from CIGS, while post Na treatment after GaOx formation did not play such a role. Furthermore, we discovered that an almost GaOx-free interface could be made by reducing the underlying ITO film thickness, which revealed that ITO/CIGS junction is inherently Schottky. In the GaOx-free condition, post-Na treatment could eliminate the Schottky barrier and create ohmic junction due to generation of conducting paths at the interface, which is supported by our photoluminescence analysis.
关键词： Schottky barrier,indium-tin oxide,photovoltaics,Na doping,Ga)Se2,ohmic contact,GaOx,transparent-conducting oxide,Cu(In
更新于2025-09-23 15:22:29