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Rational band design in metal chalcogenide Ba6Zn6HfS14: splitting orbitals, narrowing forbidden gap and boosting photocatalyst property
摘要： The insufficient light sources absorption often limits photocatalyst applications of metal chalcogenides because of their excessively broad band gap. Thus, it is necessary to discover and design a compound with rational band gap. Here, a new visible-light photocatalyst, Ba6Zn6HfS14, is prepared through the traditional high temperature solid-state reaction. A set of experiments on the visible-light decomposition of methylene blue demonstrated that the photocatalytic efficiency of Ba6Zn6HfS14 (0.00761 min-1) is improved, compared to that of Ba6Zn6ZrS14 (0.00553 min-1) which proved to be a previously reported visible-light photocatalyst with similar structure. The UV-visible reflection spectra demonstrated the energy gap of Ba6Zn6HfS14 (E1=1.45eV; E2 =2.55eV) is smaller than that of Ba6Zn6ZrS14 (E1 = 1.78eV; E2 = 2.50eV; E3 = 2.65eV). The Ba6Zn6HfS14 absorbs more visible light and exhibits preferably photocatalytic activity. The origin of splitted energy bands were elucidated via the first calculations.
关键词： band gap engineering,chalcogenides,visible-light photocatalyst
更新于2025-09-23 15:21:21
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Electrically controlled dielectric band gap engineering in a two-dimensional semiconductor
摘要： The emergent class of atomically thin two-dimensional (2D) materials has opened up completely new opportunities for manipulating electronic quantum states at the nanoscale. Here we explore the concept of dielectric band gap engineering, i.e., the controlled manipulation of the band gap of a semiconductor via its dielectric environment. Using first-principles calculations based on the GW self-energy approximation we show that the band gap of a two-dimensional (2D) semiconductor, such as the transition metal dichalcogenides, can be tuned over several hundreds of meV by varying the doping concentration in a nearby graphene sheet. Importantly, these significant band gap renormalizations are achieved via nonlocal Coulomb interactions and do not affect the structural or electronic integrity of the 2D semiconductor. We investigate various heterostructure designs, and show that, depending on the size of the intrinsic dielectric function of the 2D semiconductor, the band gap can be tuned by up to 1 eV for graphene carrier concentrations reachable by electrostatic doping. Our work provides opportunities for electrically controllable band gap engineering in 2D semiconductors.
关键词： GW self-energy approximation,transition metal dichalcogenides,graphene,two-dimensional semiconductor,dielectric band gap engineering
更新于2025-09-23 15:19:57
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Tailoring properties of hybrid perovskites by domain-width engineering with charged walls
摘要： Charged ferroelectric domain walls are fascinating electrical topological defects that can exhibit unusual properties. Here, in the search for novel phenomena, we perform and analyze first-principles calculations to investigate the effect of domain width on properties of domains with charged walls in the photovoltaic material consisting of methylammonium lead iodide hybrid perovskite. We report that such domains are stable and have rather low domain wall energy for any investigated width (that is, up to 13 lattice constants). Increasing the domain width first linearly decreases the electronic band gap from ?1.4 eV to about zero (which therefore provides an efficient band-gap engineering), before the system undergoes an insulator-to-metal transition and then remains metallic (with both the tail-to-tail and head-to-head domain walls being conductive) for the largest widths. All these results can be understood in terms of: (i) components of polarization along the normal of the domain walls being small in magnitude; (ii) an internal electric field that is basically independent of the domain width; and (iii) rather negligible charge transfer between walls. These findings deepen the knowledge of charged ferroelectric domain walls and can further broaden their potential for applications, particularly in the context of halide perovskites for photovoltaics.
关键词： charged ferroelectric domain walls,hybrid perovskites,photovoltaic materials,band-gap engineering,insulator-to-metal transition
更新于2025-09-23 15:19:57
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Design of high-performance double quantum well vertical cavity transistor lasers with GRIN base region
摘要： Different confinement structures are analyzed to achieve higher optoelectronic performances for double quantum well vertical cavity transistor laser with graded index separate confinement heterostructure. Adding the drift component to the diffusion term of the current density and solving new sets of equations, modified electro-optic performances of the device is obtained. Band-gap engineering of the original structure predicts simultaneous improvements in both current gain (more than two times) and ?3 dB optical bandwidth (by 1.5 GHz). Other less critical, yet important, performance metrics including optical output power and threshold current (up to 20%) are enhanced due to applying graded layers of AlξGa1-ξAs in the base region.
关键词： Vertical cavity transistor laser,GRIN base region,Optoelectronic performance,Double quantum well,Band-gap engineering
更新于2025-09-19 17:13:59
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A Review on Energy Band‐Gap Engineering for Perovskite Photovoltaics
摘要： Metal halide perovskites are attractive for highly efficient solar cells. As most perovskites suffer large or indirect bandgap compared with the ideal bandgap range for single-junction solar cells, bandgap engineering has received tremendous attention in terms of tailoring perovskite band structure, which plays a key role in light harvesting and conversion. In this Review, various reported bandgap engineering strategies are summarized. The recently widely used two main strategies including impurity and pressure as well as their underlying mechanisms are reviewed comprehensively. In addition, intermediate band and external electric field for bandgap engineering are also investigated. Moreover, future research directions are outlined to guide the further investigation.
关键词： band-gap engineering,pressure,photovoltaics,impurity alloy,perovskites
更新于2025-09-19 17:13:59
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From CuFeS <sub/>2</sub> to Ba <sub/>6</sub> Cu <sub/>2</sub> FeGe <sub/>4</sub> S <sub/>16</sub> : rational band gap engineering achieves large second-harmonic-generation together with high laser damage threshold
摘要： A new germanium-based sulfide, Ba6Cu2FeGe4S16, achieves a band-gap broadening of more than 1 eV relative to CuFeS2. Remarkably, Ba6Cu2FeGe4S16 exhibits excellent comprehensive NLO performance (SHG, 1.5 (cid:2) AgGaSe2; LDT, 2 (cid:2) AgGaSe2), satisfying the essential requirements of mid-IR NLO candidates.
关键词： laser damage threshold,mid-IR NLO materials,germanium-based sulfide,second-harmonic-generation,band-gap engineering
更新于2025-09-16 10:30:52
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Nano-scale sulfurization of the Cu <sub/>2</sub> ZnSnSe <sub/>4</sub> crystal surface for photovoltaic applications
摘要： The objective of this study was to find an effective method to improve VOC without JSC loss for Cu2ZnSnSe4 (CZTSe) monograin layer solar cells. Sulfurization of the surface of the kesterite absorber layer may lead to enhanced device efficiency via band gap widening at the surface. Surface sulfurization was carried out in two steps: a CdS layer was first deposited onto the CZTSe crystals by a chemical solution deposition method, and then the CdS-coated CZTSe was annealed at elevated temperature in evacuated quartz ampoules. The thickness of the sulfurized surface of CZTSe crystals was varied by adjusting the thickness of the CdS layer (from 100 nm to 200 nm) and by modifying the temperature of the annealing process from 400 to 700 °C for 60 min. SEM, EDX and Raman analysis showed that the CdS layer still existed on the surface of CZTSe crystals after annealing at 400 °C. After annealing at higher temperatures, the CdS layer disappeared and a new surface layer was formed. Annealing at 570 °C resulted in secondary phases on the surface, which are probably caused by decomposition reactions on the CZTSe crystal surface. Annealing at 700 °C formed a well-crystallized Cu2ZnSn(S, Se)4 thin layer on the surface of the CZTSe crystals, which was confirmed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The Raman peak located at 331 cm?1 provides strong evidence that a wider band gap Cu2ZnSn(S, Se)4 surface layer is formed after the sulfurization while the CdS peak at 308 cm?1 has disappeared. Compositional profiles of EDX and XPS showed that S is located in the surface layer, but Cd has diffused into the bulk of the crystal and acts as a dopant. The content of S in Cu2ZnSn(S, Se)4 depended on the CdS layer thickness.
关键词： CZTSe,band gap engineering,sulfurization,solar cells,photovoltaic applications
更新于2025-09-16 10:30:52
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On the influence of dilute charged impurity and perpendicular electric field on the electronic phase of phosphorene: Band gap engineering
摘要： Tuning the band gap plays an important role for applicability of 2D materials in the semiconductor industry. The present paper is a theoretical study on the band gap engineering using the electronic density of states (DOS) of phosphorene in the presence of dilute charged impurity and of a perpendicular electric field. The electronic DOS is numerically calculated using a combination of the continuum model Hamiltonian and the Green’s function approach. Our findings show that the band gap of phosphorene in the absence and presence of the perpendicular electric field decreases with increasing impurity concentration and/or impurity scattering potential. Further, we found that in the presence of opposite perpendicular electric fields, the electronic DOS of disordered phosphorene shows different changing behaviors stemming from the Stark effect: in the positive case the band gap increases with increasing electric-field strength; whereas in the negative case the band gap disappears. The latter, in turn, leads to the semiconductor-to-semimetal and semiconductor-to-metal phase transition for the case of strong impurity concentrations and strong impurity scattering potentials, respectively. The results can serve as a base for future applications in logic electronic devices.
关键词： Stark effect,perpendicular electric field,semiconductor-to-semimetal transition,phosphorene,band gap engineering,electronic density of states,semiconductor-to-metal transition,dilute charged impurity
更新于2025-09-10 09:29:36
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[IEEE 2018 IEEE International Conference on Semiconductor Electronics (ICSE) - Kuala Lumpur (2018.8.15-2018.8.17)] 2018 IEEE International Conference on Semiconductor Electronics (ICSE) - Bandgap Engineering of GaAsBi Alloy for Emission of up to 1.52 μm
摘要： Band gap engineering by incorporating bismuth into GaAs to form ternary GaAs1-xBix alloy was investigated. Series of GaAsBi samples with different Bi concentrations were grown by molecular beam epitaxy. Based on high resolution X-ray diffraction (HR-XRD) measurements, Bi concentration of up to 0.108 was successfully incorporated into the lattice. Sample with the highest Bi concentration, GaAs0.892Bi0.108, show room temperature photoluminescence (PL) emission with a peak wavelength of 1.52 μm and full-width-at-half-maximum (FWHM) of 89 meV. It was found that the incorporation of Bi into GaAs lattice affected both the conduction band as well as the valence band. The conduction band minimum reduces linearly by 23 meV/%Bi while the valence band maximum was best fitted by using the valence band anti-crossing (VBAC) model with coupling parameter, CBi of 1.65 eV.
关键词： band gap engineering,X-ray diffraction,molecular beam epitaxy,GaAsBi,photoluminescence
更新于2025-09-09 09:28:46