Showing papers on "Band offset published in 2022"
TL;DR: In this article , a photodetector based on doped MoS2/SnSe2 was proposed to extend the photoresponse spectrum to solar blind ultraviolet (SBUV).
Abstract: The intentionally designed band alignment of heterostructures and doping engineering are keys to implement device structure design and device performance optimization. According to the theoretical prediction of several typical materials among the transition metal dichalcogenides (TMDs) and group‐IV metal chalcogenides, MoS2 and SnSe2 present the largest staggered band offset. The large band offset is conducive to the separation of photogenerated carriers, thus MoS2/SnSe2 is a theoretically ideal candidate for fabricating photodetector, which is also verified in the experiment. Furthermore, in order to extend the photoresponse spectrum to solar‐blind ultraviolet (SBUV), doping engineering is adopted to form an additional electron state, which provides an extra carrier transition channel. In this work, pure MoS2/SnSe2 and doped MoS2/SnSe2 heterostructures are both fabricated. In terms of the photoelectric performance evaluation, the rejection ratio R254/R532 of the photodetector based on doped MoS2/SnSe2 is five orders of magnitude higher than that of pure MoS2/SnSe2, while the response time is obviously optimized by 3 orders. The results demonstrate that the combination of band alignment and doping engineering provides a new pathway for constructing SBUV photodetectors.
9 citations
TL;DR: In this article , a simulation-based study of the CZTS/ZnS-based heterojunction provides a high conduction band offset at the junction, and a high acceptor type defect density increases open-circuit voltage by shifting the Fermi level towards the valance band maximum.
9 citations
TL;DR: In this article , an ultrathin SnO2 buffer layer of ∼10 nm was applied on the high-roughness fluorine-doped tin oxide (FTO) substrate for effective interface and band engineering for superstrate CdS/Sb2(S,Se)3 solar cells.
Abstract: The environmentally friendly antimony selenosulfide (Sb2(S,Se)3) semiconductor emerges as a promising light harvester for thin-film photovoltaics owing to its excellent material and optoelectronic properties. The alloyed Sb2(S,Se)3 is endowed with the complementary benefits of Sb2S3 and Sb2Se3, such as a tunable band gap within the range of 1.10–1.70 eV. In Sb2(S,Se)3 solar cells, the n-type semiconductor CdS is extensively used as an electron transport layer (ETL), which plays a role in extracting photogenerated electrons from absorbers and transporting them to conducting substrates. However, the unsatisfactory ETL/absorber interface contact often involves severe interface recombination. Herein, we report that an ultrathin SnO2 buffer layer of ∼10 nm applied on the high-roughness fluorine-doped tin oxide (FTO) substrate aids in effective interface and band engineering for superstrate CdS/Sb2(S,Se)3 solar cells. Careful characterizations confirm that the ultrathin SnO2 buffer layer plays a positive role in inhibiting the shunt current leakage at the ETL/absorber interface and manipulating the cascade energy band structure for more effective interface passivation and efficient electron extraction. Consequently, the resultant SnO2/CdS ETL-based Sb2(S,Se)3 solar cells exhibited a remarkable device efficiency of 8.67%, coupled with a considerable open-circuit voltage of 0.72 V. Our finding demonstrates a facile approach to engineer the interface contact and band offset to accelerate electron extraction, transport, and collection efficiencies.
7 citations
TL;DR: In this paper , the optoelectronic features of a series of experimentally feasible 2D Janus transition metal dichalcogenides monolayers in a configured van der Waals nanostructure are presented.
6 citations
5 citations
TL;DR: In this article, the authors investigated the conduction band offsets and electrical properties of ErZO/β-Ga2O3 and Gallium doped ZnO (GZO) films with high crystallinity were deposited by pulsed laser deposition.
5 citations
5 citations
TL;DR: In this paper , the optical and electronic properties of the heterojunction formed between Sb2Se3, a material with a promising role in photovoltaics characterized by one-dimensional topology (ribbons), and an emerging two-dimensional (2D) material, PtSe2, exhibiting unique optical properties for photoelectronics and photonics.
Abstract: The heterojunction between two materials brought into contact, for example, in the form of vertical van der Waals heterostructures, exhibits interesting features offering functionalities to devices stimulated by light. We report in this article an investigation of the optical and electronic properties of the heterojunction formed between Sb2Se3, a material with a promising role in photovoltaics characterized by one-dimensional (1D) topology (ribbons), and an emerging two-dimensional (2D) material, PtSe2, exhibiting unique optical properties for photoelectronics and photonics. The controlled growth of PtSe2 on Sb2Se3 underlayer takes place using a transfer-free process by low-temperature selenization of 1–2 nm Pt films thermally evaporated on Sb2Se3 ultrathin substrates. X-ray photoelectron spectroscopy (XPS) data analyzed in the context of the Kraut method provided an estimate for the band offsets at the interface. The valence band offset and the conduction band offset of the PtSe2/Sb2Se3 heterojunction were found to be −0.25 and 1.0 eV, respectively, indicating a type-II heterojunction. The ultrabroad optical absorption of the heterojunction and the protection offered by PtSe2 to Sb2Se3, against oxidation of the latter, render this particular heterojunction a robust candidate for applications in photovoltaics. Finally, the current study of a heterojunction between materials of different dimensionalities may pave the way for a rational design in the field of trans-dimensional heterostructures.
5 citations
TL;DR: In this paper , the authors exploit direct and inverse photoelectron spectroscopy together with electrical characterization to investigate the cause of interface recombination in chemical bath-deposited Zn(O,S)/co-evaporated CuInS2-based devices.
Abstract: Copper indium disulfide (CuInS2) grown under Cu-rich conditions exhibits high optical quality but suffers predominantly from charge carrier interface recombination, resulting in poor solar cell performance. An unfavorable "cliff"-like conduction band alignment at the buffer/CuInS2 interface could be a possible cause of enhanced interface recombination in the device. In this work, we exploit direct and inverse photoelectron spectroscopy together with electrical characterization to investigate the cause of interface recombination in chemical bath-deposited Zn(O,S)/co-evaporated CuInS2-based devices. Temperature-dependent current-voltage analyses indeed reveal an activation energy of the dominant charge carrier recombination path, considerably smaller than the absorber bulk band gap, confirming the dominant recombination channel to be present at the Zn(O,S)/CuInS2 interface. However, photoelectron spectroscopy measurements indicate a small (0.1 eV) "spike"-like conduction band offset at the Zn(O,S)/CuInS2 interface, excluding an unfavorable energy-level alignment to be the prominent cause for strong interface recombination. The observed band bending upon interface formation also suggests Fermi-level pinning not to be the main reason, leaving near-interface defects (as recently observed in Cu-rich CuInSe2) as the likely reason for the performance-limiting interface recombination.
5 citations
TL;DR: In this paper , the authors have shown that charge transfer excitons can be activated via twisting in epitaxially fused heterodimer quantum dot (QD) molecules with quasi type-II band alignment, and even in QD homodimer molecules.
Abstract: A heterojunction with type-II band alignment has long been considered as a prerequisite to realize charge transfer (CT) excitons which are highly appealing for exploration of quantum many-body phenomena, such as excitonic Bose-Einstein condensation and superfluidity. Herein, we have shown CT excitons can be activated via twisting in epitaxially fused heterodimer quantum dot (QD) molecules with quasi type-II band alignment, and even in QD homodimer molecules, therefore breaking the constraint of band alignment. The enabling power of twisting has been revealed. It modulates the orbital spatial localization toward charge separation that is mandatory for CT excitons. Meanwhile, it manifests an effective band offset that counterbalances the distinct many-body effects felt by excitons of different nature, thus ensuring the successful generation of CT excitons. The present work extends the realm of twistroincs into zero-dimensional materials and opens a novel pathway of manipulating the properties of QD materials and closely related molecular systems.
4 citations
TL;DR: In this paper , the energy barrier heights at the Si/Ga2O3 interface for different reverse voltages (Vrev) were derived from temperature-dependent current density-voltage (J-V-T) characteristics.
Abstract: We studied electrical properties of n-Si/n-Ga2O3 heterojunctions fabricated by surface-activated bonding. The energy barrier heights (qϕb) at the Si/Ga2O3 interface for different reverse voltages (Vrev) were derived from temperature-dependent current density–voltage (J–V–T) characteristics. With shifting Vrev to the negative direction, qϕb gradually decreased and reached a constant value due to negatively charged interface states. The conduction band offset at the heterointerface was estimated to be 0.18 eV from the Vrev dependence of qϕb. The qϕb calculated from a capacitance of the heterojunction at thermal equilibrium was larger than those derived from the J–V–T characteristics, attributing to spatially inhomogeneous qϕb caused by the non-uniform distribution of the charged interface states. The density of shallow interface states was also extracted from the reverse J–V–T characteristics, which was estimated to be about 6 × 1012 cm−2 eV−1.
TL;DR: In this paper , the authors investigated the electronic properties of transition metal dichalcogenides (TMDCs) hybrid heterostructures, i.e., (WS2-MoS2)/WS2, (WS 2-MOS2)/MoS 2 and WS 2/(WS 2 MoS 2)/WS 2 , and found that strong intralayer and moderate interlayer interaction can influence the migration of photoinduced carriers.
TL;DR: In this paper , the authors investigated the natural band alignment of BAlN and BGaN alloys using the atomic solid-state energy scale approach and determined the band edge positions relative to the vacuum level.
Abstract: The natural band alignment of BAlN and BGaN alloys was investigated using the atomic solid-state energy scale approach. The band edge positions relative to the vacuum level were determined for BAlN and BGaN alloys, and the band offset values for each heterostructure were estimated. The results suggest that the natural band alignment of BAlN and BGaN alloys behaves according to the common anion rule. Further, the Schottky barrier height (SBH) was calculated based on the results of band alignment for BAlN and BGaN alloys. The predicted SBH values are expected to be an important guideline for boron nitride and its related alloy device design.
TL;DR: In this paper , a novel in-situ temperature-dependent XPS characterization technique was performed to investigate the heat effect on band offsets with the temperature from 300 K to 473 K.
TL;DR: In this paper , a hole-selective layer (HSL) for screen-printed mono-crystalline silicon solar cell (SMSC) applications was proposed and the energy band diagram of the P-Si(100)/SiO x /CuO 4.8 /Ag stacked film was shown.
TL;DR: In this article , the electronic structure and electrical properties of sputter-deposited high-k dielectrics grown on p-GaAs substrate with post-deposition annealing at 500 °C/N2 ambient were investigated.
TL;DR: In this paper , the impact of channel layer thicknesses on the operating characteristics of In2O3/ZnO heterojunction TFTs prepared via sputtering was investigated using a variety of experimental and computational modeling techniques.
Abstract: Combining low-dimensional layers of dissimilar metal oxide materials to form a heterojunction structure offers a potent strategy to improve the performance and stability of thin-film transistors (TFTs). Here, we study the impact of channel layer thicknesses on the operating characteristics of In2O3/ZnO heterojunction TFTs prepared via sputtering. The conduction band offset present at the In2O3/ZnO heterointerface affects the device's operating characteristics, as is the thickness of the individual oxide layers. The latter is investigated using a variety of experimental and computational modeling techniques. An average field-effect mobility ( μFE) of >50 cm2 V−1 s−1, accompanied by a low threshold voltage and a high on/off ratio (∼108), is achieved using an optimal channel configuration. The high μFE in these TFTs is found to correlate with the presence of a quasi-two-dimensional electron gas at the In2O3/ZnO interface. This work provides important insight into the operating principles of heterojunction metal oxide TFTs, which can aid further developments.
TL;DR: In this article , the authors investigated the band offset trends of few-layer and bulk IV-VI semiconductors MX and MX2(M = Ge, Sn; X = S, Se, Te).
Abstract: The band offsets between semiconductors are significantly associated with the optoelectronic characteristics and devices design. Here, we investigate the band offset trends of few-layer and bulk IV-VI semiconductors MX and MX2(M = Ge, Sn; X = S, Se, Te). For common-cation (anion) systems, as the atomic number increases, the valence band offset of MX decreases, while that of MX2has no distinct change, and the physical origin can be interpreted using band coupling mechanism and atomic potential trend. The band edges of GeX2system straddle redox potentials of water, making them competitive candidates for photocatalyst. Moreover, layer number modulation can induce the band offset of GeSe/SnS and GeSe2/GeS2heterojunction undergoing a transition from type I to type II, which makes them suitable for optoelectronic applications.
TL;DR: In this paper , the effect of Zn alloying and defect engineering on the buffer layer of CZTS/Zn0.75S heterojunction was investigated, and first-principles calculations showed that the Zn-alloyed CdS buffer layer reverses the unfavorable cliff-like conduction band offset (CBO) of CzTS/CdS to the desirable spike-like CBO of CzhTS/zn0, 0.25Cd0.
Abstract: The inferior electrical properties at the interface of the Cu2ZnSnS4/CdS (CZTS/CdS) heterojunction resulting in the severe loss of open-circuit voltage (Voc) highly restrict the photovoltaic efficiency of CZTS solar cell devices. Here, first-principles calculations show that the Zn-alloyed CdS buffer layer reverses the unfavorable cliff-like conduction band offset (CBO) of CZTS/CdS to the desirable spike-like CBO of CZTS/Zn0.25Cd0.75S, which suppresses carrier nonradiative recombination and blocks electron backflow. In addition, the weakened n-type conductivity of Zn0.25Cd0.75S can be enhanced by In, Ga, and Cl doping without the introduction of detrimental deep-level defects and severe band-tail states, which improves the Voc of CZTS solar cells by promoting strong band bending and large quasi-Fermi-level splitting at the absorber side of the CZTS/Zn0.25Cd0.75S heterojunction. This study finds that the synergetic effects of Zn alloying and defect engineering on the CdS buffer layer are promising for overcoming the long-standing issue of the Voc deficit in CZTS solar cells, and understanding the optimized interfacial electrical properties provides theoretical guidance for improving the efficiency of semiconductor devices.
TL;DR: In this article , the authors proposed ZnO/InGaAs solar cells, in which three methods are given to enhance the performances: reducing conduction band offset, increasing the carrier concentration and reducing the interface defect density.
TL;DR: In this paper , the electronic properties of CdS1−x (0 ≤ x ≤ 1) ternary alloys are investigated by first-principles calculation based on the density functional theory (DFT) and the performance of cdS/CdSe/cdTe devices are modeled by SCAPS to reveal why CdTe complex layers have good effects.
Abstract: The short-circuit current density (JSC) of CdTe solar cells both in the short and long wavelength regions can be effectively enhanced by using CdS/CdSe as the composite window layer. CdS/CdSe composite layers would interdiffuse to form the CdSexS1−x ternary layer during the high temperature deposition process of CdTe films. In this paper, the electronic properties of CdSexS1−x (0 ≤ x ≤ 1) ternary alloys are investigated by first-principles calculation based on the density functional theory (DFT) and the performance of CdS/CdSe/CdTe devices are modeled by SCAPS to reveal why CdS/CdSe complex layers have good effects. The calculation results show that the position of the valence band of CdSexS1−x moves towards the vacuum level as the doping concentration of Se increases and the band gap becomes narrow. According to device modeling, the highest conversion efficiency of 20.34% could be achieved through adjusting the conduction band offset (CBO) of theCdSexS1−x/CdTe interface to about 0.11 eV while the Se concentration x approaches 0.75. Further investigations suggest a 50–120 nm thickness of CdSexS1−x (x = 0.75) would obtain better device performance. It means that solar cells with a CdSexS1−x/CdTe structure need a suitable Se content and thickness of CdSexS1−x. These results can provide theoretical guidance for the design and fabrication of high efficiency CdTe solar cells.
TL;DR: In this article , the electronic properties of 2D lateral superlattices of monolayer transition metal dichalcogenides (TMDs) were investigated, and the dependence of the electronic structure, bandgap, carrier effective masses, charge density overlap on chemical components, interface type, and sub-lattice size of lateral TMD-SLs was investigated.
Abstract: Fabricating lateral heterostructures (HSs) and superlattices (SLs) provides a unique degree of freedom for modulating the physical properties of two-dimensional (2D) materials by varying the chemical component, geometric size and interface structure in the ultra-thin atomic thickness limit. While a variety of 2D lateral HSs/SLs have been synthesized, especially for transition metal dichalcogenides (TMDs), how such structures affect quantitatively the physical properties of 2D materials has not yet been established. We herein explore electronic property modulation in 2D lateral SLs of monolayer TMDs through first-principles high-throughput calculations. The dependence of the electronic structure, bandgap, carrier effective masses, charge density overlap on chemical components, interface type, and sub-lattice size of lateral TMD-SLs are investigated. We find that by comparison with their random alloy counterparts, the lateral TMD-SLs exhibit generally type-II band alignment, a wider range of bandgap tunability, larger carrier effective masses, and stronger electron-hole charge separation tendency. The bandgap variation with a sub-lattice size shows larger bowing parameters for the SLs with heterogeneous anions, by comparison with the homogeneous anion cases. A similar behavior is observed for the SLs with an armchair-type interface, by comparison with the zigzag-type interface cases. Further analyses reveal that the underlying physical mechanism can be attributed to the synergistic interplay among the band offset of sub-lattices, quantum confinement effect, and existing internal strain.
TL;DR: In this paper , the bandgap and band offsets at C2N/MSe2 (M = Mo, W) interfaces have been engineered based on density functional theory calculations, and the main findings demonstrate that the C 2N monolayer interacts with both MoSe2 and WSe2 monolayers through weak van der Waals interactions.
Abstract: Stacking layered two-dimensional materials in a type-II band alignment block has provided a high-performance method in photocatalytic water-splitting technology. The key parameters in such heterostructure configurations are the valence and conduction band offsets at the interface, which determine the device performance. Here, based on density functional theory calculations, the bandgap and band offsets at C2N/MSe2 (M = Mo, W) interfaces have been engineered. The main findings demonstrate that the C2N monolayer interacts with both MoSe2 and WSe2 monolayers through weak van der Waals interactions. These heterostructures possess a narrower indirect bandgap and a typical type-II heterostructure feature, being suitable for promoting the separation of photogenerated electron–hole pairs. The calculated Gibbs free energy of hydrogen adsorption demonstrates a reduction in the overpotential, towards the hydrogen evolution reaction, upon forming heterostructures. To further tune the bandgap values and band offsets of heterostructures, the external perturbations are included through a vertical strain and finite electric field. It is found that both the vertical strain and electric field strongly modulate the bandgap values and the magnitude of the band offsets, while the typical type-II band alignment remains preserved. It is noticeable that the band offset magnitudes of the C2N/MoSe2 and C2N/WSe2 heterostructures are more sensitive to an external electric field than to a vertical interlayer strain.
TL;DR: In this paper , a new kind of mixed-dimensional vdWs heterostructure photoelectrode and investigate the strain enhanced PEC performance at VdWs interfaces were reported.
TL;DR: In this article , As and HfS were used to construct van der Waals heterostructures by six stacking manners, and from among them the most stable structure was selected to study its electronic and optic-electronic properties and quantum regulation effects by hybrid functional HSE06 systematically.
Abstract: Stacking two or more monolayer materials to form van der Waals heterostructures is an effective strategy to realize ideal electronic and optoelectronic devices. In this work, we use As and HfS<sub>2</sub> monolayers to construct As/Hfs<sub>2</sub> heterostructures by six stacking manners, and from among them the most stable structure is selected to study its electronic and optic-electronic properties and quantum regulation effects by hybrid functional HSE06 systematically. It is found that the As/Hfs<sub>2</sub> intrinsic heterostructure is a II-type band aligned semiconductor, and its band gap can be significantly reduced (~ 0.84 eV) in comparison with two monolayers (band gap > 2.0 eV), especially the valence band offset and conduction band offset can increase up to 1.48 eV and 1.31 eV, respectively, which is very favorable for developing high-performance optoelectronic devices and solar cells. The vertical strain can effectively adjust the band structure of heterostructure. The band gap increases by tensile strain, accompanied with an indirect-direct band gap transition. However, by compressive strain, the band gap decreases rapidly until the metal phase occurs. The applied external electric field can flexibly adjust the band gap and band alignment mode of heterostructure, so that the heterostructure can realize the transformation between I-, II-, and III-type band alignments. In addition, intrinsic As/Hfs<sub>2</sub> heterostructure has ability to strongly absorb light in the visible light region, and can be further enhanced by external electric field and vertical strain. These results suggest that the intrinsic As/Hfs<sub>2</sub> heterostructure promises to have potential applications in the fields of electronic, optoelectronic devices and photovoltaic cells.
TL;DR: In this paper , the monolayer WSe2 and MoSe2 were transferred to the surface of ReS2/sapphire to form two-dimensional (2D) van der Waals heterojunctions, respectively.
Abstract: In this work, the monolayer WSe2 and MoSe2 were transferred to the surface of ReS2/sapphire to form two-dimensional (2D) ReS2/WSe2 and ReS2/MoSe2 van der Waals heterojunctions, respectively. The high quality of monolayer ReS2, WSe2 and MoSe2 was characterized by Raman spectroscopy. We determined a valence band offset of 0.16±0.15 eV at ReS2/WSe2 heterojunction using x-ray photoelectron spectroscopy, with a type-II band alignment. The valence band offset of ReS2/MoSe2 was determined to be 0.61±0.15 eV, with a type-I band alignment. By combining ultraviolet photoelectron spectroscopy, the results calculated by Anderson's affinity rule and the results of XPS showed agreement. This work not only reveals energy-band structures of the ReS2/WSe2 interface and ReS2/MoSe2 interface, but also paves the way for the future designing of 2D heterojunction-based optoelectronic devices.
TL;DR: In this paper , the authors investigate the interface between carbon nitride (C3N4) and phosphorene nanosheets (P-ene) by means of Density Functional Theory (DFT) calculations.
Abstract: We investigate the interface between carbon nitride (C3N4) and phosphorene nanosheets (P-ene) by means of Density Functional Theory (DFT) calculations. C3N4/P-ene composites have been recently obtained experimentally showing excellent photoactivity. Our results indicate that the formation of the interface is a favorable process driven by Van der Waals forces. The thickness of P-ene nanosheets determines the band edges offsets and the charge carriers' separation. The system is predicted to pass from a nearly type-II to a type-I junction when the thickness of P-ene increases, and the conduction band offset is particularly sensitive. Last, we apply the Transfer Matrix Method to estimate the efficiency for charge carriers' migration as a function of the P-ene thickness.