Search query: Bandgap engineering of two-dimensional C3N bilayers

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abstract: Semiconductors are the basis of many vital technologies such as electronics, computing, communications, optoelectronics, and sensing. Modern semiconductor technology can trace its origins to the invention of the point contact transistor in 1947. This demonstration paved the way for the development of discrete and integrated semiconductor devices and circuits that has helped to build a modern society where semiconductors are ubiquitous components of everyday life. A key property that determines the semiconductor electrical and optical properties is the bandgap. Beyond graphene, recently discovered two dimensional (2D) materials possess semiconducting bandgaps ranging from the terahertz and mid infrared in bilayer graphene and black phosphorus, visible in transition metal dichalcogenides, to the ultraviolet in hexagonal boron nitride. In particular, these 2D materials were demonstrated to exhibit highly tunable bandgaps, achieved via the control of layers number, heterostructuring, strain engineering, chemical doping, alloying, intercalation, substrate engineering, as well as an external electric field. We provide a review of the basic physical principles of these various techniques on the engineering of quasi particle and optical bandgaps, their bandgap tunability, potentials and limitations in practical realization in future 2D device technologies.
author_names: Andrey Chaves

Javad G Azadani

Hussain Alsalman

D R da Costa

Riccardo Frisenda

Seunghyun Song

Y D Kim

Daowei He

Jiadong Zhou

Andres Castellanos-Gomez

Francois M Peeters

Zheng Liu

Christopher L Hinkle

Sang-Hyun Oh

Peide D Ye

Steven J Koester

Young Hee Lee

Phaedon Avouris

Xinran Wang

Tony Low
title: Bandgap engineering of two dimensional semiconductor materials
venue: npj 2D Materials and Applications
year: 2020

abstract: Atomically thin two dimensional semiconducting transition metal dichalcogenides (TMDs) can withstand large levels of strain before their irreversible damage occurs. This unique property offers a promising route for control of the optical and electronic properties of TMDs, for instance by depositing them on nano structured surfaces, where position dependent strain can be produced on the nano scale. Here, we demonstrate strain induced modifications of the optical properties of mono and bilayer TMD WSe$_2 placed on photonic nano antennas made from gallium phosphide (GaP) Photoluminescence (PL) from the strained areas of the TMD layer is enhanced owing to the efficient coupling with the confined optical mode of the nano antenna. Thus, by following the shift of the PL peak, we deduce the changes in the strain in WSe$_2$ deposited on the nano antennas of different radii. In agreement with the presented theory, strain up to \approx 1.4 is observed for WSe$_2$ monolayers. We also estimate that >3\ strain is achieved in bilayers, accompanied with the emergence of a direct bandgap in this normally indirect bandgap semiconductor. At cryogenic temperatures, we find evidence of the exciton confinement in the most strained nano scale parts of the WSe$_2$ layers, as also predicted by our theoretical model. Our results, of direct relevance for both dielectric and plasmonic nano antennas, show that strain in atomically thin semiconductors can be used as an additional parameter for engineering light matter interaction in nano photonic devices.
author_names: Luca Sortino

Matthew Brooks

Panaiot G Zotev

Armando Genco

Javier Cambiasso

Sandro Mignuzzi

Stefan A Maier

Guido Burkard

Riccardo Sapienza

Alexander I Tartakovskii
title: Dielectric Nanoantennas for Strain Engineering in Atomically Thin Two Dimensional Semiconductors
year: 2020

abstract: Multiple quantum wells based on 2D semiconductors are realized by monolithic bandgap engineering and van der Waals stacking. Quantum wells (QWs) enabling effective exciton confinement and strong light matter interaction, form an essential building block for quantum optoelectronics. For two dimensional (2D) semiconductors, however, constructing the QWs is still challenging because suitable materials and fabrication techniques are lacking for bandgap engineering and indirect bandgap transitions occur at the multilayer. Here, we demonstrate an unexplored approach to fabricate atomic layer confined multiple QWs (MQWs) via monolithic bandgap engineering of transition metal dichalcogenides and van der Waals stacking. The WOX/WSe2 hetero bilayer formed by monolithic oxidation of the WSe2 bilayer exhibited the type I band alignment, facilitating as a building block for MQWs. A superlinear enhancement of photoluminescence with increasing the number of QWs was achieved. Furthermore, quantum confined radiative recombination in MQWs was verified by a large exciton binding energy of 193 meV and a short exciton lifetime of 170 ps. This work paves the way toward monolithic integration of band engineered heterostructures for 2D quantum optoelectronics.
author_names: Yoon Seok Kim

Sojung Kang

Jae-Pil So

Jong Chan Kim

Kangwon Kim

Seunghoon Yang

Ye Seul Jung

Yongjun Shin

Seong Won Lee

Donghun Lee

Jin-Woo Park

Hyeonsik Cheong

Hu Young Jeong

Hong-Gyu Park

Gwan-Hyoung Lee

Chul-Ho Lee
title: Atomic layer confined multiple quantum wells enabled by monolithic bandgap engineering of transition metal dichalcogenides
venue: Science Advances
year: 2021

abstract: Band engineering of two dimensional transition metal dichalcogenides (2D TMDCs) is of great significance with regard to both fundamental exploration and practical application. Here we report on a study of the band evolution of monolayer and bilayer TMDCs (WS2, WSe2, and MoS2) under vertical electric fields. Our results show that the electric field has a negligible influence on the bandgaps of monolayer TMDCs. For bilayer TMDCs, our results show that their intralayer direct bandgaps are also immune to the electric field. However, the indirect bandgaps of bilayer TMDCs can be effectively tuned by a vertical electric field. Interestingly, we find that the field tunability of the bandgap in bilayer WSe2 is much larger than those in bilayer WS2 and MoS2.Band engineering of two dimensional transition metal dichalcogenides (2D TMDCs) is of great significance with regard to both fundamental exploration and practical application. Here we report on a study of the band evolution of monolayer and bilayer TMDCs (WS2, WSe2, and MoS2) under vertical electric fields. Our results show that the electric field has a negligible influence on the bandgaps of monolayer TMDCs. For bilayer TMDCs, our results show that their intralayer direct bandgaps are also immune to the electric field. However, the indirect bandgaps of bilayer TMDCs can be effectively tuned by a vertical electric field. Interestingly, we find that the field tunability of the bandgap in bilayer WSe2 is much larger than those in bilayer WS2 and MoS2.
author_names: Peng Chen

Cai Cheng

Cheng Shen

Jinshan Zhang

Shuang Wu

Xiaobo Lu

Shuopei Wang

Luojun Du

Kenji Watanabe

Takashi Taniguchi

Jiatao Sun

Rong Yang

Dongxia Shi

Kaihui Liu

Sheng Meng

Guangyu Zhang
title: Band evolution of two dimensional transition metal dichalcogenides under electric fields
venue: Applied Physics Letters
year: 2019

abstract: Abstract In this work, the structural, electronic and optical properties of monolayer and bilayer of boron doped C3N are investigated by means of density functional theory based first principles calculations. Our results show that with increasing the B dopant concentration from 3.1% to 12.5% in the hexagonal pattern, an indirect to direct band gap (0.8 eV) transition occurs. Furthermore, we study the effect of electric field and strain on the B doped C3N bilayer (B C3N@2L) It is shown that by increasing E field strength from 0.1 to 0.6V/A, the band gap displays almost a linear decreasing trend, while for the 0.6V/A, we find dual narrow band gap with of 50 meV (in parallel E field) and 0.4 eV (in antiparallel E field) Our results reveal that in plane and out of plane strains can modulate the band gap and band edge positions of the B C3N@2L. Overall, we predict that B C3N@2L is a new platform for the study of novel physical properties in layered two dimensional materials (2DM) which may provide new opportunities to realize high speed low dissipation devices.
author_names: Asadollah Bafekry

Mehmet Yagmurcukardes

Masoud Shahrokhi

Mitra Ghergherehchi
title: Electro optical properties of monolayer and bilayer boron doped C3N: Tunable electronic structure via strain engineering and electric field
year: 2020

abstract: Using first principles calculations we systematically investigate the atomic, electronic and magnetic properties of novel two dimensional materials (2DM) with a stoichiometry C$_{3}$N which has recently been synthesized. We investigate how the number of layers affect the electronic properties by considering monolayer, bilayer and trilayer structures, with different stacking of the layers. We find that a transition from semiconducting to metallic character occurs which could offer potential applications in future nanoelectronic devices. We also study the affect of width of C$_{3}$N nanoribbons, as well as the radius and length of C$_{3}$N nanotubes, on the atomic, electronic and magnetic properties. Our results show that these properties can be modified depending on these dimensions, and depend markedly on the nature of the edge states. Functionalization of the nanostructures by the adsorption of H adatoms is found induce metallic, half metallic, semiconducting and ferromagnetic behavior, which offers an approach to tailor the properties, as can the application of strain. Our calculations give insight into this new family of C$_{3}$N nanostructures, which reveal unusual electronic and magnetic properties, and may have great potential in applications such as sensors, electronics and optoelectronic at the nanoscale.
author_names: Asadollah Bafekry

Catherine Stampfl

S Farjami Shayesteh
title: A first principles study of C3N nanostructures: Control and engineering of the electronic and magnetic properties of nanosheets, tubes and ribbons.
venue: Chemphyschem a European journal of chemical physics and physical chemistry
year: 2019

abstract: Abstract In this contribution, using DFT calculations, we take systematic insights into the modified structural and electronic properties of two dimensional (2D) blue phosphorus (blueP)/graphene like (g C3N) heterostructure via an external vertical strain. First, four types of representative stacking configurations are considered, i.e. I, II, III and IV pattern, respectively. The calculated results indicate that the III configuration behaves more energetically, structurally and dynamic stable, under which it is chosen for the following calculations. The lattice constants of the individual blueP and g C3N monolayers, along with their calculated band gaps, are consistent with the previous reported works, supporting the reliability of our theoretical models and computational details. Besides, the relatively large difference in the work function (WF) between the isolated blueP and C3N monolayers illustrates a charge transfer from g C3N to blueP layer, in good accordance to the analysis of charge density difference and Mulliken atomic population of 0.16 e. A built in electric field (Eint) has been formed due to the charge transfer at the interface region, which can efficiently hinder the recombination of photongenerated electron hole pairs, suggesting its significant application prospect in novel optoelectronic devices. A type II band alignment is presented for the blueP/g C3N heterostructure, demonstrating it great significance for the application in photoelectronic materials. Furthermore, tunable interlayer distances from 2.2 to 5.0 A are employed to obtain modulated electronic properties for the blueP/g C3N heterostructure. Interestingly, there occurs a semiconductor to metal transition when D larger than 4.6 A, indicating its promising application in the field of electronics and nano electronics. Moreover, tailored work functions can also be acquired by changing the interlayer distance. These findings together predict significant potential for the blueP/g C3N heterostructure with tunable interlayer distances applied as next generation nanoelectronic and optoelectronic devices, along with a photocatalyst.
author_names: Xusheng Gao

Yanqing Shen

Yanyan Ma

Shengyao Wu

Zhongxiang Zhou
title: First principles insights into efficient band gap engineering of the blue phosphorus/g C3N bilayer heterostructure via an external vertical strain
venue: Applied Surface Science
year: 2019

abstract: In this paper, we report a comprehensive modeling and simulation study of constructing hybrid layered materials by alternately stacking MoS2 and WSe2 monolayers. Such hybrid MoS2/WSe2 hetero multilayers exhibited direct bandgap semiconductor characteristics with bandgap energy (E g) in a range of 0.45 0.55 eV at room temperature, very attractive for optoelectronics (wavelength range 2.5 2.75 mm) based on thicker two dimensional (2D) materials. It was also found that the interlayer distance has a significant impact on the electronic properties of the hetero multilayers, for example a five orders of magnitude change in the conductance was observed. Three material phases, direct bandgap semiconductor, indirect bandgap semiconductor, and metal were observed in MoS2/WSe2 hetero multilayers, as the interlayer distance decreased from its relaxed (i.e. equilibrium) value of about 6.73 A down to 5.50 A, representing a vertical pressure of about 0.8 GPa for the bilayer and 1.5 GPa for the trilayer. Such new hybrid layered materials are very interesting for future nanoelectronic pressure sensor and nanophotonic applications. This study describes a new approach to explore and engineer the construction and application of tunable 2D semiconductors.
author_names: Kunming Gu

Sheng Yu

Kwesi Eshun

Haiwen Yuan

Huixian Ye

Jiao-ning Tang

Dimitris E Ioannou

Changshi Xiao

Hui Wang

Qiliang Li
title: Two dimensional hybrid layered materials: strain engineering on the band structure of MoS2/WSe2 hetero multilayers.
venue: Nanotechnology
year: 2017

abstract: Two Dimensional (2D) materials such as graphene, Transition Metal Dichalcogenides (TMDs) and Metal Monochalcogenides (MMs) are the next generation of smart devices because of their outstanding novel properties. Monolayer (one molecule thick. of famous TMDs such as MoS2, MoSe2, WS2 and WSe2 exhibit phenomenal physical properties including but not limited to low energy direct bandgap and large piezoelectric responses. These have made them potential candidates for cutting edge electronic and mechanical devices such as novel transistors and PN junctions, on chip energy storage and piezoelectric devices which could be applied in smart sensors and actuators technologies. Additionally, reversible structural phase transition in these materials from semiconducting phase (1H) to metallic phase (1T' as a function of strain, provide compelling physics which facilitates new era of sophisticated flexoelectric devices, novel switches and a giant leap in new regime of transistors. One iconic characteristics of monolayer 2D materials is their incredible stretchability which allows them to be subjected to several percent strains before yielding. In this thesis I provide facile techniques based on polymer encapsulation to apply several percent (6.5% controllable, non destructive and reproducible strains. This is the highest reproducible strain reported so far. Then I show our experimental techniques and object detection algorithm to verify the amount of strain. These followed up by device fabrication techniques as well as in depth polarized and unpolarized Raman spectroscopy. Then, I show interesting physics of monolayer and bilayer TMDs under strain and how their photoluminescence behaviors change under tensile and compressive strains. Monolayers of TMDs and MMs exhibit 1 10 larger piezoelectric coefficients comparing to bulk piezo materials. These surprising characteristics together with being able to apply large range strains, opens a new avenue of piezoelectricity with enormous magnitudes higher than those commercially available. Further on 2D materials, I show our transport experiments on doped and pristine graphene micro devices and unveil the discoveries of magneto conductance behaviors. To complete, we present our computerized techniques and experimental platforms to make these 2D materials.
author_names: Abdollah Motmaen Dadgar
title: Strain Engineering, Quantum Transport and Synthesis of Atomically thin Two dimensional Materials
year: 2017

abstract: The application of strain to semiconductors allows for controlled modification of their band structure. This principle is employed for the manufacturing of devices ranging from high performance transistors to solid state lasers. Traditionally, strain is typically achieved via growth on lattice mismatched substrates. For two dimensional (2D) semiconductors, this is not feasible as they typically do not interact epitaxially with the substrate. Here, we demonstrate controlled strain engineering of 2D semiconductors during synthesis by utilizing the thermal coefficient of expansion mismatch between the substrate and semiconductor. Using WSe2 as a model system, we demonstrate stable built in strains ranging from 1% tensile to 0.2% compressive on substrates with different thermal coefficient of expansion. Consequently, we observe a dramatic modulation of the band structure, manifested by a strain driven indirect to direct bandgap transition and brightening of the dark exciton in bilayer and monolayer WSe2, respectively. The growth method developed here should enable flexibility in design of more sophisticated devices based on 2D materials.Strain engineering is an essential tool for modifying local electronic properties in silicon based electronics. Here, Ahn et al. demonstrate control of biaxial strain in two dimensional materials based on the growth substrate, enabling more complex low dimensional electronics.
author_names: Geun Ho Ahn

Matin Amani

Haider Imad Rasool

Der-Hsien Lien

James P Mastandrea

Joel W Ager Iii

Madan Dubey

Daryl C Chrzan

Andrew M Minor

Ali Javey
title: Strain engineered growth of two dimensional materials
venue: Nature Communications
year: 2017