Bandgap engineering of two-dimensional semiconductor materials

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.

Uniaxial strain-induced phase transition in the 2D topological semimetal IrTe2

“…sing external stimuli to manipulate the diverse phenomena observed in quantum materials may allow for tunable control over technologically relevant material properties. Within this context uniaxial strain has recently emerged as a powerful approach to influence the properties of solids [1][2][3][4][5][6] and offers a path to tailor both physical properties and device functionalities, particularly in the 2D transition metal dichalcogides (TMDs) [7][8][9][10] . While efforts to control phase transition behavior with strain have focused predominantly on oxide materials, there also exist many opportunities within the 2D semimetals, which routinely host multiple nearly degenerate structural, electronic, and topological phases 11 , thereby making them sensitive to external perturbation.…”

Tunable Optical Properties of 2D Materials and Their Applications

“…[ 144 ] The strain provided the possibility to reversibly and locally manipulate exciton motion for information processing and energy conversion applications. Moreover, strain engineering can also apply to lateral heterojunctions of dissimilar 2D materials, [ 138 ] enabling broad tuning of optical and electronic properties in superlattices. [ 145 ]…”

“…Strain engineering has been proven to allow more characteristics tuning and delicate manipulations for various devices such as optical modulators [135] and sensors, [122,136,137] which is realized through tuning the bandgap energy in semiconductors by the applications of external strain. [138][139][140][141] For instance, experiments on bandgap changes in four different monolayer TMDCs via strain engineering have been demonstrated by Frisenda et al [135] With the large thermal expansion in a polymer substrate, a controllable uniform biaxial tensile strain on the single-layer TMDCs flakes can be achieved, resulting in a redshift of the bandgap (largest in WS 2 and lowest in MoSe 2 ). Moreover, another team further showed that the uniaxial strain can reversibly change the bandgap of a single-layer MoSe 2 by −27 ± 2 meV % −1 of strain.…”

“…[140] Beyond the aforementioned homogeneous strain, different local straining approaches [141][142][143] have also been induced in 2D semiconductors to modulate the bandgap to improve device performances. [138] Recently, Moon et al demonstrated a local strain center in a suspended monolayer WSe 2 to modulate the bandgap, leading to the exciton funneling effect. [144] The strain provided the possibility to reversibly and locally manipulate exciton motion for information processing and energy conversion applications.…”

Coproduction of hydrogen and lactic acid from glucose photocatalysis on band-engineered Zn1-xCdxS homojunction

“…Alternatively, a homojunction constructed by a twinning superlattice (TSL) in nanocrystals stands out in terms of its efficient charge separation for photocatalyst design with the II-VI and III-V group semiconductors ( Algra, et al., 2008 ; Liu, et al., 2013 ; Jin, et al., 2020 ). Considering the redox potential regulation, bandgap engineering should be also combined with homojunction to improve the product selectivity from glucose photocatalysis ( Chaves, et al., 2020 ; Ning, et al., 2017 ). To realize these concepts in rational photocatalyst design, solid solution, an alloy phase in which solute atoms are dissolved in the solvent lattice while still maintaining the solvent type, shows significant advantages compared with other approaches like quantum size effect and doping in terms of preparation procedure and uniformity ( Holmes, et al., 2012 ; Asahi, et al., 2014 ; Choi, et al., 1994 ).…”