Real-space detection and manipulation of two-dimensional quantum well states in few-layer 
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Wang, Yu; Wu, Linlu; Zheng, Wei; Liu, Zijia; Cheng, Peng; Zhang, Yi‐Qi; Feng, Baojie; Zhang, Guangyu; Ji, Wei; Wu, Kehui; Chen, Lan

doi:10.1103/physrevb.105.l081404

Cited by 6 publications

(13 citation statements)

References 68 publications

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“…The d I /d V spectrum of monolayer InSe, shown in Figure c, exhibits a stair-like DOS in the conduction band that rises from 0.61 ± 0.03 V. For comparison, the typical d I /d V spectrum of HOPG taken with the same tip condition is also shown in Figure c. This stair-like feature in the d I /d V spectrum is quite different from the usual peak-like DOS on most 2D materials (e.g., MoS 2 ) but is very similar to the DOS of the 2DEG on noble metal surfaces or surface reconstructions. − …”

Section: Resultsmentioning

confidence: 87%

“…However, real systems often possess finite barriers height and large well widths, resulting in broadening and overlapping of the QWSs bands. Experimentally reported examples of multiple QWSs often show DOS peaks instead of the stair-like function, including QWSs in Pb and MoS 2 films. , Stair-like DOS had been observed only in a few potential wells consisting of surface-vacuum interface, but with typically only one stair. − To the best of our knowledge, an ideal 2DEG system containing multiple QWSs has not been reported thus far. To overcome this problem, another solution to achieve QWSs is periodic square potential wells described as the Kronig–Penney (KP) model. , Such a system has been realized by semiconductor superlattices, but it is challenging to achieve a sharp interfaces, narrow width, and large barrier height simultaneously. , …”

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confidence: 97%

“…However including QWSs in Pb and MoS 2 films. 26,27 Stair-like DOS had been observed only in a few potential wells consisting of surface-vacuum interface, but with typically only one stair. 10−12 To the best of our knowledge, an ideal 2DEG system containing multiple QWSs has not been reported thus far.…”

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confidence: 99%

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Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig–Penney States Observed in Few-Layer InSe

Wang

Gao

et al. 2022

ACS Nano

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A theoretical ideal two-dimensional electron gas (2DEG) was characterized by a flat density of states independent of energy. Compared with conventional two-dimensional free-electron systems in semiconductor heterojunctions and noble metal surfaces, we report here the achievement of ideal 2DEG with multiple quantized states in few-layer InSe films. The multiple quantum well states (QWSs) in few-layer InSe films are found, and the number of QWSs is strictly equal to the number of atomic layers. The multiple stair-like DOS as well as multiple bands with parabolic dispersion both characterize ideal 2DEG features in these QWSs. Density functional theory calculations and numerical simulations based on quasi-bounded square potential wells described as the Kronig–Penney model provide a consistent explanation of 2DEG in the QWSs. Our work demonstrates that 2D van der Waals materials are ideal systems for realizing 2DEG hosted by multiple quantized Kronig–Penney states, and the semiconducting nature of the material provides a better chance for construction of high-performance electronic devices utilizing these states, for example, superlattice devices with negative differential resistance.

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Section: Resultsmentioning

confidence: 87%

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confidence: 97%

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Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig–Penney States Observed in Few-Layer InSe

Wang

Gao

et al. 2022

ACS Nano

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“…The precise control over layer thickness enabled by MBE is not only beneficial to the phase engineering of GaTe, but also likely contributes to band splitting, a phenomenon commonly observed in many 2D vdW semiconductors such as MoS 2 , WSe 2 , and MoTe 2 . Delicate quantum well states (QWSs) emerge due to the band splitting, similar to the case of conventional semiconducting and metal thin films ( e.g ., GaAs, Ag, and Pb films , ).…”

Section: Introductionmentioning

confidence: 99%

Substantial Energy Band Modulation of Semiconducting Hexagonal GaTe Quantum Wells by Layer Thickness and Mirror Twin Boundaries

Quan,

Lu,

et al. 2024

ACS Nano

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Exploring emerging two-dimensional (2D) van der Waals (vdW) semiconducting materials and precisely tuning their electronic properties at the atomic level have long been recognized as crucial issues for developing their high-end electronic and optoelectronic applications. As a III−VI semiconductor, ultrathin layered hexagonal GaTe (h-GaTe) remains unexplored in terms of its intrinsic electronic properties and band engineering strategies. Herein, we report the successful synthesis of ultrathin h-GaTe layers on a selected graphene/SiC(0001) substrate, via molecular beam epitaxy (MBE). The widely tunable quasiparticle band gaps (∼2.60−1.55 eV), as well as the vdW quantum well states (QWSs) that can be strictly counted by the layer numbers, are well characterized by onsite scanning tunneling microscopy/ spectroscopy (STM/STS), and their origins are clearly addressed by density functional theory (DFT) calculations. More intriguingly, distinctive 8|8E and 4| 4P (Ga) mirror twin boundaries (MTBs) are identified in the ultrathin h-GaTe flakes, which can induce decreased band gaps and prominent p-doping effects. This work should deepen our understanding on the electronic tunability of 2D III−VI semiconductors by thickness control and line defect engineering, which may hold promise for fabricating atomic-scale vertical and lateral homojunctions toward ultrascaled electronics and optoelectronics.

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“…The third interesting feature in Figure b is the clear peaks in the valence band side, which are also visible in Figure S12 and Figure S15. In a recent conventional-STM study of few-layer MoS 2 , peaks were detected in the valence band side which were explained as subbands of the quantum-well states in the vertical direction. However, the measured and calculated energy separations between the subbands in that work are much smaller than what we observe here.…”

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confidence: 98%

Measuring Band Modulation of MoS₂ with Ferroelectric Gates

et al. 2023

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Electronic properties of two-dimensional (2D) materials can be significantly tuned by an external electric field. Ferroelectric gates can provide a strong polarization electric field. Here, we report the measurements of the band structure of few-layer MoS 2 modulated by a ferroelectric P(VDF-TrFE) gate with contact-mode scanning tunneling spectroscopy. When P(VDF-TrFE) is fully polarized, an electric field up to ∼0.62 V/nm through the MoS 2 layers is inferred from the measured band edges, which affects the band structure significantly. First, strong band bending in the vertical direction signifies the Franz-Keldysh effect and a large extension of the optical absorption edge. Photons with energy of half the band gap are still absorbed with 20% of the absorption probability of photons at the band gap. Second, the electric field greatly enlarges the energy separations between the quantum-well subbands. Our study intuitively demonstrates the great potential of ferroelectric gates in band structure manipulation of 2D materials.

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Real-space detection and manipulation of two-dimensional quantum well states in few-layer MoS2

Cited by 6 publications

References 68 publications

Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig–Penney States Observed in Few-Layer InSe

Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig–Penney States Observed in Few-Layer InSe

Substantial Energy Band Modulation of Semiconducting Hexagonal GaTe Quantum Wells by Layer Thickness and Mirror Twin Boundaries

Measuring Band Modulation of MoS₂ with Ferroelectric Gates

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Real-space detection and manipulation of two-dimensional quantum well states in few-layer MoS2

Cited by 6 publications

References 68 publications

Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig–Penney States Observed in Few-Layer InSe

Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig–Penney States Observed in Few-Layer InSe

Substantial Energy Band Modulation of Semiconducting Hexagonal GaTe Quantum Wells by Layer Thickness and Mirror Twin Boundaries

Measuring Band Modulation of MoS2 with Ferroelectric Gates

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Measuring Band Modulation of MoS₂ with Ferroelectric Gates