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

Abstract

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.

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

“…In this regard, the VB1−VB5 states around the VBM regions can be identified as 2D vdW QWSs, whose evolution is facilitated by the interlayer coupling of 2D h-GaTe layers through the hybridization of Te p z orbitals. Considering the tunable electronic properties, this 2D vdW quantum well (i.e., layered h-GaTe) should serve as an intriguing platform for exploring diverse 2D QWS-related physics, e.g., intersubband transitions, 12 2D electron gas, 19,20 and quantum Hall effect. 2,30 As mentioned earlier, MTBs are commonly observed at the merging areas of antiparallel h-GaTe domains (Figure 4a).…”

“…The QWSs were reported to exert significant impacts on the electronic properties of 2D materials, yielding intriguing physical phenomena such as intersubband transitions and resonant tunneling effects that can be harnessed for infrared optoelectronics. In this regard, 2D materials with evident QWSs have been extensively pursued, among which great success was made in a III–VI metal chalcogenide, InSe, ,− which presented 2D electron gas and high carrier mobility at a few-layer level. As a structural analogue to InSe, ultrathin h -GaTe should be an equivalently promising platform for exploring intriguing physical issues.…”