Direct Visualization and Manipulation of Tunable Quantum Well State in Semiconducting Nb₂SiTe₄

Abstract

Quantum well states (QWSs) can form at the surface or interfaces of materials with confinement potential. They have broad applications in electronic and optical devices such as high mobility electron transistor, photodetector and quantum well laser. The properties of the QWSs

Controllable Synthesis of Narrow-Gap van der Waals Semiconductor Nb2GeTe4 with Asymmetric Architecture for Ultrafast Photonics

“…The relative size of the atomic number can be determined qualitatively according to the brightness of the atomic image in the high-angle annular dark-field (HAADF) image. As shown in Figure b, there are obvious chain structures comprising bright atoms parallel to the yellow dotted line on the (001) surface, and the arrangement of Te atoms on the surface forms a fixed position interval, corresponding to the Te atom (represented by the red spheres) arrangement in the crystal plane of (001), which is almost in accordance with the scanning tunneling microscope (STM) characterization of Nb 2 SiTe 4 reported recently . The measured lattice parameters, which are 6.45 and 7.94 Å, can be distinguished by measuring the distance between the tellurium atoms, very consistent with the interplanar crystal spacing of (100) and (010) with a zone axis of [001], respectively.…”

“…Most recently, an important member of the ternary vdW material family, NbA x Te 2 (1/3 ≤ x ≤ 1/2; A = Si or Ge) demonstrated many fascinating physical properties as the amount of Si or Ge that is altered, changing from a topological semimetal ( x = 1/3) to a narrow-gap semiconductor ( x = 1/2). − Among them, Nb 2 ATe 4 (A = Si, Ge) is theoretically predicted to be a stable ferroelastic narrow-gap semiconductor with high mobility and high optical absorbance (∼10 5 cm –1 ) at the region of ultraviolet to infrared, broader than the absorption range of MoS 2 . − Experimentally, Nb 2 SiTe 4 , a homologous telluride, was confirmed to be an air-stable 2D narrow-gap semiconductor with a band gap of 0.39 eV, which is highly desirable for MIR detection, and a field-effect mobility (98 cm 2 V –1 s –1 at ∼300 K) relatively higher than that of the majority of 2D materials . Furthermore, the bulk Nb 2 GeTe 4 crystal displays brilliant high Hall mobility at ∼300 K, 424.37 cm 2 V –1 s –1 , slightly higher than the Hall mobility of a black phosphorus bulk crystal at room temperature (350 cm 2 V –1 s –1 ). − Therefore, these excellent properties render Nb 2 GeTe 4 a reliable saturable absorber candidate for ultrashort pulse generation.…”

Observation of dimension-crossover of a tunable 1D Dirac fermion in topological semimetal NbSixTe2

“…Low dimensional electronic states bear fascinating emergent physics and have attracted great research interests in the past decade. For example, some of the two-dimensional (2D) electronic states under intensive investigation include electronic structure of van der Waals (vdW) materials in the atomic limit [1][2][3][4][5][6][7] , the quantum well states confined on the surface/interfaces of semiconductors 1,8,9 and topological surface states of strong topological insulators [10][11][12][13] . They host profound physics including Ising superconductivity [14][15][16] , charge density wave [17][18][19][20] , spin-momentum locking 21,22 , and magnetism [23][24][25] .…”