Phase‐Dependent Band Gap Engineering in Alloys of Metal‐Semiconductor Transition Metal Dichalcogenides. (22nd September 2020)

• Record Type: Journal Article
• Authors: Wang, Shuxi; Cavin, John; Hemmat, Zahra; Kumar, Khagesh; Ruckel, Alexander; Majidi, Leily; Gholivand, Hamed; Dawood, Radwa; Cabana, Jordi; Guisinger, Nathan; Klie, Robert F.; Khalili‐Araghi, Fatemeh; Mishra, Rohan; Salehi‐Khojin, Amin
• Is Part Of: Advanced functional materials. Volume 30:Number 51(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-22
• Subjects: alloy -- bandgap engineering -- charge density wave -- density functional theory -- transition metal dichalcogenides; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.202004912
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract: Bandgap engineering plays a critical role in optimizing the electrical, optical and (photo)‐electrochemical applications of semiconductors. Alloying has been a historically successful way of tuning bandgaps by making solid solutions of two isovalent semiconductors. In this work, a novel form of bandgap engineering involving alloying non‐isovalent cations in a 2D transition metal dichalcogenide (TMDC) is presented. By alloying semiconducting MoSe2 with metallic NbSe2, two structural phases of Mo0.5 Nb0.5 Se2, the 1T and 2H phases, are produced each with emergent electronic structure. At room temperature, it is observed that the 1T and 2H phases are semiconducting and metallic, respectively. For the 1T structure, scanning tunneling microscopy/spectroscopy (STM/STS) is used to measure band gaps in the range of 0.42–0.58 at 77 K. Electron diffraction patterns of the 1T structure obtained at room temperature show the presence of a nearly commensurate charge density wave (NCCDW) phase with periodic lattice distortions that result in an uncommon 4 × 4 supercell, rotated approximately 4° from the lattice. Density‐functional‐theory calculations confirm that local distortions, such as those in a NCCDW, can open up a band gap in 1T ‐Mo0.5 Nb0.5 Se2, but not in the 2H phase. This work expands the boundaries of alloy‐based bandgap engineering by introducing a novel technique that facilitates CDW phases through alloying. Abstract : Two structural phases, 1T and 2H of TMDC alloy Mo0.5 Nb0.5 Se2 are synthesized and characterized by various methods. 2H‐Mo0.5 Nb0.5 Se2 is found to be metallic and 1T‐Mo0.5 Nb0.5 Se2 is semiconducting, with a 0.42–0.58 eV bandgap at 77 K. Electron diffraction patterns and density‐function‐theory calculations reveal that the nearly commensurate charge density wave phase in 1T phase is the reason for the bandgap opening.