Chemical trends of deep levels in van der Waals semiconductors

Abstract

Properties of semiconductors are largely defined by crystal imperfections including native defects. Van der Waals (vdW) semiconductors, a newly emerged class of materials, are no exception: defects exist even in the purest materials and strongly affect their electrical, optical, magnetic, catalytic and sensing properties. However, unlike conventional semiconductors where energy levels of defects are well documented, they are experimentally unknown in even the best studied vdW semiconductors, impeding the understanding and utilization of these materials. Here, we directly evaluate deep levels and their chemical trends in the bandgap of MoS2, WS2 and their alloys by transient spectroscopic study. One of the deep levels is found to follow the conduction band minimum of each host, attributed to the native sulfur vacancy. A switchable, DX center - like deep level has also been identified, whose energy lines up instead on a fixed level across different hosts, explaining a persistent photoconductivity above 400 K.

Thin film transition metal dichalcogenide photoelectrodes for solar hydrogen evolution: a review

“…15. First, an intrinsic reason, connected with the material properties such as the weak vdW bonding, is the bad adhesion to the substrate, high intrinsic defect densities due to chalcogen vacancies, 153 strong electrical and mechanical anisotropy, and easy oxidation due to weaker bonding of chalcogen atoms (S, Se, and Te). Second, an extrinsic reason is connected with research and development efforts in the past 5 decades, which were far below (orders of magnitude with respect to many years) the efforts, which were devoted to the research and development of commercial semiconductors such as GaN, InP, GaAs, and Si and their derivatives.…”

Ultralow Power Optical Synapses Based on MoS2 Layers by Indium‐Induced Surface Charge Doping for Biomimetic Eyes

“…Sulfur vacancies of MoS 2 has been reported as the deep-level defects, which result in the formation of PPC effects in the MoS 2 device. [36,37] When the visible light stimulates the MoS 2 device, photogenerated electron-hole pairs are produced, whereas the interlayers and defects of multilayer MoS 2 can restrict the rapid recombination between the electrons and holes. Therefore, the channel currents in the MoS 2 device will not immediately disappear after the light is switched off.…”

p-/n-Type modulation of 2D transition metal dichalcogenides for electronic and optoelectronic devices

“…It is well known that the intrinsic lattice structure of a material is not perfect. Indeed, different kinds of crystal defects are unavoidably or intentionally generated, such as vacancies, interstitials, and antisites, that would severely disturb the periodic potential field of the host lattice, generate defect energy levels and even provoke phase transitions [60][61][62]. Some defects with relatively shallow energy levels would lead to the change of carrier distribution and eventually regulate conduction properties [63][64][65].…”