Abstract
In this work, structure, optical, and thermoelectric properties of layered ZrS2−xSex single crystals with selenium composition of x = 0, 1, and 2 were examined. Single crystals of zirconium dichalcogenides layer compounds were grown by chemical vapor transport method using I2 as the transport agent. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) results indicated that ZrS2−xSex (x = 0, 1, and 2) were crystalized in hexagonal CdI2 structure with one-layer trigonal (1T) stacking type. X-ray photoelectron and energy dispersive X-ray measurements revealed oxidation sensitive behavior of the chalcogenides series. Transmittance and optical absorption showed an indirect optical gap of about 1.78 eV, 1.32 eV, and 1.12 eV for the ZrS2−xSex with x = 0, 1, and 2, respectively. From the result of thermoelectric experiment, ZrSe2 owns the highest figure-of merit (ZT) of ~0.085 among the surface-oxidized ZrS2−xSex series layer crystals at 300 K. The ZT values of the ZrS2−xSex (x = 0, 1, and 2) series also reveal increase with the increase of Se content owing to the increase of carrier concentration and mobility in the highly Se-incorporated zirconium dichalcogenides with surface states.
Highlights
= S, Se) [1,2,3,4,5] and III-VI layer compounds as NX (N = Ga, In and X = S, Se) [6,7,8] have recently received considerable attentions on their excellent optical and electrical properties available for application in electronics and optoelectronics devices [9] because their specific characteristics of flexible, large-area, and ultra-thin, etc
The lattice constant a will be expanded when more Se atoms are incorporated into the ZrS2−x Sex (x = 0, 1, and 2) series crystals
The lattice constant c measured from X-ray diffraction (XRD) can be determined to be 5.818 Å for ZrS2, 5.980 Å for ZrSSe, and 6.101 Å for ZrSe2, respectively
Summary
= S, Se) [1,2,3,4,5] and III-VI layer compounds as NX (N = Ga, In and X = S, Se) [6,7,8] have recently received considerable attentions on their excellent optical and electrical properties available for application in electronics and optoelectronics devices [9] because their specific characteristics of flexible, large-area, and ultra-thin, etc These materials have a proper band gap of 1~2.5 eV (in near infrared to visible region) [10,11] that suitable for solar-energy applications. Despite their TMDC counterparts of MoS2 series undergoing an indirect-to-direct band gap transition in the monolayer form [18], the ZrX2 series TMDCs may remain in indirect band gap in all thicknesses [19]
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