Large bulk photovoltaic effect and second-harmonic generation in few-layer pentagonal semiconductors PdS2and PdSe2
Journal
New Journal of Physics
Journal Volume
23
Journal Issue
9
Date Issued
2021
Author(s)
Gudelli V.K
Abstract
Recently, atomically thin PdSe2 semiconductors with rare pentagonal Se-Pd-Se monolayers were synthesized and were also found to possess superior properties such as ultrahigh air stability, tunable band gap and high carrier mobility, thus offering a new family of two-dimensional (2D) materials for exploration of 2D semiconductor physics and for applications in advanced opto-electronic and nonlinear photonic devices. In this work, we systematically study the nonlinear optical (NLO) responses [namely, bulk photovoltaic effect (BPVE), second-harmonic generation (SHG) and linear electric-optic (LEO) effect] of noncentrosymmetric bilayer (BL) and four-layer PdS2 and PdSe2 by applying the first-principles density functional theory with the generalized gradient approximation plus scissors-correction. First of all, we find that these few-layer PdX 2 (X = S and Se) exhibit prominent BPVE. In particular, the calculated shift current conductivity is in the order of 130 μA V-2, being very high compared to known BPVE materials. Similarly, their injection current susceptibilities are in the order of 100 108 A V-2 s-1, again being large. Secondly, the calculated SHG coefficients (χ (2)) of these materials are also large, being one order higher than that of the best-known few-layer group 6B transition metal dichalcogenides. For example, the maximum magnitude of χ (2) can reach 1.4 103 pm V-1 for BL PdSe2 at 1.9 eV and 1.2 103 pm V-1 at 3.1 eV for BL PdS2. Thirdly we find significant LEO coefficients for these structures in the low photon energy. All these indicate that 2D PdX 2 semiconductors will find promising NLO applications in light signal modulators, frequency converters, electro-optical switches and photovoltaic solar cells. Fourthly, we find that the large BPVE and SHG of the few-layer PdX 2 structures are due to strong intralayer directional covalent bonding and also 2D quantum confinement. Finally, we also discuss the prominent features of these NLO spectra of these materials in terms of their electronic structure and optical dielectric functions. ? 2021 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
Subjects
bulk photovoltaic effect; injection current; nonlinear optics; second-harmonic generation; shift current; two-dimensional; Chemical bonds; Density functional theory; Electronic properties; Energy gap; Harmonic analysis; Harmonic generation; Monolayers; Nonlinear optics; Optical switches; Photonic devices; Photovoltaic effects; Semiconductor devices; Solar cells; Solar power generation; Transition metals; 'current; Bi-layer; Bulk photovoltaic effect; Harmonics generation; Injection currents; Second harmonics; Second-harmonic generation; Shift current; Synthesised; Two-dimensional; Palladium compounds
SDGs
Type
journal article