Layer-dependent optical and dielectric properties of centimeter-scale PdSe2 films grown by chemical vapor deposition

Abstract

Palladium diselenide (PdSe2), a new type of two-dimensional noble metal dihalides (NMDCs), has received widespread attention for its excellent electrical and optoelectronic properties. Herein, high-quality continuous centimeter-scale PdSe2 films with layers in the range of 3L–15L were grown using Chemical Vapor Deposition (CVD) method. The absorption spectra and DFT calculations revealed that the bandgap of the PdSe2 films decreased with the increasing number of layers, which is due to the enhancement of orbital hybridization. Spectroscopic ellipsometry (SE) analysis shows that PdSe2 has significant layer-dependent optical and dielectric properties. This is mainly due to the unique strong exciton effect of the thin PdSe2 film in the UV band. In particular, the effect of temperature on the optical properties of PdSe2 films was also observed, and the thermo-optical coefficients of PdSe2 films with the different number of layers were calculated. This study provides fundamental guidance for the fabrication and optimization of PdSe2-based optoelectronic devices.

Stabilized Synthesis of 2D Verbeekite: Monoclinic PdSe2 Crystals with High Mobility and In-Plane Optical and Electrical Anisotropy

“…Even though various synthetic methods for 2D layered orthorhombic PdSe 2 (O-PdSe 2 ) have been demonstrated, including molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), ,− the growth of other polymorphic PdSe 2 phases are rarely reported, particularly through bottom-up techniques. Currently, these polymorphs are formed either through high-pressure phase transition from the orthorhombic phase or by high-pressure/high-temperature growth. , One of the polymorphs is monoclinic-PdSe 2 (M-PdSe 2 ), also called verbeekite, which has been theoretically predicted to possess high carrier mobility and a high-pressure-induced topological band crossing that has application for photovoltaics and quantum materials .…”

Investigations of Optical Functions and Optical Transitions of 2D Semiconductors by Spectroscopic Ellipsometry and DFT

“…Ultra-thin two-dimensional (2D) semiconductors, representatively including the 2D transition metal dichalcogenides (TMDCs) [ 1 ], phosphorene [ 2 ], 2D hybrid perovskites [ 3 ], etc., have attracted extensive scientific attentions during the past two decades. Two-dimensional semiconductors have atomic thicknesses in the vertical direction, and the reduced dimensionality introduces various unique optical and electrical properties different from those in their 3D counterparts, such as the tunable bandgap [ 4 , 5 , 6 , 7 ], giant optical anisotropy [ 8 , 9 ], spintronics [ 10 ], valleytronics [ 11 ], high mobility and on/off ratio [ 2 , 12 ], etc. On the basis of these outstanding characteristics, 2D semiconductors have been widely applied to various optoelectronic devices, such as field-effect transistors [ 13 , 14 ], light-emitting diodes [ 15 ], solar cells [ 16 ], photodetectors [ 17 ], sensors [ 18 ], etc.…”

“…Although some well-known techniques, such as the angle-resolved photoemission spectroscopy (ARPES) [ 37 ], scanning tunneling microscopy and spectroscopy (STM/STS) [ 38 ], and photoluminescence (PL) [ 30 ], can provide some information about optical transitions by probing the band structures, they fail to obtain the optical functions. Optical functions of 2D semiconductors can be experimentally determined by optical spectroscopic techniques, including the conventional absorption/reflectance/transmission (ART) spectroscopy and its derivative techniques [ 39 , 40 , 41 , 42 ], and the spectroscopic ellipsometry (SE) [ 4 , 5 , 6 , 7 , 8 , 9 , 31 , 43 , 44 , 45 ]. Compared with the ART-based methods that need additional physical constraint functions, e.g., the Krames–Kronig relation and Fresnel equations, to extract the complex optical functions [ 39 , 42 ], the SE has been proved to be a powerful, self-consistent and highly sensitive tool to characterize the optical and dielectric properties of nanomaterials [ 31 ].…”

Thermoelectric Efficiency of Two-Dimensional Pentagonal-PdSe2 at High Temperatures and the Role of Strain

“…Pentagonal 2D transition-metal dichalcogenide (TMD) PdSe 2 has been experimentally reported recently. , The quasi-monolayer of PdSe 2 can be exfoliated from its bulk structure. It shows air stability and semiconducting character (energy gap of 1.3 eV) with high electrical conductivity ( i.e.…”