Optical and electrical properties of two-dimensional palladium diselenide

Two-dimensional (2D) noble-metal dichalcogenides exhibit exceptionally strong thickness-dependent bandgaps, which can be leveraged in a wide variety of device applications. A detailed study of their optical (e.g., optical bandgaps) and electrical properties (e.g., mobilities) is important in determining potential future applications of these materials. In this work, we perform detailed optical and electrical characterization of 2D PdSe₂ nanoflakes mechanically exfoliated from a single-crystalline source. Layer-dependent bandgap analysis from optical absorption results indicates that this material is an indirect semiconductor with bandgaps of approximately 1.37 and 0.50 eV for the monolayer and bulk, respectively. Spectral photoresponse measurements further confirm these bandgap values. Moreover, temperature-dependent electrical measurements of a 6.8-nm-thick PdSe₂ flake-based transistor show effective electron mobilities of 130 and 520 cm² V⁻¹ s⁻¹ at 300 K and 77 K, respectively. Finally, we demonstrate that PdSe₂ can be utilized for short-wave infrared photodetectors. A room-temperature specific detectivity (D^*) of 1.8 × 10¹⁰ cm Hz^1/2 W⁻¹ at 1 μm with a band edge at 1.94 μm is achieved on a 6.8-nm-thick PdSe₂ flake-based photodetector.