Penta-MX2 (M = Ni, Pd and Pt; X = P and As) monolayers: direct band-gap semiconductors with high carrier mobility

Abstract

Two-dimensional binary MX₂ (M = Ni, Pd and Pt; X = P and As) exhibiting a beautiful pentagonal ring network is discussed through first principles calculations. We predict that MX₂ sheets possess narrow direct band gaps of about 0.3–0.8 eV and ultrahigh mobilities both for holes and electrons. The hole mobility of PdAs₂ is even up to 50 × 10⁴ cm² V⁻¹ s⁻¹ and the electron mobility of PtAs₂ is up to 25 × 10⁴ cm² V⁻¹ s⁻¹. Besides fascinating electronic properties, 2D MX₂ also exhibits optical absorption over the entire visible-light range. Additionally, like graphene and carbon nanotubes, a MX₂ sheet can be rolled into various forms of MX₂ nanotubes as well. Interestingly, NiP₂ nanotubes exhibit rich band gap behaviour which can be adjusted by the roll-up vector. With a desired band gap, high carrier mobility and optical properties, 2D MX₂ sheets promise to be potential candidates for electronic devices.