Huge permittivity and premature metallicity in Bi2O2Se single crystals

Giant Modulation of the Electron Mobility in Semiconductor Bi2O2Se via Incipient Ferroelectric Phase Transition

“…The conduction band minimum (CBM) of Bi 2 O 2 Se is located at the Γ point of the Brillouin zone . The calculated in-plane and out-of-plane electron effective masses, 0.13 m 0 and 0.40 m 0 ( m 0 is the free-electron mass), respectively, are in good agreement with the corresponding experimental values of 0.14 m 0 , and 0.37 m 0 . , The conduction band of Bi 2 O 2 Se close to the CBM was found to mainly derive from the p z orbitals of Bi and, to a lesser extent, the s orbitals of O. On the other hand, the valence bands close to the band edge have a predominately Se p x /p y character (Figures S1 and S2).…”

“…The value of ϵ 0 in the out-of-plane direction, ϵ 0 ∥ = 117.5, is also significant. Such a large low-frequency relative permittivity, supported by the recent experimentally measured value of 155 by one of the authors, is expected to strongly suppress ionized impurity scattering in Bi 2 O 2 Se, as schematically illustrated in Figure b. Indeed, as shown in Figure c, after including the contributions from both ionized impurity-limited mobility μ I and phonon-limited mobility μ P using Matthiessen’s rule μ Total –1 = μ I –1 + μ P –1 , the calculated total electron mobility μ Total of Bi 2 O 2 Se at 10 K and an impurity concentration of N I = 10 16 cm –3 can reach an exceptionally high value of 46 000 cm 2 V –1 s –1 .…”

“…Given that μ I ≪ μ P is valid over a wide range of temperatures and carrier concentrations in Bi 2 O 2 Se, its electron mobility, when limited by μ I , has significant room for further improvement. (2) Unlike SrTiO 3 , the static dielectric constant of Bi 2 O 2 Se, whose calculated and experimentally measured values are in the range between 150 and 200, without a strong temperature dependence between 2 K and room temperature, can still be significantly increased via biaxial strain before the electron transport reaches the cross-section-limited regime. Indeed, as shown in Figure d, the low-temperature electron mobility of Bi 2 O 2 Se is still in the μ I < μ I c regime below a carrier concentration of 3 × 10 17 cm –3 when its dielectric constant is increased to 2000.…”

Giant modulation of the electron mobility in semiconductor Bi$_2$O$_2$Se via incipient ferroelectric phase transition

“…The value of 0 in the out-of-plane direction, 0,zz = 117.5, is also significant. Such large relative dielectric permittivity, supported by the recent experimental measurements by one of the authors [27], is expected to strongly suppress ionized impurity scattering in Bi 2 O 2 Se, as schematically illustrated in Fig. 3b.…”

Thermoelectric properties of Bi2O2Se single crystals

“…BOS is a layered semiconductor, hosting moderate band gap ( ≈ 0.8 eV) 5 , high electron mobility [6][7][8] and large relative permittivity (ε r ≈ 155) 9 . Most recently, it was considered to be a promising candidate as a next-generation lowpower, high-performance semiconductor.…”