Ab initio study of carrier mobility in Bi$_2$O$_2$Se

TL;DR

The paper addresses the need for a rigorous, parameter-free understanding of carrier mobility in Bi2O2Se. It develops an ab initio framework that solves the Boltzmann transport equation iteratively, including both electron-phonon coupling and ionized impurity scattering with dynamical quadrupole corrections. The results show high electron mobilities in both in-plane and out-of-plane directions and substantial but anisotropic hole mobility, with LO phonons dominating scattering and Hall mobilities in good agreement with experiments. This work provides a robust theoretical benchmark for Bi2O2Se transport and informs the design of high-performance devices such as planar p-n junctions based on this material.

Abstract

Bi$_2$O$_2$Se is an emerging high-performance layered semiconductor with excellent stability. While experimental studies have explored carrier transport across various doping levels for both $n$-type and $p$-type conduction, a comprehensive theoretical understanding remains incomplete. In this work, we present parameter-free first-principles calculations of the electron and hole mobilities in Bi$_2$O$_2$Se, based on iterative solution of the Boltzmann transport equation that includes electron-phonon scattering and ionized impurity scattering on an equal footing. Intriguingly, we find that Bi$_2$O$_2$Se exhibits high electron mobilities in both the in-plane and out-of-plane directions, whereas the hole mobilities are only significant in the in-plane direction, displaying a unique three-dimensional (3D) electron transport and two-dimensional (2D) hole transport behavior. At 300~K, the calculated intrinsic electron and hole mobilities along the in-plane direction are 447~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$ and 29~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$, respectively, which are primarily affected by Fröhlich electron-phonon interactions. Due to its large static dielectric permittivity, Bi$_2$O$_2$Se exhibits an exceptionally high low-temperature electron mobilities above $1.0\times10^5~\mathrm{cm^2\,V^{-1}\,s^{-1}}$, and its electron mobilities above 50~K is robust against ionized impurity scattering over a wide range of impurity concentrations. By incorporating the Hall effect into our analysis, we predict an in-plane electron Hall mobility of 517~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$ at 300~K, in excellent agreement with experimental data. These results provide valuable insights into the carrier transport mechanisms in Bi$_2$O$_2$Se, and offer predictive benchmarks for future theoretical and experimental investigations.

Figures (6)

• Figure 1: (a) Atomistic structure of Bi2O2Se in a tetragonal conventional unit cell. (b) Electronic band structure of Bi2O2Se, with the conduction band minimum (CBM) and valence band maximum (VBM) labeled. Inset shows the reciprocal space path employed in the band structure. (c) Isosurfaces of the electron wave function at the CBM (gray). (d) Isosurfaces of the hole wave function at the VBM (gray). (e) Evolution of the Fermi surfaces at energies of 0.1, 0.2, and 0.3 eV below the VBM, shown from bird's-eye views and side views of the Brillouin zones. The front- and back-side colors of Fermi surfaces are blue and green, respectively.
• Figure 2: (a) Temperature dependence of the in-plane intrinsic phonon-limited electron mobilities. In-plane mobilities are compared with momentum relaxation-time approximation (MRTA) and self-energy relaxation-time approximation (SERTA). (b) Temperature dependence of the out-of-plane intrinsic phonon-limited electron mobilities. Out-of-plane mobilities are compared with momentum relaxation-time approximation (MRTA) and self-energy relaxation-time approximation (SERTA).
• Figure 3: (a) Temperature dependence of the Fermi level for ionized impurity concentrations ranging from $10^{14}~\mathrm{cm^{-3}}$ to $10^{18}~\mathrm{cm^{-3}}$, with the conduction band minimum set to zero. (b) Temperature dependence of in-plane intrinsic phonon-limited electron mobilities. (c) Temperature dependence of in-plane total electron mobilities, including both phonon and ionized impurity scattering. (d) Temperature dependence of out-of-plane total electron mobilities, including both phonon and ionized impurity scattering. In (b), (c), and (d), ionized impurity concentrations range from $10^{14}~\mathrm{cm^{-3}}$ to $10^{17}~\mathrm{cm^{-3}}$.
• Figure 4: (a) Temperature dependence of the in-plane and out-of-plane hole mobilities when the carrier concentration is $10^{14}~\mathrm{cm^{-3}}$. (b) Schematic diagram illustrating a planar p-n junction of Bi2O2Se.
• Figure 5: (a) Spectral decomposition of the angularly averaged electron scattering rates as a function of phonon energy at 300 K, calculated using a fine $200^3$$\mathbf{k}$- and $\mathbf{q}$-point grid size. (b) Spectral decomposition of the angularly averaged hole scattering rates as a function of phonon energy at 300 K, calculated using a fine $90^3$$\mathbf{k}$- and $\mathbf{q}$-point grid size. In (a) and (b), dashed lines indicate the cumulative integrals of the scattering rates (axes on the right).