Electrical scattering mechanism evolution in un-doped and halogen-doped Bi₂O₂Se single crystals

Recently the layered oxide semiconductor Bi₂O₂Se was hotly explored for its ultrahigh mobility and ultrafast photo-response whose physical origins need to be further explored or elucidated. Here, we have grown halogen (Cl, Br, I) doped and un-doped Bi₂O₂Se single crystals by a melt-solidification method. Comparative electrical transport characterizations and detailed data-analysis substantiate that the electron-electron scattering is the major source of resistivity in un-doped Bi₂O₂Se crystals; however, in halogen-doped Bi₂O₂Se crystals, electron-electron scattering is only effective at low temperature (<60 K) and subsequently electron-phonon-interaction scattering is dominated to resistivity. Hall measurement and analysis show that electron concentration of halogen-doped Bi₂O₂Se (∼10²⁰cm^-3) is one-order higher than un-doped one (∼10¹⁹cm^-3), but the carrier mobility of halogen-doped Bi₂O₂Se at 2 K (∼10²cm²V^-1s^-1) is reduced by more than two orders than un-doped ones (∼10⁴cm²V^-1s^-1). Three kinds of relaxation time (due to the impurity scattering, electron-electron scattering and electron-phonon scattering), calculated by linear-response theory and electron-/phonon-dispersion, are in agreement with experimental results quantitatively. The scattering mechanism evolution from sole electron-electron scattering (un-doped Bi₂O₂Se) to electron-phonon scattering (doped Bi₂O₂Se) at high temperature (>60 K) is attributed to the net effect of decreased screened Coulomb-interaction and increased Fermi energy in halogen-doped Bi₂O₂Se. This work may provide clues of physical origins of superior electrical/photoelectrical properties of Bi₂O₂Se.