Mobility-Fluctuation-Controlled Linear Positive Magnetoresistance in 2D Semiconductor Bi₂O₂Se Nanoplates

Linear magnetoresistance is generally observed in polycrystalline zero-gap semimetals and polycrystalline Dirac semimetals with ultrahigh carrier mobility. We report the observation of positive and linear magnetoresistance in a single-crystalline semiconductor Bi₂O₂Se grown by chemical vapor deposition. Both Se-poor and Se-rich Bi₂O₂Se single-crystalline nanoplates display a linear magnetoresistance at high fields. The Se-poor Bi₂O₂Se exhibits a typical 2D conduction feature with a small effective mass of 0.032m₀. The average transport Hall mobility, which is lower than 5500 cm² V^-1 s^-1, is significantly reduced, compared with the ultrahigh quantum mobility as high as 16260 cm² V^-1 s^-1. More interestingly, the pronounced Shubnikov-de Hass oscillations can be clearly observed from the very large and nearly linear magnetoresistance (>500% at 14 T and 2 K) in Se-poor Bi₂O₂Se. A close analysis of the results reveals that the large and linear magnetoresistance observed can be ascribed to the spatial mobility fluctuation, which is strongly supported by Fermi energy inhomogeneity in the nanoplate samples detected using an electrostatic force microscopy images and multiple frequencies in a Shubnikov-de Hass oscillation. On the contrary, the Se-rich Bi₂O₂Se exhibits a transport mobility (<300 cm² V^-1 s^-1) much smaller than that observed in Se-poor samples and shows a much smaller linear magnetoresistance ratio (less than 150% at 14 T and 2 K). More strikingly, no Shubnikov-de Hass oscillations can be observed. Therefore, the linear magnetoresistance in Se-rich Bi₂O₂Se is governed by the average mobility rather than the mobility fluctuation.