Epitaxial growth of Bi-stabilized <i>β</i>-In2Se3 films for fast visible to near-infrared photodetectors

In this work, we study the molecular beam epitaxial growth of phase-pure In2Se3 films on mica with Bi doping for fast visible to near-infrared photodetectors. Through the Bi doping strategy, phase-pure β-In2−xBixSe3 (0 &amp;lt; x &amp;lt; 0.62) thin films with sole (0 0 1) crystal orientation can be prepared at a relatively low growth temperature of 420 K. The Bi doping concentration is up to around 30 at. % owing to the high similarity of In2Se3 and Bi2Se3 lattice structures. At low doping concentrations (0.2–2 at. %), the β-In2−xBixSe3 films possess improved crystallinity and present good layer-by-layer epitaxial growth. However, higher doping levels (2–31 at. %) significantly degrade the film crystallinity due to the enhanced structure stress and distortion induced by the difference in ionic radii between In and Bi and the segregation of excess dopants. Devices are fabricated consisting of 0.2 at. % Bi doped In2Se3 (In1.996Bi0.004Se3) films on mica with layered semimetal Bi4Se3 contacts. Such devices are sensitive to visible and near-infrared light illumination, exhibiting a fast response with a rise/decay time of 3.7/17.5 ms, decent responsivity and detectivity, and good repeatability and stability. In the visible region, the responsivity and detectivity can be up to 20 mA W−1 and 2.3 × 1010 Jones, respectively.