Phase Controlled Growth of Cd₃As₂ Nanowires and Their Negative Photoconductivity

The bottom-up synthesis process often allows the growth of metastable phase nanowires instead of the thermodynamically stable phase. Herein, we synthesized Cd₃As₂ nanowires with a controlled three-dimensional Dirac semimetal phase using a chemical vapor transport method. Three different phases such as the body centered tetragonal (bct), and two metastable primitive tetragonal (<i>P</i>4₂/<i>nbc</i> and <i>P</i>4₂/<i>nmc</i>) phases were identified. The conversion between three phases (bct → <i>P</i>4₂/<i>nbc</i> → <i>P</i>4₂/<i>nmc</i>) was achieved by increasing the growth temperature. The growth direction is [110] for bct and <i>P</i>4₂/<i>nbc</i> and [100] for <i>P</i>4₂/<i>nmc</i>, corresponding to the same crystallographic axis. Field effect transistors and photodetector devices showed the nearly same electrical and photoelectrical properties for three phases. Differential conductance measurement confirms excellent electron mobility (2 × 10⁴ cm²/(V s) at 10 K). Negative photoconductance was first observed, and the photoresponsivity reached 3 × 10⁴ A/W, which is ascribed to the surface defects acting as trap sites for the photogenerated electrons.