Mixed-dimensional Heterojunction by 3D CdS Nanowire Arrays Bridged with 2D WSe2 for Ultrafast Photoelectric Gas Sensor

Heterojunctions are of essential importance for electronic sensors due to their unique properties at the junctions. However, a planar junction made of two-dimensional (2D) materials commonly suffers from slow response and irreversible recovery because of slow physisorption and desorption rates. Herein, we present a unique design of a mixed-dimensional heterojunction built from patterned growth of 3D n-type CdS nanowire arrays and p-type 2D WSe2 nanosheets for photoelectric gas sensor. This heterojunction sensor showed highly selective and reversible response to NO2 and NH3 with detection limits of 60 and 54 ppb, respectively, under UV illumination at room temperature. Notably, the sensor exhibited ultrafast response time of less than 1s to 1 ppm NO2 and NH3, which outperforms most previous reports on NO2 and NH3 detection at room temperature. The outstanding sensing performance are attributed to the tuning of the Schottky barrier at the CdS/WSe2 heterojunction through the gas adsorption/desorption under UV excitation. The hybrid junction structure proposed herein will pave the way to engineer new electronic devices from a broad selection of materials to achieve improved sensing performances at room temperature.