Janus MoXYCl (X = S, Se, Te; Y = N, P, As) monolayers: a promising family of 2D materials for high-performance p–i–n photodetectors and spintronic applications

The development of two-dimensional p-i-n homojunctions offers promising potential for future electronic and optoelectronic devices. This study introduces a new Janus monolayer family, MoXYCl (X = S, Se, Te; Y = N, P, As), and investigates their potential as p-i-n photodetectors. Using first-principles calculations, we analyze their electronic, spintronic, transport, and optical properties. Stability is confirmed <i>via</i> phonon spectra, AIMD simulations, and cohesive energy calculations. Most monolayers, except MoSAsCl, MoSeNCl, and MoTeNCl, exhibit direct bandgaps at the K-point, with HSE-calculated values ranging from 1.16 to 2.02 eV (PBE: 0.80-1.66 eV). Spin-orbit coupling induces significant Zeeman and Rashba spin-splittings, with MoSePCl showing the highest Rashba coefficient (1.143 eV Å), highlighting spintronic potential. Mobility calculations reveal a large electron-hole disparity, with MoSeNCl exhibiting the highest hole mobility (6113 cm² V^-1 s^-1) and MoSPCl the highest electron mobility (334.37 cm² V^-1 s^-1). All MoXYCl monolayers exhibit high absorption coefficients (≥10⁵ cm^-1) within the visible spectrum, and those with Y = P or As display substantial absorption in the infrared region. MoXYCl-based p-i-n photodetectors achieve high photocurrent (up to 25 A m^-2) and photo-responsivity (up to 0.8 A W^-1) in visible and near-infrared regions. Increasing the channel length enhances photocurrent density and photo-responsivity, reaching 18.9 A m^-2 and 1 A W^-1 (33.3 A m^-2 and 0.7 A W^-1) at 1.16 eV (3 eV) photon energy for <i>L</i> = 9 nm. These results underscore the potential of MoXYCl monolayers for optoelectronic and photodetector applications.