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 via 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 L = 9 nm. These results underscore the potential of MoXYCl monolayers for optoelectronic and photodetector applications.