Modulating high order susceptibility in monolayer MoS2 using doping for integrated quantum photonics

Photon-pair generation through nonlinear optical processes such as spontaneous parametric down-conversion (SPDC) and four-wave mixing (FWM) is foundational to quantum photonic technologies. Conventional integrated platforms, such as AlGaAs waveguides, have demonstrated high coincidence-to-accidental ratios under continuous-wave (CW) excitation, yet these systems often rely on long interaction lengths and stringent phase-matching conditions to achieve efficient photon generation. In this work, we propose a materials-centric approach for enabling photon-count tunability in quantum photonic systems through the intrinsic nonlinear optical response of monolayer MoS2. Using first-principles calculations based on density functional theory (DFT), we compute the second-order susceptibilities χ(2) of pristine and substitutionally doped monolayer MoS2. Dopants such as Ta and Nb are introduced to modulate the electronic band structure and suppress nonlinear optical response near resonant transitions, particularly within the telecom and visible spectral ranges. Ta and Nb dopants lower χ(2) values by 33% and 36%, respectively, in the 0.8-1.5 eV range, with decreasing the susceptibility values to 500 pm/V. The calculated values scale as Eg-4 with the increased band gaps (1.86→1.95eV for Ta), while maintaining the direct-gap character crucial for device integration. This computational study establishes specific design rules: 16.6% doping concentration optimizes the trade-off between χ(2) reduction and structural stability, while Ta outperforms Nb due to stronger 5d-4d orbital hybridization that amplifies velocity matrix elements near telecom bands.