Influence of defects and doping on phonon transport properties of monolayer MoSe₂

The doping of monolayer MoSe₂ by tungsten (W) can suppress the Se vacancy concentration, but how doping and resulting change in defect concentration can tune its thermal properties is not understood yet. We use first-principles density functional theory (DFT) along with the phonon Boltzmann transport equation (BTE) to study the phonon transport properties of pristine MoSe₂ and W doped MoSe₂ with and without the presence of Se vacancies. We found that for samples without Se vacancy, the W doping could enhance the thermal transport of monolayer MoSe₂ due to reduced three-phonon scattering phase space. For example, we observed that the 16.7% W doping increases the thermal conductivity of the monolayer MoSe₂ with 2% Se vacancy by 80% if all vacancies can be suppressed by W-doping. However, the W doping in the defective MoSe₂ amplifies the influence of the phonon scattering caused by the Se vacancies, which results in a further decrease in thermal conductivity of monolayer MoSe₂ with defects. This is found to be related with higher phonon density of states of Mo_0.83W_0.17Se₂ and larger mass difference between W and Se atoms compared to Mo and Se atoms. This study deciphers the effect of defects and doping on the thermal conductivity of monolayer MoSe₂, which helps us understand the mechanism of defect-induced phonon transport, and provides insights into enhancing the heat dissipation in MoSe₂-based electronic devices.