First-principles study of lateral WSe₂ <i>p-n</i> junction

While the two-dimensional (2D) p-n junctions have been extensively studied for electronic and optoelectronic devices, the semiclassical approaches without considering atomistic details are still insufficient to describe its electronic structures, such as long depletion width and band edge profiles. To overcome such limitations, we combine the multi-space constrained-search density functional theory (MS-DFT) formalism together with the simulation doping method for describing the doped p-n junction under finite-bias conditions. Then, by calculating the lateral WSe₂ p-n junctions, we find that the depletion width calculated within the first-principles approach is several times longer than that of the analytic expressions, which affects the current-voltage characteristics in the 2D p-n junctions. Thanks to the MS-DFT that uniquely allows plotting quasi-Fermi levels (QFLs) profiles within the first-principles calculation, we also extract the QFLs profiles from the lateral WSe₂ p-n junctions under finite-bias conditions. Finally, based on the QFLs profiles and electronic structures, we study the recombination-generation processes of charge carriers inside the depletion layer, including quantum effects.