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We present a detailed first principles density functional theory study ofintrinsic and extrinsic point defects in monolayer (ML) WSe2. Among theintrinsic point defects, Se vacancies (Sevac) have the lowest formation energy(disregarding Se adatoms that can be removed with annealing). The defects withthe next smallest formation energies (at least 1 eV larger) are SeW (Sesubstituting W atoms in an antisite defect), Wvac (W vacancies) and 2Sevac (Sedivacancies). All these intrinsic defects have gap states that are notspin-polarized. The presence of a graphite substrate does not change theformation energies of these defects significantly. For the extrinsic pointdefects, we focus on O, O2, H, H2 and C interacting with perfect WSe2 and itsintrinsic point defects. The preferred binding site in perfect WSe2 is theinterstitial site for atomic O, H and C. These interstitial defects have no gapstates. The gap states of the intrinsic defects are modified by interactionwith O, O2, H, H2 and C. In particular, the gap states of Sevac and 2Sevac arecompletely removed by interaction with O and O2. This is consistent with thesignificantly larger stability of O-related defects compared to H- andC-related defects. The preferred binding site for O is Sevac, while that for His SeW. H bonded to SeW results in spin-polarized gap states, which may beuseful in defect engineering for spintronics applications. The chargetransition levels and ionization energies of these defects are also computed. Hin the interstitial site is an effective donor, while all the other defects aredeep donors or acceptors in isolated WSe2 ML.

First Principles Study of Intrinsic and Extrinsic Point Defects in Monolayer WSe2