Migration-Enhanced Metal–Organic Chemical Vapor\nDeposition of Wafer-Scale Fully Coalesced WS₂ and WSe₂ Monolayers

Abstract

Metal–organic\nchemical vapor deposition (MOCVD) is widely\nemployed for the wafer-scale synthesis of transition metal dichalcogenide\n(TMDC) monolayers (MLs). Despite large efforts devoted to understanding\nthe intricate nucleation and lateral growth mechanisms of TMDCs, little\nattention has been paid to the migration of adatoms on the top of\nan ML and its influence on parasitic/premature bilayer (BL) nucleation.\nIn this work, using a commercial multi-wafer MOCVD platform, a novel\ntwo-stage migration-enhanced MOCVD process is introduced to realize\nthe deposition of wafer-scale fully coalesced tungsten disulfide (WS₂) and tungsten diselenide (WSe₂) MLs with only\nsparse BL nucleation in a reasonable deposition time. With the WS₂ ML coverage exceeding 99% on 2 in. sapphire substrates within\n3 h, BL coverage is suppressed to ∼15%. Following the same\nmigration enhancement approach, WSe₂ MLs are synthesized\nin 90 min with <20% BL coverage. The migration of W adatoms on\nthe already formed stable WS₂ (or WSe₂) ML domains\nis promoted by ramping down the delivery of the tungsten precursor.\nFrom the qualitative analysis of the nanomorphology, the migration\nlength of W adatoms is estimated to be ≤100 nm. This approach\ncan be seen as a reliable and solid basis for the development of future\nlarge-scale TMDC ML deposition techniques.