Direct MOCVD of WS2 monolayers on SiO2/Si substrates for transfer-free FET fabrication

The metal–organic chemical vapor deposition (MOCVD) of transition metal dichalcogenides (TMDCs) is promising for large-area device integration. However, the subsequent transfer of TMDC films, typically grown on sapphire, is required for field-effect transistor (FET) fabrication but could impact material and interface quality. Utilizing SiO 2 /Si substrates enables fully transfer-free FETs. Here we demonstrate direct MOCVD of uniform wafer-scale tungsten disulfide (WS 2 ) monolayers (MLs) on 2-inch amorphous SiO 2 /Si and reference crystalline sapphire under identical conditions. Compared to films on sapphire, the WS 2 films on SiO 2 /Si feature a higher initial nucleation density and consequently a larger grain boundary density. Nevertheless, transfer-free FETs based on as-grown WS 2 on SiO 2 /Si exhibit maximum drain currents, outperforming their transferred counterparts from sapphire by one order of magnitude and those from the same SiO 2 /Si to another SiO 2 /Si by two orders. These differences are attributed to transfer-induced material degradation and electron depletion caused by ambient adsorbates and interfacial impurities, as supported by comparative Raman and photoluminescence (PL) analyses. Our work demonstrates a transfer-free fabrication pathway for TMDC-based FETs, enabling reliable electrical characterization without any transfer-related impacts.