| AVS 62nd International Symposium & Exhibition | |
| 2D Materials Focus Topic | Thursday Sessions |
| Session 2D+EM+MG+NS+SS+TF-ThA |
| Session: | Heterostructures of 2D Materials |
| Presenter: | JunHong Park, UC San Diego |
| Authors: | J.H. Park, UC San Diego S. Fathipour, University of Notre Dame I.J. Kwak, UC San Diego H.C.P. Movva, UT-Austin S. Vishwanath, Cornell University H. Xing, Cornell University S.K. Banerjee, UT-Austin A.C. Seabaugh, University of Notre Dame A.C. Kummel, University of California at San Diego |
| Correspondent: | Click to Email |
Several novel designs for beyond CMOS devices have emerged using two-dimensional semiconductors. These devices require deposition of thin insulators on 2D semiconductors or between two sheets of 2D semiconductors. However, 2D semiconductors are nearly inert surfaces thereby making uniform nucleation of oxide growth challenging preventing scaling of the insulator thickness. A new technique has been developed to employ a monolayer of ordered metal phthalocyanines (MPc) on 2D semiconductors directly as a nucleation layer for growth of ALD dielectric. TiOPc monolayers were deposited on HOPG surfaces and WSe2 by organic molecular beam epitaxy. TiOPc forms a monolayer with only few defects, and the crystal structure of monolayer has four-fold symmetry in a 1.6 x 1.6 nm grid on both HOPG and WSe2. Observation of bright protrusions on each O-TiPc indicates that each O-TiPc in the monolayer is directed outward to vacuum. After exposure O-TiPc monolayer to 5 cycles ALD pulse (tri-methyl-aluminum (TMA)+H2O), insulating aluminum oxide was deposited uniformly on TiOPc/HOPG. After formation of AlOx on TiOPc/HOPG, the band gap of surface increases from 1.7 eV to 3.4 eV, while the conductance decreased. A metal-oxide-TiOPc-graphene capacitor has the lower thickness and the higher capacitance value than any reported graphene MOSCAPs. In the dual gated graphene FET with 40 cycles of AlOx, TiOPc assisted AlOx shows very low leakage current. Employing the TiOPc seeding layer also can be expanded to other TMD materials. The bottom gated WSe2 FET was fabricated. On the bottom gated WSe2 FET, the TiOPc monolayer was deposited, then 50 cycle of AlOx was deposited via ALD. In this dual gated WSe2 FET, the leakage current of the AlOx is measured as ~0.05 pA/μm2 at 0.5 VTG. As a control, 20 cycles of Al2O3, and 140 cycles of HfO2 were deposited on bare WSe2. The leakage current of the TiOPc assisted 50 cycle Al2O3 oxide is 3 orders of magnitude lower than HfO2/Al2O3/WSe2, consistent with a high nucleation.