AVS 60th International Symposium and Exhibition
    Electronic Materials and Processing Monday Sessions
       Session EM+TF-MoM

Paper EM+TF-MoM1
Ultrathin Titanyl Phthalocyanine Active Layer on Graphene for Atomic Layer Deposition

Monday, October 28, 2013, 8:20 am, Room 101 B

Session: High-k Gate Oxides for High Mobility Semiconductors I
Presenter: H.H. Park, University of California, San Diego
Authors: A.C. Kummel, University of California, San Diego
H.H. Park, University of California, San Diego
S.W. Park, 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 insulator on the 2D semiconductor or between two sheets of 2D semiconductors. However, 2D semiconductors are nearly inert surface thereby making uniform nucleation of oxide growth challenging thereby preventing scaling of the insulator thickness. A new technique has been developed to employ a monolayer of ordered metal phthalocyanines (MPc) on graphene directly as a monolayer low-k dielectic or as a nucleation layer for growth of high-k insulator. MPc molecules act as electron donors during reaction with oxidative species; therefore, they are expected to react with high-k gate oxide metal precursors. This study demonstrates the molecular scale observation of formation of O-TiPc mono and bilayers on graphene UHV scanning tunneling microscopy. O-TiPc monolayers were deposited on HOPG surfaces by organic molecular beam epitaxy. After deposition, O-TiPc forms a monolayer with only few defects, and the crystal structure of monolayer has four-fold symmetry.In the monolayer, a bright spot at the center of each O-TiPc molecules is assigned to O. Observation of bright protrusion indicates that O-TiPc of monolayer is directed outward to vacuum consistent with previous photoelectron studies. After further deposition of O-TiPc on the monolayer, growth of second layer is observed. O-TiPc of second layer covers the first layer, and both the first and second layers are highly ordered with four fold crystal structure. However, in second layer, central ion appears as a dark hole, unlike with in the monolayer. This implies O species of O-TiPc is directed downwards.For bilayer 2D semiconductors devices, when using O-Ti-Pc as a low-k insulator, the stacking of the 1st and 2nd layers of Ti-OPc is critical since the monolayer might provide differential doping of the top and bottom layer while the bilayer would provide a non-polar low K insulating layer. Scanning tunneling spectroscopy showed that the Fermi level of O-TiPc is slightly shifted to the lowest unoccupied molecular orbital, although EF is still in the midgap. O-TiPc is “N-type” in vacuum, while it becomes to “ P-type” in air due to reaction with oxygen species. In the air, oxidative molecules take electrons from O-TiPc during chemisorption via central ion of O-TiPc. At same time, holes are injected into the O-TiPc layer.Due to this property, O-TiPc molecules are expected to have strong reactivity with ALD precursors. Consequently, O-TiPc can not only act as a low-K dielectric but also induce nucleation of ALD source on central ion of O-TiPc for high-k dielectric growth.