Energy gap formation and gap states analysis in bilayer graphene

The targeted issue for bilayer graphene is low $I_{\mathrm{on}}$/$I_{\mathrm{off}}$ at the room temperature, which is explained by the variable range hopping in ?gap states?. However, there will be intrinsically no interface states in bilayer graphene because there is no dangling bonds, compared with P$_{\mathrm{b}}$ centers in SiO$_{\mathrm{2}}$/Si system. The origin for the gap states is still open question. In spite of this, the detailed measurements on $D_{\mathrm{it}}$ and time constant for gap states have not been reported yet. One of reasons could be the leakage current through the top gate insulator since robust methodology is not established. Here, we demonstrates a considerable suppression of the low-field leakage in bilayer graphene by applying the high-pressure O$_{\mathrm{2}}$ annealing to Y$_{\mathrm{2}}$O$_{\mathrm{3}}$ top gate insulator. The reliable Y$_{\mathrm{2}}$O$_{\mathrm{3}}$ top gate insulator provides the access to the carrier response issue in the largely-opened band gap. In this talk, we focus on the conductance measurements for bilayer graphene to extract $D_{\mathrm{it}}$ and time constant. Based on these measurements, two possible origins for the gap states, (i) border traps at the edge of Y$_{\mathrm{2}}$O$_{\mathrm{3}}$ and (ii) the local breakdown of A-B stacking in bilayer graphene, are discussed.