Romero Hugo E, Shen Ning, Joshi Prasoon, Gutierrez Humberto R, Tadigadapa Srinivas A, Sofo Jorge O, Eklund Peter C
Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
ACS Nano. 2008 Oct 28;2(10):2037-44. doi: 10.1021/nn800354m.
Results are presented from an experimental and theoretical study of the electronic properties of back-gated graphene field effect transistors (FETs) on Si/SiO(2) substrates. The excess charge on the graphene was observed by sweeping the gate voltage to determine the charge neutrality point in the graphene. Devices exposed to laboratory environment for several days were always found to be initially p-type. After approximately 20 h at 200 degrees C in approximately 5 x 10(-7) Torr vacuum, the FET slowly evolved to n-type behavior with a final excess electron density on the graphene of approximately 4 x 10(12) e/cm(2). This value is in excellent agreement with our theoretical calculations on SiO(2), where we have used molecular dynamics to build the SiO(2) structure and then density functional theory to compute the electronic structure. The essential theoretical result is that the SiO(2) has a significant surface state density just below the conduction band edge that donates electrons to the graphene to balance the chemical potential at the interface. An electrostatic model for the FET is also presented that produces an expression for the gate bias dependence of the carrier density.
本文展示了对硅/二氧化硅衬底上背栅石墨烯场效应晶体管（FET）电学性质的实验和理论研究结果。通过扫描栅极电压以确定石墨烯中的电荷中性点，从而观测到石墨烯上的过量电荷。发现暴露在实验室环境中数天的器件最初总是呈现p型。在约5×10⁻⁷托的真空中于200℃下经过约20小时后，该FET缓慢演变为n型行为，石墨烯上最终的过量电子密度约为4×10¹² e/cm²。该值与我们在二氧化硅上的理论计算结果高度吻合，我们使用分子动力学构建二氧化硅结构，然后用密度泛函理论计算电子结构。重要的理论结果是，二氧化硅在导带边缘下方具有显著的表面态密度，该表面态向石墨烯提供电子以平衡界面处的化学势。还提出了一个FET的静电模型，该模型给出了载流子密度对栅极偏置的依赖表达式。
