Structural and electronic properties of epitaxial graphene on SiC(0 0 0 1): a review of growth, characterization, transfer doping and hydrogen intercalation
Structural and electronic properties of epitaxial graphene on SiC(0 0 0 1): a review of growth, characterization, transfer doping and hydrogen intercalation
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DOI：
10.1088/0022-3727/43/37/374009
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发表时间：
2010-09-02
影响因子：
3.4
通讯作者：
Starke, U.
中科院分区：
文献类型：
--
作者：
Riedl, C.;Coletti, C.;Starke, U.
石墨烯是一种单原子石墨层，具有大电子迁移率的二维电子气体系统，这使其成为未来碳纳米器件的潜在候选者。在碳化硅（SiC）晶圆上外延生长，大面积石墨烯样品似乎是可行的，并且可以设想与现有器件技术的集成。本文综述了SiC（0 0 0 1）外延石墨烯层的可控生长及其电子结构的调控。我们发现，碳化硅上的外延石墨烯生长在碳界面层的顶部，尽管它具有类似石墨的原子结构，但由于与衬底的强共价键，它没有显示出典型的石墨烯的线性pi带。只有在这个界面上的第二层碳层像单层石墨烯一样。再加一层碳，就形成了石墨烯双层体系。在SiC（0 0 0 1）外延石墨烯的生长过程中，可以通过监测pi带结构来精确控制石墨烯层数。建立了原位生长控制的实验指纹图谱。然而，由于界面层的影响，SiC（0 0 0 1）上的外延石墨烯本质上是n掺杂的，并且层的态密度呈长波状。结果，π带交叉处的狄拉克点能量从费米能量中移开，使得石墨烯的双极性特性无法被利用。我们展示了补偿和消除这种接口结构和电子影响的方法。我们发现，通过用四氟-四氰喹诺二甲烷（F4-TCNQ）分子功能化石墨烯表面，可以精确地定制SiC（0 0 0 1）外延石墨烯的能带结构。单层和双层石墨烯均可实现电荷中性。在外延双层石墨烯上，由于界面施加的非对称电场导致带隙打开，该带隙的大小可以增加到其初始值的两倍以上。空穴掺杂使费米能级跃迁到能带隙中。通过氢嵌入技术将石墨烯与SiC衬底解耦，可以完全消除界面层的影响。我们证明了氢可以在界面层下迁移并钝化下面的SiC衬底。单独的界面层转变成一个准独立的单层。外延单层石墨烯变为去耦双层。与常压石墨化相结合，嵌入工艺允许在大型SiC晶圆上生产准独立的外延石墨烯，代表了基于外延石墨烯的纳米电子学的一个非常有前途的途径。
Graphene, a monoatomic layer of graphite, hosts a two-dimensional electron gas system with large electron mobilities which makes it a prospective candidate for future carbon nanodevices. Grown epitaxially on silicon carbide (SiC) wafers, large area graphene samples appear feasible and integration in existing device technology can be envisioned. This paper reviews the controlled growth of epitaxial graphene layers on SiC(0 0 0 1) and the manipulation of their electronic structure. We show that epitaxial graphene on SiC grows on top of a carbon interface layer that-although it has a graphite-like atomic structure-does not display the linear pi-bands typical for graphene due to a strong covalent bonding to the substrate. Only the second carbon layer on top of this interface acts like monolayer graphene. With a further carbon layer, a graphene bilayer system develops. During the growth of epitaxial graphene on SiC(0 0 0 1) the number of graphene layers can be precisely controlled by monitoring the pi-band structure. Experimental fingerprints for in situ growth control could be established. However, due to the influence of the interface layer, epitaxial graphene on SiC(0 0 0 1) is intrinsically n-doped and the layers have a long-range corrugation in their density of states. As a result, the Dirac point energy where the pi-bands cross is shifted away from the Fermi energy, so that the ambipolar properties of graphene cannot be exploited. We demonstrate methods to compensate and eliminate this structural and electronic influence of the interface. We show that the band structure of epitaxial graphene on SiC(0 0 0 1) can be precisely tailored by functionalizing the graphene surface with tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) molecules. Charge neutrality can be achieved for mono-and bilayer graphene. On epitaxial bilayer graphene, where a band gap opens due to the asymmetric electric field across the layers imposed by the interface, the magnitude of this band gap can be increased up to more than double its initial value. The hole doping allows the Fermi level to shift into the energy band gap. The impact of the interface layer can be completely eliminated by decoupling the graphene from the SiC substrate by a hydrogen intercalation technique. We demonstrate that hydrogen can migrate under the interface layer and passivate the underlying SiC substrate. The interface layer alone transforms into a quasi-free standing monolayer. Epitaxial monolayer graphene turns into a decoupled bilayer. In combination with atmospheric pressure graphitization, the intercalation process allows the production of quasi-free standing epitaxial graphene on large SiC wafers and represents a highly promising route towards epitaxial graphene based nanoelectronics.