Raman spectroscopy of electrochemically gated graphene transistors: Geometrical capacitance, electron-phonon, electron-electron, and electron-defect scattering
Raman spectroscopy of electrochemically gated graphene transistors: Geometrical capacitance, electron-phonon, electron-electron, and electron-defect scattering
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DOI：
10.1103/physrevb.91.205413
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发表时间：
2015-05-12
影响因子：
3.7
通讯作者：
Berciaud, Stephane
中科院分区：
文献类型：
--
作者：
Froehlicher, Guillaume;Berciaud, Stephane
我们报告了电化学门控石墨烯场效应晶体管的全面微拉曼散射研究。电化学顶栅的几何电容是通过双栅拉曼测量精确确定的，从而可以对石墨烯主要拉曼特征的频率、线宽和积分强度进行定量分析。观察到的 G 模式声子的异常行为与理论预测非常一致，并提供了区域中心（伽玛点）光学声子的电子-声子耦合常数的测量。此外，2D 模式特征的积分强度随着掺杂的增加而降低，使得确定近区边缘（K 和 K' 点）光学声子的电子声子耦合常数成为可能。我们发现 Gamma 处的电子-声子耦合强度比 K (K') 处弱五倍，这与共振内（2D' 模式）和间隔（2D 模式）拉曼特征的积分强度之比的直接测量非常一致。我们还表明，可以利用大栅极偏压下发生的电化学反应来有效地在石墨烯中产生缺陷，其浓度高达约1.4 x 10(12) cm(-2)。在这样的缺陷浓度下，我们估计电子缺陷散射率仍然远小于电子声子散射率。掺杂后 G 模式和 2D 模式特征的演变不受缺陷存在的影响，并且 D 模式的掺杂依赖性与其双声子（2D 模式）泛音密切相关。最后，G 模式声子的线宽和频率以及掺杂石墨烯中 G 模式和 2D 模式声子的频率遵循与样本无关的相关性，可用于准确估计载流子密度。
We report a comprehensive micro-Raman scattering study of electrochemically gated graphene field-effect transistors. The geometrical capacitance of the electrochemical top-gates is accurately determined from dual-gated Raman measurements, allowing a quantitative analysis of the frequency, linewidth, and integrated intensity of the main Raman features of graphene. The anomalous behavior observed for the G-mode phonon is in very good agreement with theoretical predictions and provides a measurement of the electron-phonon coupling constant for zone-center (Gamma point) optical phonons. In addition, the decrease of the integrated intensity of the 2D-mode feature with increasing doping, makes it possible to determine the electron-phonon coupling constant for near zone-edge (K and K' points) optical phonons. We find that the electron-phonon coupling strength at Gamma is five times weaker than at K (K'), in very good agreement with a direct measurement of the ratio of the integrated intensities of the resonant intra- (2D' mode) and intervalley (2D mode) Raman features. We also show that electrochemical reactions, occurring at large gate biases, can be harnessed to efficiently create defects in graphene, with concentrations up to approximately 1.4 x 10(12) cm(-2). At such defect concentrations, we estimate that the electron-defect scattering rate remains much smaller than the electron-phonon scattering rate. The evolution of the G- and 2D-mode features upon doping remain unaffected by the presence of defects and the doping dependence of the D mode closely follows that of its two-phonon (2D mode) overtone. Finally, the linewidth and frequency of the G-mode phonon as well as the frequencies of the G- and 2D-mode phonons in doped graphene follow sample-independent correlations that can be utilized for accurate estimations of the charge carrier density.