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Study of N-doping of Graphene and Field-Effect Transistors

Author: GuoBeiDou
Tutor: FangLiang；GongJianRu
School: Chongqing University
Course: Condensed Matter Physics
Keywords: Graphene doping Raman spectroscopy reduced Field-Effect Transistor
CLC: O483
Type: Master's thesis
Year: 2011
Downloads: 491
Quote: 0
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Abstract


Graphene, a two-dimensional （2D） network of sp2 hybridized carbon atoms packed into hexagonal structure, is a basic building block for graphitic materials of all other dimensionalities. Since long-rangeπ-conjugation in graphene yields extraordinary thermal, mechanical, and electrical properties, an enormous effort has been devoted to exploration of its many applications in nanoelectronics, materials science, condensed-matter physics, and low-dimensional physics. However, most electronic applications are handicapped by the absence of a bandgap in the intrinsic material. In the quest to opening and tuning an energy gap in graphene, various approaches have been developed to improve the semiconducting properties, exemplified by forming confined geometries of quantum dots, nanoribbons, and nanomesh, or binding graphene to particular substrates. One of the most feasible methods to control the semiconducting properties of graphene is by doping, which is a process intentionally used to tailor the electrical properties of intrinsic semiconductors.In this paper, we studied the doping of graphene and reduced graphene oxide by N+ ions irradiation.We studied the N-doping graphene firstly. As we know, pristine graphene has perfect honeycomb structure, and it is difficult to introduce hetero atoms into graphene and control the electrical properties of graphene. In this paper, we carried out N+ ions irradiation on mechanical exfoliated single-layer pristine graphene to induce the defects. Then, controllable N-doping in graphene was realized by NH3 annealing after ion irradiation. The main conclusions are as follows:①Raman spectroscopy is a much more important tool for the characterization of graphene. We studied the evolution of the defects of graphene with the increasing fluence of ions irradiation using Raman spectroscopy. At last, we got the proper influence of ions irradiation: 1×1014 cm-2. Under this fluence, there were enough defects in graphene for doping, and these defects can be also restored after annealing.②We compared the Raman spectroscopy of irradiated graphene after annealing in N)2 and NH3, respectively. The peaks of Raman spectroscopy of irradiated graphene after annealing in N2 showed more blue shift than that annealed in NH3. The resaon was that the N atoms were substitutional doping in graphene after annealing in NH3, resulting in lower stress and strain in graphene. ③XPS and AES were carried out on the irradiated graphene after annealing in N2 and NH3. The results of XPS and AES of samples annealed in NH3 showed N single, while there had no N single after annealing in N2. These results revealing that controllable N-doping in graphene was realized by NH3 annealing after N+ ion irradiation.④To investigate the electronic properties of different graphene samples, the graphene-based back-gate FETs were fabricated. Results showed that pristine graphene field effect transistor was bipolar transistor, and its minimum conductance point of FET located at positive voltage range, indicating that the garphene was p-type property. The biolar property of FET mabe by irratiated graphene after annealing in N2 disappeared, and the minimun conductance located at positive votltages, indicating p-type property. While the bipolar paoperty of FET made by irradiated graphene after annealing in NH3 restored, and the minimum conductance located at negitive voltage range, indicating n-type property.We also studied the doping of reduced graphene oxide. We investigated the structure of reduced graphene oxide after N+ ions irradiation using Raman specroscopy and FTIR. At last, we fabricated FET using reduced graphene oxide bafore and after N+ ions irradiation, and measured its electrical properties. We found that N+ reacted with the functional group on reduced graphene oxide. We also found that the threshold voltage could be controlled by N+ ions irradiation. And the carrier was electron when the gate voltage was zero, indicating that the sample was n-type property.

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