Identifying the mechanisms of p-to-n conversion in unipolar graphene field-effect transistors Yap, Ray Chin Chong; Li, Hong; Chow, Wai Leong; Lu, Cong Xiang; Tay, Beng Kang; Teo, Edwin Hang Tong, E-mail: ebktay@ntu.edu.sg [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)] 36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; AMMONIA; COMPARATIVE EVALUATIONS; CONVERSION; DEPOSITION; ELECTRIC POTENTIAL; FIELD EFFECT TRANSISTORS; GRAPHENE; LAYERS; PASSIVATION; PEAKS; RAMAN SPECTROSCOPY; SILICA; SILICON NITRIDES; SILICON OXIDES; SURFACES; THICKNESS; THIN FILMS; TITANIUM The mechanisms of p-to-n conversion and vice versa in unipolar graphene field-effect transistors (GFETs) were systematically studied using Raman spectroscopy. Unipolar p-type GFETs are achieved by decorating the graphene surface with a thin layer of titanium (Ti) film, resulting in a Raman D peak. The D peak is observed to recover by annealing the GFET in nitrogen ambient followed by silicon nitride (Si{sub 3}N{sub 4}) deposition, suggesting that the Ti adatoms are being partially removed. Furthermore, unipolar n-type GFETs are obtained after the passivation on p-type GFETs. The threshold voltage of the n-type GFET is dependent on the thickness of the Si{sub 3}N{sub 4} layer, which increases as the thickness decreases. A comparison between the Si{sub 3}N{sub 4} and SiO{sub 2} passivation layers shows that SiO{sub 2} passivation does not convert the GFET into n-type graphene, which identifies the significance of ammonia (NH{sub 3}) for the formation of the n-type GFETs. This study provides an insight into the mechanism of controlling the conduction behavior of unipolar GFETs. (paper) Available from http://dx.doi.org/10.1088/0957-4484/24/19/195202 United Kingdom 2013-05-17 English Journal Article Journal Name: Nanotechnology (Print); Journal Volume: 24; Journal Issue: 19; Other Information: Country of input: International Atomic Energy Agency (IAEA) Medium: X; Size: [7 page(s)] https://doi.org/10.1088/0957-4484/24/19/195202 [] 19 24 Journal ID: ISSN 0957-4484; TRN: GB13P1897071389 INIS 2013-08-15 22114738