Exploration of epitaxial graphene on silicon carbide

Michael Lee Bolen, Purdue University

Abstract

The creation of graphene through the thermal decomposition of silicon carbide is explored. Four broad categories of experiments are carried out based on the polar face being decomposed, Si- or C-face, and the decomposition pressure, vacuum or near atmospheric. The graphene film is characterized by a plethora of analysis techniques including atomic force microscopy, scanning tunneling microscopy, transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Hall mobility measurements, and others. Each one of the four experiment categories provides unique results which are discussed in-depth. The analysis allows for gaining a better understanding of graphene formation mechanisms on silicon carbide. For the Si-face, the study of thermal decomposition in vacuum focused on understanding how a pristine SiC surface progressed toward becoming fully graphitized. Different growth features were found and characterized on the surface, a crystallographic preference for erosion was discovered, and the kinetics of graphene formation were calculated. The activation energy was found to be 90 kcal mol−1 and the reaction rate was calculated to be −0.044 ± 0.004 min−1. Thermal decomposition at near atmospheric pressure was found to produce a discontinuous graphitic film with a lower Hall mobility than the decomposition under vacuum conditions. Under a growth pressure of 10 mbar, the average Hall mobility was 1500 cm 2V−1s−1, but increased to 1900 cm2V−1s−1 when decomposed in vacuum. For the C-face, thermal decomposition in vacuum rapidly produced a graphitic film that varied linearly in thickness with temperature, 1.7 nm at 1475°C and 5.7 nm at 1600°C. Given the fast formation of graphene in vacuum, the chamber pressure was increased to slow the formation. A thermodynamic and kinetic study was undertaken to understand the effect of pressure and temperature on graphene formation. This study revealed differences in rate limiting kinetic steps of graphene formation as the decomposition environment changed. Furthermore, the increase of chamber pressure was found to correlate with an increase in Hall mobility values. Vacuum decomposition produced Hall bars with an average Hall mobility of 3900 cm2V−1 s−1, while decomposition at 50 mbar gave rise to an average Hall mobility of 17500 cm2V−1s −1. Various analytical techniques were used to probe Hall bars in an attempt to understand the reasons behind this correlation.

Degree

Ph.D.

Advisors

Capano, Purdue University.

Subject Area

Electrical engineering|Nanotechnology|Materials science

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