Effect of High-Temperature Annealing on Graphene with Nickel Contacts

Graphene has shown great potential for ultra-high frequency electronics. However, using graphene in electronic devices creates a requirement for electrodes with low contact resistance. Thermal annealing is sometimes used to improve the performance of contact electrodes. However, high-temperature annealing may introduce additional doping or defects to graphene. Moreover, an extensive increase in temperature may damage electrodes by destroying the metal-graphene contact. In this work, we studied the effect of high-temperature annealing on graphene and nickel-graphene contacts. Annealing was done in the temperature range of 200-800 degrees C and the effect of the annealing temperature was observed by two and four-point probe resistance measurements and by Raman spectroscopy. We observed that the annealing of a graphene sample above 300 degrees C increased the level of doping, but did not always improve electrical contacts. Above 600 degrees C, the nickel-graphene contact started to degrade, while graphene survived even higher process temperatures.