College Park (MD) – Researchers found that electrons can travel substantially faster in graphene than in silicon, a standard material used in semiconductor products today. The fairly new material is believed to accelerate the electron flow by a factor of 100x and bring big advantage for applications that require rapid switching.
According to Michael Fuhrer’s research group at the University of Maryland, graphene could turn out to provide record levels of conductivity at room temperature, much higher than those of silicon and even indium antimonide, the highest mobility conventional semiconductor known today.
Conductivity is often described in terms of “mobility” and how quickly electrons can travel through a material. The maximum speed is limited by thermal atomic vibrations: Depending on the temperature, electrons can bounce off vibrating atoms, resulting in increasing electrical resistance. This resistance cannot be completely eliminated, unless the material is cooled to absolute zero temperature (which is done for example in superconducting magnets), according to Fuhrer’s group.
In graphene, a single-atom-thick sheet of graphite, vibrating atoms at room temperature were measured to produce a resistivity of about 1.0 microOhm-cm, which is about 35% less than the resistivity of the lowest resistivity material known at room temperature: Copper. Since current graphene samples are “fairly dirty”, there is “extra resistivity”, which gives the material higher resistivity than copper, Fuhrer conceded. “However, graphene has far fewer electrons than copper, so in graphene the electrical current is carried by only a few electrons moving much faster than the electrons in copper,” he said.
In terms of mobility, graphene could be playing in a different league, when compared to silicon. “The limit to mobility of electrons in graphene is set by thermal vibration of the atoms and is about 200,000 cm2/Vs at room temperature, compared to about 1400 cm2/Vs in silicon, and 77,000 cm2/Vs in indium antimonide,” the research group found. Current applications, however, show only around 10,000 cm2/Vs for graphene, indicating how much work is actually left to reach the 200,000 cm2/Vs limit.
Fuhrer believes that the potential of graphene makes it a promising material for applications in which transistors much switch extremely fast, such as in processing extremely high frequency signals as well as chemical and bio-chemical sensing applications. “The low resistivity and extremely thin nature of graphene also promises applications in thin, mechanically tough, electrically conducting, transparent films. Such films are sorely needed in a variety of electronics applications from touch screens to photovoltaic cells,” the research group said.