Graphene Optoelectronics

The remarkable physical properties of graphene and nanotubes make them perfect candidates for new classes of optoelectronic and spintronics devices. Graphene is a two-dimensional membrane formed by carbon atoms in a hexagonal structure, shown in Fig. 1. Although it is only one atom thin, it can universally absorb a remarkable 2.3% of light from the visible to infrared range, which ranks graphene as one of the materials with the strongest interband transition. Graphene’s electronic structure can be controlled by its size and shape, applied electrical field, and chemical modifications. With its extremely high electron mobility, graphene is an extraordinary material for engineering fully-integrated, high-speed and flexible optoelectronics carved from single graphene sheets.

A roll of graphene forms a one-dimensional nanotube shown in Fig. 2, which can be either metallic or semiconducting depending on the graphene rolling axis. Nanotubes provide a great system for quantum optoelectronic applications. Their 1D nature quantizes the electron motion in the circumference, and strong Coulomb interaction between electron and hole inside the nanotube leads to a large exciton binding energy. Carrier impact ionization has recently been demonstrated in a nanotube photodiode, which holds the promise of making high-efficiency photovoltaics from carbon-based nanomaterials.

Our goal is to combine the graphene and nanotube growth, optoelectronic device design and fabrications, and photoluminence, photocurrent, and ultrafast pump-probe spectroscopy to understand the opto-electronic properties of the carbon based nanoscale devices.

Click here for an example of photocurrent spectroscopy of a graphene photodetector.

Fig. 1. Left: A microscope image of single layer graphene fabricated by mechanical exfoliation of graphite onto 90nm SiO2/Si substrate. scale bar: 50 um. Right: A scanning TEM image of graphene hexagonal latice structure. Scale bar: 5 angstroms.

Fig. 2. Left: SEM image of arrays of as-grown carbon nanotubes on Sio2/Si substrate. Right: AFM image of nanotube cross junction devices.