Background:

Photodetectors comprise layers of photosensitive materials that can detect incident light of certain photon energies (which may also be expressed as wavelengths) related to the bandgap of the material. A bandgap is defined as the gap, expressed as an energy, between the lowest point of the conduction band and the highest point of the valence band of the material's electron energy dispersion relation (E-k) diagram, an example of which is shown as FIG. 1. Absorption of photons having at least the bandgap energy excites electrons from the valence band energy to the conduction band energy, thereby producing a photocurrent which can then be measured.

In existing photodetector technology, various materials having different bandgaps are used to detect different spectral ranges of incident electromagnetic radiation. However, the bandgaps, and thus the detectable range of photon energies, are fixed for the materials that are used in the device. This presents a profound limitation of the usefulness of the photodetector device.

Summary:

In a method according to the present invention, the sensitivity of a photodetector is adjusted by inducing strain in the photodetection material, thereby altering its bandgap. In embodiments of the invention, the photodetection material may be graphene layers, carbon nanotubes or graphene nanoribbons. The use of graphene as a photodetection material permits a dynamically adjustable sensitivity to incident photons. In an embodiment of the method, strain is induced in the graphene layer by an electrostatic actuator.

In a photodetector according to the present invention, a photodetection material is suspended over an electrically-conductive substrate by a layer of insulating material. An opening in the insulating layer exposes the graphene to the substrate. A voltage is applied across the graphene layer and the substrate. Adjusting the voltage varies the strain induced in the graphene layer, changing the bandgap of the graphene and, thus, the sensitivity of the photodetector to photons of different energies.

Benefits:

- Bandwidth tuning of photodetectors

Applications:

- Photodetectors for a wide band of electromagnetic radiation can be fabricated

Full Patent: Active Bandgap Tuning Of Materials For Tunable Photodetection Applications