Graphene-based PhotodetectorsWhen: Wednesday, April 17, 2013 at 12:00 pm
Where: DA 114
Speaker: Fangze Liu
Organization: Northeastern University
Sponsor: Introduction to Physics Research
Graphene-based photonic applications have attracted significant attention due to its broad spectral bandwidth and fast response time. However, the responsivity of photodetectors that use graphene as the photon-absorbing medium, such as graphene-metal junctions, is usually limited to ~10-2 A/W (at visible wavelengths) due to its weak light absorption (2.3 %). Here, we report on the development of a completely new type of graphene-based photodetector that operates by “borrowing” photoexcited carriers from an adjacent silicon substrate. The “photo”-current due to these extra carriers scales with the applied voltage across the graphene channel, and photocurrent responsivity values exceeding 104A/W(corresponding to quantum gain values exceeding 104 at 488nm wavelength) could be obtained at V=3.2 V. The responsivity can be further tuned by applying an additional reverse-bias voltage at the graphene/silicon junction or by controlling the geometry of the device. These devices can easily detect sub-nanoWatt incident powers and further optimization could push them to detection levels of picoWatts, making them highly attractive for a broad range of optoelectronic devices such as weak-signal detectors, camera-pixels, and optical switches. The fabrication of the devices and characterizations including optical power and wavelength dependence will be described. The possible underlying mechanism of this extremely high-gain photodetection will be discussed.