Abstract
Graphene's unique optoelectronic properties are promising to realize photodetectors with ultrafast photoresponse over a wide spectral range from far-infrared to ultraviolet radiation. The underlying mechanism of the photoresponse has been a particular focus of recent work and was found to be either photoelectric or photo-thermoelectric in nature and enhanced by hot carrier effects. Graphene supported by a substrate was found to be dominated by the photo-thermoelectric effect, which is known to be an order of magnitude slower than the photoelectric effect. Here we demonstrate fully-suspended chemical vapor deposition grown graphene microribbon arrays that are dominated by the faster photoelectric effect. Substrate removal was found to enhance the photoresponse by four-fold compared to substrate-supported microribbons. Furthermore, we show that the light-current input/output curves give valuable information about the underlying photophysical process responsible for the generated photocurrent. These findings are promising towards wafer-scale fabrication of graphene photodetectors approaching THz cut-off frequencies.
Highlights
Graphene’s unique optoelectronic properties are promising to realize photodetectors with ultrafast photoresponse over a wide spectral range from far-infrared to ultraviolet radiation
Graphene supported by a substrate was found to be dominated by the photo-thermoelectric effect, which is known to be an order of magnitude slower than the photoelectric effect
The photoresponse in samples with closely spaced metal electrodes was attributed to the photoelectric effect driven by the band bending at the contacts[1,2,3,9,12], while junctions between monolayer and bilayer graphene flakes[13] as well as p-n junctions created via electrostatic gating are found to be dominated by the photo-thermoelectric effect[15,16,17,18,19]
Summary
Graphene’s unique optoelectronic properties are promising to realize photodetectors with ultrafast photoresponse over a wide spectral range from far-infrared to ultraviolet radiation. We show that the light-current input/output curves give valuable information about the underlying photophysical process responsible for the generated photocurrent These findings are promising towards wafer-scale fabrication of graphene photodetectors approaching THz cut-off frequencies. A recent time-resolved study of the photoresponse in CVD-grown graphene embedded in a coplanar stripeline circuit reveals that the time constant of the photo-thermoelectric effect is, at 130 ps, more than an order of magnitude slower than the photoelectric effect, at 4 ps[26]. We show that the slope of the light-current input/output curves (L-I curves) gives valuable information about the underlying photophysical process responsible for time-integrated photocurrents
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