Abstract
A sensitive optical detector is presented based on a deeply depleted graphene-insulator-semiconducting (D2GIS) junction, which offers the possibility of simultaneously leveraging the advantages of both charge integration and localized amplification. Direct read-out and built-in amplification are accomplished via photogating of a graphene field-effect transistor (GFET) by carriers generated within a deeply depleted low-doped silicon substrate. Analogous to a depleted metal-oxide-semiconducting junction, photo-generated charge collects in the potential well that forms at the semiconductor/insulator interface and induces charges of opposite polarity within the graphene film modifying its conductivity. This device enables simultaneous photo-induced charge integration with continuous “on detector” readout through use of graphene. The resulting devices exhibit responsivities as high as 2,500 A/W (25,000 S/W) for visible wavelengths and a dynamic range of 30 dB. As both the graphene and device principles are transferrable to arbitrary semiconductor absorbers, D2GIS devices offer a high-performance paradigm for imaging across the electromagnetic spectrum.
Highlights
To circumvent these difficulties, graphene can be utilized—in an alternative paradigm—as an atomically-thin, transparent, charge-sensing layer that detects absorption within a thicker adjacent substrate, rather than serving as the light-absorbing medium itself
Individual deeply depleted graphene-oxide-semiconductor (D2GOS) photodetectors are realized by transferring graphene atop a low-doped silicon substrate that is coated with a thin oxide
We have presented the fabrication, characterization, and analysis of a hybrid graphene/depleted-absorber device termed here as a deeply-depleted graphene-semiconductor (D2GOS) detector
Summary
Graphene can be utilized—in an alternative paradigm—as an atomically-thin, transparent, charge-sensing layer that detects absorption within a thicker adjacent substrate, rather than serving as the light-absorbing medium itself. Since the source-drain current (Isd) of the graphene channel is proportional to product of carrier density and mobility (Isd ∝ μnE), graphene’s large ambipolar mobility (~103–105 cm2/Vs)[10] acts as a built-in photogain (i.e., amplifier) mechanism enhancing the detector response For this reason, sensitivities of photogated graphene devices are higher than other architectures reaching values in excess 1,000 A/W11–14. Here—unlike previous reports of photogated graphene devices14,17,19 —we show that by operating a graphene-insulator junction with the semiconductor in deep-depletion, a sensitive photocharge integrating detector with continuous localized read-out (from the graphene) and high-sensitivity can be created These capabilities, in turn, open up the possibility of alternative detecting modalities in which the advantages of signal integration and continuous monitoring can be leveraged. Possessing responsivities exceeding 2,500 A/W, an SNR of ~ 3, and up to 30 dB of dynamic range at room temperature, the device response is explained entirely through a semi-analytical calculation taking into account the basic transfer characteristics of a graphene field-effect transistor combined with depletion and subsequent carrier generation in a low-doped semiconductor
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