Split Gate Photodiode based on Graphene-HgTe Heterostructure with few ns Photoresponse
Résumé
Hopping transport associated with the granular nature of nanocrystal arrays has led to the thought that nanocrystal-based devices might be incompatible with fast operations. Here we explore the design of HgTe nanocrystal-based sensors operating in the shortwave infrared and with very fast time response down to a few ns. To reach this goal, the design relies on a planar geometry to reduce the device capacitance. A strong in-built electric field is tailored via electrostatic control from two bottom split-gate electrodes, which promotes the charge extraction. While using graphene electrodes patterned over the two gate electrodes, we optimize the control on the electrostatic design of the p-n junction inside the nanocrystal array. Taking advantage of a high-k dielectric spacer, we demonstrate that the device can be operated under low gate bias (<6 V). The split-gate photodetector appears to be versatile, and can be used either in phototransistor or diode modes, upon the two gates voltages that are set to design isotype or diode-type heterojunctions. We finally highlight that time response enabled by the planar diode configuration can be made much faster than the one associated with the conventional vertical geometry.
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