Organic–Inorganic Heterointerfaces for Ultrasensitive Detection of Ultraviolet Light

Abstract

The performance of graphene field-effect transistors is limited by the drastically reduced carrier mobility of graphene on silicon dioxide (SiO2) substrates. Here we demonstrate an ultrasensitive ultraviolet (UV) phototransistor featuring an organic self-assembled monolayer (SAM) sandwiched between an inorganic ZnO quantum dots decorated graphene channel and a conventional SiO2/Si substrate. Remarkably, the room-temperature mobility of the chemical-vapor-deposition grown graphene channel on the SAM is an order-of-magnitude higher than on SiO2, thereby drastically reducing electron transit-time in the channel. The resulting recirculation of electrons (in the graphene channel) within the lifetime of the photogenerated holes (in the ZnO) increases the photoresponsivity and gain of the transistor to ∼10(8) A/W and ∼3 × 10(9), respectively with a UV to visible rejection ratio of ∼10(3). Our UV photodetector device manufacturing is also compatible with current semiconductor processing, and suitable for large volume production.

Electrochemical half-reaction-assisted sub-bandgap photon sensing in a graphene hybrid phsotodetector

“…Figure 6), assuming the same sensing mechanism as previously reported for a graphenesemiconductor hybrid phototransistor. [9][10][11][12][13] By contrast, a high photoresponse was observed with visible light illumination, suggesting a new sensing mechanism in our phototransistor. Figure 1b shows the photocurrent (after dark current subtraction) of the as-prepared AgX-G photodetectors at room temperature under chopped light illumination (white light illumination with a power of~54.9 nW) at a 1-V source-drain voltage (V SD ) and a 0-V back-gate voltage (V G ).…”

“…10 Therefore, the photoconductive gain is estimated to be~3.04 × 10 9 by adopting τ lifetime = 8.4 s (Figure 1b, 50% photocurrent decay), which is over 30 times larger than the value of a PbS QD-graphene hybrid photodetector. 9 Because the photoconductive gain scales linearly with the mobility of graphene, we can expect that the responsivity can be further improved by adopting boron nitride 27 or a self-assembled monolayer-coated oxide 10 as the substrate.…”

“…Without a favorable redox couple (for example, in the ZnO-graphene hybrid), the internal photoemission from graphene to the semiconductor is insignificant and the sub-bandgap photoresponse is negligible. 10,11 Since our phototransistor involves an electrochemical redox reaction, it is important to assess the stability of our device, which is determined by the reversibility of the redox reaction. The AgCl-G sample was stored under ambient conditions for 6 months and then subjected to a long stress test under chopped illumination (Figure 1d).…”

“…By contrast, graphene hybrid phototransistors [4][5][6][7][8] provide high photoresponsivity by incorporating a layer of light absorbing material, such as a layer of semiconducting quantum dots (QDs), [9][10][11][12][13] which is in contact with the graphene. Upon illumination, the photoexcited carriers in the QDs can be injected into graphene while the charged QDs layer can modulate the conductance of graphene by capacitive coupling.…”

“…9 Since the photon is absorbed by the incorporated light absorbing material, the spectral response of the graphene hybrid phototransistor seems to be fundamentally limited by the bandgap of the integrated materials as shown in previous studies. [5][6][7][8][9][10][11][12] However, the internal photoemission from graphene in the graphene-semiconductor hybrid structure provides an alternative method to realizing broadband photo sensing. [14][15][16] In this hybrid structure, the photocurrent is generated as the photoexcited hot electron in graphene is injected into the conduction band of the adjacent semiconductor.…”