Effects of Size and Localized States in Charge Carrier Dynamics and Performance of Solution-Processed Graphene Quantum Dots/Silicon Heterojunction Near-UV Photodetectors

Abstract

The influence of size and localized defect states on photogenerated carrier recombination dynamics, which affects the performance of graphene quantum dots (GQDs)-based Si-compatible near-UV heterojunction photodetectors, is reported. GQDs of varying size from ∼3.0 to ∼8.0 nm have been prepared by a top-down method of oxidative cutting of graphene oxide followed by hydrothermal reduction and gradient centrifugation at different speeds. Structural, compositional, and photophysical characteristics as well as photocarrier dynamics of different sized samples have been studied. Spectroscopic features and carrier dynamics of GQDs are effectively controlled by their size and localized surface states, which also determine the average recombination lifetime of photogenerated carriers. Two-terminal vertical heterojunction photodetector devices fabricated by using solution-processed quantum dots exhibit superior performance over a broad spectrum with a peak response in the near-UV (380 nm) region. The device fabricated by using ∼6.0 nm diameter GQDs displayed the highest peak responsivity of 3.5 A/W, showing an interesting correlation with carrier dynamics. To our best knowledge, this is the only report in graphene quantum dots or carbon nanostructure genre showing the direct correlation between size of the quantum dots and localized surface states on photocarrier dynamics and consequential performance of photodetector devices.

Photoluminescent sea urchin-shaped carbon-nanobranched polymers as nanoprobes for the selective and sensitive assay of hypochlorite

“…The former peak mainly originates from the π–π* transition of double bonds, such as C C and C N, implying a rich electronic conjugate arrangement and verifying the heterocyclic skeleton. 30 The latter peak is mainly derived from the n–π* transitions of C O and S O bonds on the SUCNP surfaces. 31 From the macroscopic view, the light yellow aqueous solution of SUCNPs emitted intense blue luminescence under UV excitation (350 nm, inset of Fig.…”

Graphene/Quantum Dot Heterostructure Photodetectors: From Material to Performance

“…[105] Therefore, QDs with suitable sizes can be used to detect specific light waves. [106] Gerasimos [52] et al prepared PbS QDs on graphene (Figure 10a). With increasing the size of PbS QDs, the E g can be reduced from ≈3 to ≈2.5 eV (Figure 10b).…”

Silicon Nanowire Arrays with Nitrogen-Doped Graphene Quantum Dots for Photodetectors

“…Also, the physical and chemical properties of GQDs and their conductivity (both n and p-type) can be adjusted during the synthesis process. 27 Recently because of the high market cost of inorganic QDs and due to their high toxicity, industrial use of these materials has been restricted. Here, GQDs find a significant research interest in various optoelectronic applications due to their tunable electro-optical properties and nontoxicity making it an alternative candidate for replacing inorganic QDs.…”

“…As a most promising alternative to CQDs, GQDs have the advantages of easy cost-effective synthesis, easy functionalization with other elements, good water solubility, stable photoluminescence, etc. Also, the physical and chemical properties of GQDs and their conductivity (both n and p-type) can be adjusted during the synthesis process . Recently because of the high market cost of inorganic QDs and due to their high toxicity, industrial use of these materials has been restricted.…”