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A tunable colloidal quantum dot photo field-effect transistor
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Image of FIG. 1.
FIG. 1.

(Color online) (a) Schematic of the device structure used in this study. (b) Energy band diagram showing dissociation of electrons upon photo-excitation at the oxide semiconductor and the colloidal quantum dot interface. Photo-excited electrons are subsequentlyy collected through the Au electrode by applying an electric field.

Image of FIG. 2.
FIG. 2.

SEM images of a colloidal quantum dot film atop AZO at magnification (a) 10 K and (b) 50 K. The CQD film was deposited by spin-coating of PbS CQDs dispersed in octane, at a concentration of 0.5 mg/mL. The images clearly show that these conditions yield the desired discontinuous CQD films.

Image of FIG. 3.
FIG. 3.

(Color online) (a) Absorption spectra of different CQDs used in this study (b) Band alignment of AZO films with respect to colloidal quantum dots. The electron affinity of AZO films was calculated from cyclic voltammetry measurements whereas the electron affinity of colloidal quantum dots was estimated based on the work of Hyun et al. 5

Image of FIG. 4.
FIG. 4.

(Color online) Time-dependent photoresponse (indicated by ON-OFF sequence) of sub-monolayer films of colloidal quantum dots with bandgaps of (a) and (b) 727 nm and (c) and (d) 1475 nm, on top of (a) and (c) 5% and (b) and (d) 20% O2 rich AZO channels. Measurements were carried out under an applied field of 1000 V/cm and illumination of red light (time period 5 s) of intensity 225 μW/cm2. Calculated external photoconductive gains at illumination intensities of (e) 12 μW/cm2 and (f) 645 μW/cm2, showing that the gain increases as the band offset between the EAC material and the CQDs decreases. The photoconductive gain also decreases with light intensity.


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Scitation: A tunable colloidal quantum dot photo field-effect transistor