Abstract
The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 105 and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics.
Highlights
The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics
The external quantum efficiency (EQE) of these systems is a trade-off between light absorption, which increases for thicker sensitizing layers, and charge transfer, which decreases for thicker layers as it is limited by carrier diffusion towards the graphene channel
The colloidal quantum dots (CQDs) photodiode consists of an indium tin oxide (ITO) top-contact acting as the cathode of the CQD photodiode, whereas graphene acts as the hole acceptor contact and the charge transport channel for the phototransistor
Summary
The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. A vast number of applications calls for highly sensitive detectors that can sense light from the ultraviolet to the short-wave infrared (SWIR) range, covering a broad spectrum of 300–3,000 nm[1] These detector technologies should be based on CMOS compatible platforms for monolithic integration with read-out electronics to cater for high-density, high-throughput and low-cost manufacturing. The external quantum efficiency (EQE) of these systems is a trade-off between light absorption, which increases for thicker sensitizing layers, and charge transfer, which decreases for thicker layers as it is limited by carrier diffusion towards the graphene channel This has limited the quantum efficiency to about 25% for an optimized layer of CQDs of thickness 80 nm[14], the time response, which is limited by the long trapping times of the sensitizing centres[20] and the dynamic range, which is determined by the density of the trap-state sensitizing centres[21]
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