Infrared imaging systems have wide range of military or civil applications and 2-dimensional (2D) nanomaterials have recently emerged as potential sensing materials that may outperform conventional ones such as HgCdTe, InGaAs, and InSb. As an example, 2D black phosphorus (BP) thin film has a thickness-dependent direct bandgap with low shot noise and non-cryogenic operation for visible to mid-infrared photodetection. In this talk, I will first discuss our study on the negative photoconductivity mechanism in flexible BP transistors built on freestanding polyimide film. Near-infrared laser (λ = 830 nm) excitation leads to significantly suppressed device on-state current with a very high responsivity of up to 53 A/W. The underlying mechanism of the negative photoconductivity is attributed to the strong photothermal effect induced by the low thermal conductivity of polyimide substrate used. The heat generated by the infrared light illumination results in enhanced phonon scattering, reduced carrier mobility, and consequently negative photocurrent. Such phenomenon was not observed in similar BP devices built on SiO2/Si substrate whose thermal conductivity is much higher. The above photothermal mechanism is further supported by temperature-dependent electrical characterization and device simulation. Next, the use of a single-pixel BP photodetector for near-infrared imaging application will be discussed. The imaging is achieved by combining the photodetector with a digital micromirror device to encode and subsequently reconstruct the image based on compressive sensing algorithm. Stationary images of a near-infrared laser spot with up to 64 × 64 pixels were captured using the BP camera with 2000 times of measurements, which is only half of the total number of pixels. The imaging platform in this work circumvents the grand challenges of scalable BP material growth for photodetector array fabrication and shows the efficacy of utilizing the outstanding performance of BP photodetector for future high-speed infrared camera and wearable or bio-integrated imaging systems.

2D black phosphorus photodetector for near-infrared imaging applications

256th National Meeting (2018)

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