Carrier transport dynamics in 2D semiconductors optoelectronic devices

Despite that 2D semiconductors have promising optoelectronic and electronic applications, our fundamental understanding of its carrier transport dynamics is still in its infancy. In general, it remains challenging to unravel the carrier transport properties in devices since they are altered in the presence of defects/impurities or trap states. An ultrafast probe or high quantum efficiency device (the ratio between electrons collected to photon number), or both, are required to elicit carrier transport properties before significant carrier trapping into trap states and recombination occur.
In this work, we integrate black phosphorus and WS₂ in an ultra-high-speed photodetector structure with sub-25 ps response time to study the carrier transport dynamics. We elucidate the nature of transport mechanisms in different temporal regimes: pre-trapping and band-like transport in early time up to nanoseconds, followed by multiple trapping and release (MTR) hopping transport. In addition to demonstrating visible and infrared high-speed photodetectors, our study reveals the fundamental device physics, leading to device performance manipulation.