Hybrid Black Phosphorus/Zero-Dimensional Quantum Dot Phototransistors: Tunable Photodoping and Enhanced Photoresponsivity

Recently, black phosphorus (BP) with direct band gap exhibited excellent potential for optoelectronic applications because of its high charge carrier mobility and low dark current as well as the variable band gap of 0.3-1.5 eV depending on the number of layers. However, few-layer BP-based phototransistors (photo-FETs) have been limited in sensitivity and wavelength selectivity. To overcome the drawback of these photo-FETs, we studied hybrid photo-FETs combined with the novel properties of the two materials between the channel and sensitizer layers. By combining a strong absorbance of a quantum dot (QD) layer and a two-dimensional layer material with high carrier mobility, the hybrid photo-FETs are expected to produce high-performance photodetectors that can effectively control the responsivity, detectivity, and response time. In this study, we demonstrate that the photogenerated carriers formed from QD sensitizer layers migrate to the BP transport layer with high charge mobility and not only improve the photodetector performance but also enhance the photodoping effect of the BP transport layer with an ambipolar characteristic by electrons transferred from n-type CdSe QDs or holes injected from p-type PbS QDs. The responsivity and detectivity of hybrid BP/0D photo-FETs exhibit 1.16 × 10⁹ A W^-1 and 7.53 × 10¹⁶ Jones for the BP/CdSe QD photo-FET and 5.36 × 10⁸ A W^-1 and 1.89 × 10¹⁶ Jones for the BP/PbS QD photo-FET, respectively. The photocurrent rise (τ_rise) and decay (τ_decay) times were τ_rise = 0.406 s and τ_decay = 0.815 s for BP/CdSe QD photo-FET and τ_rise = 0.576 s and τ_decay = 0.773 s for BP/PbS QD photo-FET, respectively.