Theoretical Investigations Of Gate Tunable Few-layer Black Phosphorus Photodetector

Photodetection technology mainly studies how to convert optical signals into observable signals,especially the problem of converting photon into electrical signals,which is a very important content in the practical application of optoelectronics.It has been developed and applied as early as more than one hundred and eighty years ago.After that,many high-performance photodetectors have been studied experimentally and theoretically.Among the candidate materials for photodetectors,multilayer black phosphorus(BP)stands out due to its unique electrical and optical properties.In the photodetection process of the multilayer black phosphor photodetector,the bias voltage induced current may be the main contribution of the dark current,and it may even exceed the photocurrent generated by the light itself.Therefore,the researchers further propose a self-powered photodetector that does not need an external electric field.In self-powered photodetectors,due to the presence of built-in electronic field along the current transport direction,the photocurrent can be generated by the photogalvanic effect or the photovoltaic effect.To achieve this built-in electric field,the p-n junction,heterojunction,and schottky junction are usually investigated,which requires complicated experimental procedures and subtle engineering of device interfaces.Utilizing the unique gate induced giant stark effect in few-layer black phosphorus(BP),we theoretically propose a broadband photodetector device based on pure few-layer black phosphorus from atomic first-principles calculations.By applying the vertical gate voltage in the few-layer black phosphorus,the intrinsic inversion symmetry of the system can be broken.We found that the photocurrent can be generated via photogalvanic(or photovoltaic)effect(PGE)without the need for an external bias voltage,which means the gated few-layer BP photodetector is self-powered and the dark current can be greatly suppressed.Most importantly,due to the giant stark effect of the gated few-layer black phosphorus,the photodetection range can be well controlled and further enlarged from the mid-infrared range(MIR)to far-infrared range(FIR).Furthermore,the few-layer black phosphorus based photodetector device also presents high polarization sensitivity with extinction ratios up to 10~5 and large anisotropic photoresponse.Moreover,the photoresponse of the three-layer black phosphorus(BP)is not only sensitive to the photon energy and polarization angle,but also to the incident angle.The last part studies the photoresponse of different layers of few-layer black phosphorous(BP)photodetectors versus the joint density of states(JDOS).The results show that the number of layers is also another degree of freedom for adjusting the photoresponse.Our numerical findings pave a feasible way for the few-layer BP's novel application in the self-powered and well-controlled broadband photodetector.