Two-dimensional Black Phosphorous Based Heterojunction Photodetector

Black phosphorus,as a member of a large family of two-dimensional materials,has recently attracted great attention in the field of optoelectronics.The reason is its anisotropic optoelectronic properties,ultra-high carrier mobility,thickness-tunable direct bandgap(between 1.5 e V for monolayers to 0.3 e V for bulk),which has great application potential in the field of optoelectronics in the future,especially infrared photodetection.So far,many photodetectors based on black phosphorus have been reported,which fully proves its application prospects in the next generation of infrared photodetectors.However,the current black phosphorous-based photodetectors have the following two problems:(1)The dark current of pure black phosphorous photoconductive detectors is large,and the signal-to-noise ratio is low,which results in a low detectivity rate of the photodetector and limits its photodetection performance;(2)So far,infrared room temperature photodetectors based on black phosphorous heterojunctions are rare,and only have a high response in the near-infrared or short-wave infrared bands.The reason is that light absorption and excitation of photogenerated carriers is only the first step of photoresponse.The subsequent separation,recombination,and trapping of carriers are the decisive processes for generating photoresponse.Therefore,how to optimize the photodetector structure and achieve high-performance wide-band photodetectors has become a problem we have to consider.In this thesis,we have implemented two high-performance wide-band optical detectors using black phosphorous through heterojunction engineering and interface engineering.The details are as follows:1.Using p-type black phosphorous material and narrow-bandgap n-type semiconductor bismuth oxyselenide,a high-performance wide-band photodetector is fabricated.The device exhibits high responsivity of 500 A/W,9.5 A/W,4.3 A/W and 2.3A/W under illumination at 700 nm,850 nm,1310 nm and 1550 nm,respectively.In addition,due to the low dark current of the heterojunction,the specific detectivity under700 nm illumination reaches 2.8×10¹¹Jones,which is two orders of magnitude higher than the pure black phosphorous detector(3.0×10⁹Jones)and the pure bismuth oxyselenide photodetector(3.8×10⁹Jones).Finally,the ultra-fast carrier separation at the heterojunction interface ensures a fast photoelectric response(9 ms)of the device,which is more than 20times faster than that of pure black phosphorus(190 ms)and pure bismuth oxyselenide photodetector(180 ms).2.Through ultraviolet-ozone treatment,a layer of phosphorus oxide interface is introduced on the surface of black phosphorus to construct a black phosphorus-phosphorus oxide-graphene heterojunction,realizing a high-performance photodetector.Experimental results have proved that the phosphorus oxide interface layer can effectively inhibit the interface recombination between graphene and black phosphorus and introduce ultra-high photogain(10⁸),so that the performance of the black phosphorus-phosphorus oxide-graphene heterojunction photodetector has been significantly improved.The results show that the black phosphorus-phosphorus oxide-graphene heterojunction photodetector shows a maximum responsivity of 10⁴A/W and a specific detectivity of 10¹¹Jones at 700nm.Compared with the black phosphorus-graphene heterojunction photodetector,it has improved by three orders of magnitude.In addition,the device also has ultra-broadband detection capabilities(visible light?4?m mid-infrared region),the maximum responsivity is 118 A/W at 1.6?m,98 A/W at 2.1?m,and 0.8 A/W at 3.4?m.