| A photoelectric detector is a device that converts optical signals into electrical signals.It is widely used in military and civil fields.Ultraviolet(UV)photodetectors are detectors operating in the UV band.Because of its high detection sensitivity and low false alarm rate,it can be used for cosmic ray detection in outer space,missile wake detection in military,sewage monitoring in daily life,and daily monitoring of UV radiation.The existing commercial UV photodetectors are not conducive to daily carrying because of their large size and energy consumption.Nanomaterials,such as two-dimensional and one-dimensional materials,are believed to be potential for miniaturizing the UV photodetectors.One-dimensional materials such as nanowires,due to their high photoresponsivity and good independence,have become one of the best choices for miniaturization of photodetectors.ZnO is a direct band gap semiconductor.The intrinsic ZnO band gap is about 3.4 eV,and the corresponding intrinsic absorption wavelength is 369 nm.It is in the near UV region and is a good material for UV photodetectors.ZnO appears as an n-type semiconductor due to the presence of oxygen vacancies inside the ZnO crystal lattice.NiO is a direct band gap semiconductor.The band gap of intrinsic NiO is about 3.7 eV,corresponding to the intrinsic absorption wavelength of 336 nm,in the near UV region.NiO appears as a p-type semiconductor because of the presence of nickel atom vacancies inside the NiO crystal.Considering the band structure of ZnO and NiO,the intrinsic absorption wavelength is in the UV range.If a one-dimensional nanowire is used to fabricate a heterojunction structure UV photodetector,a miniaturized selfpowered UV photodetector can be realized.1.Ni nanowires were synthesized by hydrothermal reduction method,and then the nanowires annealed at different temperatures were tested.The nanowires begin to oxidize at 300°C,but the degree of oxidation is lower and the oxidation rate is slower.When the annealing temperature reaches 450°C,the nanowires can be completely oxidized.When the annealing temperature reaches 600°C,the nanowires have a tubular structure.The degree of oxidation of nanowires increases linearly with the increase of annealing temperature.The oxidation degree of nanowires reaches 55% at 400°C,and the nanowire structure is the core-shell structure of NiO coated Ni,and has good conductivity,exhibiting the properties of a p-type semiconductor.2.A nanowire p-n heterojunction constructed from a single NiO coated Ni coreshell nanowire combined with ZnO film has been fabricated,which shows a typical rectification effect with a rectification ratio of 6000 at ±2 V applied bias and a turn-on voltage of 0.5 V,and dark current is 0.25 pA(0 V).The UV photodetector based on this nanowire heterostructure shows excellent performances on self-powered UV photodetection with the peak photoresponsivity of 17 mA/W under zero bias at the wavelength of 312 nm.The cutoff wavelength is located at 362 nm.Our findings provide a stable alternative approach to miniaturize the UV detectors based on nanowire-heterojunction materials for daily carrying. |
PDF Full Text Request