| The UV-detection technique has a wide application in both military and civilian fields,such as plume sensing,space exploration,environmental monitoring,flame detection,etc.The core of the UV-detection technique is the high-performance UV detector.Considering the selection of active layer materials,ZnO has received more and more attention due to their intrinsic visible blindness,esay to tuning band-gap,high saturated carrier drift rate,and high radiation hardness.Therefore,ZnO-based semiconductors are regarded as one of the most ideal materials to prepare the solar-blind and visibleblind UV photodetectors.The basis of a high-performance detector is a high-quality material film.Therefore,the preparation of high-quality ZnMgO films in the miscible phase region and the bandgap control are important factors affecting the subsequent application of UV detectors in this band.At present,the preparation of Zn Mg O thin films in the mixed-phase region still has problems such as poor crystal quality and phase separation.In addition,as the increasing requirements of the high spectral selectivity UV detector,the advant Ages of the pure ZnO-based detector with a broad detection band may also become its short board.How to achieve a highly wavelength selective ZnO-based detector while does not greatly reduce the sensitivity of the detector,even increasing the sensitivity,is a problem that we need to solve.In our thesis,for these two problems,we conducted a series of related scientific research,and have achieved breakthrough results.The specific results are as follows:(1)The epitaxial growth of high quality ZnO films and ZnMgO films on c-plane sapphire substrates was achieved by using plasma-assisted molecular beam epitaxy.The effect of substrate temperature on the bandgap modulation and crystalline quality of Zn MgO films was investigated.We propose that the low substrate temperature is the reason for the simultaneous coexistence of the hex Agonal phase and cubic phase Zn MgO in which the components are close together,and the heterogeneous Zn MgO thin film realized at a low substrate temperature has a single absorption edge due to the close composition.In addition,the low substrate temperature suppresses the escape of Zn atoms on the surface of the film during the growth process,and thus obtains relatively good crystal quality,and is more suitable for the preparation of the photodetector in the miscible phase region.On this basis,we have implemented high-performance mid-UV and solar-blind UV detectors with device responsivity of 258A/W,dark current as low as 75 p A,response time of milliseconds grade,and the UV-visible rejection ratio up to four orders of mAgnitude.It is worth to highlight that,after encapsulating,the series of UV detectors still has a 6.8 A/W or more response in the solar-blind area,can reach the practical level.(2)By FDTD theoretical simulation,it was verified that the large-size Ag nanoparticles on the surface of ZnO can excite the surface plasmon polaritons.The resonance mode is dominated by higher-order resonances.A random distribution of Ag nanoparticle clusters with near-extinction peak intensity in the ultraviolet region and the visible region were achieved.Furthermore,the intensity of the high resonance peaks in the ultraviolet region can be controlled by the sputtering time and the morphology and size of the Ag nanoparticles.An Ag/ZnO composite film was prepared on the surface of sapphire,and the room temperature photoluminescence of the composite film was enhanced,and the luminous intensity was improved by 1.5 times with respect to pure ZnO film.(3)An Ag/ZnO composite photoconductive UV detector with a stripe electrode was prepared.Compared with the pure ZnO device with the same structure,the peak response at 380 nm increased from 2.16 A/W to 2.86 A/W,the dark current is reduced from 60 mA/cm~2 to 38 mA/cm~2,and the detection half-width is as narrow as 10 nm,which improves the sensitivity of the device and also increases the band selectivity of the spectrum.This improvement in performance is due to the energy matching and energy transfer of the exciton-responsive region of ZnO with the higher-order resonant mode surface plasmon polaritons of Ag nanoparticles,the weakening of the received light intensity by coverage Ag metal on the surface,and the passivation caused by surface Ag modification and the local Schottky junction effect.For the first time,the enhancement of the detector using metal surface plasmon polaritons in the higher-order resonance mode has been achieved.We believe that our findings would open a way to harness the high-order plasmon modes in the field of UV optoelectronic devices. |
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