In this study, the unipolar resistive switching(URS) and bipolar resistive switching(BRS) are demonstrated to be coexistent in the Ag/Zn O/Pt memory device, and both modes are observed to strongly depend on the polarity of forming voltage. The mechanisms of the URS and BRS behaviors could be attributed to the electric-field-induced migration of oxygen vacancies(VO) and metal-Ag conducting filaments(CFs) respectively, which are confirmed by investigating the temperature dependences of low resistance states in both modes. Furthermore, we compare the resistive switching(RS)characteristics(e.g., forming and switching voltages, reset current and resistance states) between these two modes based on VO- and Ag-CFs. The BRS mode shows better switching uniformity and lower power than the URS mode. Both of these modes exhibit good RS performances, including good retention, reliable cycling and high-speed switching. The result indicates that the coexistence of URS and BRS behaviors in a single device has great potential applications in future nonvolatile multi-level memory.
Zn Se nanoribbons were synthesized with chemical vapor deposition route. The excitation power-dependent photoluminescence and surface photovoltage(SPV) techniques were used to study the optoelectronic properties of the as-grown Zn Se nanoribbons. Three deep defect(DD)-related emission bands, respectively, centered at 623 nm(DD1), 563 nm(DD2)and 525 nm(DD3), emerge orderly with increasing the excitation power, which is attributed to the saturation of the DD states from deeper to shallower level. The SPV spectrum and the corresponding phase spectrum show that DD1 mainly acts as recombination center, while DD2 and DD3 can act as both the recombination center and electron traps. The influence of the trapping electrons on the SPV response dynamic was studied with transient SPV.
Chao FanQinglin ZhangXiaoli ZhuXiujuan ZhuangAnlian Pan
The electron transport layer(ETL) plays an important role in planar heterojunction perovskite solar cell(PSCs),by affecting the light-harvesting, electron injection and transportation processes, and especially the crystallization of perovskite absorber. In this work, we utilized a commercial TKD-TiO_2 nanoparticle with a small diameter of 6 nm for the first time to prepare a compact ETL by spin coating. The packing of small-size particles endowed TKD-TiO_2 ETL an appropriate surface-wettability, which is beneficial to the crystallization of perovskite deposited via solution-processed method. The uniform and high-transmittance TKD-TiO_2 films were successfully incorporated into PSCs as ETLs. Further careful optimization of ETL thickness gave birth to a highest power conversion efficiency of 11.0%, which was much higher than that of PSC using an ETL with the same thickness made by spray pyrolysis. This TKD-TiO_2 provided a universal solar material suitable for the further large-scale production of PSCs. The excellent morphology and the convenient preparation method of TKD-TiO_2 film gave it an extensive application in photovoltaic devices.
Peng ChenYinglin WangMeiqi WangXintong ZhangLingling WangYichun Liu
Wide bandgap(3.37 eV)and high excitonbinding energy of ZnO(60 meV)make it a promising candidate for ultraviolet light-emitting diodes(LEDs)and low-threshold lasing diodes(LDs).However,the difficulty in producing stable and reproducible high-quality p-type ZnO has hindered the development of ZnO p–n homojunction LEDs.An alternative strategy for achieving ZnO electroluminescence is to fabricate heterojunction devices by employing other available p-type materials(such as p-GaN)or building new device structures.In this article,we will briefly review the recent progress in ZnO LEDs/LDs based on p–n heterostructures and metal–insulatorsemiconductor heterostructures.Some methods to improve device efficiency are also introduced in detail,including the introduction of Ag localized surface plasmons and single-crystalline nanowires into ZnO LEDs/LDs.
The defect-related photoconductivity gain and persistent photoconductivity(PPC)observed in Ga_(2)O_(3)Schottky photodetectors lead to a contradiction between high responsivity and fast recovery speed.In this work,a metal-semiconductor-metal(MSM)Schottky photodetector,a unidirectional Schottky photodetector,and a photoconductor were constructed on Ga_(2)O_(3)films.The MSM Schottky devices have high gain(>13)and high responsivity(>2.5 A/W)at 230-250 nm,as well as slow recovery speed caused by PPC.Interestingly,applying a positive pulse voltage to the reverse-biased Ga_(2)O_(3)/Au Schottky junction can effectively suppress the PPC in the photodetector,while maintaining high gain.The mechanisms of gain and PPC do not strictly follow the interface trap trapping holes or the self-trapped holes models,which is attributed to the correlation with ionized oxygen vacancies in the Schottky junction.The positive pulse voltage modulates the width of the Schottky junction to help quickly neutralize electrons and ionized oxygen vacancies.The realization of suppression PPC functions and the establishment of physical models will facilitate the realization of high responsivity and fast response Schottky devices.
Single-phased,high-color-rendering index(CRI)white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes(WLEDs)and as an alternative to blends of tricolor phosphors.However,it is a challenge to create a high CRI white light from a single-doped activator.Here,we present a high CRI(Ra 591)white-light phosphor,Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:Eu^(2+),composed of Sr5(PO4)3Cl as the beginning member and Sr_(5)(BO_(3))_(3)Cl as the end member.This work utilized the solid-solution method,and tunable Eu^(2+) emission was achieved.Color-tunable Eu^(2+) emissions in response to structural variation were observed in Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl solid solutions.This was further confirmed using X-ray Rietveld refinement,electron paramagnetic resonance spectroscopy,and in the photoluminescence spectra.The color-tunable emissions included the white light that originated from the combination of the blue emission of Sr_(5)(PO_(4))_(3)Cl:Eu^(2+) and an induced Eu^(2+) yellow emission at approximately 550 nm in the solid solution.Importantly,the white-light phosphors showed a greater R9590.2 under excitation at 365 nm.This result has rarely been reported in the literature and is greater than that of(R9514.3)commercial Y_(3)A_(l5)O_(12):Ce^(3+)-based WLEDs.These findings demonstrate the great potential of Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:0.04Eu^(2+) as a white-light phosphor for near-UV phosphor-converted WLEDs.These results also provide a shortcut for developing a high CRI white-light phosphor from a single Eu^(2+)-doped compound.
Peng-Peng DaiCong LiXin-Tong ZhangJun XuXi ChenXiu-Li WangYan JiaXiaojun WangYi-Chun Liu
