Study On The Fabrication Of The Transparent Homojunction/Heterojunction And Resistance Switching Properties Of NiO

NiO is a typical p-type semiconductor with good optical and eletcrical properties. Meanwhile, NiO isa popular material for resistance random access memory research. ZnO is also an important photoelectricmaterial and it has been recognized as one of the most promising materials for blue and ultravioletoptoelectronic devices. ZnO is a suitable material for fabricating NiO-based heterojunction optoelectronicdevices.Resistive random access memory as a non-volatile memory is expected to be one of the mostcompetitive candidates due to its superior characteristics including simple structure, high densityintegration, low power consumption and good compatibility with conventional CMOS process. However,there exists dispute on the resistive swiching mechanism. At present, most of the studies have been focusedon the exploration of the physical mechanism.This paper developed a series of basic research based on the NiO semiconductor materials. The mainwork is as follows:Undoped NiO thin films were grown on quartz substrates under different oxygen pressure by pulsedlaser deposition. Hall and the I-V measurements of different metal-semiconductor contacts showed that thelevel of oxygen pressure strongly affect the conductivity type of the NiO thin films. Oxygen atoms are easyto dissociate under low oxygen pressure, resulting Ni and O atomic ratio is greater than1. Ni metal atomsare surplus, causing that the electron concentration is higher than the hole concentration and a conversionof NiO thin films conductivity type is from n-type to p-type. Optical transmission spectroscopy indicatedthat the average transmittance of n-type NiO and p-type NiO thin films are74%and81%, respectively, which further confirmed that the Ni metal atoms are surplus in the NiO thin film and the transmittancedecreases. Based on the fabrication of two type of conductivity NiO films through the regulation of oxygenpressure, we further prepared the n-NiO/p-NiO homojunction on the ITO substrate. I-V test indicates thatthe homojunction has good rectifying characteristics, and the homojunction carrier transport mechanismfits the space-charge-limited current theory. The average transmittance of the homojunction in the visiblelight region reachs72%，which all indicates that the homojunction is suitable as transparent electronicsdevices.ZnO thin films were prepared by pulsed laser deposition on quartz substrates, as a comparison withthe ZnO single crystal. The high Hall mobility and XRD pattern prove well-crystallized with highly （002）preferred orientation.71%transmittance in the visible region is shown in the transmittance spectrum. Avariety of characterization methods proved that the main drawback of ZnO thin films prepared by PLD isZn interstitial （Zni）, which provides the basis for the application of ZnO thin films. The p-NiO/n-ZnOheterojunction is futher prepared and the optical and electrical measurements are peformed. The averagetransmittance of the heterojunction in the visible light region reachs76%，which shows good transparency.The open voltage V_thof p-n heterojunction is about1.5V, the reverse breakdown voltage V_Bis about-7V,and the reverse saturation current is in the10^-5A magnitude when the bias voltage is in the-2V^<sup>-5 Vrange, implying that the heterojunction exists excellent rectification characteristics. The internal carriertransport mechanism in heterojunction was studied as follow, and we find that the heterojunction containedcarrier transport in line with the space-charge-limited current theory. Our work might provide a basis forthe future transparent electronics devices.Two conductivity type of NiO films were deposited on the commercial ITO suvstrate by pulsed laserdeposition, respectively. The metal electrodes which can formed Schottky barrier were deposited, in order to research the resistive characteristics of the single Schottky barrier. The I-V test curves show thatW/p-NiO/ITO and Pt/n-NiO/ITO structures both have a unipolar resistive switching behavior. Based onanalysis, we suspect that the resistive switching mechanism is jointly determined by the interface barrierand the filament mechanism. About the current conductive mechanism, we found that they are in line withthe Ohmic behavior in LRS and HRS at low electric field while HRS at high field it obeys the P-F emissionby fitting various curves and formulas. We further tested the resistive switching characteristics ofn-NiO/p-NiO homojunction structure. Bipolar resistive switching phenomenon are observed before spacecharge region breakdown. While forward breakdown, unconventional resistive phenomenon are found. Themain reason can be attributed to the carrier trapping and detrapping in the barrier area. While that variousdefect levels trap and detrap carriers can not be ignored. Synthesis above, the resistance switchingphenomenon of M/NiO/ITO structure and the n-NiO/p-NiO homojunction we prepared can be attributed tothe body effect and interfacial effect combined effect.