Growth And Characterization Of Oxide-based Transparent P-n Junctions

Transparent electronics,with the aim of investigating invisible devices and circuits,have received growing interest.This is mainly due to the high potential applications in consumer electronics,especially in the display.Transparent p-n junction is the fundamental component of transparent electronics.Thus,its optical and electrical properties are of great importance for the development of transparent electronics.This work mainly focuses on the preparation of transparent p-n heterojunctions composed of wide band oxide semiconductors,as well as the study on their optical and electrical properties.The main contents are as follows:The Zn O,Co O_x and Ni O thin films were prepared by pulsed DC reactive magnetron sputtering.All the thin films possess good adhesion to the substrates,while the film surface is smooth and uniform.In the case of Co O_x and NiO thin films,different oxygen flow rates have employed to tune their phase structures or properties.Various techniques have been utilized to characterize the phase structures,optical and electrical properties of these thin films.In addition,transparent p-n junctions have been fabricated by using ZnO thin films as n-type semiconductors,and CoO_x and NiO thin as p-type materials.The performances of these p-n junctions are characterized by the I-V measurements.The experimental results and conclusions are summezied as below:?1?X-ray diffraction,UV-Vis spectrophotometer and four probes were used to study the phase structure,optical properties and resistivity,respectively.It is shown that ZnO thin films possess the wurtzite structure with the<001>preferred growth orientation.?2?The phase structures of CoO_x thin films can be tuned by changing the oxygen flow rates.,Rockslat CoO,wurtzite Co O and spinel Co₃O₄ thin films have been successfully synthesized.Various oxygen flow rates have been used to deposited NiO,and the thin films always crystalline in rocksalt phase structure.The rocksalt phase structure of thin films,and don't change with the increase of oxygen flow rate during the deposition.?3?ZnO,Co O and NiO thin films have good transparency in the visible range,while Co₃O₄ thin films absorbe the visible light almost entirely.The resistivity of Zn O is about 596 ohm cm.The resistivity of NiO increases first and then decreases when increasing the oxygen flow rate.NiO thin films grown at the 12 sccm oxygen flow rate has the highest resistivity.?4?The Keithley 2400 source meter was used to measure the I-V curves of the assembled p-n junctions.Then the physical parameters such as threshold voltage,rectifier ratio and ideality factor were obtained.The results show that the rectifying properties are achieved in p-CoO_x/n-Zn O heterojunctions,but the leakage current at the reverse bias is too large.Besides,the stability and repeatability of these devices are poor.?5?The overall performance of p-NiO/n-Zn O junctions are better,including the lower threshold voltage and larger rectifier ratio.In addition,the threshold voltage of p-NiO/n-ZnO junctions can be tuned by the oxygen flow rate to synthesize NiO thin films.With the increase of oxygen flow rate,the threshold voltage decreases first and then increases.The p-n junctions composed of Ni O with the maximum resistivity has the best electrical properties,including larger rectifier ratio,smaller threshold voltage and smaller ideality factor.