Title:investagation On Synthesis Of Ag-doped Rgo Reinforced And Contact Characteristics Between Ag-doped Rgo And Semiconductors

For the optoelectronic devices with the contact of the metal and semiconductor with rectification characteristics,the high-purity noble metal electrode has some shortcomings,such as high cost,large resistance,low transmittance and complicated manufacturing process.Hence,it is necessary to search for a new material to replace the noble metal electrode.Graphene,a novel two-dimensional material,has been widely used in the semiconductor devices due to its special structure and intriguing properties.Currently,the chemical vapor deposition(CVD)and oxidation-reduction method(redox)are used to prepare graphene for the optoelectronic devices.Nevertheless,it is still difficult for the CVD method to prepare and transfer graphene,which is not suitable for large scale manufacture.Compared with the CVD method,it is much easier for the redox method to fabricate graphene and,thus,has become the most potential technology.However,the poor dispersion restricts the industrial application.In order to tackle this issue,the graphene oxide was reduced while Ag particles were also introduced during the hydrothermal reduction process,and Ag-doped rGO composite powder was successfully synthesized,which could effectively inhabit the aggregration of graphene.The structure and morphology of Ag-doped rGO composite powder were characterized by X-ray difraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy(Raman),transmission electron microscopy(TEM).Moreover,the preparation process and properties of the rGO reinforced silver matrix bulk composites were studied,and the strengthening mechanism was explored as well.Furthermore,the Ag-doped rGO materials was deposited on the surface of semiconductor utilzing the spin coating method to fabricate Schottky contact junction,and the mechanism of carrier transport and barrier height formation at the interface of Ag-doped rGO materials/semiconductor were clarified by the combination of the current-voltage measurement(I-V-T)and thermionic emission(TE)model.The theoretical basis for the application of Ag-doped rGO materials in the semiconductor devices,which is of important academic signifance and engineering value.Based on the above investigations,the conclusions can be drawn as follows:Ag-doped rGO composite powders with different Ag contents were synthesized by chemical reduction method with GO and AgNO3 as the precursors and hydrazine hydrate as the reducing agent.The phase constituents,morphology and structure of Ag-doped rGO with different Ag contents were characterized by XRD,SEM and TEM.It is observed that Ag particles are completely anchored among the layers of rGO using an appropriate AgNO3 concentration,which can effectively prevent the agglomeration of rGO.However,when Ag+1 concentration is above 4.08×10-3 mol/L,it brings about an adverse effect on the dispersion of rGO due to the introduction of excessive Ag particles.In the range of experiments,the optimal process for synthesizing Ag-doped rGO composite powder is as follows:50 mg GO is firstly added into 50 mL deionized water,and 50 mg AgNO3 is added into 10 ml absolute ethanol,followed by mixing for 2 h in a ultrasonic cleaner.Furthermore,the 10 mL hydrazine hydrate is dropped in the mixed solution under 90℃ water bath along with the electromagnetic stirring for 1h.At the mass ratio of GO to AgNO3 is 1:1,the nanosized Ag particles with the size ranging from 50 nm to 100 nm are well dispersed in the Ag-doped rGO powder,and the rGO presents transparent morphology.The Ag-doped rGO synthesized by reduction method was mixed with nanosized Ag powder by ultrasonic treatment.Based on XRD and SEM analiysis,it is found that the nanosized Ag particles are uniformly distributed among the rGO layers,and uniformly distributed rGO with few layers are wrapped around the nanosized Ag particles.Ag-doped rGO reinforced silver matrix bulk composites were successfully prepared by SPS technology.XRD and SEM analysis results show that there are Ag diffraction peaks of(111),(200),(220)and(311)plane without the presence of other phases,indicating that no impurities are not introduced into the rGO reinforced Ag matrix bulk composites during the sintering process.The hardness and tensile properties of Ag-doped rGO reinforced Ag matrix bulk composites were tested.With increase of the Ag-doped rGO content,both the hardness and tensile strength increase and then decrease.At 4wt.%Ag-doped rGO,the hardness and tensile strength can reach up to 196.08 MPa and 67.35 HV,respectively.This can be ascribed to the large diameter-thickness ratio and fold effect of rGO,which can promote the load transfer.For the Ag-doped rGO reinforced Ag matrix bulk composites,the load transfer is the dominant strengthening mode while the component strengthening is auxiliary one.By determining the electrical conductivity of the bulk composites,it is found that the electrical conductivity increases and then decreases with increasing Ag-doped rGO content.The friction test shows that the wear mechanism of the Ag matrix bulk composite belongs to adhesive wear.With increase of Ag-doped rGO content,it shows an enhanced trend for the wear resistance.At 4wt.%Ag-doped rGO,there is the smallest wear rate,which is only 5.41%.Ag-doped rGO was spin-coated on the surface of CdZnTe(CZT),GaN and ZnO semiconductors to form Ag-doped rGO contact with Schottky contact.By the I-V-T test,it is revealed that the barrier height increases at the Schottky contact interface,while the ideal factor decreases with increasing temperature.This is caused by the inhomogeneity of barrier height at the interface.Especially for the ideal factor greater than 1,it is primarily related to the defect energy level and the tunneling current at the interface formed by direct traversing barrier for the electrons in the conduction band.Based on the analysis of the Gaussian distribution of barrier height and the relationship between (?)b0 and q/2kT,it can verify the inhomogeneity of barrier height at the interface of Ag-doped rGO/semi conductor Schottky contact.For the Ag-doped rGO/GaN Schottky contact,the barrier height shows the double Gaussian distributions,whereas there is a single Gaussian distribution for both Ag-doped rGO/CZT and Ag-doped rGO/ZnO Schottky contacts.Compared the barrier height of the Gaussian distribution with that calculated by the thermionic emission model,Ag doped rGO/CZT Schottky contact has the most significant lateral inhomogeneity distribution of barrier height,Ag-doped rGO/ZnO Schottky contact has the minimum lateral inhomogeneity of barrier height,and Ag doped rGO/GaN Schottky contact is at the intermediate between Ag doped rGO/CZT and Ag-doped rGO/ZnO Schottky contact.By combining the relationship between ln(I0/T2)-(q2σ02/2k2T2)and q/2kT,the Richardson constant used for calculation of the barrier height in TE model was modified.It is found that there is some difference between the modified value and the calculated value.The modified Richardson constant has the largest deviation for the Ag-doped rGO/ZnO Schottky contact,Ag-doped rGO/GaN Schottky contact has the minimum lateral inhomogeneity of modified Richardson constant.This can further confirm the inhomogeneity of barrier height at the interface.In addition,there is a sudden change in the potential at the interface.