Study On The Contact Characteristics Of Graphene Supported Precious Metals With Semiconductors

With the development of microelectronics,mobile communications,and military applications,Schottky devices have triggered a research boom,which is due to high-temperature resistance,high-frequency response,and low power dissipation.As for the traditional Schottky devices,precious metals were used for electrode materials,which have been unable to meet the defects,heat dissipation,energy consumption,and resource shortage of devices.Therefore,there is an urgent need to find a new type of electrode material to compensate for the shortcomings of precious metal electrodes.As a new two-dimensional material,graphene has been widely studied due to its excellent performance.Compared to traditional Schottky devices,it has many advantages such as simple structure,fast switching speed,high frequency,and forward voltage reduction,when the Schottky barrier was formed between the graphene and semiconductor.As a derivative of graphene,graphene oxide（GO）has the advantages of easy preparation,low cost,and mass production.Therefore,in this paper,reduced graphene oxide loaded with precious metal nanoparticle composites（rGO-PMNPs）were firstly prepared by the hydrothermal method using GO as the raw material with a view to replacing precious metal electrodes.Then,the composites were deposited on the surface of silicon（Si）and aluminum-doped zinc oxide（AZO）,and the loading of precious metal nanoparticles（PMNPs）was varied to optimize the Schottky contact characteristics by modulating the microscopic morphology of the composites.Finally,the charge carrier transport mechanism and the factors influencing of Schottky contact characteristics were analyzed in conjunction with current-voltage（I-V）and capacitance-voltage（C-V）tests.The following conclusions were drawn from the above research:In this paper,by the hydrothermal method,the rGO-PMNPs composites have been prepared,which are suitable for both Au and Pt precious metal loadings.Combining X-ray diffraction,scanning electron microscope,transmission electron microscope,X-ray photoelectron spectroscopy,Fourier transform infrared spectroscopy and Raman spectroscopy were used to analyze for the phase,morphologies,and structures of rGO-AuNPs and rGO-Pt NPs.The results show that rGO-AuNPs and rGO-Pt NPs composites with less aggregation of rGO,uniform distribution of NPs,and a particle size of about 100 nm can be obtained by regulating the loading of Au and Pt.The analysis showed that PMNPs in the composites could inhibit the aggregation of rGO and promote the reduction.In the field of experimental research,the optimal loading process was as follows:when the hydrothermal reaction temperature is160℃,and the mass ratio of HAu Cl₄ to GO is 3:1,the loading effect of rGO-AuNPs composite is the best;when the mass ratio of H₂Pt Cl₆×6H₂O to GO is 1:1,the loading effect of rGO-Pt NPs composite material is the best.Through I-V and C-V tests,it was observed that good rectification characteristics were presented between rGO-AuNPs and rGO-Pt NPs composites and n-Si.Charge transfer can occur between the introduced PMNPs and rGO,which leads to increasing carrier concentration,rising Schottky barrier height（SBH）,and improved Schottky contact characteristics.Combined with the thermal emission（TE）model,it is assumed that the metal loading and particle size affect the morphology of rGO,which further affects the electrical properties of rGO and the SBH of rGO-PMNPs/n-Si.It is found that the SBH value tends to increase and then decrease with the metal loading increasing.The rGO-AuNPs/n-Si heterojunction prepared with 75 wt%Au loading had the highest SBH value of 0.695 e V with an ideal factor of 2.39,while the rGO-Pt NPs/n-Si heterojunction prepared with 50 wt%Pt loading had the highest SBH value of 0.731e V with an ideal factor of 2.88.The presence of incomplete rGO reduction,agglomerates,and defects in the composite may lead to series resistance,SBH transverse inhomogeneities,and leakage currents,causing the ideal factor to deviate from the theoretical value of 1.The prepared rGO-AuNPs and rGO-Pt NPs composites were spin-coated onto the surface of AZO semiconductor material prepared by the sol-gel method to form Schottky contacts.The I-V characteristics revealed that the rGO-AuNPs and rGO-Pt NPs composites in contact with AZO films exhibited rectification properties.The 3 wt%Al³⁺doping can effectively reduce the oxygen vacancy defects in Zn O,increase the carrier concentration,reduce the leakage current,and increase the SBH,thus improving the Schottky contact characteristics.The optimum SBHs of the rGO-AuNPs/AZO and rGO-Pt NPs/AZO heterojunctions were 0.654 e V and 0.67 e V,respectively,with ideal factors of 2.83 and 2.3.The analysis shows that the deviation of the ideal factor from the theoretical value of 1 may be related to oxygen vacancy defects from the AZO films and rGO of the composites,which will lead to the transversal inhomogeneities of Schottky barrier,the series resistance,and the leakage currents in the rGO-PMNPs/AZO,thus causing mirroring forces as well as tunneling effects,so that the carrier transport mechanism deviates from the TE model.