| Many industries today require electronic devices that work in high-temperature environments,such as aerospace,thermal power generation,petroleum exploration,and nuclear energy.However,the current limit application temperature of Si-based devices is only 200? and unable to meet the application requirements.Because SiC semiconductor material has the advantages of wide band gap,high thermal conductivity and high breakdown voltage,it can easily break through the physical limit of Si,and is widely used in the preparation of high-power,high-temperature,and high-frequency devices.The application temperature of SiC material itself can reach 1000?.What really restricts the application of SiC semiconductor material is the electrical performance and thermal stability of its ohmic contact.The research on SiC ohmic contact mostly focuses on 4H-SiC matrix,because it has the widest band gap(3.2 eV)among SiC polytypes.There are few studies on the ohmic contact of 3C-SiC substrates,and there are few reports on its high-temperature stability.In fact,3C-SiC materials have more advantages in the preparation of large-size devices.They are the only materials that can be heterogeneous on Si substrates.An epitaxially grown SiC crystal material,that is,it is not limited to the preparation of large-size SiC wafers.Therefore,this work made a targeted study on the high temperature stability of 3C-SiC ohmic contacts in air and 400?.1 The ohmic contact performance of Ni/3C-SiC structure was investigated.Under the annealing condition of 850?,950? and 1050?,specific contact resistance of 1.62×10-3 ?·cm2,5.31×10-4 ?·cm2 and 2.68×10-4 ?·cm2 were achieved,respectively.The interface and surface of Ni/3C-SiC system were analyzed by XRD,TEM,AFM,SEM and other test methods,which indicated that a large number of carbon clusters were formed near the interface and contact surface,and the presence of carbon clusters roughens the contact surface.Furthermore,it's prone to failure in the aging process.2 In order to address the problem of free carbon segregation to form carbon clusters,a metal stack structure of Ir/Ni/Ti/Ni/SiC was designed in this wok.After annealing at 850?,950? and 1050?,specific contact resistances of 8.61×10-4?·cm2,8.35×10-5 ?·cm2 and 6.94×10-5 ?·cm2 were obtained respectively,which significantly reduced the specific contact resistance of Ni/SiC system.Analysis utilizing XRD,AFM,SEM and other test methods found that no carbon clusters were formed after annealing,and free carbon was absorbed by Ti to form TiC,which significantly reduced the roughness of the contact surface.In addition,the Ir-Ni mixed layer on the top of the contact layer hinders the internal diffusion of oxygen,thereby improving the thermal stability of the ohmic contact.After aging at 400? and air for 200 h,the specific contact resistance has increased from the initial 8.35×10-5 ?·cm2 only grew to 9.13×10-4 ?·cm2.3 In order to improve the poor oxidation resistance of Ti,in this study,Ti was replaced with W,that is,the ohmic contact performance of the Ir/Ni/W/Ni/SiC system was investigated,which found that the electrical properties,thermal stability and smoothness of the contact surface of the ohmic contact are better than Ir/Ni/Ti/Ni/SiC or Ni/SiC systems.After annealing at 850?,950? and 1050?,specific contact resistances of 7.62×10-4?·cm2,4.07×10-5 ?·cm2 and 2.74×10-5 ?·cm2 were obtained respectively.It is found that carbon clusters are not formed at the interface between SiC and the contact metal,but formed a thin layer of WC,and the interface is relatively regular.In addition,there is an obvious Ir-Ni mixed layer on the top of the contact layer,which not only blocks the external diffusion of free carbon,but also hinders the internal diffusion of oxygen,making the contact surface very smooth,and significantly improving the thermal stability of the ohmic contact.After 200 hours of high temperature aging treatment,the specific contact resistance only increased from 4.07×10-5 ?·cm2 to 3.39×10-4 ?·cm2. |
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