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Tham khảo tài liệu 'silicon carbide materials processing and applications in electronic devices part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Introducing Ohmic Contacts into Silicon Carbide Technology 305 the possible enhancement of electric field at these features and semiconductor doping at these locations 3 formation of intermediate semiconductor layer between the deposited metals and semiconductor which consists of silicides or carbides could divide the high barrier height into lower ones thus reducing the effective barrier height. The findings presented first demonstrate that no Al is clearly segregated around the interfacial region in particular at the top few layers of SiC which rules out the possibility of additional Al doping. Though a small amount of residual Al is found to be present mostly in a form of Al4C3 compound it may locate on the surface of annealed contacts rather than in the layer directly contacted to the SiC thus playing a negligible role in Ohmic contact formation. The majority of deposited Al is evaporated during annealing because of its low melting point and high equilibrium vapor pressure. The dominant role played by Al in the TiAl system is to assist the formation of liquid alloy so as to facilitate chemical reaction. Furthermore careful characterization of the interfacial region reveals that the substrate and the generated compound are epitaxially oriented and well matched at interface with no clear evidence of high density of defects. This suggests that the morphology might not be the key to understanding the contact formation. In support of this speculation it has been observed previously that Ti Ohmic contacts can be possibly generated without any pitting and that pit-free Ohmic contacts can be fabricated. One remaining theory is the alloy-assisted Ohmic contact formation. This alloy is determined to be ternary Ti3SiC2 which has also been corroborated by other expriments. Since the bulk Ti3SiC2 has already been found to be of metallic nature both in experiment and theory the contact between Ti3SiC2 and its covered metals should show Ohmic character and thus the SiC .
