Ohmic contact materials for wide-gap semiconductors : Fabrication and STP analysis.

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Wide-band-gap compound semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have excellent intrinsic properties, and thus are suitable for application to next-generation communication and power electronic devices. In order to realize these devices, ohmic contact materials with low contact resistances are required to develop. However, a guideline of designing and developing the contact materials for the wide-gap semiconductors is not established. This study are focused on two fold purpose : (i)understanding of correlation between electrical (contact) properties and interfacial microstructures of the contact/semiconductor interfaces, and (ii)scanning tunneling microscopy/potentiometry (STM/STP) measurements of electrical potentials.First, the contact materials for SiC and GaN were prepared by depositing metal layers and subsequently annealing in a vacuum. As for the contacts for SiC, the reaction and products formed at the contact/SiC interfaces, i.e.Ti_3SiC_2 compounds … More for TiAl-based contacts, was found to play an important role in formation of the ohmic contacts from the results of microstructural analysis. On the other hand, the density of the threading dislocations, which were formed in the MOCVD-GaN substrates, was found to have strong influences on the contact formation or current transport in the contacts. Consequently, understanding and control of the microstructures were very important in order to fabricate high performance ohmic contacts for the wide-gap semiconductors. In addition, the potential distribution (voltage drop) near the contact/semiconductor interfaces was measured by the STM/STP technique. The procedures of the sample preparation for the STP measurements were optimized, and the potential changes were detected slightly at the interface. Although the measurements are not technically straightforward, this technique was believed to apply extensively in order to identify the paths of the current transport at the contact/semiconductor interfaces. Less