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

碳化硅、氮化镓等宽带隙化合物半导体材料具有优良的本征特性，适合应用于下一代通信和电力电子器件。为了实现这些器件，需要开发低接触电阻的欧姆接触材料。然而，设计和开发宽禁带半导体接触材料的指导方针还没有建立起来。本研究的目的有两个：(1)了解接触/半导体界面的电(接触)性质与界面微结构之间的关系，(2)扫描隧道显微镜/电位法(STM/STP)测量电势。首先，通过沉积金属层并在真空中进行热处理来制备碳化硅和GaN的接触材料。对于碳化硅的接触，在接触/碳化硅界面上形成的反应和产物，即Ti3SiC2化合物…微观结构分析结果表明，对于TiAl基接触，在欧姆接触的形成过程中起着重要的作用。另一方面，在MOCVD-GaN衬底中形成的丝状位错密度对接触的形成或接触中的电流传输有很大的影响。因此，为了制备高性能的宽禁带半导体欧姆接触，对微结构的理解和控制是非常重要的。此外，用STM/STP技术测量了接触/半导体界面附近的电位分布(电压降)。优化了STP测量的样品制备程序，在界面处检测到了轻微的电位变化。虽然这种测量在技术上并不简单，但人们认为这项技术可以广泛应用于识别触点/半导体界面上的电流传输路径。较少

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