The influence of the interfacial metal thickness of a bilayer-metal electrode on metal/insulator electron energy barriers measured using internal photoemission spectroscopy

Metal/insulator interfaces impact the performance of electron devices through a variety of process dependent extrinsic effects. Bilayer-metal electrodes employing a reactive interfacial metal are often used to promote the adhesion of an overlying inert cap metal to an oxide. Bilayer-metal stacks have been proposed to decouple the influence of some extrinsic effects, such as interfacial defects from others such as strain and metal grain size, to assist in the optimization of silicon quantum bits. In this work, we used internal photoemission spectroscopy to directly measure the influence of the interfacial Ti thickness on the electron energy barrier at the Pt/Ti/Al2O3 bilayer-metal/insulator interface of Pt/Ti/Al2O3/TiN devices. We found that a 0.5 to 1.0 nm thick layer of Ti was sufficient to completely dominate the electron energy barrier. Insertion of a Ti layer also resulted in band tailing, likely due to oxygen scavenging, but had no impact on the bottom Al2O3/TiN electrode barrier.