Perspectives from research on metal-semiconductor contacts: Examples from Ga2O3, SiC, (nano)diamond, and SnS

Abstract

As part of a Special Issue in Honor of 30 years of the American Vacuum Society’s Nellie Yeoh Whetten Award, this Invited Perspective discusses results and trends from the authors’ and other published research on metal contacts to β-Ga2O3, (4H and 6H)-SiC, nanocrystalline diamond (NCD), and nanocrystalline thin films and single-crystalline nanoribbons of α-SnS. The paper is not a comprehensive review of research on contacts to each of these semiconductors; it is instead a perspective that focuses on Schottky barrier height (Φb) measurements and factors that affect Φb, such as metal work function (Φm) and crystallographic surface plane. Metals and the associated processing conditions that form ohmic or Schottky contacts to each of these semiconductors are also described. Estimates of the index of interface behavior, S, which measures the dependence of Φb on Φm, show large variations both among different semiconductors (e.g., S ∼ 0.3 for NCD and S ∼ 1.0 for SnS nanoribbons) and between different surface planes of the same semiconductor [e.g., (2¯01) vs (100) Ga2O3]. The results indicate that Φb is strongly affected by the nature of the semiconductor surface and near-surface region and suggest that the sharp distinction between covalent and ionic semiconductors as described in seminal theories can be adjustable.