Absence of Evidence for Fixed Charge in Metal–Aluminum Oxide–Silicon Tunnel Diodes

Abstract

Here, a controlled variation in the fixed charge density (NF) and thickness of aluminum oxide tunnel insulators is reported, and the impact on Schottky barrier height in metal–insulator–semiconductor (MIS) diodes is studied. Analysis of metal–aluminum oxide–silicon capacitor structures indicates a change in NF from +1 × 1012 cm−2 in as‐deposited films to −2 × 1012 cm−2 in annealed films. An analytical model and numerical device physics simulations are used to predict changes in ­based on these changes in NF and alumina thickness. Surprisingly, Mott–Schottky derived values did not follow the trends predicted by these electrostatic models. In fact, there seems to be no discernable effect of NF in diodes with alumina thicknesses below 2 nm, contrary to contactless measurements of the fixed charge of films of similar thickness. The trends are better explained by a dipole model. It is further shown that in as‐deposited MIS diodes, the dipole is a function of alumina layer thickness, whereas in annealed MIS diodes, the dipole and were roughly constant independent of alumina thickness. These data suggest a strategy by which the of MIS tunnel contacts can be controlled and which has implication for the design of electrical contacts.