Grain and Grain Boundary Conduction Channels in Copper Iodide Thin Films

Due to the textured nature of random in-plane orientation of sputtered γ-CuI (111) thin films, the crystalline grains and grain boundaries (GBs) influence charge carrier transport. Herein, current probe atomic force microscopy (cp-AFM) measurements for differentiation and correlation of these morphological features and their contribution to electrical conductivity are presented, thus showing a clear difference between the conductive behavior of grains and GBs. A localized high and linearly voltage-dependent current at the boundaries as well as a rectifying behavior between the platinum-coated AFM tip and the grain surfaces is observed. Also, a different temporal evolution of voltage-dependent conductivity is observed for grains and GBs. Further, the charge carrier transport through the surface vanishes with time. It is suspected that atmospheric oxygen causes these time-dependent surface changes because accelerated degradation of the conductivity after oxygen plasma treatment is also measured.