Investigation of Atomic-Layer-Deposited TiOx as Selective Electron and Hole Contacts to Crystalline Silicon

The applicability of atomic-layer-deposited titanium oxide (TiOx) thin films for the formation of carrier selective contacts to crystalline silicon (c-Si) is investigated. While relatively good electron selectivity was presented recently by other groups, we show that carrier selectivity can be engineered from electron to hole selective depending on the deposition conditions, post deposition annealing and the contact material covering the TiOx layer. For both the electron and hole contacts, an open-circuit voltage (Voc) of ~ >650 mV is obtained. The fact that the Voc is correlated with the (asymmetric) induced c-Si band bending suggests that carrier selectivity is mainly governed by the effective work function and/or the fixed charge rather than by the asymmetric band offsets at the Si/TiOx interface, which provides important insight into the basic function of metal-oxide-based contact systems.