Charge Trapping in Substoichiometric Germanium Oxide

Electron and hole trapping in substoichiometric germanium oxides are investigated through the use of hybrid density functionals. We consider disordered model structures generated by Monte-Carlo bond switching and by ab initio molecular dynamics (MD). The Monte-Carlo model consists of fourfold coordinated Ge atoms and of twofold coordinated O atoms, and does not show trap levels neither for electron nor for holes. At variance, the MD model shows threefold coordinated O and Ge atoms forming valence alternation pairs and is found to present trap states for both carriers. The trapping states correspond to the formation and breaking of Ge-Ge bonds. The associated defect levels are determined within a band diagram of the Ge/GeO2 interface.