Water induced electrical hysteresis in germanium nanowires: a theoretical study.

We apply DFT calculations to evaluate the electronic properties of germanium nanowires (GeNWs) upon adsorption of water molecules and reveal the possible causes of the experimentally observed electrical hysteresis in GeNWs based electronic devices. We show that the absorption of water molecules on the GeNW surface would lead to the formation of hydroxyl passivated GeNWs (OH-GeNWs). The first step of the formation mechanism is physisorption of water molecules toward a Ge atom then followed by dissociation of water molecules to form OH-GeNWs, consistent with experimental observation of reversible and irreversible electrical hystereses. More importantly, we also predict that the effective masses of OH-GeNWs depend strongly on their growth orientation and depend nonlinearly on the OH coverage percentage. We propose that the electrical hysteresis phenomenon observed in experiment can be attributed to the formation of OH-GeNWs with different OH coverage percentages, along with different alignments of the OH groups on the GeNW surface, and also the presence of surface trap state defects, during the different stages of I-V measurement.