Tunneling Properties of the Charge Carriers through Sub-2-nm-Thick Oxide in Ge/a - Ge O2/Ge Structures Using the First-Principles Scattering-State Method

The quantum-mechanical tunneling passing through the sub-2-nm-thick oxide in Ge/a-GeO2/Ge structures is presented, using the first-principles scattering-state method, where a stands for the amorphous phase. The suboxide interface layer (IL) between Ge and the dioxide region (DOX) does not play a critical role in blocking tunneling due to the presence of Ge - Ge bonds in it. The thickness of DOX, where all the Ge has four Ge - O bonds, is the effective tunneling-blocking thickness and the thickness for the thinnest usable a-GeO2 is approximately 0.85 nm. The width and magnitude of the band offset differently affect the tunneling in the sub-2-nm-thick oxide. The valence-band offset is larger and thicker than the conduction-band offset for all the structures, resulting in the smaller tunneling current of the holes than of the electrons. It is also found that the effect of the hydrogen passivation at the IL on tunneling is not evident in semiconductor/a-oxide. The crystallographic orientation of Ge has no distinct effect on the band-gap alignment and the tunneling current in Ge/a-GeO2/Ge structures, consistent with the experimental results about the effect of the Ge orientation on the interface properties.