Si passivation effects on atomic bonding and electronic properties at HfO_2/GaAs interface: A first-principles study

摘要

A theoretical study on atomic structures and electronic properties of the interface between GaAs and HfO_2 is reported. The intrinsic gap states are mainly originated from Ga dangling bonds, partial Ga-oxidation, and As-As dimers in the reconstructed interface structures. Si passivation interlayer can introduce two types of Si local bonding configuration of Si interstitial or substitutional defects (Si_(Hf)). Si_(Hf)-passivated interfaces are found to be energetically stable and can suppress the interfacial flat bandgap state stemming from partial Ga-oxidation into the valence band of bulk GaAs. Furthermore, gap states near the conduction bandedge are partially reduced. With the increase of Si concentration at the interface, the charge state of interfacial Ga decreases from +1.26 to between +0.73 and +0.80, and this change shows a Ga oxidation state transformation from Ga_2O_3 (+1.7) to Ga_2O (+0.52) states. The metastable Si interstitials also eliminate Ga_2O_3-oxidation state and creates Ga_2O-like Ga charge state at the interface. However, the gap states near the conduction bandedge cannot be passivated by substitutional (Si_(Hf)) nor by interstitial (Si_i) silicon. The detailed nature of the gap states examined in this modeling study would facilitate further development of interface passivation and the optimization of Si-passivation layers.