The dispersion in accumulation at InGaAs-based metal/oxide/semiconductor gate stacks with a bi-layered dielectric structure

摘要

InGaAs gate stacks comprising the moderate dielectric constant (k) Al_2O_3 have a significantly lower dispersion in accumulation in comparison to stacks with the high-k HfO_2 of the same physical thickness. As a result, a HfO_2/Al_2O_3 bi-layer structure seems attractive in terms of both high effective dielectric constant and low dispersion in accumulation. The influence of Al_2O_3 thickness on the dispersion was investigated in metal/HfO_2/Al_2O_3/InGaAs gate stacks with a fixed overall dielectric thickness. An effective suppression of the dispersion with the increase of the Al_2O_3 thickness was observed. However, the Al_2O_3 thickness required for passivation of the dispersion in accumulation was significantly higher in comparison to both the border traps related tunneling distance in Al_2O_3 and the minimal thickness required for the Al_2O_3/InGaAs band offset stabilization. The phenomenon can be explained by the lower dielectric constant of Al_2O_3 film (compared to the subsequently deposited HfO_2 layer), where Al_2O_3 dielectric constant dependence on the film thickness enhances the dispersion intensity. As a result, the guidelines for the passivation layer engineering are: maximization of both majority carriers band offsets and of the dielectric constant of the passivation layer.