An investigation of border traps and interface states in high-k/InGaAs metal-oxide-semiconductor systems

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Lin, Jun
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University College Cork
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One approach to saving energy in metal-oxide-semiconductor field effect transistors (MOSFETs) is to replace SiO2/Si structure with high dielectric constant (high-k) oxides on high mobility channel materials (e.g. InGaAs), which have the potential to achieve a comparable on current and operating frequency to silicon, but at a reduced supply voltage. In this thesis, investigation into border traps (or charge trapping) and interface states, both of which can induce device instability, in HfO2/InGaAs and Al2O3/InGaAs metal-oxidesemiconductor (MOS) structures was carried out with an emphasis on the characterization of border traps using capacitance-voltage (C-V) hysteresis measurement. The charge trapping is observed to be mainly a reversible process. The trapped charge is predominantly localized as a sheet charge near/at the high-k/InGaAs interfacial layer (~1nm), which can contain native oxides of InGaAs. The engineering of the high-k/InGaAs interface is therefore the key to reducing C-V hysteresis and improving device reliability. This work demonstrates the ability to reduce border trap density with forming gas annealing (5% H2 / 95% N2) in the range 3500C~4500C for Al2O3/InGaAs and HfO2/InGaAs MOS structures. Moreover, it is observed that C-V hysteresis increases with a power law dependence with the increasing stress time (in accumulation) at the initial stage of stressing and tends to reach a plateau at sufficiently long stress times due to the filling of almost all the pre-existing border traps. This therefore provides a method to estimate the total trap density under certain oxide field. Furthermore, a combined C-V and hard x-ray photoelectron spectroscopy (HAXPES) study was performed on Al2O3/InGaAs MOS structure, revealing a partially pinned Al2O3/InGaAs interface. The Fermi level position at zero gate bias was calculated using both techniques, and a reasonable agreement was achieved. This combined study thus provides more certainty on the interface state profile extractions.
InGaAs MOS , Border traps , Interface states
Lin, J. 2017. An investigation of border traps and interface states in high-k/InGaAs metal-oxide-semiconductor systems. PhD Thesis, University College Cork.