%0 Thesis
%A Tromm, Thomas Carl Ulrich
%T High-k rare-earth oxides on GaN and ferroelectric properties of hafnia based thin films
%I RWTH Aachen University
%V Dissertation
%M FZJ-2019-02847
%P 133 p.
%D 2019
%Z Dissertation, RWTH Aachen University, 2014
%X The continuous improvement of the transistors is the basis for the increase of computing power. For enhanced metal-oxide-semiconductor (MOS) field-effect-transistors(FETs) and other devices suitable gate dielectrics are required, that exhibit a high relative permittivity, good insulating properties like a large band gap, and a goodlayer quality. Additionally, new device structures like negative capacitance FET (NCFET) are developed.In this thesis the ternary rare-earth oxides GdScO3 (GSO), LaLuO3 (LLO) and SmScO3 (SSO) are grown on GaN by pulsed laser deposition (PLD). Those oxidesreveal a hexagonal phase, that has been discovered few years ago. The oxides have a large lattice mismatch to the GaN and are not at thermodynamic equilibrium,according to ab-initio calculations. The hexagonal ternary rare-earth oxides reveal a permittivity of 30 (GSO) and of 32 (LLO) and a bandgap above 5 eV. To understandthe growth mechanism of the rare-earth oxides, the layer and especially the interface are investigated. First of all hexagonal GSO reveals a decomposition of Scand Gd at the interface, so that it exhibits twice as much Sc than Gd, which reduces the length of the in-plane axis of the GSO and subsequently the lattice mismatch.Secondly, the grains are tilted in-plane, revealing a fibre texture with the c-axis as fibre axis perpendicular to the interface. Thirdly, the distance of the lattice planesat the interface is enhanced, revealing a distance of 3.1 Å. The SSO also reveals a fibre texture and an enhanced interface distance, thought the decomposition of theSm and the Sc occurs in places. The hexagonal LLO reveals a fibre texture and a small decomposition.For a novel NCFET a ferroelectric is placed in between the gate metal and the oxide of a MOSFET. The ferroelectric should exhibit a negative capacitance and inthis way cause a voltage amplification, resulting in a subthreshold slope (SS) below 60 mV/dec. PLD grown ferroelectric HfO2 with 5% Gd and HfO2 with 5% Lu(HfLuO) reveal a remanent polarization of 12 μC/cm2, while the HfO2 with 5% Y, grown by atomic layer deposition, reveals one of 20 μC/cm2 and a steeper hysteresis.HfLuO exhibits a pinched hysteresis at the initial state, if the sample is annealed at 500 °C, which could be related to an antiferroelectric phase. At an annealingtemperature of 700 °C the HfLuO layer becomes ferroelectric.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%U https://juser.fz-juelich.de/record/862553