This title appears in the Scientific Report : 2016

##### Growth and characterization of crystalline rare-earth based thin oxide films for the application as gate dielectric in nanotechnology
Personal Name(s): Schäfer, Anna (Corresponding author) Halbleiter-Nanoelektronik; PGI-9 Jülich Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2015 xiii, 157 S. RWTH Aachen, Diss., 2015 978-3-95806-111-8 Book Dissertation / PhD Thesis Controlling Electron Charge-Based Phenomena Schriften des Forschungszentrums Jülich. Reihe Information / Information 46 OpenAccess OpenAccess Publikationsportal JuSER
Please use the identifier: http://hdl.handle.net/2128/9996 in citations.
 For standard metal oxides semiconductor (MOS) field effect transistors (FETs), but also for any other MOS based device appropriate gate dielectrics are needed. Such dielectrics, usually oxides, need to exhibit good layer quality and stability, good insulating properties and typically high permittivities. The aim of this work is to develop new oxides for the use in standard Si transistors on the one hand and for GaN based devices such as high electron mobility transistors on the other hand. For Si MOSFETs a standard atomic layer deposition (ALD) HfO$_{2}$ process is extended to dope HfO$_{2}$ with Al and Lu. After process optimization Hf$_{0.89}$Al$_{0.11}$O$_{2-\Delta}$ and Hf$_{0.8}$Lu$_{0.2}$O$_{2-\Delta}$ transform into a polycrystalline layer with large fractions of a high $\ kappa$ phase of HfO$_{2}$, most probably the cubic one, and exhibit permittivities of 30 and 33, respectively. All layers are smooth, the density of interface traps hardly changes due to doping and leakage current densities for Hf$_{0.8}$Lu$_{0.2}$O$_{2-\Delta}$ are as low as 10$^{0}8$A/cm$^{2}$ for an equivalent oxide thickness of 1.5 nm. For the application on GaN, crystalline GdScO$_{3}$ and LaLuO$_{3}$ are investigated. Calculations on GdScO$_{3}$ reveal that the orthorhombic and cubic form of GdScO$_{3}$ have almost equal energies of formation while a hexagonal crystal has a 500 eV per formula unit enhanced energy. Even though the energy of formation is fairly high, the novel hexagonal forms of GdScO$_{3}$ and LaLuO$_{3}$ could be stabilized by pulsed laser deposition on GaN and on Y$_{2}$O$_{3}$ on Si(111) which is used as alternative growth template with hexagonal geometry. Thus the nature of the substrate (polar/ non-polar) apparently determines the structure of the oxide formed. Further analysis shows that the two growth templates can promote the hexagonal or the cubic forms of GdScO$_{3}$ and LaLuO$_{3}$ depending on growth temperature and Y$_{2}$O$_{3}$ layer thickness. Relative permittivities of approximately 26 are extracted for both hexagonal GdScO$_{3}$ and hexagonal LaLuO$_{3}$. All known phases of the two oxides have band gaps above 5 eV which is important for the use as gate dielectric, e.g. to minimize tunneling currents. Current voltage measurements reveal leakage current densities of 1.2 X 10$^{-8}$ Acm$^{-2}$ at 1V for $\textit{EOT}$ = 3nm and a dielectric breakdown above 2MVcm$^{-1}$ for hexagonal GdScO$_{3}$ on GaN.