The orientational distribution in partially ordered solids, drawn polymers, etc. is related with NMR and ESR line shapes governed by anisotropic shift, dipolar, or quadrupolar couplings. In principle, the theory yields the complete orientational distribution by numerical deconvolution or spectral fitting procedures. Furthermore, the line shape can be decomposed into subspectra that correspond to the moments of the orientational distribution. The theory is applied to 2D-NMR line shapes in partially ordered solid benzene, and to ESR nitroxide spin label spectra.

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The discovery of the ferroelectric orthorhombic phase in doped hafnia films has sparked immense research efforts. Presently, a major obstacle for hafnia's use in high‐endurance memory applications like nonvolatile random‐access memories is its unstable ferroelectric response during field cycling. Different mechanisms are proposed to explain this instability including field‐induced phase change, electron trapping, and oxygen vacancy diffusion. However, none of these is able to fully explain the complete behavior and interdependencies of these phenomena. Up to now, no complete root cause for fatigue, wake‐up, and imprint effects is presented. In this study, the first evidence for the presence of singly and doubly positively charged oxygen vacancies in hafnia–zirconia films using thermally stimulated currents and impedance spectroscopy is presented. Moreover, it is shown that interaction of these defects with electrons at the interfaces to the electrodes may cause the observed instability of the ferroelectric performance.

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Articles you may be interested inHigh quality HfO2/p-GaSb (001) metal-oxide-semiconductor capacitors with 0.8 nm equivalent oxide thickness Appl. Phys. Lett. 105, 222103 (2014); 10.1063/1.4903068 Quantitative characterization of interface traps in Al2O3/AlGaN/GaN metal-oxide-semiconductor high-electronmobility transistors by dynamic capacitance dispersion technique Appl. Phys. Lett. 103, 033510 (2013); 10.1063/1.4813912 Study of gate oxide traps in HfO2/AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors by use of ac transconductance method A comprehensive analytical model for threshold voltage calculation in GaN based metal-oxide-semiconductor high-electron-mobility transistors Appl. Phys. Lett. 100, 113509 (2012); 10.1063/1.3694768 Trap states in AlGaN/GaN metal-oxide-semiconductor structures with Al 2 O 3 prepared by atomic layer depositionIn this work, we present the terrace etching technique to obtain excessive thickness series of atomic layer deposition (ALD) grown Al 2 O 3 and HfO 2 on GaN-cap/AlGaN/GaN heterostructures allowing for the detailed study of oxide charge distribution and its impact of the metal-insulatorsemiconductor high electron mobility transistor (MISHEMT) threshold voltage. By modeling the experimental plot of threshold voltage versus oxide thickness on the basis of experimentally determined two-dimensional electron gas charge density in AlGaN/GaN MISHEMTs, we separated the interface and bulk charge components and determined the oxide-metal barrier height for the investigated gate dielectrics. In both Al 2 O 3 and HfO 2 gate dielectrics, the oxide charges are mainly located at the oxide/GaN interface. Determining the interface trap charges from comparison of the pulsed capacitance-voltage (CV) technique with very fast voltage sweep to the modulation type CV method with slow DC voltage ramp, we extracted positive fixed charges of N Ox ¼ 2:7 Â 10 12 cm À2 for Al 2 O 3 and N Ox ¼ 7:8 Â 10 12 cm À2 for HfO 2 . We found a strong V th shift of opposite direction for both high-k materials, corresponding to negatively charged up trap states at the HfO 2 /GaN interface and positively charged up trap states at the Al 2 O 3 /GaN interface. The evaluation of the metal-oxide barrier height in dependence of the metal work function followed the trend of the Schottky model, whereas HfO 2 showed less Fermi level pinning compared to Al 2 O 3 indicating the presence of an increased number of interface states in Al 2 O 3 on GaN. V C 2015 AIP Publishing LLC. [http://dx.