The formation of epitaxial γ-Al2O3 thin films on 4H-SiC was found to be strongly dependent on the film thickness. An abrupt interface was observed in films up to 200 Å thick with an epitaxial relationship of γ-Al2O3(111)‖4H-SiC(0001) and γ-Al2O3(44¯0)‖4H-SiC(112¯0). The in-plane alignment between the film and the substrate is nearly complete for γ-Al2O3 films up to 115 Å thick, but quickly diminishes in thicker films. The films are found to be slightly strained laterally in tension; the strain increases with thickness and then decreases in films thicker than 200 Å, indicating strain relaxation which is accompanied by increased misorientation. By controlling the structure of ultrathin Al2O3 films, metal–oxide–semiconductor capacitors with Al2O3 gate dielectrics on 4H-SiC were found to have a very low leakage current density, suggesting suitability of Al2O3 for SiC device integration.

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Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. We report in this work the optical properties of Er 3+ -doped Y 2 O 3 , deposited by radical enhanced atomic layer deposition. Specifically, the 1.53 m absorption cross section of Er 3+ in Y 2 O 3 was measured by cavity ring-down spectroscopy to be ͑1.9± 0.5͒ ϫ 10 −20 cm 2 , about two times that for Er 3+ in SiO 2 . This is consistent with the larger Er 3+ effective absorption cross section at 488 nm, determined based on the 1.53 m photoluminescence yield as a function of the pump power. X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy were used to determine the film composition, which in turn was used to analyze the extended x-ray absorption fine structure data, showing that Er was locally coordinated to only O in the first shell and its second shell was a mixture of Y and Er. These results demonstrated that the optical properties of Er 3+ -doped Y 2 O 3 are enhanced, likely due to the fully oxygen coordinated, spatially controlled, and uniformly distributed Er 3+ dopants in the host. These findings are likely universal in rare-earth doped oxide materials, making it possible to design materials with improved optical properties for their use in optoelectronic devices.

Al 2 O 3 thin films were grown on 4H-SiC (0001) by thermal atomic layer deposition and were crystallized to the γ-Al2O3 phase by rapid thermal annealing in N2 at 1100°C. The films were found to be chemically stable during processing based on x-ray photoelectron spectroscopy. The change in film structure was initially confirmed by reflection high-energy electron diffraction. As shown by high-resolution transmission electron microscopy images, the abrupt interface of the as-deposited films with the 4H-SiC substrate was preserved during crystallization, indicating no interfacial reaction. Selected area electron diffraction and synchrotron-based x-ray diffraction established an epitaxial relationship of γ-Al2O3 (111) ‖ 4H-SiC (0001) and in-plane orientation of γ-Al2O3 (11¯0) ‖ 4H-SiC (112¯0). No other alumina phases or orientations were observed and no in-plane misorientation was observed in the 27Å Al2O3 films. The full width at half maximum of the γ-Al2O3 (222) rocking curve is 0.056°, indicating a lack of mosaic spread and a high-quality crystalline film. Twinning around the γ-Al2O3 [111] axis was the only defect observed in these films.

Material and electrical characterizations of sputter-deposited HfxRuy and HfxRuyNz gate electrodes atop atomic layer deposited HfO2 were performed with a focus on optimizing their compositions for suitable applications in p-metal oxide semiconductor field effect transistors (pMOSFETs), since Fermi level pinning is a more severe issue for higher work function metals. The alloys of HfxRuy with effective work functions (EWFs) ranging from 4.4 to 5.0 eV were achieved when the Ru metal ratio was varied from 53% to 74%. Nitrided hafnium ruthenium alloys, HfxRuyNz (0%–25% N), with EWFs of 4.9–5.2 eV were also synthesized. Among these materials, Hf0.26Ru0.74 and Hf0.05Ru0.77N0.18 were determined to have EWFs adequate for pMOSFET devices of 5.0 and 5.2 eV, respectively. The slightly higher than expected EWFs of these metal gates are attributed to the presence of oxygen. The depth profiling of the as-deposited gate stacks showed reasonably sharp interfaces between the gate electrode and the gate dielectric with the HfxRuy alloy exhibiting better interfacial properties. Upon annealing, the HfxRuy alloys were found to be more stable than the HfxRuyNz alloys on HfO2.

Hafnium aluminate thin films were synthesized by atomic layer deposition (ALD) to assess the effect of aluminum oxide incorporation on the dielectric/Ge interfacial properties. In these HfxAlyOz thin films, the Hf to Al cation ratio was effectively controlled by changing the ratio of hafnium oxide to aluminum oxide ALD cycles, while their short range order was changed upon increasing aluminum oxide incorporation, as observed by extended x-ray absorption fine structure analysis. The incorporation of aluminum oxide was shown to improve the electrical characteristics of hafnium oxide/Ge devices, including lower interface state densities and leakage current densities.