Carlos A Ramos - Academia.edu (original) (raw)
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Papers by Carlos A Ramos
Al 1 −x In x N heteroepitaxial layers covering the full composition range have been realized by m... more Al 1 −x In x N heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al 1 −x In x N single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (~13% mismatch), heteroepitaxy is achieved. However, RT-grown Al 1 −x In x N films directly deposited on nonisostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al 1 − x In x N structural quality with increasing indium content is attributed to the formation of more point-and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al 1 −x In x N films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegard's rule is applicable to determine x in the RT-grown Al 1 −x In x N epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials.
Al 1 −x In x N heteroepitaxial layers covering the full composition range have been realized by m... more Al 1 −x In x N heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al 1 −x In x N single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (~13% mismatch), heteroepitaxy is achieved. However, RT-grown Al 1 −x In x N films directly deposited on nonisostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al 1 − x In x N structural quality with increasing indium content is attributed to the formation of more point-and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al 1 −x In x N films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegard's rule is applicable to determine x in the RT-grown Al 1 −x In x N epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials.