ORCID Profile
0000-0002-9796-8995
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Publisher: Elsevier BV
Date: 09-2016
Publisher: MDPI AG
Date: 02-09-2017
DOI: 10.3390/EN10091322
Abstract: We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB2/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology.
Publisher: IOP Publishing
Date: 06-05-2015
DOI: 10.1088/0957-4484/26/21/215602
Abstract: Catalystless growth of InxAl(1-x)N core-shell nanorods have been realized by reactive magnetron sputter epitaxy onto Si(111) substrates. The s les were characterized by scanning electron microscopy, x-ray diffraction, scanning transmission electron microscopy, and energy dispersive x-ray spectroscopy. The composition and morphology of InxAl(1-x)N nanorods are found to be strongly influenced by the growth temperature. At lower temperatures, the grown materials form well-separated and uniform core-shell nanorods with high In-content cores, while a deposition at higher temperature leads to the formation of an Al-rich InxAl(1-x)N film with vertical domains of low In-content as a result of merging Al-rich shells. The thickness and In content of the cores (domains) increase with decreasing growth temperature. The growth of the InxAl(1-x)N is traced to the initial stage, showing that the formation of the core-shell nanostructures starts very close to the interface. Phase separation due to spinodal decomposition is suggested as the origin of the resultant structures. Moreover, the in-plane crystallographic relationship of the nanorods and substrate was modified from a fiber textured to an epitaxial growth with an epitaxial relationship of InxAl(1-x)N[0001]//Si[111] and InxAl(1-x)N[1120]//Si[110 by removing the native SiOx layer from the substrate.
Publisher: Springer Science and Business Media LLC
Date: 05-10-2017
DOI: 10.1038/S41598-017-12702-Y
Abstract: Selective-area growth (SAG) of single-crystal wurtzite GaN nanorods (NRs) directly onto Si(001) substrates with un-etched native SiO x amorphous layer, assisted by a patterning TiN x mask fabricated by nanosphere lithography (NSL), has been realized by reactive magnetron sputter epitaxy (MSE). The GaN NRs were grown vertically to the substrate surface with the growth direction along c -axis in the well-defined nano-opening areas. A 5-step structural and morphological evolution of the SAG NRs observed at different sputtering times depicts a comprehensive growth model, listed in sequence as: formation of a polycrystalline wetting layer, predominating c -axis oriented nucleation, coarsening and coalescence of multi-islands, single NR evolution, and finally quasi-equilibrium crystal shape formation. Room-temperature cathodoluminescence spectroscopy shows a strong GaN bandedge emission with a uniform luminescence across the NRs, indicating that the SAG NRs are grown with high quality and purity. In addition, single-longitudinal-mode lasing, attributed to well-faceted NR geometry forming a Fabry–Pérot cavity, was achieved by optical pumping, paving a way for fabricating high-performance laser optoelectronics using MSE.
Publisher: Elsevier BV
Date: 08-2018
Publisher: MDPI AG
Date: 23-07-2020
Abstract: Selective-area grown, catalyst-free GaN nanorod (NR) arrays grown on Si substrates have been realized using liquid-target reactive magnetron sputter epitaxy (MSE). Focused ion beam lithography (FIBL) was applied to pattern Si substrates with TiNx masks. A liquid Ga target was sputtered in a mixture gas of Ar and N2, ranging the N2 partial pressure (PN₂) ratio from 100% to 50%. The growth of NRs shows a strong correlation with PN₂ on the selectivity, coalescence, and growth rate of NRs in both radial and axial directions. The growth rate of NRs formed inside the nanoholes increases monotonically with PN₂. The PN₂ ratio between 80% and 90% was found to render both a high growth rate and high selectivity. When the PN₂ ratio was below 80%, multiple NRs were formed in the nanoholes. For a PN₂ ratio higher than 90%, parasitic NRs were grown on the mask. An observed dependence of growth behavior upon the PN₂ ratio is attributed to a change in the effective Ga/N ratio on the substrate surface, as an effect of impinging reactive species, surface diffusivity, and residence time of adatoms. The mechanism of NR growth control was further investigated by studying the effect of nanoholes array pitch and growth temperature. The surface diffusion and the direct impingement of adatoms were found to be the dominant factors affecting the lateral and axial growth rates of NR, respectively, which were well elucidated by the collection area model.
No related grants have been discovered for Elena Alexandra Serban.