Monolithic subwavelength gratings integrated with metal (metalMHCG) enable nearly total transmission of light and can be fabricated with common semiconductor materials, however, they require a very high-aspect ratio between height and period of the metalMHCG stripes which is technologically challenging. This study aims the optimization of metalMHCG fabrication procedure by plasma etching taking into account the influence of process gas flow, their composition, pressure, power, and temperature on the wall shape of metaMHCG, etch rate, and etch selectivity. In the result, metalMHCG with high-aspect ratio and dimensions enabling nearly total transmission are fabricated.
In this work we presents effect of ultra high pressure annealing on Si-implanted GaN n-type and p-type epilayers on ammonothermally grown bulk GaN substrates. Samples were blanked implanted with different Si ion fluences from 3x1014 cm-2 to 3x1015 cm-2 and then annealed using UHPA at temperature of 1200, 1300 and 1400°C for 5 minutes at 1 GPa. Ion distribution before and after annealing where investigated using SIMS method showing no Si diffusion in p-type GaN along with Mg diffusion from epilayer and very low Si diffusion in n-type GaN epilayers. X-ray diffraction studies shows that not all defects were recovered after annealing, especially for high ion fluences. Annealing at 1400°C causes changes in implanted GaN morphology. The surface roughness where increased after annealing especially for samples implanted with 3x1015 cm-2Si dose. Our results shows that more work is needed to optimize UHPA parameters for defect recovery in Si-implanted GaN especially for high ion fluences.
Recently much attention gained development of “buffer free” AlGaN/GaN HEMT structures with thin high quality AlN nucleation layer for better carrier confinement in the transistor channel mitigating short channel effects and with reduced thermal resistance. In this work results of development of low resistivity Ti/Al/TiN/Au ohmic contacts to such a structures will be presented . The impact of annealing temperature and different metal layer thickness on the ohmic contact formation, morphology and structural and electrical properties was studied. Low contact resistance of 0.28 Ωmm was obtained for metal stack with Ti/Al 20nm/80nm thickness after annealing at 750°C. Developed ohmic contacts were integrated in the AlGaN/GaN HEMT fabrication process. Good electrical characteristics were obtained showing high on-state current up to 0.95 A/mm. These prove applicability of developed process in technology of buffer-free AlGaN/GaN high electron mobility transistors.
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