In AlGaN/GaN high electron mobility transis-1 tors (HEMTs), high temperature processes (such as ohmic 2 annealing with >800 • C value) could deform the crystal 3 structure and induce trap states within the bulk and surface. 4 Expanded defect densities cause crucial problems, such as 5 threshold voltage (V th ) instability, current collapse, and high 6 leakages. In this work, a low temperature ohmic contact 7 process (630 • C, 10 minutes) is adopted with recess etch, 8 and contact resistances <0.1 •mm with low sheet resis-9 tances are achieved. The positive impact of this low thermal 10 budget process on surface morphology, DC operation, long-11 term stability, and forward gate bias stress of the device is 12 studied.

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Metamaterials and their two-dimensional forms, metasurfaces, have been studied intensively due to their unique features that usually do not exist in nature. Due to their unusual properties, they have found their way into many different application areas. One of these application areas is metalens application, where the metasurfaces are formed as flat lenses and they bend the wavefront of the outgoing electromagnetic wave. Metalenses are a candidate to replace the spherical lenses because they are much smaller, they are easy to fabricate, and they are a solution to aberration problems. In this paper, a metalens structure with \(11 \mu\)m operating wavelength is studied. In addition to working at the long infrared wavelength, the dynamic feature is brought to the metalens with the addition of vanadium dioxide, and power control at the focal point is obtained.