Additional scattering of electrons in the complex MOSFET channel caused by off-cut angle of (0001) 4H-SiC wafer, makes accurate crystal face acquisition much desired. Molten KOH was used to etch the circular grooves on the SiC wafer surface in muffle furnace, and hexagonal grooves with SiC crystal symmetry were obtained. Average etching rates at 500°C along <;11-20> and <1-100> direction were about 4.826 um/min and 4.112 um/min, respectively,with a etching anisotropy ratio of 1.18. The m face was obtained by controlling the etching time and Si face was obtained by selfstopping effect. The method we developed in this paper has potential applications in the accurate crystal face acquisition of (0001) 4H-SiC epi-wafer, and the preparation of structures based on 4H-SiC.
Localized plasmon modes are excited and probed in a large-area grating-gate GaN/AlGaN high-electron-mobility transistor structure embedded in a Fabry-Pérot cavity using a terahertz time-domain spectroscopy (THz-TDS) at cryogenic temperature. Determined by the length of grating finger and the electron concentration, the frequency of localized plasmon modes can be continuously tuned by the gate voltage in the spectral range from 0.1 THz to 1.5 THz. When the plasmon frequency is tuned to be in resonance with the terahertz Fabry-Pérot cavity mode, a strong coupling between the plasmon mode and the cavity mode is observed and the terahertz plasmon-polaritons are formed in such a cavity-coupled two-dimensional electron system. The electromagnetic simulations have confirmed the strong coupling between them.