In this thesis, an interface passivation by a lattice matched atomic layer deposition (ALD) epitaxial magnesium calcium oxide (MgCaO) on wide-bandgap gallium nitride (GaN) has been applied for the first time and expensively studied via various characterization methods (including AC conductance methods, pulsed current-voltage, and single pulse charge pumping). Also, beta-Ga2O3 with a monoclinic crystal structure that offers several surface oriented channels has been demonstrated as potential beta-Ga2O3 FET. On the other hand, low frequency noise studies in 2-D MoS2 NC-FETs was reported for the first time. Low frequency noise of the devices is systematically studied depending on various interfacial oxides, different thicknesses of interfacial oxide, and ferroelectric hafnium zirconium oxide. Interestingly enough, the low frequency noise is found to decrease with thicker ferroelectric HZO in the subthreshold regime of the MoS2 NC-FETs, in stark contrast to the conventional high-k transistors. Also, the ferroelectric switching speed is found to be related with the maximum electric field applied during the fast gate voltage sweep, suggesting the internal ferroelectric switching speed can be even faster depending on the device’s electrical bias conditions and promises a high speed performance in our ferroelectric HZO