Electrical properties of $\beta$-Ga2O3 homoepitaxial layer measured by terahertz time-domain spectroscopy

Gallium oxide (Ga 2 O 3 ) bulk substrate and homoepitaxial layer were investigated using terahertz time-domain spectroscopy in the frequency region from 0.2 to 3.0 THz and with polarization along the $a$ crystal axis. From the transmittance measurement, the refractive index spectra of the bulk substrate and the epilayer were obtained. The carrier density, electron mobility, and resistivity of the epilayer were then extracted by employing the Drude-Lorentz model.