Optical properties of doped silicon wafers have been measured by means of terahertz time domain reflection spectroscopy. A method is proposed to obtain the relative phase by reflection accurately. By using this method, the relative phase is obtained within an error of less than 10 mrad at 1 THz. The experimentally obtained complex conductivity of relatively high-doped silicon (ϭ0.136 ⍀ cm) in the terahertz region agrees with the simple Drude model.

Complex conductivity of moderately P-doped silicon wafers (1.1±0.2 Ω cm at room temperature) has been measured by using a terahertz (THz) time-domain spectroscopy for the temperature and frequency ranges of 20–300 K and 0.2–1.1 THz, respectively. The strong frequency dependence of the complex conductivity due to the free carriers in the THz region is observed and it changes rapidly with temperature, which is interpreted in terms of the increase in mobility and freezing of the free carrier as analyzed by using the simple Drude model. The experimental data deviate slightly from the simple Drude model at low temperatures and becomes apparent with decreasing temperature.

We demonstrate the noncontact and nondestructive evaluation of electrical properties of n-type GaN thin films on sapphire substrates using time domain spectroscopy in the THz frequency region (THz-TDS). DC resistivities of the GaN films with various free carrier densities are deduced by fitting the transmission spectra of the sample to the Drude model. The DC resistivities obtained by the THz-TDS show good agreement with those obtained by the conventional contact measurements. Mobilities of the free carriers in lightly doped GaN films are also determined by the Drude fit. It is found that the temperature dependence of the mobilities for the lightly doped films shows a peak at $150 K. The temperature dependences of the free carrier densities for the lightly doped films obtained by the THz measurements are compared with that predicted by a model with two kinds of donors reported previously.

We demonstrate noncontact measurements of electrical properties of GaN thin films using the time domain spectroscopy in the THz frequency region (THz-TDS). The carrier density and temperature dependence of DC resistivity and mobility of the GaN films are investigated.