Papers by Author: Seigo Ohno

Abstract: THz imaging was performed in 2 s intervals with 1 mm resolution on a 3 in., 0.42 mm thick, as-cut n-type Silicon Carbide wafer. Carrier density, relaxation time, mobility, and resistivity obtained from imaging results are 0.91 × 10¹⁸ cm^-3, 4.36 × 10^-14 s, 218 cm²V^-1s^-1, and 3.14 × 10^-2 Ωcm, respectively. Compared with the standard values provided by the manufacturers, the results suggest that THz imaging has reliable precision and accuracy.

Abstract: Rapid imaging of the carrier density of n-type silicon (Si) was carried out at the rate of 2 s per point using a terahertz wave of 4.4 THz generated from a tunable terahertz source. Reflectance of 4.4 THz as a function of carrier density was calculated using a simple Drude model. The carrier densities obtained from the terahertz imaging were 1 × 10¹⁸ cm⁻³ and 3 × 10¹⁸ cm⁻³, respectively.

Abstract: A new nondestructive method using terahertz waves for determining the carrier density of GaAs is proposed. The reflectance around the longitudinal optical (LO) phonon frequency changes with carrier density, whereas the reflectance around the transverse optical (TO) phonon frequency is constant. The relative reflectance, which is evaluated from the reflectance at the two frequencies related to the TO and LO phonon, as a function of the carrier density of GaAs was calculated from the dielectric function. A broadband tunable terahertz source is convenient for producing two waves around these phonon frequencies. Imaging of n-type GaAs wafer using this new terahertz method is described.

Abstract: The reflectance around the longitudinal optical (LO) phonon frequency in the terahertz region changes with the carrier density of silicon carbide (SiC), while the reflectance around the transverse optical (TO) phonon frequency remains constantly high. The relative reflectance obtained from the reflectance at the two frequencies related to the TO and LO phonon was evaluated as a function of the carrier density of SiC. Two waves around these phonon frequencies can be generated easily using a tunable terahertz source. Nondestructive imaging of the carrier density of cubic SiC (3C-SiC) at the rate of 1 s per point was carried out successfully using this tunable terahertz source.