In this paper, we propose the use of a tunable monochromatic terahertz (THz) wave source to measure the carrier properties of semiconductors. We also report on the recent improvement of our measurement system and demonstrate its ability to measure an as-grown sample; our system involves reference mirror-free reflective measurement. In our method, carrier properties, such as resistivity and mobility in semiconductors relating to the carrier density, can be determined by reflective measurement. This method was applied to composite semiconductors - GaN, GaAs, and SiC. In the measurement system, we improved the filter to block the infrared beam co-linearly propagating with the desired THz-wave. Consequently, the signal intensity was 13 times higher than that achieved in our previous work. We demonstrated the measured carrier properties in an as-grown n-type GaN wafer. We observed flat features via our THz-reflective measurement, whereas the sample showed prominent surface roughness in a picture taken with visible light.
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