Thesis (M.Sc.)--Chulalongkorn University, 2008

Motion of charged carriers in semiconductor is directly related to its electrical transport properties, i.e. resistivity, mobility and carrier concentration. The widely used technique to obtain such properties is the van der Pauw (vdP) method and the Hall effect measurement, both employ the four-point probe technique. In this thesis, the computer-controlled vdP and Hall effect measurement system have been designed and used for studying electrical transport properties of semiconductors such as InSb, Indium-Tin-Oxide (ITO) and Aluminum-doped Zinc Oxide (AZO). The InSb was used as a sample to calibrate the system. The measurement results at 77 K were in good agreement with those issued from the manufacturer. For the ITO thin films, it was observed that the resistivity was rising with increasing temperature due to the lattice vibration, indicating the behavior of metallic conduction. For the measurement results of AZO thin films, it was found that there were two mechanisms involving in the conduction of the carriers. The thermally activated band conduction was dominant in the high temperature range (T > 100 K). From this result, the activation energy was approximately 19 meV. For the low temperature range (T < 80 K), the variable range hopping became dominant. Thus, the cross-over region for the two competing mechanisms was between 80-100 K.