Investigation of Nondestructive and Noncontact Electrical Characterization of GaN Thin Film on ScAlMgO₄ Substrate Using Terahertz Time-Domain Spectroscopic Ellipsometry with Characteristic Impedance Analytical Model

Semiconductor evaluation methods frequently require sample processing and carry the risk of defects and property changes. Therefore, nondestructive and noncontact electrical property measurement techniques are necessary. Terahertz time-domain spectroscopic ellipsometry (THz-TDSE) can simultaneously estimate the electrical properties and film thickness of a sample. However, whether this method can simultaneously determine electrical properties and film thickness for semiconductor thin films of 1 mu m or less remains unclear. This study uses THz-TDSE to evaluate the electrical properties and film thickness of a GaN thin film (approximate to 0.8 mu m thick) on a ScAlMgO4 substrate. Using the conventional analysis based on Fresnel's formula (FR model), which is used in the field of optics, uniquely determining the electrical properties and film thickness is not possible owing to multiple optimal solutions. Therefore, a model combining the characteristic impedance model used in the radio-wave region with the FR model is employed in the analysis. The obtained values of electrical properties of the GaN thin film evaluated using THz-TDSE are consistent with those using Hall effect measurement. Moreover, the film thickness is consistent with that measured from the cross-sectional transmission electron microscopy observation.