Characterization of the electrical properties and thickness of thin epitaxial semiconductor layers by THz reflection spectroscopy

We have measured the dielectric properties and thickness of thin semiconductor epitaxy layers by the reflection of THz radiation from the surface of a two-layered semiconductor wafer. When reflecting from two interfaces the electromagnetic pulse has a destructive interference at a specific wavelength dependent on the thickness of the outer layer and its dielectric function. Near that frequency the reflection coefficient has a significant drop. By extending the incident pulse spectrum to include this interference frequency, a measurement of the thickness can be obtained together with a direct measurement of the carrier number density. By this technique epitaxy layers of thickness down to 15 μm are characterized.