Thermoelectrical properties deterrmination by laser stimulated Seebeck effect

L.-D. Patiño Lopez, A. Salhi, S. Dilhaire, S. Grauby, W. Claeys

CPMOH – University of Bordeaux, 351 cours de la Libération, 33 405 TALENCE

We propose in this paper an in-depth study at a technique for the determination of thermoelectric properties, in single, or multilayer systems. We use a modulated laser beam as a heater in order to generate a thermally induced emf. The excitation beam is modulated so as to profit from lock-in detection advantages. The laser beam can be focused at any point x along the sample, allowing a spatially resolved determination of thermoelectric properties. Seebeck emf measurements, associated with a versatile model based on the thermal quadrupoles method allows the determination of sample properties.

A low power beam from a visible laser diode is strip-focused into a single PN bismuth telluride couple in order to heat it. The laser power is sinus shape modulated. The Seebeck induced emf is measured by means of a Lock-in amplifier locked at the laser excitation frequency. The sample response depends on layers thermal conductivity, thermal diffussivity and Seebeck coefficient. The beam’s line profile allows the analysis of the sample heat transfer as a two-dimensional problem, as there is no temperature variation in z direction. Moreover, if we integrate the temperature field in the voltage measurement probe direction (y), the problem is easily solved using the thermal quadrupole method.