Microcontroller-based test system for determining the P-N type and Seebeck coefficient of the thermoelectric semiconductors

Abstract

In this study, a microcontroller-based test system is designed and realized to determine the Seebeck coefficient (α) and electrical conductivity type of thermoelectric (TE) semiconductors. The test system uses Hot-Probe method, which benefits from the Seebeck effect. It is an embedded system based on the principle of measuring the Seebeck voltage (thermo-emf) produced once a temperature difference (ΔT) between the surfaces of the TE semiconductors is created. Seebeck coefficient of TE semiconductors can be determined depending on the thermo-emf and temperature measurements in the system. TE semiconductor electrical conductivity type (P or N) can also be determined according to the sign of the measured thermo-emf. The system consists of two major components, the main unit and the multifunctional probe. Thanks to the developed multifunctional probe, it is possible to provide the necessary heat for the temperature difference as well as Seebeck voltage and temperature measurements. In the main unit of the system, an 8-bit Atmega328 microcontroller is used and its software is developed with mikroC Pro for AVR. For various temperature differences between the surfaces of 9 P-type and 9 N-type TE semiconductors of various shapes and sizes obtained by Zone Melting (ZM), Hot Pressing (HP) and Hot Extrusion (HE) methods, the changes in thermos-emfs of the materials are investigated. In addition, Seebeck coefficient, P-N electrical conductivity type, and figure-of-merit (ZT) parameters of semiconductors, which are important for TE module production, are found. According to the experimental results, with the developed test system, the thermo-emf measurements can be made in an accuracy of ±0.1 mV within 0–100 mV range, and the temperature measurements can have accuracy of ±1 °C within 0–75 °C range. As a result, it is seen that the developed test system is a research device which can determine the Seebeck coefficient and P-N electrical conductivity type practically, quickly and reliably irrespective of the shape and size of TE semiconductors.