Thermoelektrische Ladungstrennung in p-n Übergängen und Nutzung des Effektes zur Verbesserung herkömmlicher thermoelektrischer Generatoren
In this work, a fundamental investigation of the phenomenon of thermoelectric charge separation within a p-n junction is carried out. This effect, together with the conventional thermoelectric effect in a thermoelectric generator (TEG), leads to an improvement in its overall performance. For this purpose, an alternative design to the conventional TEGs is used. Hereby the p- and n-legs of the TEG are connected, thus forming a direct p-n junction. The additional electrical power of the p-n TEGs is caused by the separation of thermally generated charge carriers within the space charge region, along the p-n junction. This effect is experimentally verified for the first time within this work. For these investigations, an idealized system was fabricated within this work, where the generation volume was extended by an intrinsic silicon substrate "i" in a p-i-n structure. The fabricated p-i-n silicon structure is used to provide direct access to the electrical power generated by this effect and is demonstrated while suppressing the conventional thermoelectric contribution from the p‑ and n-legs. The thermally generated charge carriers in the i-region are separated within the electric field, between the p- and n-region. The required non-equilibrium condition is caused by the temperature difference along the p-i-n junction. An estimation demonstrated that this effect can generate a considerable additional electrical power. Under ideal conditions, a power density of 104 Wm-2 could be calculated at a temperature difference of 600 K. In this work it is demonstrated for the first time, that the experimental determined electrical power of a p-n junction TEG exceeds the determined performance of a conventional TEG within a certain temperature range. The results were successfully verified by numerical simulations. Furthermore, the behavior of the p-n TEG is reproduced and analyzed very precisely using an electrical equivalent circuit. In addition, the use of physical simulation program, such as Atlas, allows, the analysis of the p-n TEGs and the investigation of the influence of material parameters on the performance of the p-n TEG. Good agreement between measurement and simulation results was achieved and demonstrated. Furthermore, a p-n heterostructure of antimony telluride and bismuth telluride was used to show that this principle can also be transferred to systems made from hetero-materials.
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