Experimental evidence for the separation of thermally excited bipolar charge carries within a p-n junction: A new approach to thermoelectric materials and generators

Common thermoelectric generators are based on the Seebeck effect, which describes the thermal diffusion of majority charge carriers within a temperature gradient in a solid. It is a unipolar transport phenomenon that gets suppressed if bipolar charge carriers occur. Here, we demonstrate by experiments that thermally excited bipolar charge carriers can be separated by the built-in field without external bias within a p-n junction. Such a phenomenon has been predicted theoretically before but was never proven experimentally. In the experiment, a nominal intrinsic silicon wafer (doping concentration less than 1013 cm−3) was inserted in a p-i-n structure. It could be shown that electric power can be extracted from the space charge region (i-region), while the conventional thermoelectric contribution from the p- and n-regions is suppressed by short-circuiting. While the measured and simulated overall Seebeck effect of intrinsic silicon predicts a zero crossing of output power with increasing hot-side temperature due to a transition from p-type to n-type transport, the measured and simulated output power of the p-i-n structure increases monotonically with increasing hot-side temperature, indicating clearly the different nature of both mechanisms.Common thermoelectric generators are based on the Seebeck effect, which describes the thermal diffusion of majority charge carriers within a temperature gradient in a solid. It is a unipolar transport phenomenon that gets suppressed if bipolar charge carriers occur. Here, we demonstrate by experiments that thermally excited bipolar charge carriers can be separated by the built-in field without external bias within a p-n junction. Such a phenomenon has been predicted theoretically before but was never proven experimentally. In the experiment, a nominal intrinsic silicon wafer (doping concentration less than 1013 cm−3) was inserted in a p-i-n structure. It could be shown that electric power can be extracted from the space charge region (i-region), while the conventional thermoelectric contribution from the p- and n-regions is suppressed by short-circuiting. While the measured and simulated overall Seebeck effect of intrinsic silicon predicts a zero crossing of output power with increasing hot-side temperatu...