Enhanced Cooling in Doped Semiconductors Due to Nonlinear Peltier Effect
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1044-U10-04
Enhanced Cooling in Doped Semiconductors Due to Nonlinear Peltier Effect Mona Zebarjadi1, Keivan Esfarjani2, and Ali Shakouri1 1 Electrical Engineering, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA, 95064 2 Physics Department, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA, 95064 ABSTRACT Thermoelectric coefficients become a function of the applied field and temperature gradient if the latter are large enough. Nonlinearity is common in electronic devices but it has not been investigated in detail in thermoelectric transport. We show that non-linearity is a consequence of electron heating and it could happen in relatively low currents (e.g. 105 A/cm2) for InGaAs at room temperature. At low temperatures the Peltier coefficient of degenerate semiconductors and metals goes to zero. However, we show that nonlinear Peltier is not a strong function of temperature. Since the nonlinear heat current depends on the third power of current, there are regimes in which non-linear Peltier can overcome the joule heating. We will show that at T=77K the cooling power of a single barrier InGaAs microcooler can be enhanced by a factor of seven compared to that predicted by linear thermoelectric transport. Nonlinearity of the Seebeck coefficient is also investigated. We show that non-linear Seebeck is only important when high temperature gradients on the order of degrees over nanometer length are applied.
INTRODUCTION As the size of semiconductor-based devices is scaled down to nm range, heat management becomes an important issue. High power dissipation densities on the order of kWcm-2 and high-localized temperatures reduce the device performance and its lifetime [1]. More than 7 decades ago scientists started looking for good thermoelectric materials with high efficiency for solid state refrigeration and power generation. It is shown that a dimensionless parameter ZT can be used as a measure of the efficiency of thermoelectric materials. Bismuth telluride was and is the best bulk thermoelectric material at room temperature. Yet, it has a ZT on the order of 1, which is low in comparison with compressor-based refrigerators with efficiencies that correspond to ZT of 4-6. So the hope of replacing conventional refrigerators with thermoelectric ones died for a while. In recent years, there are new approaches to enhance ZT by going to lower dimensions [2], using electron transmitting, phonon blocking superlattices [3], by adding nano-particles [4,5], by hot electron filtering using heterostructure barriers [6] and by breaking the conservation of lateral momentum [7]. Small-scale thermoelectric refrigerators can be used to cool individual electronic and optoelectronic devices. While the performance in linear regime is determined by the ZT parameter, it is possible to have non-linear transport in short barrier (micron thick) solid-state thermionic coolers. Previous theoretical calculation by Kulik [8] gave the electric field dependence of the third-order Peltier coefficient in metals at l
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