Superlattice design for optimal thermoelectric generator performance

Abstract

We consider the design of an optimal superlattice thermoelectric generator via the energy bandpass filter approach. Various configurations of superlattice structures are explored to obtain a bandpass transmission spectrum that approaches the ideal "boxcar" form, which is now well known to manifest the largest efficiency at a given output power. Using the non-equilibrium Green's function formalism coupled self-consistently with the Poisson's equation, we identify such an ideal structure and also demonstrate that it is almost immune to the deleterious effect of self-consistent charging and device variability. Analyzing various superlattice designs, we conclude that superlattices with a Gaussian distribution of the barrier thickness offers the best thermoelectric efficiency at maximum power. It is observed that the best operating regime of this device design provides a maximum power in the range of 0.32-0.46 M W/m 2 at efficiencies between 54%-43% of Carnot efficiency. We also analyze our device designs with the conventional figure of merit approach to counter support the results so obtained. We note a high zT el = 6 value in the case of Gaussian distribution of the barrier thickness. With the existing advanced thin-film growth technology, the suggested superlattice structures can be achieved, and such optimized thermoelectric performances can be realized.

Graphene as a nanoelectromechanical reference piezoresistor

“…Rapid miniaturization of MEMS systems as a result of state-of-the-art nanofabrication techniques, on one hand, offers multiple applications in a single chip, and on the other, necessitates the revamping of the theoretical understanding of electronic transport processes at a microscopic level in both the ballistic [33][34][35][36][37][38] and the diffusive regimes [39,40]. A deeper theoretical understanding of electronic transport across these systems will hence lead to novel functionalities that govern the next-generation NEMS devices.…”

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“…5(b), (c), (d) for FP-I, FP-II and FP-III, respectively. The maximum attainable limit of efficiency that can be achieved through optimal cavity engineering is 64.4% for the aforementioned range of power which is even better than 61.7% of the superlattice based generators [27]. Obtained results clearly point towards an improved power-efficiency trade-off characteristics which will be discussed next.…”

“…4(b), (c), (d) for the configurations FP-I, FP-II and FP-III, respectively. Obtained results show that FP-II and FP-III designs can generate maximum power (P max ) up to 1.03M W/m 2 and 1.06M W/m 2 , respectively, as compared to 0.9M W/m 2 of the ARC based proposal (FP-I) and 0.46M W/m 2 of the superlattice based generators [27]. The position of P max of the new proposals is at E f = 5.5k B T which is slightly higher than that of FP-I whose P max occurs at E f = 5k B T .…”

“…A few recent studies [16,27] utilized the miniband feature of superlattice based devices [28,29] to achieve the boxcar transmission profile. Further advancing on such ideas, recently, thermoelectric generator (TEG) setups augmented with an electronic anti-reflection cavity * bm@ee.iitb.ac.in (a) FIG.…”

“…These ideas proved to be far superior in terms of achieving excellent power-efficiency trade-off in comparison with the competing device proposals [16][17][18]. However, it should be noted that, in the presence of charging effects, the superlattice designs [27] suffer from serious lineshape imperfections which badly affects the power and trade-off characteristics. Moreover, the large number of constituting layers in such devices poses a serious threat to the precise epitaxial growth with the existing technology.…”