Thermal rectification optimization in nanoporous Si using Monte Carlo simulations

Abstract

We investigate thermal rectification in nanoporous silicon using a semi-classical Monte Carlo (MC) simulation method. We consider geometrically asymmetric nanoporous structures, and investigate the combined effects of porosity, inter-pore distance, and pore position relative to the device boundaries. Two basis geometries are considered, one in which the pores are arranged in rectangular arrays, and ones in which they form triangular arrangements. We show that systems: i) with denser, compressed pore arrangements (i.e with smaller inter-pore distances), ii) with pores positioned closer to the device edge/contact, and iii) with pores in a triangular arrangement, can achieve rectification of over 55%. Introducing smaller pores into existing porous geometries in a hierarchical fashion increases rectification even further to over 60%. Importantly, for the structures we simulate, we show that sharp rectifying junctions, separating regions of long from short phonon mean-free-paths are more beneficial for rectification than spreading the asymmetry throughout the material along the heat direction in a graded fashion.

Computationally efficient Monte Carlo electron transport algorithm for nanostructured thermoelectric material configurations

“…Another way to solve the BTE is based on stochastic solution methods using Monte Carlo (MC) computational algorithms, which use statistical sampling to solve the BTE numerically, and are frequently used for electronic device applications [16][17][18][19][20][21][22]. Over the last several years, MC techniques also found extensive use in the fields of charge and energy transport in semiconductor materials [23][24][25][26][27][28]. MC simulation methods are particularly useful for nanostructured materials, where the carriers encounter a plethora of defects along their transport direction and interact with them, while analytical solutions in these cases are not as accurate.…”

“…[38][39][40][41][42][43] . The recent improvement in the performance of TE materials originates in most cases from reduced thermal conductivity due to phonon scattering with the boundaries of the nano-defects, and thus MC simulations are typically performed for phonon transport in real space in such materials [23,31,33,44,45]. Nevertheless, studies on electronic transport using MC are also emerging for nanostructured TE materials after it was pointed out that specific designs can also improve the so-called power factor, which directly determines the efficiency of a TE material as well [46,47].…”

A review of thermal rectification in solid-state devices

“…An improved understanding of thermal rectification and the development of thermal diodes also carries promise for the implementation of this concept in thermal logic circuits, memory, and energy storage systems. η Although thermal rectification will theoretically always exist in the presence of nonlinear interactions and broken inversion symmetry [10] , the heat flux transmitted by a thermal diode in one direction must be appreciably different from that in the opposite direction for the device to be of practical significance. Spatially asymmetric heat flow properties are essential to achieve thermal rectification since modifications that uniformly enhance or degrade the mobility of electrons and phonons (energy carriers) in the system will not encourage unidirectional transport.…”

Phonon transport simulation with an extended VOF scheme for nano-structured thin film

“…The shapes of pores/holes is of course relevant, such as circular 8 and pacman-shaped 9 holes; hole arrangements also seem important. 10 To design effective structures, numerical simulation of phonon transport is useful. As the characteristic scale of structures is of the same order of phonon MFP, we cannot assume the conventional Fourier's law for heat flow but have to treat the distribution of phonons in the reciprocal (or wave number) space.…”