High-temperature thermoelectric transport at small scales: Thermal generation, transport and recombination of minority carriers

Abstract

Thermoelectric transport in semiconductors is usually considered under small thermal gradients and when it is dominated by the role of the majority carriers. Not much is known about effects that arise under the large thermal gradients that can be established in high-temperature, small-scale electronic devices. Here, we report a surprisingly large asymmetry in self-heating of symmetric highly doped silicon microwires with the hottest region shifted along the direction of minority carrier flow. We show that at sufficiently high temperatures and strong thermal gradients (~1 K/nm), energy transport by generation, transport and recombination of minority carriers along these structures becomes very significant and overcomes convective energy transport by majority carriers in the opposite direction. These results are important for high-temperature nanoelectronics such as emerging phase-change memory devices which also employ highly doped semiconducting materials and in which local temperatures reach ~1000 K and thermal gradients reach ~10–100 K/nm.

Activation energy of metastable amorphous Ge2Sb2Te5 from room temperature to melt

“…The average total energy (kinetic + potential) transported by a carrier is defined as Peltier coefficient, Π = ST, and in case of a degenerate semiconductor the energy for a hole (the majority carrier for fcc GST) Π h is approximately 18 In conclusion, the resistivity function of metastable amorphous GST and molten GST shows a continuum suggesting that metastable GST behaves as a super-cooled liquid, molten GST is a p-type semiconductor at T melt = 858 K and molten GST transitions to metallic phase at ~930 K. The effective activation energy of metastable amorphous GST shows a parabolic behavior in temperature, and is expected to correspond to a distribution of trap levels that contribute to conduction. The Seebeck versus temperature data for mixed amorphous-fcc GST suggest that the single crystal fcc GST is a degenerate semiconductor having the Fermi level 0.16 eV below the valence band edge.…”

Phase Change Pipe for Nonvolatile Routing

“…2-4) using a smaller CMOS footprint [5]. The electro-thermal model used to demonstrate this device concept self-consistently solves the current continuity (1) and heat transfer (2) [6], [7] and phase field (3) equations in COMSOL Multiphysics:…”

Suppression of thermoelectric Thomson effect in silicon microwires under large electrical bias and implications for phase-change memory devices

“…We have referred to this process as generation-transport-recombination (GTR) of minority carriers as introduced and analyzed in detail in Ref. 9. The process of GTR is captured in the overall Seebeck coefficient, which decreases in magnitude beyond 1100 K. Once the wire starts melting, the hottest spot is assumed to be at the center of the melting region (1690 K < T < 1700 K) for tracing the time evolution of the asymmetry in the temperature profiles.…”

“…[3][4][5][6][7] We have previously demonstrated that Thomson effect causes significant asymmetry in heating and melting of Si microwires biased with microsecond voltage pulses. 8,9 The electrical current polarity dependence of the heating profiles was demonstrated using low frequency AC biases causing the hottest spot on the wires to alternate between left and right locations. 8,9 For these Si wires, the main mechanism behind the asymmetry is understood as energy transfer from hotter to cooler regions of the wire through minority carrier generation and recombination (further discussed in Ref.…”

“…8,9 For these Si wires, the main mechanism behind the asymmetry is understood as energy transfer from hotter to cooler regions of the wire through minority carrier generation and recombination (further discussed in Ref. 9). During further experiments on self-heating of Si wires through electrical pulses, we have found that the asymmetries disappear when the wires are subjected to larger amplitude, shorter duration electrical pulses.…”