Exploiting intervalley scattering to harness hot carriers in III–V solar cells

Esmaielpour, Hamidreza; Dorman, Kyle R.; Ferry, D. K.; Mıshıma, Tetsuya D.; Santos, M. B.; Whiteside, Vincent R.; Sellers, Ian R.

doi:10.1038/s41560-020-0602-0

“…I n modern semiconductor electronic devices, current-carrying electrons are locally driven far away from equilibrium (with an effective electron temperature T e largely exceeding the lattice temperature T L ) 1,2 , and these hot electrons accelerate/decelerate frequently to fulfil intended functions. The excess energy of hot electrons typically dissipates locally to the lattice as the Joule heat, which not only leads to a major heat concern for post-Moore-era nanoelectronics 3 but also exert a thermodynamic limitation to the energy efficiencies in all solid-sate electronic devices (such as the Shockley-Queisser limit 4 , being only~30% for Si solar cells). To suppress net energy loss to lattice, the excess energy carried by hot electrons has to be transmitted along with the charge transport.…”

mentioning

confidence: 99%

Quasiadiabatic electron transport in room temperature nanoelectronic devices induced by hot-phonon bottleneck

Weng

¹

,

Yang

²

,

An

³

et al. 2021

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Since the invention of transistors, the flow of electrons has become controllable in solid-state electronics. The flow of energy, however, remains elusive, and energy is readily dissipated to lattice via electron-phonon interactions. Hence, minimizing the energy dissipation has long been sought by eliminating phonon-emission process. Here, we report a different scenario for facilitating energy transmission at room temperature that electrons exert diffusive but quasiadiabatic transport, free from substantial energy loss. Direct nanothermometric mapping of electrons and lattice in current-carrying GaAs/AlGaAs devices exhibit remarkable discrepancies, indicating unexpected thermal isolation between the two subsystems. This surprising effect arises from the overpopulated hot longitudinal-optical (LO) phonons generated through frequent emission by hot electrons, which induce equally frequent LO-phonon reabsorption (“hot-phonon bottleneck”) cancelling the net energy loss. Our work sheds light on energy manipulation in nanoelectronics and power-electronics and provides important hints to energy-harvesting in optoelectronics (such as hot-carrier solar-cells).

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“…Very recently, Hamidreza et al. have reported the intervalley-scattering type solar cells, where photo-excited hot electrons are designed to occupy the upper valley states instead of relaxing to the bottom Γ valley [ 5 ]. Our study suggests that such a strategy may be much more feasible since hot electrons at upper satellite valleys are long-lived and show a much longer mean free path.…”

Section: Resultsmentioning

confidence: 99%

Direct observation and manipulation of hot electrons at room temperature

Wang

¹

,

Wang

²

,

Xia

³

et al. 2020

National Science Review

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In modern electronics and optoelectronics, hot electron behaviors are highly concerned since they determine the performance limit of a device or system, like the associated thermal or power constraint of chips, the Shockley-Queisser limit for solar cell efficiency. Up-to-date, however, the manipulation of hot electrons is mostly based on conceptual interpretations rather than a direct observation. The problem arises from a fundamental fact that energy-differential electrons are mixed up in real-space, making it hard to distinguish them from each other by standard measurements. Here we demonstrate a distinct approach to artificially (spatially) separate hot electrons from cold ones in semiconductor nanowire transistors, which thus offers a unique opportunity to observe and modulate electron occupied state, energy, mobility, and even its path. Such a process is accomplished through the scanning-photocurrent-microscopy (SPCM) measurements by activating the intervalley-scattering events and one-dimensional charge-neutrality rule. Findings discovered here may provide a new degree of freedom in manipulating nonequilibrium electrons for both electronic and optoelectronic applications.

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“…Alternatively, even though the onset of the plateau occurs several 100’s of meV below the excitation energy required to expect easy inter-valley scattering to the L-valley 3 , 16 , 17 , 35 , 36 , the electric field of the THz probe is approximately double the required field to result in a Gunn effect in these samples ( 17 kV/cm) 16 . However, if hot electrons persist and are even heated through electron-phonon interactions after their initial excitation some degree of band tilting due to the THz field may scatter e1 electrons into the L-valley 37 to contribute to the complicated transient response.…”

Section: Discussionmentioning

confidence: 99%

Hot-carrier dynamics in InAs/AlAsSb multiple-quantum wells

Piyathilaka

¹

,

Sooriyagoda

²

,

Esmaielpour

³

et al. 2021

Sci Rep

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A type-II InAs/AlAs$$_{0.16}$$ 0.16 Sb$$_{0.84}$$ 0.84 multiple-quantum well sample is investigated for the photoexcited carrier dynamics as a function of excitation photon energy and lattice temperature. Time-resolved measurements are performed using a near-infrared pump pulse, with photon energies near to and above the band gap, probed with a terahertz probe pulse. The transient terahertz absorption is characterized by a multi-rise, multi-decay function that captures long-lived decay times and a metastable state for an excess-photon energy of $$>100$$ > 100 meV. For sufficient excess-photon energy, excitation of the metastable state is followed by a transition to the long-lived states. Excitation dependence of the long-lived states map onto a nearly-direct band gap ($$E{_g}$$ E g ) density of states with an Urbach tail below $$E{_g}$$ E g . As temperature increases, the long-lived decay times increase $$<E{_g}$$ < E g , due to the increased phonon interaction of the unintentional defect states, and by phonon stabilization of the hot carriers $$>E{_g}$$ > E g . Additionally, Auger (and/or trap-assisted Auger) scattering above the onset of the plateau may also contribute to longer hot-carrier lifetimes. Meanwhile, the initial decay component shows strong dependence on excitation energy and temperature, reflecting the complicated initial transfer of energy between valence-band and defect states, indicating methods to further prolong hot carriers for technological applications.

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Exploiting intervalley scattering to harness hot carriers in III–V solar cells

Cited by 51 publications

References 29 publications

Quasiadiabatic electron transport in room temperature nanoelectronic devices induced by hot-phonon bottleneck

Quasiadiabatic electron transport in room temperature nanoelectronic devices induced by hot-phonon bottleneck

Direct observation and manipulation of hot electrons at room temperature

Hot-carrier dynamics in InAs/AlAsSb multiple-quantum wells

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