Long-Lived Hot Carriers in III-V Nanowires.
Heat management mechanisms play a pivotal role in driving the design of nanowire (NW)-based devices. In particular, the rate at which charge carriers cool down after an external excitation is crucial for the efficiency of solar cells, lasers, and high-speed transistors. Here, we investigate the thermalization properties of photogenerated carriers by continuous-wave (cw) photoluminescence (PL) in InP and GaAs NWs. A quantitative analysis of the PL spectra recorded up to 310 K shows that carriers can thermalize at a temperature much higher than that of the lattice. We find that the mismatch between carrier and lattice temperature, ΔT, increases exponentially with lattice temperature and depends inversely on the NW diameter. ΔT is instead independent of other NW characteristics, such as crystal structure (wurtzite vs zincblende), chemical composition (InP vs GaAs), shape (tapered vs columnar NWs), and growth method (vapor-liquid-solid vs selective-area growth). Remarkably, carrier temperatures as high as 500 K are reached at the lattice temperature of 310 K in NWs with ∼70 nm diameter. While a population of nonequilibrium carriers, usually referred to as "hot carriers", is routinely generated by high-power laser pulses and detected by ultrafast spectroscopy, it is quite remarkable that it can be observed in cw PL measurements, when a steady-state population of carriers is established. Time-resolved PL measurements show that even in the thinnest NWs carriers have enough time (∼1 ns) after photoexcitation to interact with phonons and thus to release their excess energy. Nevertheless, the inability of carriers to reach a full thermal equilibrium with the lattice points to inhibited phonon emission primarily caused by the large surface-to-volume ratio of small diameter NWs.
Dipartimento di Fisica, Sapienza Università di Roma , Piazzale A. Moro 2, 00185 Roma, Italy.
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Tedeschi
Dipartimento di Fisica, Sapienza Università di Roma , Piazzale A. Moro 2, 00185 Roma, Italy.
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De Luca
Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University , Canberra, ACT 2601, Australia.
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Fonseka
Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University , Canberra, ACT 2601, Australia.
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Gao
Dipartimento di Chimica and Sapienza Nanoscience & Nanotechnology Lab (SNN-LAB), Sapienza Università di Roma , Piazzale A. Moro 2, 00185 Roma, Italy.
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Mura
Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University , Canberra, ACT 2601, Australia.
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Tan
Istituto Officina dei Materiali CNR , Basovizza SS 14 km 163.5, 34149 Trieste, Italy.
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Rubini
Istituto per la Microelettronica e i Microsistemi CNR , Via del fosso del cavaliere 100, 00133 Roma, Italy.
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Martelli
Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University , Canberra, ACT 2601, Australia.
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Jagadish
Dipartimento di Fisica, Sapienza Università di Roma , Piazzale A. Moro 2, 00185 Roma, Italy.
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Capizzi
Dipartimento di Fisica, Sapienza Università di Roma , Piazzale A. Moro 2, 00185 Roma, Italy.
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Polimeni
InP and GaAs nanowires; hot carriers; photoluminescence; wurtzite; zincblende