Control of electronic, optical and thermal properties in semiconductor nanostructures allows for design of electronic, optoelectronic and thermoelectric devices. For some applications, a prolonged excited-state carrier lifetime is desired without carrier thermalization or recombination. Engineering charge separation and indirect recombination pathways leads to hot electrons dominating the device response. In this work, transient absorption of terhertz (THz) probe pulses measure the recombination dynamics of photoexcited carriers in a type-II InAs/InAsSb multiple quantum well (MQW). THz measures free-photocarrier absorption and lattice expansions within the MQW as a result of phonons or polarons. The carriers are photoexcited close to the fundamental excited-state resonance of the MQW for a range of lattice temperatures between 5 K and 300. Excitation above the MQW resonance at low temperature shows fast (~15 ps), intermediate (~150 ps) and slow (~1500 ps) recombination times. As the lattice temperature is increased, fast recombination subsides and the slower recombination components grow. This switch of recombination components is almost conservative and is agreement with photoluminescence results suggesting that radiative recombination occurs strongly for the entire temperature range. Fast recombination results from direct recombination within the MQW, as conduction electrons combine with localized holes arising from alloy fluctuations that are frozen in low temperature. At higher temperatures, recombination processes are indirect, between the well’s conduction electrons and barrier’s valence holes. The identical temperature dependence of slower recombination contributions indicated this to be a two-step mechanism that is also reliant on the electron-phonon coupling. Type-II MQWs can enhance this recombination times to prolong hot carriers for optoelectronic devices.
Alan D. Bristow, Herath P. Piyathilaka, Hamidreza M. Esmaielpour, Vincent R. Whiteside, Michael B. Santos, and Ian R. Sellers, "Hot-carrier dynamics in type-II semiconductor quantum wells (Conference Presentation)," Proc. SPIE 10530, Ultrafast Phenomena and Nanophotonics XXII, 105300U (Presented at SPIE OPTO: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291922.5751516117001.
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