Abstract
Hot electrons established by the absorption of high-energy photons typically thermalize on a picosecond time scale in a semiconductor, dissipating energy via various phonon-mediated relaxation pathways. Here it is shown that a strong hot carrier distribution can be produced using a type-II quantum well structure. In such systems it is shown that the dominant hot carrier thermalization process is limited by the radiative recombination lifetime of electrons with reduced wavefunction overlap with holes. It is proposed that the subsequent reabsorption of acoustic and optical phonons is facilitated by a mismatch in phonon dispersions at the InAs-AlAsSb interface and serves to further stabilize hot electrons in this system. This lengthens the time scale for thermalization to nanoseconds and results in a hot electron distribution with a temperature of 490 K for a quantum well structure under steady-state illumination at room temperature.
Highlights
Hot electrons established by the absorption of high-energy photons typically thermalize on a picosecond time scale in a semiconductor, dissipating energy via various phonon-mediated relaxation pathways
These LO phonons subsequently dissipate by transferring their energy to multiple acoustic phonons[16], or through the combination of a low energy transverse optical (TO) phonon and an acoustic phonon, a process known as the Ridley mechanism[17]
The structure under investigation consists of a 10 nm AlAs0.16Sb0.84 barrier followed by 30 repetitions of a 2.4 nm InAs quantum wells (QWs) and a 10 nm AlAs0.16Sb0.84 barrier grown by molecular beam epitaxy (MBE) on a semi-insulating (SI) GaAs (001) substrate
Summary
In the case of AlSb there is a large difference in the cation and anion mass, resulting in a larger phonon band gap (tan shaded region of Fig. 4(a))[8,16] than for InAs. Since the ratio of the optical and acoustic modes is ~2 for AlSb, the Klemens path is significantly reduced. The contribution of Raman peaks due to the AlAs0.16Sb0.84 barrier is relatively weak in the full MQW structure, which is dominated by the LO phonon contribution of the strained InAs buffer (230 cm−1) and InAs QWs (238 cm−1) This is further evidence of both the limited contribution of phonon processes in the barriers in carrier thermalization and the strong confinement of hot electron-phonon processes within the QWs. The cooling processes in the QW were modeled using an energy loss process in which the LO-phonon emission was invoked to determine the dynamics of the system (see Supplementary Information S7). A more detailed description of the phononic properties of the coupled InAs-AlAsSb system, including effects related to relaxation of momentum conservation at the interfaces, zone-folding, phononic confinement in the superlattice, and the effects of thermal transport across the interfaces is underway
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