Enhanced hot electron lifetimes in quantum wells with inhibited phonon coupling

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.

Hot-carrier cooling dynamics of type-II InAs/AlA1-xSbx quantum wells

“…In steady-state photoluminescence (PL), these MQWs have shown evidence of hot carriers 14 , non-monotonic emission energy as a function of lattice temperature due to the complicated valence band structure 15 and even intervalley scattering of electrons to the long-lived L-valley states 16 . Transient absorption directly shows long-lived carriers complementing the evidence of hot carriers and the non-monotonic temperature dependence 8 . Phonon band-structure calculations supports suppression of Klemens' process that successfully converts optical to acoustic phonons 4 in favor of the Ridley mechanism, which is less effective 5 .…”

“…For example, bandgap engineering of monolithic structures to include quantum confinement enhances optical absorption 10 , type-II band-aligned quantum wells spatially separate electrons and holes to increase the excited-state carrier lifetime 8,11 , and structures with highly contrasting media can reduce the cooling through phonons 12,13 . These properties all occur in InAs/AlAs 0.16 Sb 0.84 multiple-quantum wells (MQWs), where a hot-carrier distribution is shown along with extended carrier lifetimes as a result of inhibited phonon-phonon interactions 8 .…”

“…For example, bandgap engineering of monolithic structures to include quantum confinement enhances optical absorption 10 , type-II band-aligned quantum wells spatially separate electrons and holes to increase the excited-state carrier lifetime 8,11 , and structures with highly contrasting media can reduce the cooling through phonons 12,13 . These properties all occur in InAs/AlAs 0.16 Sb 0.84 multiple-quantum wells (MQWs), where a hot-carrier distribution is shown along with extended carrier lifetimes as a result of inhibited phonon-phonon interactions 8 . In steady-state photoluminescence (PL), these MQWs have shown evidence of hot carriers 14 , non-monotonic emission energy as a function of lattice temperature due to the complicated valence band structure 15 and even intervalley scattering of electrons to the long-lived L-valley states 16 .…”

Coherent Resonant Tunneling through Double Metallic Quantum Well States

“…In semiconductor QW, hot electrons typically thermalize in a picosecond time scale, dissipating energy via various phonon-mediated relaxation pathways. 36 In metallic QW, electron thermalization is even enhanced due to the smaller electron mean-free path compared to the semiconductor. Therefore, the electrons will quickly lose their phase and energy coherence if they are confined in a QW for a longer time and the reception side with another QW structure has no available resonant QW energy level under that bias.…”

Optoelectronic reciprocity in hot carrier solar cells with ideal energy selective contacts

“…Extensive experimental evidence dating back several decades exists, which demonstrates a transient difference between the electronic carrier temperature and the lattice temperature 5 typically lasting a few picoseconds. Several of these early spectroscopic results have been repeated in the context of photovoltaic hot carrier devices using III–V semiconductors 6 and later in various semiconductor nanostructures 7,8 . InN has unsusal vibronic properties that has resulted in transient temperature differences seen over a timespan of a few hundred picoseconds 9 .…”