Nonequilibrium electron distributions in a three-subband InGaAs/InAlAs quantum well studied via double resonance spectroscopy

Abstract

Midinfrared optical pumping of electrons from the ground (n=1) to the first excited (n=2) subband of the quantum well produces a strongly nonthermal electron distribution which is probed spectroscopically. Two sharp induced absorption peaks appear, associated with electrons which have scattered from the upper subband via longitudinal optical (LO) phonon emission and absorption. The presence of the phonon absorption channel evidences the importance of nonequilibrium LO phonon populations (nph∼1), and the impact on the nonradiative intersubband scattering rates in quantum cascade laser devices is explored.

Influence of longitudinal electric field on the hot-phonon effect in quantum wells

“…Such hot carriers emit hot phonons during carrier energy relaxation processes, while some of the phonons can be reabsorbed by the carriers. 11 Recently the hot-phonon population in QCLs was measured in a range of lattice temperatures ͑75-280 K͒. Thus the HPE slows down the cooling of hot plasma, and this was indeed observed in experiments 1,3-5 and supported by theoretical studies.…”

“…In the hot-phonon population measurement by Spagnolo et al, 19 only the interface modes were probed as the Raman spectra were measured in parallel polarization. 11 Now, in Fig. This can provide experimental evidence in addressing the roles played by the interface and bulklike phonons in the hot-carrier dynamics in QCLs.…”

“…Our calculation indicates that with further increasing the electric field strength the IF 1 occupation number slightly increases while the LO 2 population decreases. 11 A direct comparison with the experiment cannot be made here, because ͑i͒ the electron densities in the second subband generated by the pump pulses are not known; and ͑ii͒ what was measured in the experiment 11 is the intraband absorption spectrum rather than the nonequilibrium phonon population as in experiment. In the hot-phonon population measurement by Spagnolo et al, 19 only the interface modes were probed as the Raman spectra were measured in parallel polarization.…”

“…2 the GaAs-like interface mode IF 1 and the bulklike mode LO 2 have much larger population than other modes. In the intraband pump-probe experiment on the nonequilibrium electron distribution, 11 the energy gap between the lowest two subbands is 139 meV. Although the IF 1 population peaks with a larger value than the LO 2 population, the latter has a larger wave vector width than the IF 1 population.…”

Transient reshaping of intraband transitions by hot electrons

“…[7][8][9][10][11] Yet there are few demonstrations of hot carrier effects on intraband transitions. [12][13][14] This work studies the effects of hot electrons on intraband transitions using cadmium selenide colloidal quantum wells (CQWs), which exhibit a class of intraband transitions, termed intersubband transitions, from the first to second conduction bands occuring in the near-infrared. Because intersubband transitions are the critical element of quantum cascade lasers 15 and quantum well infrared photodetectors, 16 the effects of hot electrons on these intraband transitions can alter gain spectra, thresholds, or current levels.…”