LO-phonon emission in an ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs-${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As single quantum well with two occupied electronic subbands

Longitudinal-optic (LO) phonon emission by heated electrons in an ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs- ${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As single quantum well (SQW) is studied by taking into account of a two-dimensional electron gas (2DEG) where the two lowest electronic subbands are populated by electrons. The power and angular dependences of the emission of LO phonons are investigated theoretically by using quantum formulas of energy-loss rate and by including the effects of electron temperature and electron-electron (e-e) screening. The results presented in this paper are useful to interpret the phenomena observed from phonon emission experiments in relatively high input power regime. Our results show that in a SQW with the well width L=20 nm, (i) the generation of LO phonons through the intersubband scattering process is much weaker than that through intrasubband process; (ii) over a wide angle range (θ>5°) the emission of LO phonons depends weakly on the emission angle θ; and (iii) LO phonon emission results in the increase in the background phonon signal detected at large energy excitation levels. The presence of the e-e screening has a stronger effect on electron temperature in a low input power regime whereas a weaker effect of e-e screening on the detected phonon signal can be observed in all energy excitations.