Well-width dependence of exciton-phonon scattering in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ single quantum wells

The temperature and density dependencies of the exciton dephasing time in ${\mathrm{In}}_{0.18}{\mathrm{Ga}}_{0.82}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ single quantum wells with different thicknesses have been measured by degenerate four-wave mixing. The exciton-phonon scattering contribution to the dephasing is isolated by extrapolating the dephasing rate to zero-exciton density. From the temperature dependence of this rate we have deduced the linewidth broadening coefficients for acoustic and optical phonons. We find acoustic-phonon coefficients that increase from 1.6 to 3 μeV/K when increasing the well width from 1 to 4 nm. This is in quantitative agreement with theoretical predictions when the spatial extension of the exciton wave function, strongly penetrating into the GaAs barrier in thin ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells, is taken into account. The optical-phonon coefficient does not show a systematic dependence on well thickness, and is comparable with the value for bulk GaAs.