Extremely low inhomogeneous broadening of exciton lines in shallow (In,Ga)As/GaAs quantum wells

We study radiative linewidth of exciton resonance in shallow InxGa1−xAs/GaAsInxGa1−xAs/GaAs single quantum wells as a function of indium concentration in the range x=0.02…0.10x=0.02…0.10 and well thickness in the range LZ=1…30nm using method of Brewster reflection spectroscopy. Record linewidths of heavy-hole exciton resonance of about 130…180μeV are measured in reflection spectra for single quantum wells with LZ=2nm and x=0.02 at temperature of 9 K. In these spectra, the non-radiative linewidth including inhomogeneous broadening can be comparable or even less than radiative linewidth. It is shown that radiative linewidth weakly depends on x   and LZLZ in these ranges. In multiple-quantum-well Bragg structure with ten periods, the oscillator strength per individual quantum well is similar to that of single quantum well, while the total radiative linewidth exceeds inhomogeneous broadening by 4 times.