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

We study radiative linewidth of exciton resonance in shallow In x Ga 1 − x As / GaAs single quantum wells as a function of indium concentration in the range x = 0.02 … 0.10 and well thickness in the range L Z = 1 … 30 nm using method of Brewster reflection spectroscopy. Record linewidths of heavy-hole exciton resonance of about 130 … 180 μ eV are measured in reflection spectra for single quantum wells with L Z = 2 nm 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 L Z 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.