Excitonic behavior in pseudomorphic InGaAs/(Al,Ga)As quantum wells grown by molecular-beam epitaxy

Photoluminescence and photoluminescence excitation spectroscopy have been used to study excitons in undoped InGaAs pseudomorphic quantum wells with GaAs and AlGaAs barrier layers. Luminescence features from samples incorporating a top AlGaAs barrier layer were strikingly different from those with bottom AlGaAs barriers. The 2-K luminescence from the latter structures showed free and bound exciton contributions with a linewidth ≤1.5 meV. In contrast, the luminescence from samples with top AlGaAs barriers was much broader, presumably the result of statistical variations in well width due to island formation at the top interface. Fits to the temperature dependence of the PL linewidth show that while the homogeneous broadening is similar in all the structures, the inhomogeneous broadening introduced by the interfaces is fundamentally different. The results could have important implications for the optimization of heterostructure devices in this pseudomorphic system.