Differential spectroscopy of GaAs-Ga1-xA

We present differential photoluminescence and reflectivity studies of GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As quantum wells, using both wavelength-modulation and piezomodulation techniques. Our experiments permit unambiguous identification of light- and heavy-hole exciton transitions.