Highly resolved excitonic spectra in GaAs/AlGaAs superlattices grown by organometallic chemical vapor deposition

We report the first observation of highly resolved photoluminescence and excitation spectra in GaAs/AlGaAs superlattices grown by organometallic chemical vapor deposition. Luminescence linewidths as narrow as 0.5 meV, and negligible Stokes shifts between luminescence and excitation peaks are measured for samples with 80-280 Å GaAs wells and 20 Å Al_0.3Ga _0.7As barriers. Both free heavy and light hole exciton and neutral donor-bound exciton peaks are observed in luminescence; excitation and temperature dependence is studied over the ranges 0.28 mW/cm²-10 W/cm² and 1.7-30 K, respectively. The bound exciton luminescence saturates with respect to that of free excitons at high excitation, and rapid dissociation into free excitons is observed as the temperature increases. The free exciton peaks broaden at high temperature, while the bound exciton peaks remain sharp.