DYNAMICS OF CARRIER RECOMBINATION IN GAAS/ALGAAS QUANTUM-WELL STRUCTURES

The dynamics of carrier recombination in GaAs/AlxGa1-xAs quantum well (QW) structures is investigated using continuous wave and time resolved photoluminescence (PL) spectroscopy. We find that the recombination occurs from excitons localized at crystal defects at low temperature, while both free exciton and free carrier recombinations are observed for T greater-than-or-equal-to 70-100 K. The relative weight of the PL contributions at high temperature only depends on T and results in agreement with the 2D law of mass action for the equilibrium population densities. The relevance of the non radiative processes in the determination of the photoluminescence decay time is stressed and the behaviour of the radiative recombination time constant is deduced from the simultaneous measurement of the PL decay time and the PL integrated intensity. A consistent picture of the radiative recombination dynamics is eventually achieved at least for high temperature and weak excitation; a more complicated phenomenology is observed after excitation higher than a few tens of W/cm2.