Optical Spectroscopy of InGaN/GaN Quantum Wells

We apply photoluminescence, photoluminescence excitation and time-resolved optical spectroscopy for studying a well-characterized set of InGaN/GaN periodic structures. The energy differences between the absorption edge and the photoluminescence peak and the photoluminescence decay times drastically increase with the InGaN quantum well thickness. We quite accurately determined the radiative and non-radiative decay times of excitons in these structures from the measured decay times, the integrated photoluminescence intensity and the photoluminescence intensity immediately after the excitation pulse, at various temperatures. The intrinsic radiative lifetimes, which are inversely proportional to the exciton oscillator strengths, are then calculated from the temperature dependence of the radiative lifetimes. These experimental findings are analyzed using an eightband k P model, which quantitatively explains both the Stokes shifts and the intrinsic radiative lifetimes. Their strong dependence on the quantum well width is due to a strong lattice-mismatch strain induced piezoelectric field along the growth axis.