Measured and calculated radiative lifetime and optical absorption of InxGa1-xN/GaN quantum structures

We apply photoluminescence, photoluminescence excitation, and time-resolved optical spectroscopy for studying a set of InxGa1-xN/GaN periodic structur es, which were characterized by high-resolution x-ray diffraction including x-ray mapping in reciprocal space. We found that the energy differences be tween the absorption edge and the photoluminescence peak (Stokes shift), an d the photoluminescence decay time drastically increase with the InxGa1-xN layer thickness. The decay time strongly increases with the sample temperat ure. We were able to quite accurately determine the radiative and nonradiat ive decay times of excitons in these structures by measuring the temperatur e dependence of the decay times, the integrated photoluminescence intensiti es, and the photoluminescence intensities immediately after the picosecond excitation pulse. The intrinsic radiative Lifetimes, which are inversely pr oportional to the exciton oscillator strengths, were then calculated from t he temperature dependence of the radiative lifetimes. These experimental fi ndings are analyzed using an eight-band k.P model, which quantitatively exp lains both the Stokes shifts and the intrinsic radiative lifetimes. Their s trong dependence on the quantum well width is due to a large (similar to 1 MV/cm) lattice-mismatch strain-induced piezoelectric field along the growth axis.