Optical and Transport Properties of GaN/Al0.15Ga0.85N Quantum Wells

We have investigated the optical and phototransport properties of GaN/AlGaN quantum wells by photoluminescence and photovoltage spectroscopy. We show that the internal piezoelectric and spontaneous polarization fields cause a strong red-shift of the ground level energy of the quantum wells. Furthermore, identical quantum wells grown on different buffer layers (GaN or AlGaN) exhibit different emission energies, but similar well-width dependence of the n = 1 state, due to the different distribution of strain between well and barrier. The built-in field also causes a strong reduction of the exciton oscillator strength, which is not observable in photovoltage spectra. A long-living (thousands of seconds) charge storage effect is observed in the phototransport spectra due to the presence of point defects, presumably associated to Ga vacancies.