Time-resolved spectroscopy of (Al,Ga,In)N based quantum wells: Localization effects and effective reduction of internal electric fields

We investigate the microscopic mechanisms of the highly intense light emission from (Al,Ga,In)N/(Al,Ga,In)N quantum wells (QW’s). We concentrate on the competition between radiative and nonradiative recombination of electron-hole pairs for ${\mathrm{Al}}_{0.12}{\mathrm{Ga}}_{0.84}{\mathrm{In}}_{0.04}\mathrm{N}/{\mathrm{Al}}_{0.30}{\mathrm{Ga}}_{0.69}{\mathrm{In}}_{0.01}\mathrm{N}$ multiple quantum wells of various widths. These nominal compositions correspond to the maximization of the luminescence intensity. By using time-resolved photoluminescence, we verify that such particular compositions of the quaternaries are capable of minimizing the magnitude of the longitudinal electric field which usually appears in such hexagonal group-III nitride based QW’s. We find that the radiative lifetime is nearly independent of the well width, whereas it should show an exponential dependence in the case of a strong electric field. We discuss our results via a theoretical estimation of the internal electric field. We also analyze the role played by local potential fluctuations in the quaternary alloy on the localization of carriers, by measuring the change of the photoluminescence energy, intensity, and dynamics versus the temperature.