Near-Strain-Free GaN/AlGaN Narrow Line Width UV Light Emission with Very Stable Wavelength on Excitation Power by Using Superlattices

Because of the strong strain in nitrides, superlattice layers have been used to release the strain in the QW and reduce the quantum confined Stark effect. However, few reports discuss comprehensively the strain relaxation behavior and optical performance of a GaN/AlGaN single quantum well (QW) with inserted GaN/AlGaN superlattices (SLs). In this work, we examined a group of graded Al content GaN/AlxGa1-xN SL layers under the GaN/Al0.3Ga0.7N single QW grown on c-plane sapphire. Both the excitation power and temperature dependence of the time-integrated micro-photoluminescence (μ-PL) and time-resolved μ-PL were measured. The samples exhibited very narrow UV emission and had almost unchanged emission wavelength and stable line width behavior with excitation power as well as "S-shape"and weak "W-shape"characteristics with temperature due to the localization. The temperature-dependent PL lifetime was measured from 5 to 300 K, and the relatively fast recombination lifetime of the two samples was examined. Micro-Raman spectroscopy was also conducted to probe the strain state. All the results showed that adopting SLs around the QW structure produced a much more stable and desirable performance, which can be attributed to an effective relaxation of the strain in the QW.