Correlation of the Carrier Decay Time and Barrier Thickness for Asymmetric Cubic GaN/Al0.64Ga0.36N Double Quantum Wells

The carrier transfer via non-resonant tunneling is of great significance for many devices like the quantum cascade laser. In this study time-resolved photoluminescence is used for an investigation of this effect in asymmetric double quantum wells for low temperatures. The Al content in these asymmetric double quantum wells was determined by HRXRD to x=0.64 +/- 0.03. The growth of the asymmetric cubic GaN/AlxGa1-xN double quantum wells was performed by a radio-frequency plasma-assisted molecular beam epitaxy. As a substrate, 3C-SiC (001) on top of Si (001) was used. Three samples with different barrier thickness d were analysed (1nm, 3nm, 15nm). The two quantum wells are designed with the thicknesses 2.5nm and 1.35nm. Thus, three expected emission bands measured in luminescence can be resolved. The maximum intensities are 3.49eV (wide well), 3.73eV (narrow well) and 4.12eV (AlGaN). A correlation between the carrier lifetimes of the quantum wells (QWs) and the barrier width is found. Exploiting rate equations, the intensity ratio of both QW emissions is calculated. The coupling of the two QWs starts below 3nm barrier thickness, above this value there is no coupling.