Photoluminescence and persistent photoconductivity of Al_xGa_1-xN/GaN heterostructures

We have investigated the optical properties of Al(x)Ga(1-x)N/GaN heterostructures (x=0.08, 0.15, 0.33) grown by metal organic chemical vapor deposition on sapphire using photoluminescence (PL) and persistent photoconductivity (PPC) measurements. For the Al(x)Ga(1-x)N/GaN heterostructures (HS) containing high Al composition, we observed an anomalous temperature-dependent photoluminescence and persistent photoconductivity effects. These results show a strong dependence of the physical properties of Al(x)Ga(1-x)N/GaN HS on the Al content and layer thickness. The anomalous temperature-dependent PL is usually attributed to the presence of carrier localization states. These phenomena are explained based on the alloy compositional fluctuations in the Al(x)Ga(1-x)N/GaN HS. From the PPC measurements, the photocurrent (PC) quenching was observed for Al(x)Ga(1-x)N/GaN HS and it is explained by the metastable states formed in the underlying GaN layer. Also, the mechanisms behind the PC quenching and PPC phenomena are explained in detail.