Electrical and optical properties of convex-type metamorphic In0.75Ga0.25As/In0.7Al0.3As quantum well structures grown by MBE on GaAs

In_0.75Ga_0.25As/In_0.7Al_0.3As quantum well (QW) structures were grown by molecular beam epitaxy on GaAs(0 0 1) substrates by using linear- and convex-graded In _x Al_1-x As metamorphic buffer layers (MBLs). Influence of a type of the In _x Al_1-x As MBL, as well as design and growth conditions of the QW active region (for the convex-type MBL) on electrical and optical properties of the QW structures was studied. The convex-graded In _x Al_1-x As MBL was found to result in obtaining the In_0.75Ga_0.25As/In_0.7Al_0.3As QWs with the higher electron mobility in comparison with the linear MBL. Effect of persistent photoconductivity was observed and explained by localization of charge carriers on potential fluctuations caused by the QW interface roughness and In-rich regions formed in the InAlAs barriers and InGaAs QW. Two conductivity channels in the vicinity of the bottom and top interfaces of the In_0.75Ga_0.25As/In_0.7Al_0.3As QW were found to exist even for optimized structures grown on convex-graded In _x Al_1-x As MBL.