Diode characteristics of ZnO/ZnMgO nanowire p-n junctions grown on Si by molecular beam epitaxy

•ZnO/ZnMgO QW nanowires on Si substrate were grown by molecular beam epitaxy.•Electro-optical properties of the samples were investigated PL and DLTS.•Information on optical transitions dedicated to QWs and defect levels was obtained.•Parameters of defects were determined and their possible origin has been discussed.•The impact of defects on efficiency of nanowire n-ZnMgO/p-Si diodes was commented.