Electrical and structural properties of AlGaN/AlGaN superlattice structures grown by metal-organic chemical vapor deposition

280 nm thick Al0.2Ga0.8N/Al0.7Ga0.3N superlattice structures with various well and barrier layer thickness and different silicon doping were grown on 1.2 mum thick Al0.63Ga0.37N-on-sapphire films by metal-organic chemical vapor deposition. Whereas unintentionally doped samples were highly resistive, silicon doped structures exhibited sheet carrier densities up to 5.5 x 10(13) cm(-2) at 300 K. The highest electron mobility values of similar to140 cm(2)/V s were measured for samples with thick wells or thin barriers. When examined by high resolution X-ray diffraction (HRXRD), all samples showed higher order superlattice fringes indicating good layer periodicity. The HRXRD measurements also revealed, that the silicon doping promoted the relaxation of the superlattice stacks with respect to the Al0.63Ga0.37N base layer. Furthermore the silicon doping led to an increased surface/interface roughness caused by pit formation. (C) 2003 Elsevier Science B.V. All rights reserved.