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

Abstract 280 nm thick Al 0.2 Ga 0.8 N/Al 0.7 Ga 0.3 N superlattice structures with various well and barrier layer thickness and different silicon doping were grown on 1.2 μm thick Al 0.63 Ga 0.37 N-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 × 10 13 cm −2 at 300 K. The highest electron mobility values of ∼140 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 Al 0.63 Ga 0.37 N base layer. Furthermore the silicon doping led to an increased surface/interface roughness caused by pit formation.