Physical Properties of AlGaN/GaN Heterostructures Grown on Vicinal Substrates

We report on the growth of Al_0.25Ga_0.75N/GaN heterostructures grown on low dislocation density vicinal surfaces of semi-insulating c-axis GaN substrates. Atomic force microscopy (AFM), photoluminescence (PL), cathodoluminescence (CL), high-resolution x-ray diffraction (HRXRD), secondary-ion mass spectroscopy (SIMS), Hall effect, and Raman spectroscopy have been used to assess structural and electrical properties as a function of substrate offcut. Bulk GaN substrates with vicinal offcut between 0.5° and 1.4° are optimal with respect to surface roughness and dopant incorporation. AFM, PL, and CL show decreasing Mg incorporation with increasing offcut angle. Raman spectroscopy, used to analyze biaxial strain, confirms essentially strain-free heterostructure growth on vicinal substrates with offcut angles between 0.5° and 1.4° off 0001] toward 1`1] 00] 1\overline{1} 00] . Aluminum (Al) incorporation in the Al _x Ga_1−x N barrier assessed by Raman vibration is in excellent agreement with trends found by HRXRD.