Growth and characterization of thick Si-doped AlGaN epilayers on sapphire substrates

AlxGa1-xN epilayers with x = (0.07 to 0.13) were grown by MOCVD on AlGaN nu cleation layer deposited on sapphire substrates. The epilayers grown under constant TMA and TMG flows demonstrated a nonuniform in-depth Al distributi on. This effect can be suppressed by varying the TMA/(TMA+ TMG) mole flow r atio during the growth and by using an AlN-coated susceptor. Photoluminesce nce (PL) studies revealed the so-called "S-shaped" PL:maximum energy shift with increase in the temperature of observation. Rapid thermal annealing at 1100 to 1300 degrees C for 30 to 120 s resulted in a complete suppression of this behavior and the PL maximum energy was shifted towards the higher-e nergy side of the spectrum by more than 20 meV. The room-temperature electr on mobility was increased from 30 to 40 cm(2) V-1 s(-1) for the as-grown sa mples to 200 cm(2) V-1 s-(1) for the annealed samples without significant c hange in the electron concentration (1.0 to 1.5) x 10(18) cm(-3).