Electron transport in AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

High quality AlGaN/GaN heterostructures have been grown by rf plasma-assist ed molecular beam epitaxy (MBE) on n-type GaN templates grown on sapphire b y metalorganic chemical vapor deposition (MOCVD). By optimizing the AlGaN t hickness and the Al content, record low temperature mobilities have been ac hieved. Temperature and magnetic field dependent Hall effect,, and Shubniko v-de Haas oscillations, were used to probe the two-dimensional electron gas (2DEG) with consistent results. The unintentionally doped Al0.09Ga0.91N he terostructures exhibit a measured 77 K Hall mobility of 24,000 cm(2)/V.s (n (sh) = 2.5 x 10(12)), 12 K mobility of 52,000 cm(2)/V.s and similar to4 K m obility of 60,000 cm(2)/V.s (n(sh) = 2.25 x 10(12)), all records for this m aterial system. The magnetic field dependent Hall effect revealed carriers from the bulk GaN freeze out and that a single carrier system is dominant b elow 80 K.