Very low sheet resistance and Shubnikov-de-Haas oscillations in two-dimensional electron gases at ultrathin binary AlN/GaN heterojunctions

Very low sheet resistance two-dimensional electron gases have been obtained at ultrathin AlN/GaN heterojunctions. By investigating the molecular beam epitaxy growth conditions, the interface roughness at the heterojunction has been reduced, leading to high room-temperature electron mobilities (mu similar to 1400-1600 cm(2)/V s) and high electron sheet densities due to spontaneous and piezoelectric polarization (n(s)similar to 1-3x10(13) cm(-2)) depending on the AlN thickness. This combination led to a large reduction of the room-temperature sheet resistance of 148 Omega/square, a new record. The improved transport properties have made it possible to observe Shubnikov-de-Haas oscillations of the magnetoresistance of the two-dimensional electron gas at ultrathin binary AlN/GaN heterojunctions for the first time. The results are indicative of the vast potential of high-quality AlN/GaN structures for a variety of device applications. (C) 2008 American Institute of Physics.