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

Abstract
Very low sheet resistance two-dimensional electron gases have been obtained at ultrathin Al N ∕ Ga N 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 ( μ ∼ 1400 – 1600 cm 2 ∕ V s ) and high electron sheet densities due to spontaneous and piezoelectric polarization ( n s ∼ 1 – 3 × 10 13 cm − 2 ) depending on the AlN thickness. This combination led to a large reduction of the room-temperature sheet resistance of 148 Ω ∕ ◻ , 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 Al N ∕ Ga N heterojunctions for the first time. The results are indicative of the vast potential of high-quality Al N ∕ Ga N structures for a variety of device applications.