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 $(μ∼1400–1600cm2∕Vs)$ and high electron sheet densities due to spontaneous and piezoelectric polarization $(ns∼1–3×1013cm−2)$ depending on the AlN thickness. This combination led to a large reduction of the room-temperature sheet resistance of $148Ω∕◻$⁠, 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.