Creation and Control of Two-Dimensional Electron Gas Using Al-Based Amorphous Oxides/SrTiO\(_3\) Heterostructures Grown by Atomic Layer Deposition

The formation of a two-dimensional electron gas (2-DEG) using \(SrTiO_3\) (STO)-based heterostructures provides promising opportunities in oxide electronics. We realized the formation of 2-DEG using several amorphous layers grown by the atomic layer deposition (ALD) technique at 300°C which is a process compatible with mass production and thereby can provide the realization of potential applications. We found that the amorphous \(LaAlO_3\) (LAO) layer grown by the ALD process can generate 2-DEG \((\sim 1 × 10^{13}/cm^{2})\) with an electron mobility of \(4–5 cm^2/V·s\). A much higher electron mobility was observed at lower temperatures. More remarkably, amorphous \(YAlO_3\) (YAO) and \(Al_2O_3\) layers, which are not polar-perovskite-structured oxides, can create 2-DEG as well. 2-DEG was created by means of the important role of trimethylaluminum, \(Me_3Al\), as a reducing agent for STO during LAO and YAO ALD as well as the \(Al_2O_3\) ALD process at 300°C. The deposited oxide layer also plays an essential role as a catalyst that enables \(Me_3Al\) to reduce the STO. The electrons were localized very near to the STO surface, and the source of carriers was explained based on the oxygen vacancies generated in the STO substrate.