Creation and Control of Two-Dimensional Electron Gas Using Al-Based Amorphous Oxides/SrTiO₃ Heterostructures Grown by Atomic Layer Deposition

The formation of a two-dimensional electron gas (2-DEG) using SrTiO₃ (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 LaAlO₃ (LAO) layer grown by the ALD process can generate 2-DEG (∼1 × 10¹³/cm²) with an electron mobility of 4–5 cm²/V·s. A much higher electron mobility was observed at lower temperatures. More remarkably, amorphous YAlO₃ (YAO) and Al₂O₃ 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, Me₃Al, as a reducing agent for STO during LAO and YAO ALD as well as the Al₂O₃ ALD process at 300 °C. The deposited oxide layer also plays an essential role as a catalyst that enables Me₃Al 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