The high-mobility conducting interface (CI) between LaAlO₃ (LAO) and SrTiO₃ (STO) has revealed many fascinating phenomena, including exotic magnetism and superconductivity. But, the formation mechanism of the CI has not been conclusively explained. Here, using in situ angle-resolved photoemission spectroscopy, we elucidated the mechanisms for the CI formation. In as-grown samples, we observed a built-in potential (V_bi) proportional to the polar LAO thickness starting from the first unit cell (UC) with CI formation appearing above 3 UCs. However, we found that the V_bi is removed by synchrotron ultraviolet (UV)-irradiation; The built-in potential is recovered by oxygen gas (O₂(g))-exposure. Furthermore, after UV-irradiation, the CI appears even below 3UC of LAO. Our results demonstrate not only the V_bi-driven CI formation in as-grown LAO/STO, but also a new route to control of the interface state by UV lithographic patterning or other surface modification.

LaAlO ₃（LAO）和SrTiO ₃（STO ）之间的高迁移率导电界面（CI）揭示了许多引人入胜的现象，包括外来磁性和超导电性。但是，尚未最终解释CI的形成机制。在这里，使用原位角分辨光发射光谱，我们阐明了CI形成的机制。在成长期的样品中，我们观察到与第一个单位晶胞（UC）开始的极性LAO厚度成比例的内在电势（V _bi），CI的形成出现在3个UCs以上。但是，我们发现通过同步加速器紫外线（UV）辐照除去了V _bi。内置电位通过氧气（O ₂（g））暴露。此外，在紫外线照射后，CI甚至出现在LAO的3UC以下。我们的结果不仅证明了在成长期的LAO / STO中由V _bi驱动的CI的形成，而且还提出了通过UV光刻图案化或其他表面改性来控制界面状态的新途径。