  We report very large bandgap enhancement in SrTiO3 (STO) films (fabricated by
pulsed laser deposition below 800 {\deg}C), which can be up to 20% greater than
the bulk value, depending on the deposition temperature. The origin is
comprehensively investigated and finally attributed to Sr/Ti antisite point
defects, supported by density functional theory calculations. More importantly,
the bandgap enhancement can be utilized to tailor the electronic and magnetic
phases of the two-dimensional electron gas (2DEG) in STO-based interface
systems. For example, the oxygen-vacancy-induced 2DEG (2DEG-V) at the interface
between amorphous LaAlO3 and STO films is more localized and the ferromagnetic
order in the STO-film-based 2DEG-V can be clearly seen from low-temperature
magnetotransport measurements. This opens an attractive path to tailor
electronic, magnetic and optical properties of STO-based oxide interface
systems under intensive focus in the oxide electronics community. Meanwhile,
our study provides key insight into the origin of the fundamental issue that
STO films are difficult to be doped into the fully metallic state by oxygen
vacancies.
