Roles of point defects in thermally enhanced generation and transfer of electrons and holes in LaAlO₃

Thermal annealing was given to single crystal LaAlO₃ and its effects were examined by measuring electron spin resonance (ESR) and optical absorption. When LaAlO₃ was annealed at temperatures above 500°C in an oxidizing atmosphere, the intensities of ESR signals due to transition metal, likely ascribable to Fe³⁺, decreased. Concurrently with this, two optical absorption bands at 2.7 and 3.5 eV, attributable to a combination of a hole and a La³⁺ (or Al³⁺) vacancy, increased. These results indicate that thermal electron-hole generation is induced by oxidizing annealing and that the generated electrons and holes are then captured by Fe³⁺ ions and La³⁺ or Al³⁺ vacancies, respectively. It is also assumed that captured electrons and holes are released and recombine with each other by reducing annealing.