Effects of ultraviolet photon irradiation on the transition metal impurities in LaAlO3

Abstract

By measuring electron spin resonance (ESR) spectra at the X-band frequency and absorption spectra from the visible to ultraviolet region at room temperature, it was confirmed that perovskite single crystal LaAlO3 contains Cr and Fe as impurities. When LaAlO3 is exposed to photons with energies higher than 4.5 eV, the intensities of ESR signals due to Cr3+ and Fe3+ decrease, which indicates that electrons released by the photon irradiation are captured by Cr3+ and Fe3+. Concurrently with this, a broad optical absorption band at about 3.0 eV and two new broad and weak ESR signals appear. The former is attributable to a combination of a hole and a La3+ (or Al3+) vacancy, and the two weak ESR signals are assigned to the O− center and F+ center.

Magnetic Modes in Rare Earth Perovskites: A Magnetic-Field-Dependent Inelastic Light Scattering study

“…We rule out a role of any magnetic impurity element such as Cr 3+ and Fe 3+ in the Al-based compounds1417), especially in LSAT and LSAO and possibly in LaAlO 3 as well. PIXE measurements showed that no impurities could be detected within the resolution limit (~10 ppm) in LaAlO 3 (see Figure S12) and any of these substrates except SrTiO 3 (~7 ppm of Cr and ~160 ppm of Fe; not shown in Figure).…”

“…This material is a promising gate insulator for advanced Metal-Oxide-Semiconductor (MOS) devices101112. However, it has been reported to possess localized mid-gap states due to various types of defects — interstitials, vacancies, anti-sites, impurities — causing leakage current and it is important to understand the various defects and their dynamics both experimentally and theoretically13141516171819. On the other hand, lattice strain plays an important role on the defects and their dynamics and hence on the related physical properties20.…”

Spectroscopic properties of oxygen vacancies inLaAlO3

“…Electron spin resonance (ESR) studies can allow measurements of the V + O defect in LAO. Indeed ESR studies of LAO [30,31] have attributed certain signals in their measured spectra to this defect. In order to confirm the prediction that these signals are due to the V + O defect the g-tensor and hyperfine values of the defect can be calculated and compared to Singh et al [31].…”

“…Experimentally, defects in LAO have been probed using photoluminescence (PL) spectroscopy [28,29] and electron spin resonance (ESR) [30,31]. Kawabe et al [28] excited LAO using a 266 nm pulsed laser and observed slow emission at 2.5 eV (490 nm), which they attributed to oxygen vacancies, due to its sensitivity to the oxygen content.…”

“…They suggested that the excitations occur from the O 2p valence band to states within the gap, and therefore PL is a result of decay from these levels. In the ESR experiments [30,31] a broad signal is attributed to an F + like centre, which was cautiously associated with a charged oxygen vacancy (V + O ). Accurate modeling of the neutral and charged oxygen vacancies in LAO will allow more confident assignment of these transitions and will help to predict their behavior in the presence of external stimuli.…”