Temperature-dependent dielectric function of bulkSrTiO3: Urbach tail, band edges, and excitonic effects

Abstract

We report the temperature-dependent complex dielectric function of pristine bulk SrTiO3 between 4.2 and 300 K within the energy range of 0.6-6.5 eV determined by spectroscopic ellipsometry. Fundamental indirect and direct band-gap energies have been extracted and are discussed with regard to existing state-of-the-art theoretical calculations. Furthermore, the dielectric function around the fundamental direct gap is analyzed by considering excitonic states. The excitonic effects, including the Coulomb enhancement of the continuum, are characterized using an extension of the Elliott's formula considering both the real and imaginary parts of the dielectric function. The Urbach tail below the indirect edge shows an unconventional temperature-dependent behavior correlated to the microstructural changes near the structural phase transition around 105 K from the lowtemperature tetragonal phase to the cubic phase. The temperature-dependent characterization reveals that the fundamental indirect edge as well as the Urbach tail are affected conspicuously by the structural phase transition while the fundamental direct edge is not. Moreover, the indirect edge follows Varshni's rule only in the cubic phase and the direct edge exhibits an anomalous linear increase with increasing temperature.

Optical NIR-VIS-VUV constants of advanced substrates for thin-film devices

“…3). The positions of the main spectral peaks and absorption edge obtained for the STO substrate agree with previous observations [26,46,47]. Upon closer examination of the model-generated optical absorption spectra at the onset of absorption (Fig.…”

“…The exact cause for this feature is debated [49], with a general consensus pointing toward the band-tail states in the energy gap. We note that theoretical and experimental studies of optical properties of STO are still ongoing [47]. Heterovalent doping of STO has been reported to change the badgap of this material [50].…”

Enhancing ferroelectric photovoltaic effect by polar order engineering

“…S10). It should be noted that at room temperature, the phonon absorption branch usually dominates the (α h ν) 1/2 plot ( 34 ). For pure BFO, the linear portions of the direct and indirect Tauc plots almost overlap with each other, implying that this electronic transition contains both direct and indirect features, which is consistent with the flatness of the valence band edge of BFO ( 35 ).…”

Effects of quantum confinement on excited state properties ofSrTiO3fromab initiomany-body perturbation theory

“…Atomically thin two-dimensional layers in SrTiO 3 heterostructures display exotic electronic effects, such as an emergent two-dimensional electron gas [6,7], magnetism [8], and metal-insulator transitions [9]. Recently, anomalous excitonic phenomena have been observed in the optical spectrum of cubic SrTiO 3 [10][11][12]. These effects, previously overlooked, arise due to strong Coulomb interactions between excited electrons and holes in the absence of strong screening, and can be enhanced through dimensionality and quantum confinement.…”