Photoluminescence, Photocurrent, and Phase-Transition Correlations in SrTiO3

Abstract

Photoluminescence emanating from ``pure'' high resistivity SrTiO₃ has been examined between 4000 and 13 000 Å as a function of temperature and 3650 Å irradiation. One strong narrow peak (7929 Å at 95°K; half‐width ≤1 Å) and 9 associated peaks (7852, 8005, 8051, 8098, 8280, 8304, 8469, 8574, 8726 Å), each of which exhibit maximum intensity at 35° and 95°K, which are within the temperature ranges associated with the ferroelectric‐paraelectric transition, and the tetragonal‐cubic transition, respectively. As this emission extinguishes below 35°K, an asymmetric structureless broadband emission begins, which extends from ≈4200–≈8000 Å, and peaks near 5000 Å. Concurrent photocurrent measurements show: a maximum at 105°K and a minimum at 35°K; the existence of extensive trapping effects, including long‐duration (hours to days) dark‐current relaxation, a field‐induced persistent internal polarization (due to spacial separation of trapped electrons and holes), and an interaction between irradiation and ferroelectric hysteresis. Sublinear responses exist common to the photoluminescence peaks and photocurrents at various temperatures, viz. response ∝ J^β(T) where ½<β(T)<1. The behavior observed is in part interpretable on the basis of recombination processes via multiple defects.