Photoconductivity on europium oxyde single crystals and thin films

Abstract

In this paper, results of photoconductivity measurements on four EuO samples are given. Low frequency photoconductivity versus temperature (10°K < T < 300°K) and magnetic field H is investigated for two wavelengths: 6600 Å and 9000 Å. The photoconductivity kinetic is also described, and is characterized by a distribution in decay times. Temperature, magnetic field and carrier concentration have small effects on this kinetic. Quenching effect is obtained by adding a continuous illumination (λ 2) to the weak modulated light (λ 1). The kinetic is strongly affected by quenching and becomes more simple. Quenching effect is maximum for the wavelength associated to the 4ƒ 7–4ƒ 6 5 d, transition. In contrast to the Penney-Kasuya[1] model we propose another one in which the conduction of equilibrium carriers as photo-excited carriers takes place in a broad band. The variation of low frequency photoconductivity versus temperature is attributed to the mobility variation. This variation agrees well with the model of mobility controlled by spin-disorder. The photoconductivity kinetic is interpreted by a three levels recombination model: the conduction band, the 4 f levels and a distribution of trap levels. The lack of variation of photoconductivity decay in the range of metal-semiconductor transition is discussed.