Conductivity and magnetoresistance of La_0.7Ce_0.3MnO_3−δthin films under photoexcitation

Abstract

Abstract. La 0.7 Ce 0.3 MnO 3 thin films of different thicknesses, degrees of CeO 2 -phase segregation and oxygen deficiency, grown on SrTiO 3 single crystal substrates, were comparatively investigated with respect to both their spectral and temperaturedependent photoconductivity (PC) and their magnetoresistance (MR) behaviour under photoexcitation. While as-grown films were insensitive to optical excitation, oxygen reduction appeared to be an effective way to decrease the film resistance, but the film thickness was found to play a minor role. However, from the evaluation of the spectral behaviour of the PC and the comparison of the MR of the LCeMO/substrate-samples with a bare substrate under illumination we find that the photoconductivity data reflects not only contributions from (i) photogenerated charge carriers in the film and (ii) carriers injected from the photoconductive substrate (as concluded from earlier works), but also (iii) a decisive parallel photoconduction in the SrTiO 3 substrate. Furthermore -also by analyzing the MR characteristics -the unexpected occurence of a strong electroresistive effect in the sample with the highest degree of CeO 2 segregation and oxygen deficiency could be attributed to the electroresistance of the SrTiO 3 substrate as well. The results suggest a critical reconsideration and possibly a reinterpretation of several previous photoconductivity and electroresistance investigations of manganite thin films on SrTiO 3 .

Quantifying the electrical transport characteristics of electron-doped La0.7Ce0.3MnO3 thin films through hopping energies, Mn valence, and carrier localization length

“…As visible in figure 2(b), in the whole temperature range investigated here, the resistance at 5 V is clearly lower than at 1 V. Furthermore, at 5 V, an MIT appears at 135 K. Being beyond the scope of the present work, the clarification of the origin of this electrical-field induced MIT (intrinsic to the film or substrate-related) by comparative magnetoresistance investigations is currently in progress [42]. Note that the electroresistive effect turned out to be non-persistent and was observed solely in sample D.…”

Electrical-transport characteristics of as-grown and oxygen-reduced La$_{0.7}$Ce$_{0.3}$MnO$_3$ films: calculation of hopping energies, Mn valences, and carrier localization lengths

“…Interestingly -and indeed electroresistive effects in LCeMO were reported in the past [41] -the resistance of film D strongly depends on the measuring voltage. As visible in figure 2(b), in the whole temperature range investigated here, the resistance at 5 V is clearly lower than at 1 V. Furthermore, at 5 V, an MIT appears at 135 K. Being beyond the scope of the present work, the clarification of the origin of this electrical-field induced MIT (intrinsic to the film or substrate-related) by comparative magnetoresistance investigations is currently in progress [42]. Note that the electroresistive effect turned out to be non-persistent and was observed solely in sample D.…”

From colossal magnetoresistance to solar cells: An overview on 66 years of research into perovskites

“…To remove this excess and to reduce the oxygen concentration further, high‐temperature annealing in ultrahigh vacuum (e.g., 10 −9 hPa at 700 °C) can be employed for several hours. As a result, the conductivity can be varied by orders of magnitude, the insulator‐to‐metal transition upon cooling can be suppressed, and new features arise including photoconductivity and electro‐resistive effects .…”