Investigation of dislocations in Nb-doped SrTiO3 by electron-beam-induced current and transmission electron microscopy

Abstract

This paper aims to clarify the electrical activities of dislocations in Nb-doped SrTiO3 substrates and the role of dislocations in the resistance switching phenomenon in Pt/SrTiO3 Schottky contacts. The electrical activities of dislocations have been studied by electron-beam-induced current (EBIC) technique. EBIC has found that dislocations can exhibit dark or bright contrast depending on their character and band bending condition. The character of dislocations has been analysed based on chemical etching and transmission electron microscopy. These data suggested that not all the dislocations contribute to the switching phenomenon. The active dislocations for resistance switching were discussed.

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

“…This includes our oxides of choice in this review: TiO 2 [48,53], SrTiO 3 crystals [50,51,55,68,225,226], and doped SrTiO 3 such as Nb:SrTiO 3 [227], La:SrTiO 3 [228], Fe:SrTiO 3 [58], as well as related oxides such as BaTiO 3 [229,230], PbZrO 3 [231], KTaO 3 [232], NaNbO 3 [233,234], and BiFeO 3 [235]. Similar effects have also been observed for thin films, see, e.g., TiO 2 [236], SrTiO 3 , Fe:SrTiO 3 [225,[237][238][239], BaTiO 3 [230,240], HfO 2 [241][242][243][244], and NiO [245]. Here, examples of the current (resistance) mapping of SrTiO 3 and TiO 2 are given in Figures 35 and 36, respectively.…”

“…Additional supporting argument about the important role of dislocations in the electric activity of the surface layer of SrTiO 3 can be obtained from the analysis of the already above mentioned EBIC measurements for stoichiometric [242] (see also Figure 46) and as well as for doped SrTiO 3 crystals [241]. One can see that the brightness of the EBIC contrast in the vicinity of the straight lines which marking the segments of dislocations can be changed by applying a bias voltage in the case of undoped SrTiO 3 crystals (here −10 V, Figure 62) and Nb-doped SrTiO 3 (0.01%) (−2 V, Figure 63), respectively.…”

“…Moreover, etch pits investigation on such electrodegraded crystals support this notion in that the etch pits accumulate in just the same way along the bands with high concentration of filaments. It should be mentioned that the local enhancement of the conductivity of filaments with respect to the matrix amounts to three to four orders of magnitude Additional supporting argument about the important role of dislocations in the electric activity of the surface layer of SrTiO3 can be obtained from the analysis of the already above mentioned EBIC measurements for stoichiometric [242] (see also Figure 46) and as well as for doped SrTiO3 crystals [241]. One can see that the brightness of the EBIC contrast in the vicinity of the straight lines which marking the segments of dislocations can be changed by applying a bias voltage in the case of undoped SrTiO3 crystals (here −10 V, Figure 62) and Nb-doped SrTiO3 (0.01%) (−2 V, Figure 63), respectively.…”

“…When applying bias, bright contrast appeared in the vicinity of some straight lines with the directions along <112>. Adapted from [241].…”

“…Using appropriate Schottky contacts (in this case, a thin Pt electrode becomes deposited on the surface of reduced SrTiO 3 crystal [241,242]) the contributions of different locations in the surface region (i.e., below the contact) for recombination processes of the incident electron beam can be analyzed. Measurement of the current at the bottom electrode synchronously to the scanning position of the incident electron (SEM) beam gives then the planar distribution of electronically active defects in the form of a current contrast.…”