Abstract
A transparent semiconducting SrTiO3 single crystal with a resistivity of the order of 103 Ω·cm was fabricated by heating a SrTiO3 single crystal with gaseous ammonia and CeO2 powder. Conductive atomic force microscope (C-AFM) measurement revealed that micro-sized voids were formed and the high conductivity was exhibited only at around the voids. It is considered that the micro-sized voids were caused by the concentrated SrO planar defects, and TiO2-terminated structure with oxygen vacancies contributed to the two-dimensional conduction. In the heating process, the CeO2 powder acted as an oxygen source, and radicals such as NH2 and NH were generated by the reaction of oxygen and ammonia. The radicals may have contributed to the formation of three-dimensional network of the conductive paths consisting of SrO planar defects without the reduction of the bulk components. The electrons were localized on the TiO2-terminated structure, and the volume content of the conductive paths was small compared to the insulating bulk component. Therefore, the crystal was optically transparent and semiconducting.
Highlights
Transparent conductive oxides are widely used in optoelectronic applications such as solar cells, UV-light emitting diodes (LEDs), transparent thin film transistors (TFTs), photochromic devices, gas sensors, and infrared absorbing materials[1,2,3]
In contrast to their study, we have reported that the nitrogen-doped strontium titanate single crystal heated in gaseous ammonia was an excellent dielectric[16]
The bandgap of nitrogen-doped strontium titanate is generally narrower than pure SrTiO3, and SrTiO3 changed from colorless to yellow due to the substitution of oxygen by nitrogen[16,22]
Summary
Received: 16 November 2017 Accepted: 2 March 2018 Published: xx xx xxxx and CeO2 powder. The (100) surface of SrTiO3 with SrOor TiO2-terminated structure exhibits metallic states when electron is created on the surface by oxygen vacancies or hydrogen adsorption[4,5,6,7] In these materials, the energy level of the surface state is formed in the band gap of the underlying bulk crystal and the Fermi level is in the conduction band[8]. In contrast to their study, we have reported that the nitrogen-doped strontium titanate single crystal heated in gaseous ammonia was an excellent dielectric[16]. We used CeO2 powder as an oxygen source in a heating treatment of SrTiO3 single crystal with gaseous ammonia to control the amount of NH2 and NH radicals in this study. We introduce the fabrication process of the crystal and the mechanism of transparent conductivity in this article
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