Transparent semiconducting SrTiO3 crystal fabricated by heating treatment with gaseous ammonia and CeO2 powder

A transparent semiconducting SrTiO3 single crystal with a resistivity of the order of 10(3) Omega.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.