Hydrogen-Related Defects in ZnO Studied by IR Absorption Spectroscopy

Abstract

Most of the ZnO growth techniques result in n-type conductivity of the crystal, which hinders the progress of ZnO applications for electronic devices. Hydrogen incorporated during the process of crystal growth is now considered as a likely source of the n-type conductivity of ZnO. Infrared absorption spectroscopy provides detailed insights into the physical properties of the light impurities in the semiconductor matrix and is, therefore, an excellent tool to explore the structure of the hydrogen-related defects embedded in ZnO. We report a number of hydrogen-related defects observed in hydrothermally grown ZnO and ZnO grown from the vapor phase studied by Fourier transform infrared absorption spectroscopy. Three IR absorption lines at 3611.3, 3349.6, and 3312.2 cm−1 at 10 K are observed after hydrogenation of the vapor phase grown ZnO. The line at 3611.3 cm−1 is tentatively assigned to a bond-centered hydrogen, whereas the other two are identified as a Zn vacancy decorated with two hydrogen atoms. The nature of a hydrogen center responsible for the 3577.3 cm−1 line observed at 10K in as-grown hydrothermal ZnO is discussed.