Infrared absorption from OH− ions adjacent to lithium acceptors in hydrothermally grown ZnO

Abstract

An intense infrared absorption band has been observed in a hydrothermally grown ZnO crystal. At 12K, the band peaks near 3577.3cm−1 and has a half width of 0.40cm−1, and at 300K, the band peaks at 3547cm−1 and has a half width of 41.3cm−1. This absorption band is highly polarized, with its maximum intensity occurring when the electric field of the measuring light is parallel to the c axis of the crystal. Photoinduced electron-paramagnetic-resonance experiments show that the crystal contains lithium acceptors (i.e., lithium ions occupying zinc sites). Lithium and OH− ions are present in the crystal because lithium carbonate, sodium hydroxide, and potassium hydroxide are used as solvents during the hydrothermal growth. In the as-grown crystal, some of the lithium acceptors will have an OH− ion located at an adjacent axial oxygen site (to serve as a passivator), and we assign the 3577.3-cm−1 band observed at 12K to these neutral complexes. Our results illustrate the role of hydrogen as a charge compensator for singly ionized acceptors in ZnO.