Metastable state of the VZnH2 defect in ZnO.

The Zn vacancy passivated by two hydrogen atoms in ZnO (VZnH2) was studied by IR absorption. In addition to the ground state of the defect comprising two inequivalent O—H bonds aligned parallel and perpendicular to the c axis of the crystal, there exists a metastable state of the defect (VZnH2*). VZnH2* consists of two equivalent O—H bonds oriented perpendicular to the c axis. The metastable state reveals two local vibration modes at 3329.0 and 3348.4 cm-1, which represent antisymmetric and symmetric combinations of the two separate O—H stretch modes, respectively. The energy difference between the ground and the metastable states of the complex was found to be 75±9 meV. An activation energy of 0.96±0.12 eV is needed to move the hydrogen atom from the c axis to the perpendicular position. [ABSTRACT FROM AUTHOR]