Identification of a metastable state of the VZnH2 defect in ZnO

An infrared absorption study of the Zn vacancy passivated by two hydrogen atoms (VZnH2) is reported. The ground state of the defect VZnH2 consists of the inequivalent O–H bonds, which are aligned parallel and perpendicular to the c-axis, respectively. A metastable state of the defect was detected with two equivalent O–H bonds oriented perpendicular to the c-axis (VZnH2⁎). VZnH2⁎ has two local vibration modes at 3329.0 and 3348.4 cm−1 which are the antisymmetric and symmetric combinations of the two O–H stretch modes. The metastable state of the defect is 75±9 meV above the ground state of VZnH2. An activation energy of 0.96±0.12 eV for the transition from metastable to the ground state was determined.