Vibrational lifetimes of O-H stretch modes in MgO and ZnO

Hydrogen is an important and omnipresent impurity in a wide class of oxides. A more complete understanding of the role of hydrogen in wide-bandgap oxides such as MgO and ZnO is crucial for further development of oxide-based optoelectronics. We have measured for the first time the vibrational lifetime of the O-H stretch mode associated with the Mg$^{2+}$ vacancy in MgO for the charge state, V$_{OH}$-, and the neutral state, V$_{OH}$, using picosecond transient bleaching spectroscopy. For the V$_{OH}$ center we find the lifetime ($\sim $11 ps) is longer than for the charged defect state ($\sim $5 ps). These lifetimes are almost an order of magnitude shorter than in covalent semiconductors Si and Ge [1]. Similar measurements will be presented for interstitial hydrogen in ZnO. Our results provide new insight into the coupling of the ionic surroundings to the O-H vibration within the crystal lattice. [1] M. Budde et al., PRL 87, 145501 (2001).