Diffusivity of interstitial hydrogen in In2O3 from defect-pairing reaction kinetics

In2O3 is a transparent conducting oxide that finds widespread applications in transparent electrodes, flat-panel displays, and low-emissivity windows. Interstitial hydrogen (Hi+) in In2O3 gives rise to a shallow donor that is mobile at temperatures near 100 °C and that has an O–H vibrational line at 3304 cm−1 (77 K). In2O3 crystals grown by the flux method have been found to contain hydrogen with a concentration near 4 × 1017 cm−3 that is stably trapped in a form that is not readily seen by infrared spectroscopy. Hi+ can be dissociated from this trap by an anneal at an elevated temperature followed by a rapid quench, a treatment that produces the O–H line at 3304 cm−1. The released Hi+ then undergoes a diffusion-controlled reaction to become retrapped. Theory considers possibilities for the identity of the trapping center for Hi+ that has been investigated here and the activation barriers for Hi+ motion. The kinetics of this reversible trapping process reveals a diffusion constant for Hi+ that is in agreement with a recent prediction by Franckel et al.