Diffusion-controlled annealing kinetics of interstitial H in SnO₂

SnO2 is a prototypical transparent conducting oxide that finds widespread applications as transparent electrodes, gas sensors, and transparent thin-film devices. Hydrogen impurities in SnO2 give rise to unintentional n-type behavior and unexpected changes to conductivity. Interstitial H (H-i) and H at an oxygen vacancy (H-O) are both shallow donors in SnO2. An O-H vibrational line at 3155 cm(-1), that can be produced by a thermal anneal at 500 degrees C followed by a rapid quench, has been assigned to the H-i center and is unstable at room temperature on a timescale of weeks. An IR absorption study of the decay kinetics of the 3155 cm(-1) O-H line has been performed. The disappearance of H-i upon annealing has been found to follow second-order kinetics. Measurements of the decay rate for a range of temperatures have determined an activation energy for the diffusion of interstitial H in SnO2. These results provide fundamental information about how unintentional hydrogen impurities and their reactions can change the conductivity of SnO2 device materials in processes as simple as thermal annealing in an inert ambient.