Incorporation and drift of hydrogen at low temperatures in ZnO

Hydrogen is found to diffuse rapidly into ZnO from either a molecular (D-2) gas source or from a D-2 plasma at temperatures in the range of 100-200 degrees C. In samples deuterated from a plasma excited at 13.56 MHz, the incorporated deuterium concentration is saturated at 6x10(18) cm(-3) throughout the entire 1.2 mu m epi-ZnO thickness at 250 degrees C. This deuterium is stable against reverse bias application at 25 degrees C for 24 h. By sharp contrast, deuterium incorporated from exposure to D-2 gas at 100 degrees C can be entirely removed by reverse (negative) bias application in a diode structure using a Pt contact on the n-type ZnO. These results are consistent with the state of the deuterium in the ZnO being a function of both the concentration and the flux during incorporation. At low concentrations, the deuterium is likely to be in a positively charged atomic form or bound in defects that are readily dissociated by an electric field, while at higher concentrations the deuterium may be in neutral states such as D-2 or OH complexes. (c) 2007 American Institute of Physics.