Material grown at highly Zn-rich conditions in reactive sputtering of ZnO thin

films resulted in mixed conduction, indicating that stable p-type ZnO can be

produced. In n-type conductivity, neutral flaw scattering transport mechanism via

VO

0 centres seems to be dominant due to the existence of oxygen vacancies in high

concentrations. An exponential decrease in electron mobility was observed upon

cooling from room temperature to 210K while the concentration of the inactive VO

0

state increases. This was also a cause of p-type conduction in the low temperature

range (<170K). Mobility of holes has rather usual behaviour as the longitudinal

acoustic phonon scattering takes place at 35 to 170K. Ionized acceptor scattering

was shown to be effective for holes below 35K. P-type conduction was not affected

by VO

0 scattering. Quantitative evaluations of VO centres showed that fractional

distribution of VO

0, VO

+ and VO

2+ charge states are, respectively, around 4%, 95%

and 1% of the total [VO] under the room temperature conditions. The energy of

phonons interacting with the centre was estimated to be 38.5meV which was a

local phonon mode relaxation, most probably resulting in negative-U behaviour of

VO centres.

Determination of the Transport Mechanisms in Mixed Conduction of Reactively

Sputtered ZnO Thin Films. S.Tüzemen, E.Gür, S.Doğan: Journal of Physics D,

2008, 41[13], 135309