The electrical activity of nitrogen as an acceptor in ZnO has been investigated in two ways. First, nitrogen was introduced by means of diallylamine during metalorganic vapor phase epitaxy (MOVPE) yielding incorporation of nitrogen in the range 1016–1021 cm−3. This led to significant compensation of the natural donors with a minimum electron concentration of 5×1014 cm−3. Second, diffusion of nitrogen was carried out on undoped MOVPE layers under high pressure conditions stemming from the decomposition of NH4NO3. Conversion to p-type conductivity was observed in a systematic way with measured hole concentrations up to 6.5×1017 cm−3.
Unintentionally doped ZnO layers grown epitaxially on a sapphire substrate have been exposed either to a hydrogen or deuterium plasma. Secondary ion mass spectroscopy measurements performed subsequently showed a rapid diffusion of hydrogen in these layers. Furthermore, the presence of hydrogen in the ZnO samples is found to be responsible for nearly a factor of 3 increase in the free electron concentration. This effect is attributed to the hydrogen passivation of compensating acceptor impurities present in the as-grown ZnO layers.
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