Zinc oxide, a wide-gap semiconductor, typically exhibits $n$-type conductivity even when nominally undoped. The nature of the donor is contentious, but hydrogen is a prime candidate. We present ab initio calculations of the migration barrier for H, yielding a barrier of less than $\sim 0.5\mathrm{eV}$. This indicates isolated hydrogen is mobile at low temperature and that thermally stable H-related donors must logically be trapped at other defects. We argue this is also true for other oxides where H is a shallow donor.

• Received 4 November 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.205504