On the T2 trap in zinc oxide thin films

We investigated the electronic properties of the T2 deep-level in zinc oxide thin films. It was found that T2 preferentially forms under zinc-rich conditions and can be generated by either annealing the samples at reduced oxygen partial pressures ($p_{{\rm O}_{2} } < 1\;{\rm bar}$) or implanting zinc or copper ions, respectively. A strong dependence of its activation energy and high temperature limit of its cross-section for electron capture on the T2 concentration in the sample is reported. Double DLTS measurements showed that the T2 activation energy decreases with increasing electric field due to phonon assisted tunnelling. Furthermore T2 can be photo-ionised with a threshold photon energy of about 700?meV. Depth-resolved concentration profiles of the T2 level in the samples were measured by optical capacitancevoltage spectroscopy.