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The electrical properties of Schottky contacts (SCs) produced ex situ on n-type ZnO single crystals and epitaxial thin films were investigated. Electron beam induced current imaging was used to study lateral variations of the current induced in the space charge region of the SC. Further, the effective barrier height was determined by current–voltage and capacitance–voltage measurements. Pd contacts prepared on ZnO thin films that had undergone treatment in a plasma-enhanced chemical vapor deposition with nitrous oxide (N2O) as ambient gas are laterally homogeneous with an effective barrier height of (600±30) meV.

The authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n-conducting ZnO wafer grown by pressurized melt growth with nitrogen ions. The authors found the commonly observed donorlike defects E1 and E3 and two acceptorlike defects A2 and A3, as well as a broad acceptorlike defect band. The thermal activation energies of A2 and A3, were determined to be about 150 and 280meV, respectively.

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We have applied a special variant of optical DLTS to deep levels found in ZnO thin films. The optical emission rates of charge carriers from deep levels into a band have been measured over a range of photon energies from 0.7 to 3.0 eV and photoionization cross-section spectra calculated from this data. Two of the defects -among these the well-known E3 -showed no optical emission in the investigated range of photon energies. The experimental photo cross-section spectra of two optically active defects were compared and discussed using a model [Chantre, Vincent, and Bois, Phys. Rev. B 23(10), 5335 (1981)] that yields information about the band structure and defect properties. DLTS signal simulations were compared to the experimental data for the case that E4 has two states within the bandgap. These simulations revealed that a two-state model where both states independently allow electron emission is in accordance with the experimental data. The thermal DLTS peak of E4 was observed to be broadened and has been simulated under the assumption of a distribution of the carrier capture cross-section. The agreement between the simulation and the measured DLTS peak possibly explains why one of the photocross section spectra appears more broadened than can be simulated by the model cited above.