We present data for dark current of a back-illuminated CCD over the temperature range of 222 to 291 K. Using an Arrhenius law, we found that the analysis of the data leads to the relation between the prefactor and the apparent activation energy as described by the Meyer-Neldel rule. However, a more detailed analysis shows that the activation energy for the dark current changes in the temperature range investigated. This transition can be explained by the larger relative importance at high temperatures of the diffusion dark current and at low temperatures by the depletion dark current. The diffusion dark current, characterized by the band gap of silicon, is uniform for all pixels. At low temperatures, the depletion dark current, characterized by half the band gap, prevails, but it varies for different pixels. Dark current spikes are pronounced at low temperatures and can be explained by large concentrations of deep level impurities in those particular pixels. We show that fitting the data with the impurity concentration as the only variable can explain the dark current characteristics of all the pixels on the chip.

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Epitaxial ZnO͑0001͒ thin films have been grown by pulsed-laser deposition on a-Al 2 O 3 and investigated by deep level transient spectroscopy ͑DLTS͒ and by Fourier transform infrared photocurrent ͑FTIR-PC͒ spectroscopy in the midinfrared wavelength range. FTIR-PC spectra of undoped ZnO layers show several well-resolved spectral features between 100 and 500 meV due to transitions from deep defect states either to the conduction band or to the valence band. They include the commonly observed intrinsic deep defects E1 at ϳ110 meV and E3 at ϳ320 meV. DLTS and FTIR-PC measurements were repeated after annealing the samples either in vacuum, under oxygen, or nitrogen atmospheres. Based on annealing effects, the possible microscopic origin of major deep levels in the ZnO samples is discussed. Further FTIR-PC investigations of Co-and Mn-doped ZnO reveal defect levels at ϳ270, ϳ380, and ϳ450 meV and are compared with corresponding DLTS data.

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