We have used deep level transient spectroscopy (DLTS) to characterize defects in ZnO grown by pulsed-laser deposition (PLD). Using high resolution Laplace DLTS, we found that at the high temperature side of the commonly observed defect E3 (about 300 meV below the conduction band) another close lying peak (E3′ with thermal activation energy of 370 meV) is also observed. The concentration ratio of E3 and E3′ depends on the annealing history of the samples. It is most prevalent in as-grown samples and samples that had been annealed in an oxygen atmosphere. This suggests that E3′ may be related to the incorporation of oxygen in the lattice. Electron capture onto that E3′ defect strongly increases with increasing temperature.
a b s t r a c tTemperature dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements have been performed on Pd/ZnO Schottky barrier diodes in the range 60-300 K. The room temperature values for the zero bias barrier height from the I-V measurements (F I-V ) was found to be 0.52 eV and from the C-V measurements (F C-V ) as 3.83 eV. From the temperature dependence of forward bias I-V, the barrier height was observed to increase with temperature, a trend that disagrees with the negative temperature coefficient for semiconductor material. The C-V barrier height decreases with temperature, a trend that is in agreement with the negative temperature coefficient of semiconductor material. This has enabled us to fit two curves in two regions (60-120 K and 140-300 K). We have attributed this behaviour to a defect observed by DLTS with energy level 0.31 eV below the conduction band and defect concentration of between 4 Â 10 16 and 6 Â 10 16 cm À 3 that traps carriers, influencing the determination of the barrier height.
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