Study on defect states using deep level transient spectroscopy of ZnO grown by pulsed laser deposition

The pulsed laser deposition (PLD) was used for fabrication of ZnO films on a sapphire substrate. We modulated the parameters, temperature and gas pressure, for the growth condition. After the growth, X-ray diffraction, photoluminescence (PL), and deep level transient spectroscopy (DLTS) measurements were performed. We had got PL spectra of high intensity from the ZnO film grown at low temperature. And the existence of the defect states was fewer, according to the result. But the crystalline quality was good for the film grown at high temperature. It seems to be that the relation between crystallization and defined electronic bandgap is weak. The DLTS measurements show some defects, but the signal is noisy. A Schottky contact by using Ti/Au and a high conductance seem to be the cause. We had simulated the DLTS spectra from assumed defects and matched to measurement results.

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