In the paper, the photoluminescence (PL) measurements, current-voltage-temperature (I-V-T) measurements, space charge techniques (C-V and deep level transient spectroscopy (DLTS)), and photocurrent spectral characteristics have been applied to investigate defects in p-Si/MgO/ n-Zn 1Àx Mg x O heterojunction (HJ). The HJ structure was grown on p-type Si (111) substrate with resistivity equal to 0.1 X cm by the plasma-assisted molecular beam epitaxy technique. A radiofrequency cell was used for the generation of oxygen plasma. PL spectrum let us determine the Mg content $10%. Besides the excitonic Zn 0.9 Mg 0.1 O line, the PL spectrum also contains green and yellow emission bands indicating the presence of defect states in the investigated structures. I-V measurements reveal the rectifying properties of the HJ and the current thermally activated with a trap with the activation energy equal to 0.42 eV. DLTS studies yield the majority trap of the activation energy 0.42 eV, confirming the result obtained from the I-V measurements. It was found that the defects related to this trap have a point like behaviour. A spectral characteristic of the photocurrent shows that the p-Si/MgO/n-Zn 1Àx Mg x O HJ may be applied as a photodiode operating within the wavelength range of 300 nm-1100 nm. The dark current transport and photocurrent spectrum were explained using the Anderson model of a HJ. V C 2015 AIP Publishing LLC.

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