Electrical properties and carrier transport mechanisms of n-ZnO/SiOx/n-Si isotype heterojunctions with native or thermal oxide interlayers

N-type ZnO/SiOx/n-type crystalline silicon isotype heterojunctions (HJs) have been prepared by magnetron sputtering. Native and thermal oxides were employed as the interlayer between the Si substrate and the ZnO film. Transmission electron microscopy and x-ray photoelectron spectroscopy revealed that an oxide layer was inserted in the HJ interface, with thickness of similar to 1.2 nm (native oxide) and similar to 2.0 nm (thermal oxide). Atomic force microscopy and x-ray diffraction spectroscopy showed that the ZnO film on the Si substrate consists of tightly packed grains with sizes in the range 50-150 nm and is c-axis preferred orientation. The electrical properties were characterized by current-voltage (I-V), capacitance-voltage (C-V) and current-voltage-temperature (I-V-T) measurements. By a comparison of the HJ properties, the n-ZnO/thermaloxide/n-Si HJs show improved electrical properties, with a fairly low leakage current and high rectification ratio, although the series resistance increased. Studies of fitting the I-V-T measurement data suggest that the tunnelling process is a dominant current transport mechanism for the n-ZnO/native or thermal oxide/n-Si HJs at an intermediate voltage range.