Properties of ZnO thin films grown on Si substrates by ultrasonic spray and ZnO/Si heterojunctions

Experimental analysis of current-voltage and capacitance-voltage characteristics of n-ZnO/p-Si (100) heterostructures were presented. Undoped and In-doped ZnO films were deposited by the simple ultrasonic spray method on p-Si substrates (100) at varied substrate temperatures from 200 to 400 degrees C. The structural and optical properties of ZnO films were investigated using X-ray diffraction (XFD) and transmission spectra respectively. The electrical conductivity is calculated from transport measurement in a two probes coplanar structure. It is found that the doped ZnO: In films have higher (002) diffraction peak than undoped ZnO. All films exhibit a high transparency about 85%. The maximum conductivity is observed at 350 degrees C for doped films but increases with substrate temperature for undoped ones. Current-voltage (I-V) characteristics of all n-ZnO/p-Si heterojunctions exhibit non linear characteristics with a small current leakage in the reverse voltage. The obtained device shows a barrier height in the order of 0.65 eV, this is consistent with the theoretical value 0.67eV. The capacitance increases with increasing reverse bias in an approximately linear l/C-2-V relationship.