Study of n-ZnO/p-Si (100) thin film heterojunctions by pulsed laser deposition without buffer layer

Abstract

ZnO/Si heterojunctions were fabricated by growing ZnO thin films on p-type Si (100) substrate by pulsed laser deposition without buffer layers. The crystallinity of the heterojunction was analyzed by high resolution X-ray diffraction and atomic force microscopy. The optical quality of the film was analyzed by room temperature (RT) photoluminescence measurements. The high intense band to band emission confirmed the high quality of the ZnO thin films on Si. The electrical properties of the junction were studied by temperature dependent current–voltage measurements and RT capacitance–voltage (C–V) analysis. The charge carrier concentration and the barrier height (BH) were calculated, to be 5.6×1019cm−3 and 0.6eV respectively from the C–V plot. The BH and ideality factor, calculated using the thermionic emission (TE) model, were found to be highly temperature dependent. We observed a much lower value in Richardson constant, 5.19×10−7A/cm2K2 than the theoretical value (32A/cm2K2) for ZnO. This analysis revealed the existence of a Gaussian distribution (GD) with a standard deviation of σ2=0.035V. By implementing the GD to the TE, the values of BH and Richardson constant were obtained as 1.3eV and 39.97A/cm2K2 respectively from the modified Richardson plot. The obtained Richardson constant value is close to the theoretical value for n-ZnO. These high quality heterojunctions can be used for solar cell applications.