Structural, optical and electrical properties of n-ZnO/p-Si heterojunction prepared by ultrasonic spray

Heterojunction structures of n-ZnO/p-Si were prepared by growing undoped ZnO thin films onto p-type Si (1 0 0) substrates. ZnO films were deposited by ultrasonic spray method. The structural and optical properties of ZnO films were studied as a function of substrate temperature. The X-ray diffraction measurements showed that ZnO film has a nanocrystalline structure with (0 0 2) preferential orientation and grain sizes ranging from 25 to 70 nm. An increase in the deposition temperature enhances the (0 0 2) diffraction peak intensity. The transmittance measurements in the UV–vis wavelengths range indicated that the films optical gap increases with increase in substrate temperature. The heterojunction parameters were evaluated from the current–voltage (IV) and capacitance–voltage (CV) measurements carried out on the realized n-ZnO/p-Si heterostructure, in dark at different temperatures. From these measurements we inferred that the forward conduction is dominated by multi-step tunneling current at low bias voltage in the 0.2–0.5 V region. The ideality factor of the obtained heterojunction is larger than 2, the activation energy of saturation current is about 0.14 eV and the junction built-in potential deduced from C–V measurements is equal to 1.14 V at room temperature.