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. (C) 2011 Elsevier Ltd. All rights reserved.