Electrical Properties of Schottky Devices from HfO2 and ZnO/HfO2 Thin Films: Morphological, Structural, and Optical Investigations

The structural and electronic properties of thin films are crucial for the performance of heterojunction diodes, which are key components in modern electronic devices. Optimizing these properties through advanced materials and fabrication techniques is an area of significant research, particularly in reducing leakage currents and enhancing device reliability. This study investigates the structural characteristics of a monolayer HfO2 and a double layer ZnO/HfO2 interface layer. This research specifically examines the impact of an HfO2 interface layer on the current transport properties of n-ZnO/p-Si heterojunction diodes, because understanding the current transport mechanisms in ZnO and HfO2 thin films, especially in relation to reducing defects and leakage currents, presents a challenge. Current–voltage characterization reveals that these diodes, grown by sol–gel spin coating. exhibit current transport behavior consistent with tunneling, with exponential trap distributions contributing under high voltage bias conditions. A thermionic emission (TE) mechanism is observed at low voltages (V < 0.4 V), followed by space-charge limited conduction (SCLC) at medium voltages (V < 0.5 V), and a trap charge limited current (TCLC) mechanism at high voltages (V > 1 V) in the dark forward current–voltage characteristics. The incorporation of the n-ZnO/HfO2/p-Si structure significantly reduces leakage currents associated with defects. These findings advance the understanding of ZnO/HfO2-based heterojunction diodes and pave the way for their potential application in more efficient electronic devices. The X-ray diffraction (XRD) spectra have revealed that all films crystallize in the hexagonal wurtzite structure. Structural parameters such as crystallite size, dislocation density, and microstrain in the crystal structure have been calculated. The coating thicknesses and elemental distributions of thin-film samples were determined from Field emission scanning electron microscopy (FE-SEM) images obtained from both surface and cross-sectional views. The energy band gaps of HfO2 and ZnO/HfO2 thin films were determined using absorption measurements obtained with a ultraviolet (UV) spectrophotometer. The surface roughness and topography information on thin-film samples were determined from Atomic force microscopy (AFM).