Facile fabrication of carbon spheres/n-Si junction diodes based on sucrose

Carbon spheres with diameters in the range 125 nm–10 μm were produced via hydrothermal carbonization of sucrose. Annealing at 800 °C under a flow of dry N₂ gas increased the carbon content, reduced the sphere diameter making their shape more uniform, increased the crystallinity within the spheres and rendered them conducting. The band gap of the carbon spheres was found to be 2.82 eV and the conductivity was 0.15 S/cm at room temperature. A Schottky diode using these spheres was fabricated and electrically characterized. The ratio of the ON to the OFF current at ±1 V was ~20 and the turn-on voltage was ~0.6 V. Using the standard thermionic emission model of a Schottky junction, the diode ideality parameter was calculated to be ~2.4 and the barrier height was 0.52 eV. A simple circuit was designed to test the diode as a half wave rectifier with an input 100 Hz, 5 V peak-to-peak signal. The rectified output with an efficiency of 5.7 was tapped across a 22 kΩ load resistor. This is the first study demonstrating a real application using conducting carbon spheres fabricated via an easy, rapid, cheap, and green technique.